# Range wire

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**Range wire**

In my kitchen remodel, I am moving the electric range farther away from the service panel. I am replacing the entire run of wire to the panel instead of splicing it. I asked at my local electrical supply store (not a big box) and they recommended 8/3 romex, I have a 50 amp breaker and a 50 amp stove outlet. So I bought 35 ft. I was just under the house and was able to read the marking on the existing line, and it is 6/3. I know I should have looked before I bought, but is 8/3 ok, or do I need 6/3? The Kenmore slide-in range instructions states this:

range requires a single phase three wire 120/240 or a 120/208 volt, 60 Hz, AC circuit

Brian

range requires a single phase three wire 120/240 or a 120/208 volt, 60 Hz, AC circuit

Brian

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Originally Posted by

**brian6**In my kitchen remodel, I am moving the electric range farther away from the service panel. I am replacing the entire run of wire to the panel instead of splicing it. I asked at my local electrical supply store (not a big box) and they recommended 8/3 romex, I have a 50 amp breaker and a 50 amp stove outlet. So I bought 35 ft. I was just under the house and was able to read the marking on the existing line, and it is 6/3. I know I should have looked before I bought, but is 8/3 ok, or do I need 6/3? The Kenmore slide-in range instructions states this:

range requires a single phase three wire 120/240 or a 120/208 volt, 60 Hz, AC circuit

Brian

range requires a single phase three wire 120/240 or a 120/208 volt, 60 Hz, AC circuit

Brian

If you are going to use the 50 amp breaker you need #6. #8 is

rated for 40 amps. I have seen ranges that call for a 40 amp breaker. Check the namplate on the range.

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**3**
Replace the 50A breaker with a 40A, and you will be all set. Very few residential ranges require 50A, but check the nameplate or installation instructions on the range to be sure.

You are allowed to use the 50A receptacle with either a 40A or 50A breaker.

You are allowed to use the 50A receptacle with either a 40A or 50A breaker.

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Not to sound dumb, but the nameplate will list model and serial number of appliance, and in this case found on front of range?

If so, it reads:

3 wire phase 1 60 Hz

For use with 3 wire 120/240 or 120/208 V system

120/240 V 120/208 V

10.4 Kw 7.8 Kw UL listed

If so, it reads:

3 wire phase 1 60 Hz

For use with 3 wire 120/240 or 120/208 V system

120/240 V 120/208 V

10.4 Kw 7.8 Kw UL listed

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Originally Posted by

**wareagle**If you are going to use the 50 amp breaker you need #6. #8 is rated for 40 amps. ...

Yet I also commonly hear (even from inspectors here) that #8 is no for 50A, about as often as I see it pass inspection with no problems.

Is there some sort of rule regarding #8 and 50A circuits? I've seen it both ways, and feel like there is much confusion on the issue, at least in my experience.

Maybe I just keep missing the explicit code that mentions it. And everybody else is just ignoring it?

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**8**
Hi Mac

The #8 copper is 55 amps if we could use the 90C column. One of the keys here is 110.14(C). This says that we must use the 60C column ampacity if the equipment is 100 amps or less or size #1 thru #14 unless stated otherwise. So we can use the 75C column if the terminations of the equipment on both ends are rated for 75C connections. This means the wire must be also rated with at least 75C insulation.

At present no 90C connections and ampacities are allowed for anything other than deration purposes.

Note* if the wire is NM-b or UF-B or Tw we must use the 60C column regardless.

So if the range instructions just say install on 50 amp circuit then we could use #8 copper with any of the temp. designations of the 75C column. All modern ovens/ranges are rated for 75C connections and all modern panels and breakers are rated 75C.

And as you know the branch circuit conductors must carry 100% of the non-continuious load plus 125% of the continuous load. Same with the breakers.

So I'll give an example not using the diversity rules of art.220 for the range in this thread. Nameplate states 10.4KW at 240 volts

10,400/240 = 43 amps... So we cant use NM-B #8 copper because it can only have 40 amps carried on it due to 60C limitation. However if we pick a cable or wire in conduit that is 75C rated we can use #8 copper at 50 amps on a 50 amp breaker.

Any range over 8750 watts must be on at least 40 amps branch circuit rating.

If we use the diversity of art.220 then we could use a 40 amp breaker and #8 copper if the manufacturer's instruction dont tell us otherwise.

Roger

The #8 copper is 55 amps if we could use the 90C column. One of the keys here is 110.14(C). This says that we must use the 60C column ampacity if the equipment is 100 amps or less or size #1 thru #14 unless stated otherwise. So we can use the 75C column if the terminations of the equipment on both ends are rated for 75C connections. This means the wire must be also rated with at least 75C insulation.

At present no 90C connections and ampacities are allowed for anything other than deration purposes.

Note* if the wire is NM-b or UF-B or Tw we must use the 60C column regardless.

So if the range instructions just say install on 50 amp circuit then we could use #8 copper with any of the temp. designations of the 75C column. All modern ovens/ranges are rated for 75C connections and all modern panels and breakers are rated 75C.

And as you know the branch circuit conductors must carry 100% of the non-continuious load plus 125% of the continuous load. Same with the breakers.

So I'll give an example not using the diversity rules of art.220 for the range in this thread. Nameplate states 10.4KW at 240 volts

10,400/240 = 43 amps... So we cant use NM-B #8 copper because it can only have 40 amps carried on it due to 60C limitation. However if we pick a cable or wire in conduit that is 75C rated we can use #8 copper at 50 amps on a 50 amp breaker.

Any range over 8750 watts must be on at least 40 amps branch circuit rating.

If we use the diversity of art.220 then we could use a 40 amp breaker and #8 copper if the manufacturer's instruction dont tell us otherwise.

