40/50 amp breaker for dryer

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  #1  
Old 06-19-02, 03:42 AM
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40/50 amp breaker for dryer

Hey fellas, When not in this forum, I spend quite a bit of time in the Electrical Appliance forum. Someone posted a guestion asking if it is okay to run a dryer rated at 30 amp on a 40 or 50 amp breaker. They were told they could just change the outlet. I said no. Sounded like they were changing a stove outlet to a dryer outlet. I said no on that one for safety reasons. If I read the post right, an electrician told one of the people they copuld safely change the outlet to fit the dryer, but then told them to never use a breaker rated higher than the applaince for protection for that appliance! Sounds like a 'Yes, you can. No you can't' type response to me. Comments?
 
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Old 06-19-02, 06:29 AM
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In addition to changing the receptacle, you also need to change the breaker to a 30-amp breaker. It's a simple and inexpensive change, so I see no reason to try to avoid it.
 
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Old 06-19-02, 07:54 AM
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It's a simple and inexpensive change, so I see no reason to try to avoid it.

that is basically what I was trying to tell them.

Tx for your response, John.
 
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Old 06-24-02, 12:42 PM
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Dcravey
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Clarification

Hi Folks,

I was one of those original people in the appliance forum, but I'm not sure I made the situation clear. What I have is a new 30 amp dryer with a 4-prong plug. The outlet that the old dryer was plugged-into is apparently a 3-prong range outlet, or 50 amp receptacle. The circuit box for the dryer contains two 20 amp mini-breakers, but the label on the outside of the box says "30 amps."

The Sears salesman told me I would need to change the receptacle before the delivery crew would hook it up. I called an electrician to do this, but he looked at the wiring and told me it would be easier and less expensive to simply change the power cord on the new dryer to one that fits the existing receptacle. (He suggested I use the one off the old dryer, but since the appliance is brand new, I went out and bought a new cord to match.)

He also told me I would probably need to change the fuses on the dryer to circuit to 30 amps. (The old dryer was 23 amps, according to the nameplate. Not sure why it never tripped those 20 amp fuses.) It was during this discussion that he told me that the fuses/breakers should not be rated higher than the amperage of the appliance.

And so, other than making sure that the wiring is at least 10 awg copper to handle the 30 amp fuse, does anyone see any other dangers to the advice the electrician gave me? I am also aware of the need to secure the green ground wire so that I don't send electricity to the dryer's frame. (Do I simply attach this green ground wire between the white "neutral" central screw and the green screw on the frame?) The dryer arrives this afternoon, and I will be sure to look at the schematic.

I appreciate everyone's help on this matter. Who knew replacing a dryer would become so complicated?
 
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Old 06-24-02, 03:44 PM
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terrywouldbe
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(Do I simply attach this green ground wire between the white "neutral" central screw and the green screw on the frame?)
Absolutely NO! Please do not attach the ground wire, or pigtail it with the white, to the center neutral connection

You should have 10-3 w/g, a 30 amp receptacle which will have 4 slots to match the dryer's 4 prong cord. You will have 2 hot wires (red and black) 1 neutral (white) and 1 bare ground. Attach the neutral (white) to the center connection. The bare ground (of the 10-3 cable) will go to the green wire. The two hots will attach to the remaining two slots.

Am I right guys?

-Terry

Oh, and the breaker should be 30 amp
 
  #6  
Old 06-24-02, 04:13 PM
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Wgoodrich
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Terry you are absolutely right in your statement concerning a new branch circuit but wrong in your statement concerning an existing branch circuit.

A dryer requires 30 amps per the manufacturer's instructions. NEC requires a minimum wire size of 10 awg copper to serve a 30 amp rated dryer circuit using a 30 amp 240 volt breaker protecting that 10 awg branch circuit.

You are right in your statement because the NEC requires a black, red, white, and bare conductor in a cable connected to a four prong 30 amp dryer receptacle with a four wire pigtail connected to the new dryer or old dryer with the white wire of the pigtail connected ot the center tap of the dryer terminal block inside the new or old dryer.

You are wrong in your statement bacause the NEC also provides an EXCEPTION concerning an existing 30 amp branch circuit that is two insulated hot conductors and one bare neutral/grounding dual purpose conductor. This bare neutral/grounding conductor is only allowed for existing branch circuits.