Roger

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Originally Posted by

**lectriclee**I'm no code guru, 310:16, depending on the conductor insulation and temp rating.Nm(romex is 90C, correct?) I've had the same issue.

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Originally Posted by

**brian6**If so, it reads:

3 wire phase 1 60 Hz

For use with 3 wire 120/240 or 120/208 V system

120/240 V 120/208 V

10.4 Kw 7.8 Kw UL listed

10.4 kw = 42 amps. However this is not a continuous load.

I think you can use a 40 amp breaker. Your other option is the return the #8 and get #6 if you want to use the 50 breaker.

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**12**
I dont believe you can use a 40 amp breaker based on the nameplate wattage.

You can based on table 220.55. note 4.

This really is a rather interesting deal going on with the code IMO.

If I use 8000 watts using note 4 table 220.55 for one range I get 33 amps. So I need 35 amp wire minimum. If I use NM-B I need 8 awg copper at 40 amps on a minimum 40 amp breaker (considering 210.19a3)

If I use for example Thhn in conduit I could use #10 copper and a 35 amp breaker....but you cant because you cant breaker #10 at more than 30 amps (unless I'm serving a motor) So I'm forced to move to #8 awg copper on 40 amp breaker minimum.

This calculation would be ok using art. 220 diversity table 220.55.

Now on the other hand if I use article 210 and size the conductors based on the nameplate rating of 10,400 watts

And remembering that art 210.19(A)(3) requires me to use a minimum 40 amp branch circuit for any individual range of 8,750 watts or more. My calculated non-continuous load is 43 amps. So I need minimum 45 amp conductors on a minimum 45 amp breaker...probably a 50 since 45 is hard to come by. So I'll need #8 copper at 50 amps (there isnt a 45 amp ampacity) on wire rated for 75C connections. Or #6 NM-B rated 55 amps on a 45 or 50 amp breaker.

Roger

You can based on table 220.55. note 4.

This really is a rather interesting deal going on with the code IMO.

If I use 8000 watts using note 4 table 220.55 for one range I get 33 amps. So I need 35 amp wire minimum. If I use NM-B I need 8 awg copper at 40 amps on a minimum 40 amp breaker (considering 210.19a3)

If I use for example Thhn in conduit I could use #10 copper and a 35 amp breaker....but you cant because you cant breaker #10 at more than 30 amps (unless I'm serving a motor) So I'm forced to move to #8 awg copper on 40 amp breaker minimum.

This calculation would be ok using art. 220 diversity table 220.55.

Now on the other hand if I use article 210 and size the conductors based on the nameplate rating of 10,400 watts

And remembering that art 210.19(A)(3) requires me to use a minimum 40 amp branch circuit for any individual range of 8,750 watts or more. My calculated non-continuous load is 43 amps. So I need minimum 45 amp conductors on a minimum 45 amp breaker...probably a 50 since 45 is hard to come by. So I'll need #8 copper at 50 amps (there isnt a 45 amp ampacity) on wire rated for 75C connections. Or #6 NM-B rated 55 amps on a 45 or 50 amp breaker.

Roger

*Last edited by Roger; 09-13-06 at 09:58 AM.*

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**13**
#8 CU...40 amps

#6 CU...50 amps...instead of looking for what we can get away with we should look at future and safety first..IMHO...

#6 CU...50 amps...instead of looking for what we can get away with we should look at future and safety first..IMHO...

#

**14**
****

"#8 CU...40 amps

#6 CU...50 amps...instead of looking for what we can get away with we should look at future and safety first..IMHO..."

******

This is too general a statement.

Basically:

#8NM cu is good for 40 amps.

#8THHN cu is good for 50 amps.

#6NM cu is good for up to 60 amps.

#6THHN cu is good for up to 70 amps.

"#8 CU...40 amps

#6 CU...50 amps...instead of looking for what we can get away with we should look at future and safety first..IMHO..."

******

This is too general a statement.

Basically:

#8NM cu is good for 40 amps.

#8THHN cu is good for 50 amps.

#6NM cu is good for up to 60 amps.

#6THHN cu is good for up to 70 amps.

#

**15**
Bottom line is ANY household cooking appliance rated at 12kw or less may be served by a 40 amp circuit.

Here is the NEC Handbook commentary:

"Column C of Table 220.55 indicates that the maximum demand for one range (not over 12 kW rating) is 8 kW (8 kW = 8000 volt-amperes; 8000 volt-amperes ÷ 240 volts = 33.3 amperes). In accordance with the fundamental termination rule of 110.14(C)(1)(a), the allowable ampacity of an 8 AWG, copper conductor from the 60°C column of Table 310.16 is 40 amperes, and it may be used for the range branch circuit. According to this computation, the neutral of this 3-wire circuit can be smaller than 8 AWG but not smaller than 10 AWG, which has an allowable ampacity of 30 amperes (30 amperes is more than 70 percent of 40 amperes, per Exception No. 2). The maximum demand for the neutral of an 8-kW range circuit seldom exceeds 25 amperes, because the only line-to-neutral connected loads are lights, clocks, timers, and the heating elements of some ranges when the control is adjusted to the low-heat setting."

Here is the NEC Handbook commentary:

"Column C of Table 220.55 indicates that the maximum demand for one range (not over 12 kW rating) is 8 kW (8 kW = 8000 volt-amperes; 8000 volt-amperes ÷ 240 volts = 33.3 amperes). In accordance with the fundamental termination rule of 110.14(C)(1)(a), the allowable ampacity of an 8 AWG, copper conductor from the 60°C column of Table 310.16 is 40 amperes, and it may be used for the range branch circuit. According to this computation, the neutral of this 3-wire circuit can be smaller than 8 AWG but not smaller than 10 AWG, which has an allowable ampacity of 30 amperes (30 amperes is more than 70 percent of 40 amperes, per Exception No. 2). The maximum demand for the neutral of an 8-kW range circuit seldom exceeds 25 amperes, because the only line-to-neutral connected loads are lights, clocks, timers, and the heating elements of some ranges when the control is adjusted to the low-heat setting."

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**16**
Shrnamp

I wasnt going through all this to see what I could get away with in the code book. I was discussing the complexity of branch circuit calculations... if you really want to understand how the cmp guys set the code up ....to be safe.

BTW there are several other exceptiions that one needs to be aware of that can change conductor size and ocpd amperage.

I'm not a fan of the diversity method but I'm here to tell you that new construction contractors are very familiar with it. If it wasnt safe we would have all kinds of problems out there.

I'm not crazy about simplifing the trade to the point that all we need to do is say...its a range so lets put it on a 50 amp breaker and 6 awg wire. We would all be working for minimum wage if it gets that easy. Handcuffing yourself to thinking a wire has one simple ampacity is a little risky in my opinion.

Besides the only way you can use the diversity method for a branch circuit calculation is when you only are dealing with one range. Note 4 in particular... the rest is for dwelling load calculations.

My point really isnt to argue with you as your method is fine for this application. I just want to stay abreast of keeping myself current on the code compliant methods for these calculations.

I'm a long way from being a master electrician or code guru but I want to understand why we have that code book.

Now if I was going to size this branch circuit to this range I would use a calculated max.load of 43 amps.

1.) I would serve it with NM-B #6/3G copper on a 50 amp breaker.

2.) Or I would use #6/3G SER AL on a 50 amp breaker

3.) If available I may go with #8/3G SER CU on 50 amp breaker

4.) I might even use some TC cable #8/3G CU on 50 amp breaker

5.) If I was in the Chicago juristiction I would use #8 awg THHN on a 50 amp breaker metal conduit as ground.

I also agree with Speedy it is a proven method to use the diversity table of 220.55 many many thousands of ranges out there sized by that method. It is safe and economically smart for a contractor to use that method.

Roger

I wasnt going through all this to see what I could get away with in the code book. I was discussing the complexity of branch circuit calculations... if you really want to understand how the cmp guys set the code up ....to be safe.

BTW there are several other exceptiions that one needs to be aware of that can change conductor size and ocpd amperage.

I'm not a fan of the diversity method but I'm here to tell you that new construction contractors are very familiar with it. If it wasnt safe we would have all kinds of problems out there.

I'm not crazy about simplifing the trade to the point that all we need to do is say...its a range so lets put it on a 50 amp breaker and 6 awg wire. We would all be working for minimum wage if it gets that easy. Handcuffing yourself to thinking a wire has one simple ampacity is a little risky in my opinion.

Besides the only way you can use the diversity method for a branch circuit calculation is when you only are dealing with one range. Note 4 in particular... the rest is for dwelling load calculations.

My point really isnt to argue with you as your method is fine for this application. I just want to stay abreast of keeping myself current on the code compliant methods for these calculations.

I'm a long way from being a master electrician or code guru but I want to understand why we have that code book.

Now if I was going to size this branch circuit to this range I would use a calculated max.load of 43 amps.

1.) I would serve it with NM-B #6/3G copper on a 50 amp breaker.

2.) Or I would use #6/3G SER AL on a 50 amp breaker

3.) If available I may go with #8/3G SER CU on 50 amp breaker

4.) I might even use some TC cable #8/3G CU on 50 amp breaker

5.) If I was in the Chicago juristiction I would use #8 awg THHN on a 50 amp breaker metal conduit as ground.

I also agree with Speedy it is a proven method to use the diversity table of 220.55 many many thousands of ranges out there sized by that method. It is safe and economically smart for a contractor to use that method.

Roger

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OK, I just read all the posts from mine till the end, and my diy head is spinning! If I understand, it should be ok to use the 8/3 and a 40-amp breaker, but maybe I should just eat the cost of the wire (I bought it cut to length, I don't think I can return it) and buy 6/3? That was what we installed with the range when it was new 5 years ago, that will definitely work.

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**19**
Brian

As long as you have this range at 10.4 Kw that 8/3 romex is fine. You need a 40 amp breaker though. Should be able to exchange that 50.

What Bob is saying I believe is that if you install a range someday that is over 12Kw you are going to need a larger size #6 wire. As long as you stay under 12Kw your fine with what you have.

The reason for the #8 and 40 amp is that you will most likely never have the stove with every burner on high and the oven on high at the same time.

As long as you have this range at 10.4 Kw that 8/3 romex is fine. You need a 40 amp breaker though. Should be able to exchange that 50.

What Bob is saying I believe is that if you install a range someday that is over 12Kw you are going to need a larger size #6 wire. As long as you stay under 12Kw your fine with what you have.

The reason for the #8 and 40 amp is that you will most likely never have the stove with every burner on high and the oven on high at the same time.

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[QUOTE=Roger]"I dont believe you can use a 40 amp breaker based on the nameplate wattage".

Sure you can. It's specifically allowed by NEC# 210.19(3)

For any household range with a rating of 8.75KW to 12KW a 40 Amp feeder is allowed.

"If I use 8000 watts using note 4 table 220.55 for one range I get 33 amps. So I need 35 amp wire minimum".

Correct.

"If I use NM-B I need 8 awg copper at 40 amps on a minimum 35 amp breaker".

Correct (for a 8 KW range). 40 Amps max on #8 NMB.