Even though you are changing the breaker from 20 to 30 amp double pole utilizing the existing 10 awg branch circuit that has a 3 prong plug you have only performed minor repair thus allowing that existing branch circuit to remain an existing branch circuit. If you had to extend that existing branch circuit then you would have to install an entire new four wire branch circuit becuase that existing branch circuit extension would negate the existing status of that existing branch circuit becuase you changed the integrity of that existing wire.

Since you only changed the breaker size equal to the ampacity of the original 10 awg branch circuit with two insulated hot wires and one insulated Romex cable or one bare SE cable conductor then you still have an existing three wire dryer branch circuit.

You would then have to install a three wire pigtail to that new dryer and install a bonding jumper from that center screw on that terminal block in your dryer creating a green bonding jumper connecting that center neutral screw to the metal frame of the dryer to also act as you equipment grounding conductor.

Remember you are only allowed to use this existing three wire dryer branch circuit if teh cable is a Romex cable with a white insulated neutral conductor used as a dual purpose neutral/grounding conductor or if your existing dryer branch circuit is an Service entrance cable allowing the neutral conductor being used as a dual purpose neutral/grounding conductor to be bare.

If the branch circuit is a new four wire branch circuit then you must have a four prong receptacle, a four wire dryer pigtail with a separated neutral and grounding connection inside that new dryer.

If the branch circuit is an existing branch circuit as discribed above then you must have a three prong receptacle with a three wire pigtail with the neutral screw of the terminal block inside the dryer jumped to the green screw of the metal case of that new dryer.

Hope this helps

Wg
 
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Old 06-24-02, 08:24 PM
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terrywouldbe
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Wg,

Please tell me if I am understanding this. Are you referring to an existing circuit of, say, 10-2 w/g, where the black and white wires are being used as ungrounded (HOT) conductors and the bare used as the neutral? In that case, I think I am understanding. NOT SURE THOUGH

Would I wire this as follows: on the receptacle: black and white wires to their respective connections (for the Hot connections), and the bare would be connected to the center tap of the receptacle and pigtailed to the chassis of the appliance to serve as both a neutral and the Equipment Ground? in the panel: the black and white wires would be connected to the d/p Breaker and the bare would be connected to the neutral bus?

Also, am I correct that there is, in fact, a neutral in this circuit? The Dryer does operate on 120/240, right?

So, bottom line:

1). Would it be ok to use a 3-prong receptacle connected to a 30-amp d/p Breaker with 10-2 w/g Romex?

2). This would not be considered a bootleg ground ?

3). What would happen should the neutral (the bare wire) become open somewhere?

I hate to sound ignorant, but I think, therefore, I am

-Terry
 
  #8  
Old 06-24-02, 08:50 PM
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Older installations of dryers and ranges are allowed to do something that no other circuits are allowed to do -- they share a neutral and ground. Yes, in other circumstances, this would be known as a bootleg ground and would be highly illegal.

But this exception is very narrowly defined:
  • This is indeed an exception and may not be generalized to anything else.
  • This exception is allowed only for ranges and dryers.
  • This exception is only allowed for cable run under the 1996 or earlier codes -- you cannot run new wire today and hook up a range or dryer this way.
  • You cannot take advantage of this exception in a mobile home or recreational vehicle.
  • The grounded conductor is not smaller than 10-gauge copper.
  • The grounded conductor is either insulated, or is part of a Type SE cable.
  • If using SE cable, the circuit must originate on the main panel, not a subpanel (it would be nearly impossible to keep this neutral isolated in a subpanel if it is bare).
Basically, the NEC committee has reluctantly agreed to this compromise. They know that it isn't as safe as it could be. But they also recognize the tremendous expense that would be involve to upgrade all the older homes to require the safer 4-wire service.

Yes, the dryer does operate on 120/240. There is a neutral.

No, you can't pigtail from the receptacle to the chassis. This interconnection takes place at the dryer, not at the receptacle.

If you are using this exception, you must use a 3-hole receptacle and a 3-wire appliance cord.

This cannot be wired if the circuit has 10/2 cable, since 10/2 does not have an insulated ground and it is not Type SE. Furthermore, you can't install any other kind of cable either -- the cable must already be there to use this exception.

If the grounding/neutral wire were to become disconnected, you'd be in trouble. The dryer chassis would become energized when you tried to turn the drum on. Don't let this happen. Take special precautions to make sure that the neutral does not become disconnected.
 
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Old 06-24-02, 10:18 PM
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Wgoodrich
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John you said is well and clear.