"If I use for example Thhn in conduit I could use #10 copper and a 35 amp breaker....but you cant because you cant breaker #10 at more than 30 amps (unless I'm serving a motor) So I'm forced to move to #8 awg copper on 35 amp breaker minimum".

Correct, you can't use #10 on a 35 Amp breaker to supply a range.

"Now on the other hand if I use article 210 and size the conductors based on the nameplate rating of 10,400 watts

And remembering that art 210.19(A)(3) requires me to use a minimum 40 amp branch circuit for any individual range of 8,750 watts or more".

Correct.

"My calculated non-continuous load is 43 amps. So I need minimum 45 amp conductors on a minimum 45 amp breaker"

You can use a 40 Amp cable and breaker.

Also..the range nameplate rating is 10.4 KW @ 240 Volts although in most (U.S.) homes the supply voltage is 230 Volts (or less). This equates to 41.5 Amps load at 230 Volts supply (9.5 KW).

..."probably a 50 since 45 is hard to come by. So I'll need #8 copper at 50 amps (there isnt a 45 amp ampacity) on wire rated for 75C connections".

The maximum breaker size on #8 romex is 40 Amps (for

supplying a range).

NMB (Romex) cable is always selected from the 60C column in table 310.16

Read 334.80 Ampacity.

"Or #6 NM-B rated 55 amps on a 45 or 50 amp breaker".

Correct. This will work but is not required for a range less than 12KW.

I would estimate that over half of the household ranges in the U.S. are wired using 40 Amp circuits. The electrical code allows it, so it must be safe.

steve

Sure you can. It's specifically allowed by NEC# 210.19(3)

For any household range with a rating of 8.75KW to 12KW a 40 Amp feeder is allowed.

"If I use 8000 watts using note 4 table 220.55 for one range I get 33 amps. So I need 35 amp wire minimum".

Correct.

"If I use NM-B I need 8 awg copper at 40 amps on a minimum 35 amp breaker".

Correct (for a 8 KW range). 40 Amps max on #8 NMB.

"If I use for example Thhn in conduit I could use #10 copper and a 35 amp breaker....but you cant because you cant breaker #10 at more than 30 amps (unless I'm serving a motor) So I'm forced to move to #8 awg copper on 35 amp breaker minimum".

Correct, you can't use #10 on a 35 Amp breaker to supply a range.

"Now on the other hand if I use article 210 and size the conductors based on the nameplate rating of 10,400 watts

And remembering that art 210.19(A)(3) requires me to use a minimum 40 amp branch circuit for any individual range of 8,750 watts or more".

Correct.

"My calculated non-continuous load is 43 amps. So I need minimum 45 amp conductors on a minimum 45 amp breaker"

You can use a 40 Amp cable and breaker.

Also..the range nameplate rating is 10.4 KW @ 240 Volts although in most (U.S.) homes the supply voltage is 230 Volts (or less). This equates to 41.5 Amps load at 230 Volts supply (9.5 KW).

..."probably a 50 since 45 is hard to come by. So I'll need #8 copper at 50 amps (there isnt a 45 amp ampacity) on wire rated for 75C connections".

The maximum breaker size on #8 romex is 40 Amps (for

supplying a range).

NMB (Romex) cable is always selected from the 60C column in table 310.16

Read 334.80 Ampacity.

"Or #6 NM-B rated 55 amps on a 45 or 50 amp breaker".

Correct. This will work but is not required for a range less than 12KW.

I would estimate that over half of the household ranges in the U.S. are wired using 40 Amp circuits. The electrical code allows it, so it must be safe.

steve

#

**21**
The 8/3 cable with a 40A breaker is legal and very common for electric ranges less than 12kW which includes nearly every 4 burner + oven model you will find at Sears.

The discussion in the above comments apply to a general purpose 50A receptacle. However, the code specifically recognizes that electric range circuits are different than general purpose circuits for the reason Roger gave. Thus, the 8/3 on a 40A breaker is totally acceptable.

The discussion in the above comments apply to a general purpose 50A receptacle. However, the code specifically recognizes that electric range circuits are different than general purpose circuits for the reason Roger gave. Thus, the 8/3 on a 40A breaker is totally acceptable.

#

**22**
Steve

[QUOTE=Roger]"I dont believe you can use a 40 amp breaker based on the nameplate wattage".

Sure you can. It's specifically allowed by NEC# 210.19(3)

For any household range with a rating of 8.75KW to 12KW a 40 Amp feeder is allowed.

I was speaking about the range in this thread. I made it very clear in previous posts that the minimum breaker for a 8750 watt range or larger is 40 amps. It doesnt give a cut off 12 KW.

Steve

..."probably a 50 since 45 is hard to come by. So I'll need #8 copper at 50 amps (there isnt a 45 amp ampacity) on wire rated for 75C connections".

The maximum breaker size on #8 romex is 40 Amps (for

supplying a range).

NMB (Romex) cable is always selected from the 60C column in table 310.16

Read 334.80 Ampacity

Steve... I understand...I was also quite clear in previous posts that NM-B must use the 60C column for ampacity. I was speaking towards other wiring methods. Though I see I should have made this more clear since NM-B is rated 90C.

Roger

[QUOTE=Roger]"I dont believe you can use a 40 amp breaker based on the nameplate wattage".

Sure you can. It's specifically allowed by NEC# 210.19(3)

For any household range with a rating of 8.75KW to 12KW a 40 Amp feeder is allowed.

I was speaking about the range in this thread. I made it very clear in previous posts that the minimum breaker for a 8750 watt range or larger is 40 amps. It doesnt give a cut off 12 KW.

Steve

..."probably a 50 since 45 is hard to come by. So I'll need #8 copper at 50 amps (there isnt a 45 amp ampacity) on wire rated for 75C connections".

The maximum breaker size on #8 romex is 40 Amps (for

supplying a range).

NMB (Romex) cable is always selected from the 60C column in table 310.16

Read 334.80 Ampacity

Steve... I understand...I was also quite clear in previous posts that NM-B must use the 60C column for ampacity. I was speaking towards other wiring methods. Though I see I should have made this more clear since NM-B is rated 90C.

Roger

*Last edited by Roger; 09-13-06 at 02:46 PM.*

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Hello Roger.

A few points to ponder.

[QUOTE=Roger]

"I made it very clear in previous posts that the minimum breaker for a 8750 watt range or larger is 40 amps. It doesnt give a cut off 12 KW".

Beg to differ.

NEC 220.55

"The load for household ranges,......rated in excess of 1 3/4KW (1750 watts) ....is Permitted to be calculated....with Table 220.55."

Table 220.55..........................................Column C

Maximum Demand (KW)....................(Not over 12KW Rating)

Number of appliances, 1...................Maximum Demand...8 KW

I think part of the confusion is created by the fact that you can only use Table 220.55, Column C for a self contained (free standing) range (without doing any other calculation). If you're using a counter-mounted cooking unit and not more than 2 ovens on the same circuit you have to add these loads together and treat them as single load. At that point you use Column C Table 220.55 If the total (after adding) is 12KW or less, you can use 8KW as your Maximum Demand.

If the total (after adding) is more than 12KW, you add 5% to the Column C Maximum Demand for every KW (or fraction of) increase above 12KW. You can use this formula for ranges up to 27KW rating.

Individual ovens and counter-top units on their own individual circuit are calculated using their nameplate rating.

This is the confusing part.

Say for example I have a 16KW range.

The first 12KW I calculate as 8KW demand (Column C).

I add 5% for each (4) additional KW above 12 (Table 220.55 Note 1.)

4 KW x 5% = 200watts.

I add this to the maximum demand of column C.

8KW (8000 watts) plus 200 watts equals 8.2KW (8200 watts) Total Demand= 8.2 KW for a 16 KW range.

If these numbers are not correct, somebody please enlighten me.

Using this same formula, if I have a single 27KW range the Maximum Demand would only be 8.75KW, which (per NEC) would require a 40 amp circuit (240 volts).

So ... a single free standing household range that's rated 27KW or less would never require a circuit larger than 40 amps.

That's the way that I read and understand it.

"Steve... I understand...I was also quite clear in previous posts that NM-B must use the 60C column for ampacity. I was speaking towards other wiring methods. Though I see I should have made this more clear since NM-B is rated 90C."

Roger, I know that you know this, but I'm going to say it again anyway for any others that may have confusion..

The conductor insulation in NM-B cable is rated 90C although you can't (safely and per code) use it at that temperature. NEC 334.80 Ampacity...The Ampacity of Non-metallic sheathed (NM) cable (all NM, this includes NM-B) "shall be determined in accordance with 310.15. The ampacity shall be in accordance with the 60C (140 degrees F) temperature table".

NM-B (as a cable) is rated 60C.

I know that it seems like I'm splitting hairs, but some people see that 90C number and think that they can use the 90C column to figure ampacity. Most connections on older homes are rated 60C and I have seen some rated 40C. This is the maximum safe operating temperature that these connections can tolerate without failing. Most modern equipment that I see has terminals rated at 75C. You should always check the temperature rating of the connections on any electrical installation and calculate your wire ampacity to keep the terminal temperature at or below it's rating. Most problems are caused by failure of the connection, not the wire.

If you use the 90C column to pick your conductor and you fully load that conductor to it's 90C rating, you will overheat the connections and also have wiring in your wall that's hot.

90C is 194 degrees farenheit. Do you really want wires at that temperture inside the walls of your home? Not me.

I'm not trying to argue, I'm still learning.

steve

A few points to ponder.

[QUOTE=Roger]

"I made it very clear in previous posts that the minimum breaker for a 8750 watt range or larger is 40 amps. It doesnt give a cut off 12 KW".

Beg to differ.

NEC 220.55

"The load for household ranges,......rated in excess of 1 3/4KW (1750 watts) ....is Permitted to be calculated....with Table 220.55."

Table 220.55..........................................Column C

Maximum Demand (KW)....................(Not over 12KW Rating)

Number of appliances, 1...................Maximum Demand...8 KW

I think part of the confusion is created by the fact that you can only use Table 220.55, Column C for a self contained (free standing) range (without doing any other calculation). If you're using a counter-mounted cooking unit and not more than 2 ovens on the same circuit you have to add these loads together and treat them as single load. At that point you use Column C Table 220.55 If the total (after adding) is 12KW or less, you can use 8KW as your Maximum Demand.

If the total (after adding) is more than 12KW, you add 5% to the Column C Maximum Demand for every KW (or fraction of) increase above 12KW. You can use this formula for ranges up to 27KW rating.

Individual ovens and counter-top units on their own individual circuit are calculated using their nameplate rating.

This is the confusing part.

Say for example I have a 16KW range.

The first 12KW I calculate as 8KW demand (Column C).

I add 5% for each (4) additional KW above 12 (Table 220.55 Note 1.)

4 KW x 5% = 200watts.

I add this to the maximum demand of column C.

8KW (8000 watts) plus 200 watts equals 8.2KW (8200 watts) Total Demand= 8.2 KW for a 16 KW range.

If these numbers are not correct, somebody please enlighten me.

Using this same formula, if I have a single 27KW range the Maximum Demand would only be 8.75KW, which (per NEC) would require a 40 amp circuit (240 volts).

So ... a single free standing household range that's rated 27KW or less would never require a circuit larger than 40 amps.