Terry I believe there may be a question that may not be clear to you concerning Romex. IF you didn't catch it in what John was saying then read the following;

A Romex cable can only be used in an existing three wire branch circuit serving a range or dryer if that cable contains two hot colored wires most commonly black and red and an insulated white wire. There was a Romex cable that was as discribed above only without a bare conductor. This Romex cable may be used.

You mentioned a black white and bare Romex cable. This cable is forbidden to be used in this exception for existing branch circuits for ranges and dryer three wire circuits. This cable with a black and white and bare would not have a white neutral but a white hot that would force you to use the bare wire as the neutral. That is forbidden.

Hope this helps

Wg
 
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Old 06-25-02, 06:02 AM
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terrywouldbe
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Lightbulb awwwgee

Wg and John,

after working on your replies for about 2 hrs, I think the light just went on! No reflection on your descriptions, intended; just a lot of resistance in my brain!

Here's what I am thinking - oh lord, not that again

a). In the original post (Bowman and DCravey), there currently exists a 3-prong receptacle wired with 10-3 (no grnd). The two ungrounded conductors (red and black) are connected to their respective terminals on the receptacle, and the white neutral is connected to the center post on the receptacle.

b). There is a 'terminal block' inside the Dryer which has connections for a 3-prong appliance cord. On this 'block', we connect the red, black and white wires of the appliance cord, and from the neutral terminal on the block, we place a bonding jumper to the metal frame to act as the equipment ground.

Is this the case, or am I, once again, experiencing Phantom Thinking

Again, let me thank you guys for your patience and willingness to help us amateurs. It IS appreciated.

Terry
 
  #11  
Old 06-25-02, 12:46 PM
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Wgoodrich
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The red, black, white insulated wire in your existing cable allows you to continue using this existing cable even on a new electric dryer. The breaker must be 30 amp 240 volt rated with 10 awg conductors with a three prong dryer receptacle, with a three wire dryer cord with a green bonding jumper connecting the silver center screw of hte dryer terminal jumping to the metal frame of the dryer. This uses that white wire as both a neutral and an equipment grounding conuctor bonding the metal frame of hte dryer.

You have it go for broke.

Wg
 
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Old 06-25-02, 01:27 PM
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Art. 250.140 permitts grounding dryer frames to the Neutral if the dryer is being connected to an existing branch-circuit protected by a fuse/circuit-breaker located in the same panel as the service dis-connect and the Neutral is #10 minimum and insulated.(exception for SE cable W/bare Neutral).The Code does not specify exactly where the connection is to be made.If this is a new dryer equipped with a 4-prong cord-plug I would leave the cord-plug intact and connect a jumper between the Grounding terminal on the receptacle and the Neutral conductor.---------Art. 210.21 requires that the ampere rating of a single receptacle on an individual branch-circuit equal the rating of the fuse/circuit breaker.If a 4-prong 30 amp receptacle is used then a 40/50 amp breaker must be re-placed with a 30 amp breaker.
 
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Old 06-25-02, 05:05 PM
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patbaa, if you will check the manufacturer's recommendations on that new dryer that you are required to follow per 110.3.B you should find that the pigtail is supposed to be a 3 wire pigtail cord with the bonding jumper installed between the neutral screw of that dryer's terminal block and the metal frame.

The NEC fobids the installation of a 4 prong receptacle on a three wire existing branch circuit. You would create a false grounding implied in the four wire receptacle where there is no equipment grounding conductor present.



Hope this helps

Wg
 
  #14  
Old 06-26-02, 08:21 AM
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WG; You are essentialy correct on the 4-prong receptacle.Allow me to mention that your comment would be more accurate if you said-"The NEC forbids (a) 4-prong receptacle on an existing 3-wire branch-circuit without an Equiptment Grounding Conductor."The NEC does not "forbid," per se, but "requires" that the Grounding contacts of receptacles be connected to an Equiptment Grounding Conductor and that the Wiring Method provide an EGC.(Art. 406.3). A 4-prong dryer receptacle could be used if the Wiring Method is Armored Cable or Nonmetallic Cable with an EGC but could not be used if the WM was SE cable. I stand corrected on suggesting a Ground-to-Neutral jumper at the receptacle.------I'm reluctant to advise DIY'ers to tamper with,or modify, factory-installed attachments such as cord-plugs. Cheers,PATTBAA
 
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