That's the way that I read and understand it.

"Steve... I understand...I was also quite clear in previous posts that NM-B must use the 60C column for ampacity. I was speaking towards other wiring methods. Though I see I should have made this more clear since NM-B is rated 90C."

Roger, I know that you know this, but I'm going to say it again anyway for any others that may have confusion..

The conductor insulation in NM-B cable is rated 90C although you can't (safely and per code) use it at that temperature. NEC 334.80 Ampacity...The Ampacity of Non-metallic sheathed (NM) cable (all NM, this includes NM-B) "shall be determined in accordance with 310.15. The ampacity shall be in accordance with the 60C (140 degrees F) temperature table".

NM-B (as a cable) is rated 60C.

I know that it seems like I'm splitting hairs, but some people see that 90C number and think that they can use the 90C column to figure ampacity. Most connections on older homes are rated 60C and I have seen some rated 40C. This is the maximum safe operating temperature that these connections can tolerate without failing. Most modern equipment that I see has terminals rated at 75C. You should always check the temperature rating of the connections on any electrical installation and calculate your wire ampacity to keep the terminal temperature at or below it's rating. Most problems are caused by failure of the connection, not the wire.

If you use the 90C column to pick your conductor and you fully load that conductor to it's 90C rating, you will overheat the connections and also have wiring in your wall that's hot.

90C is 194 degrees farenheit. Do you really want wires at that temperture inside the walls of your home? Not me.

I'm not trying to argue, I'm still learning.

steve

#

**24**
-------------------------------------------------------------

This is the confusing part.

Say for example I have a 16KW range.

The first 12KW I calculate as 8KW demand (Column C).

I add 5% for each (4) additional KW above 12 (Table 220.55 Note 1.)

4 KW x 5% = 200watts.

I add this to the maximum demand of column C.

8KW (8000 watts) plus 200 watts equals 8.2KW (8200 watts) Total Demand= 8.2 KW for a 16 KW range.

If these numbers are not correct, somebody please enlighten me.

------------------------------------------------------------

Steve

I believe that you are not making the correct calculation. The note says that the maximum demand of column C shall be increased 5% for each KW over 12000 watts not the KW itself. The max. demand is 8000 watts. So each kw requires an increase of 5% to the max. demand of 8000. 4 x 5% or an increase of 20% to the max demand of 8000 watts. So 8000 watts x .20 = 1600 watts. Demand for a 16KW range is 9600 watts not 8200 watts.....or another way to look at it is 8000 x .05 x 4 = 1600 watts ....8000 + 1600 = 9600 watts

-------------------------------------------------------------

Using this same formula, if I have a single 27KW range the Maximum Demand would only be 8.75KW, which (per NEC) would require a 40 amp circuit (240 volts).

So ... a single free standing household range that's rated 27KW or less would never require a circuit larger than 40 amps.

That's the way that I read and understand it.

-------------------------------------------------------------

Steve

Each kw over 12000 requires a 400 watt addition (8000 x .05) to 8000 watts max.demand in column C so.. 27-12 = 15KW.... 15 kw x 400 watts is 6000 watts....or 8000 x .05 x 15 = 6000 watts....

Demand for a 27000 watt range is 8000 + 6000 = 14000watts

------------------------------------------------------------

Roger, I know that you know this, but I'm going to say it again anyway for any others that may have confusion..

The conductor insulation in NM-B cable is rated 90C although you can't (safely and per code) use it at that temperature. NEC 334.80 Ampacity...The Ampacity of Non-metallic sheathed (NM) cable (all NM, this includes NM-B) "shall be determined in accordance with 310.15. The ampacity shall be in accordance with the 60C (140 degrees F) temperature table".

NM-B (as a cable) is rated 60C.

I know that it seems like I'm splitting hairs, but some people see that 90C number and think that they can use the 90C column to figure ampacity. Most connections on older homes are rated 60C and I have seen some rated 40C. This is the maximum safe operating temperature that these connections can tolerate without failing. Most modern equipment that I see has terminals rated at 75C. You should always check the temperature rating of the connections on any electrical installation and calculate your wire ampacity to keep the terminal temperature at or below it's rating. Most problems are caused by failure of the connection, not the wire.

If you use the 90C column to pick your conductor and you fully load that conductor to it's 90C rating, you will overheat the connections and also have wiring in your wall that's hot.

90C is 194 degrees farenheit. Do you really want wires at that temperture inside the walls of your home? Not me.

I'm not trying to argue, I'm still learning.

steve[/QUOTE]

--------------------------------------------------------------

No disagreement with this Steve....I am still learning also

Roger

This is the confusing part.

Say for example I have a 16KW range.

The first 12KW I calculate as 8KW demand (Column C).

I add 5% for each (4) additional KW above 12 (Table 220.55 Note 1.)

4 KW x 5% = 200watts.

I add this to the maximum demand of column C.

8KW (8000 watts) plus 200 watts equals 8.2KW (8200 watts) Total Demand= 8.2 KW for a 16 KW range.

If these numbers are not correct, somebody please enlighten me.

------------------------------------------------------------

Steve

I believe that you are not making the correct calculation. The note says that the maximum demand of column C shall be increased 5% for each KW over 12000 watts not the KW itself. The max. demand is 8000 watts. So each kw requires an increase of 5% to the max. demand of 8000. 4 x 5% or an increase of 20% to the max demand of 8000 watts. So 8000 watts x .20 = 1600 watts. Demand for a 16KW range is 9600 watts not 8200 watts.....or another way to look at it is 8000 x .05 x 4 = 1600 watts ....8000 + 1600 = 9600 watts

-------------------------------------------------------------

Using this same formula, if I have a single 27KW range the Maximum Demand would only be 8.75KW, which (per NEC) would require a 40 amp circuit (240 volts).

So ... a single free standing household range that's rated 27KW or less would never require a circuit larger than 40 amps.

That's the way that I read and understand it.

-------------------------------------------------------------

Steve

Each kw over 12000 requires a 400 watt addition (8000 x .05) to 8000 watts max.demand in column C so.. 27-12 = 15KW.... 15 kw x 400 watts is 6000 watts....or 8000 x .05 x 15 = 6000 watts....

Demand for a 27000 watt range is 8000 + 6000 = 14000watts

------------------------------------------------------------

Roger, I know that you know this, but I'm going to say it again anyway for any others that may have confusion..

The conductor insulation in NM-B cable is rated 90C although you can't (safely and per code) use it at that temperature. NEC 334.80 Ampacity...The Ampacity of Non-metallic sheathed (NM) cable (all NM, this includes NM-B) "shall be determined in accordance with 310.15. The ampacity shall be in accordance with the 60C (140 degrees F) temperature table".

NM-B (as a cable) is rated 60C.

I know that it seems like I'm splitting hairs, but some people see that 90C number and think that they can use the 90C column to figure ampacity. Most connections on older homes are rated 60C and I have seen some rated 40C. This is the maximum safe operating temperature that these connections can tolerate without failing. Most modern equipment that I see has terminals rated at 75C. You should always check the temperature rating of the connections on any electrical installation and calculate your wire ampacity to keep the terminal temperature at or below it's rating. Most problems are caused by failure of the connection, not the wire.

If you use the 90C column to pick your conductor and you fully load that conductor to it's 90C rating, you will overheat the connections and also have wiring in your wall that's hot.

90C is 194 degrees farenheit. Do you really want wires at that temperture inside the walls of your home? Not me.

I'm not trying to argue, I'm still learning.

steve[/QUOTE]

--------------------------------------------------------------

No disagreement with this Steve....I am still learning also

Roger

*Last edited by Roger; 09-14-06 at 03:34 PM.*

#

**26**
Jw

Absolutely, in fact I made mention of this in my previous reply but decided to come back and edit that part out. I dont wont this thread to never reach an end as we open another can of worms.

Part III of Art. 220 is definitely for demand load calculations for dwellings. However, note 4 of table 220.55 allows you do perform branch circuit load calculations when dealing with 1 range using the C column of that table. Please also refer to Art. 210.20(B)(4)

Art.210.19(A)(3) IMO only states that for ranges of 8750 watts and more that you must not have them on less than 40 amps branch circuit rating. It does not explictly give you permission to place all ranges over 8.75 Kw on 40 amp conductors. This would be ridiculous. It simply is a safety catch in terms of appliance efficiency and diversity. Once the 1 range reaches more than 12 KW rating you would use the nameplate when sizing conductors... table 220.55 no longer applies. When you get into the high end residentail ranges like viking for instance they are in the neighboorhood of 13 KW and are factory spec'd for 60 amp circuits. Hence diversity goes away at 12kw for 1 range as far as the NEC is concerned when sizing conductors to cooking equipment. Pretty much after that you are looking at multiple ranges or cooktops. So only demand loads for dwelling calculations is relevant to Table 220.55 at this point.

Roger

Absolutely, in fact I made mention of this in my previous reply but decided to come back and edit that part out. I dont wont this thread to never reach an end as we open another can of worms.

Part III of Art. 220 is definitely for demand load calculations for dwellings. However, note 4 of table 220.55 allows you do perform branch circuit load calculations when dealing with 1 range using the C column of that table. Please also refer to Art. 210.20(B)(4)

Art.210.19(A)(3) IMO only states that for ranges of 8750 watts and more that you must not have them on less than 40 amps branch circuit rating. It does not explictly give you permission to place all ranges over 8.75 Kw on 40 amp conductors. This would be ridiculous. It simply is a safety catch in terms of appliance efficiency and diversity. Once the 1 range reaches more than 12 KW rating you would use the nameplate when sizing conductors... table 220.55 no longer applies. When you get into the high end residentail ranges like viking for instance they are in the neighboorhood of 13 KW and are factory spec'd for 60 amp circuits. Hence diversity goes away at 12kw for 1 range as far as the NEC is concerned when sizing conductors to cooking equipment. Pretty much after that you are looking at multiple ranges or cooktops. So only demand loads for dwelling calculations is relevant to Table 220.55 at this point.

Roger

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[QUOTE=Roger

Steve

"I believe that you are not making the correct calculation. The note says that the maximum demand of column C shall be increased 5% for each KW over 12000 watts not the KW itself. The max. demand is 8000 watts. So each kw requires an increase of 5% to the max. demand of 8000. 4 x 5% or an increase of 20% to the max demand of 8000 watts. So 8000 watts x .20 = 1600 watts. Demand for a 16KW range is 9600 watts not 8200 watts.....or another way to look at it is 8000 x .05 x 4 = 1600 watts ....8000 + 1600 = 9600 watts"

"Each kw over 12000 requires a 400 watt addition (8000 x .05) to 8000 watts max.demand in column C so.. 27-12 = 15KW.... 15 kw x 400 watts is 6000 watts....or 8000 x .05 x 15 = 6000 watts...."

"Demand for a 27000 watt range is 8000 + 6000 = 14000watts"

You're correct.

After re-reading Note 1. again I realize that I mis-interpreted what it meant...exactly. (Imagine that, someone mis-interpreting the Electrical Code).

The loads that I gave seemed really strange to me too. That's why I asked for confirmation.

I've never installed a branch circuit for a range larger than 12kw, so I've never had to do these calculations before.

They weren't on the electrical exam the day I took the test (lucky for me).

I learned something today, I can go to work now.

steve

Steve

"I believe that you are not making the correct calculation. The note says that the maximum demand of column C shall be increased 5% for each KW over 12000 watts not the KW itself. The max. demand is 8000 watts. So each kw requires an increase of 5% to the max. demand of 8000. 4 x 5% or an increase of 20% to the max demand of 8000 watts. So 8000 watts x .20 = 1600 watts. Demand for a 16KW range is 9600 watts not 8200 watts.....or another way to look at it is 8000 x .05 x 4 = 1600 watts ....8000 + 1600 = 9600 watts"

"Each kw over 12000 requires a 400 watt addition (8000 x .05) to 8000 watts max.demand in column C so.. 27-12 = 15KW.... 15 kw x 400 watts is 6000 watts....or 8000 x .05 x 15 = 6000 watts...."

"Demand for a 27000 watt range is 8000 + 6000 = 14000watts"

You're correct.

After re-reading Note 1. again I realize that I mis-interpreted what it meant...exactly. (Imagine that, someone mis-interpreting the Electrical Code).

The loads that I gave seemed really strange to me too. That's why I asked for confirmation.

I've never installed a branch circuit for a range larger than 12kw, so I've never had to do these calculations before.

They weren't on the electrical exam the day I took the test (lucky for me).

I learned something today, I can go to work now.

steve

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Originally Posted by

**Roger**Jw

I dont wont this thread to never reach an end as we open another can of worms.

Lets not quit yet.

"Art.210.19(A)(3) IMO only states that for ranges of 8750 watts and more that you must not have them on less than 40 amps branch circuit rating. It does not explictly give you permission to place all ranges over 8.75 Kw on 40 amp conductors. This would be ridiculous."

It may be ridiculous, but I believe (now) that 210.19(3) combined with 220.55 Note 4. allows all ranges up to 12kw to be supplied by a 40A circuit

It simply is a safety catch in terms of appliance efficiency and diversity. Once the 1 range reaches more than 12 KW rating you would use the nameplate when sizing conductors... table 220.55 no longer applies. Roger

I dont wont this thread to never reach an end as we open another can of worms.

Lets not quit yet.

"Art.210.19(A)(3) IMO only states that for ranges of 8750 watts and more that you must not have them on less than 40 amps branch circuit rating. It does not explictly give you permission to place all ranges over 8.75 Kw on 40 amp conductors. This would be ridiculous."

It may be ridiculous, but I believe (now) that 210.19(3) combined with 220.55 Note 4. allows all ranges up to 12kw to be supplied by a 40A circuit

It simply is a safety catch in terms of appliance efficiency and diversity. Once the 1 range reaches more than 12 KW rating you would use the nameplate when sizing conductors... table 220.55 no longer applies. Roger

Note 4. says that we can use Column C for to calculate the branch circuit for 1 range. Column C for one range cuts off at 12KW. At that point, were back to 210.19(3) which requires us to use the ampacity of the load to be served.

All Table 220.55 relates to at that point is feeder calculations for the range.

I think that I've got it now, and it's something certainly worth learning.

This was a good subject to discuss.

steve

#

**29**
Yes I agree this has been a good subject and BTW I dont consider myself a code expert though it appears I may have given that impression. 3 or 4 years ago I made the same misinterpretation on that calculation as you did only it was a test...so just want to set the record straight in that regard.

"It may be ridiculous, but I believe (now) that 210.19(3) combined with 220.55 Note 4. allows all ranges up to 12kw to be supplied by a 40A circuit"

You know what.... I am inclined to go along with that. My only caveat is that I would find it hard for (me) to put a 12000 watt range on 40 amps. You would have to be around my house at thanksgiving time to appreciate why I say that. When you think about it most ranges with four heating elements and oven are at least 10KW so I agree 40 amps would be allowed. Personnally if it wasnt a cost consideration or cost smart (new construction contractors) I dont like the diversity method of 220.55.

My point about 210.19(A)(3) is that it does not give a cut off of 12kw it just says 8750 watts or more. There is no reference to 220.55 or note 4 of that table. So unless you know all the other applicable sections you would be lead to believe that a 13 kw range could be on 40 amps. I agree once you know that these other issues are a factor then 12 kw enters the picture.

You actually explained this better than I in your previous post.

I apologize to all if I came across as a "know it all"... I'm far from it. I'm prone to poor decisions at times and plead guilty to taking this thread down a road that wasnt necessary. I do hope however that someone out there learned a little as I did.

Roger

"It may be ridiculous, but I believe (now) that 210.19(3) combined with 220.55 Note 4. allows all ranges up to 12kw to be supplied by a 40A circuit"

You know what.... I am inclined to go along with that. My only caveat is that I would find it hard for (me) to put a 12000 watt range on 40 amps. You would have to be around my house at thanksgiving time to appreciate why I say that. When you think about it most ranges with four heating elements and oven are at least 10KW so I agree 40 amps would be allowed. Personnally if it wasnt a cost consideration or cost smart (new construction contractors) I dont like the diversity method of 220.55.

My point about 210.19(A)(3) is that it does not give a cut off of 12kw it just says 8750 watts or more. There is no reference to 220.55 or note 4 of that table. So unless you know all the other applicable sections you would be lead to believe that a 13 kw range could be on 40 amps. I agree once you know that these other issues are a factor then 12 kw enters the picture.

You actually explained this better than I in your previous post.

I apologize to all if I came across as a "know it all"... I'm far from it. I'm prone to poor decisions at times and plead guilty to taking this thread down a road that wasnt necessary. I do hope however that someone out there learned a little as I did.

Roger

*Last edited by Roger; 09-15-06 at 08:02 AM.*