What gauge? [Electrical Wire Gauge Size]

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  #1  
Old 07-07-05, 09:30 AM
sklett
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What gauge? [Electrical Wire Gauge Size]

I'm sure this has been asked before, but I can't find a search facility on this website??

Anyway, I'm trying to determine what gauge wire I need for a particular application. Furthermore, I would like some fundamental clarification on the different "classes" of wiring. I have found a site(http://www.powerstream.com/Wire_Size.htm) that has am AWG/amp/length table, but it's confusing in that there are two max amperage columns, one for "chassis wiring" and another for "power transmission". There is a vague clue that leads me to believe that "power transmission" is "open air" wiring, although I don't understand this description either. Do they mean individual runs of solid copper wire, not enclosed in outer rubber(romex) or conduit? If so, in what case would that be used??

But, to get to the point, I need to run a 50 amp circuit, under the house, 220v. What gauge I need to use.?

Are there significant differences from solid copper wire and stranded? I have a 500' spool of 8AWG stranded wire and would like to use it if possible.

Thanks for any input,
Steve
 
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  #2  
Old 07-07-05, 09:36 AM
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<<But, to get to the point, I need to run a 50 amp circuit, under the house, 220v. What gauge I need to use.?>>

What is this circuit going to supply?

<<Are there significant differences from solid copper wire and stranded? I have a 500' spool of 8AWG stranded wire and would like to use it if possible.>>

You won't find insulated solid wire in gauges #8 and larger.
 
  #3  
Old 07-07-05, 10:33 AM
sklett
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sorry I didn't mention that. It will be supplying an AC condensor(pump)
 
  #4  
Old 07-07-05, 11:16 AM
ally68
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How big is this A.C. seems like the 50 amp is a little big?
 
  #5  
Old 07-07-05, 11:31 AM
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Use 2 runs of black or red #6 copper stranded wire THHN for the hot conductors and one run of green #10 copper wire for the ground. Use an additional #6 white conductor if this circuit needs a neutral (which an AC probably doesn't). Many of the "pocket editions" of the NEC, electricians' guide, etc will have the proper tables you are looking for for a few dollars.

The #8 copper could be used with a 45 amp breaker which may be okay with your pump motor. Post the full nameplate specs for the equipment and the distance from the panel.
 
  #6  
Old 07-07-05, 11:41 AM
sklett
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ally68,
it's a 3 ton unit. I don't have the unit yet, so I can't read off plate specs and the manf. web site is LAME(no equip. data sheets)

I agree it seems big, but that's what the HVAC guy told me to run. Maybe he's thinking if I ever upgrade to a larger unit(house add on?) then it would be nice to have the power?

Thanks for the post!
 
  #7  
Old 07-07-05, 11:46 AM
sklett
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ibpooks,
Thanks for the post. Don't need a common. I briefly entertained the idea of running a 120 GFCI off 1 leg of the 220, but then realized there is too much power to do that.

with a run of 3 #8, what size conduit do I need to have it in? I'm sure this is in the NEC book you mention and I fully intend to get one, but for the meantime.. is there a min/max code for this type of thing?

Also, what is THHN?

Considering I have #8 green, can I run that instead of #10? Can a ground be too big?

Also, if I can run a 45 amp circuit and utilize the #8 green I have, can I also use it for the hots if I tape the ends black/red?

Thanks again for the post!
Steve
 
  #8  
Old 07-07-05, 11:47 AM
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I can't find a search facility on this website
There's a "Search" button near the top of every page (in the blue bar with white letters).
 
  #9  
Old 07-07-05, 11:52 AM
sklett
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I don't see it. Maybe it's my browser (Firefox)
I have:
User CP
FAQ
Members List
Calendar
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  #10  
Old 07-07-05, 11:54 AM
sklett
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Doh!
at the very top. I'm dumb.

Thanks for the clue!
 
  #11  
Old 07-07-05, 12:12 PM
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Originally Posted by sklett
with a run of 3 #8, what size conduit do I need to have it in? I'm sure this is in the NEC book you mention and I fully intend to get one, but for the meantime.. is there a min/max code for this type of thing?
If you use 3 #8 conductors, you can use 1/2 conduit EMT or PVC. If you use 2 #6 and 1 #8, you must use at least 3/4 EMT or PVC. The NEC itself will not help you, it's very technical and not easy to read or understand. Look for a home wiring type of book that reprints and explains the NEC tables.

Also, what is THHN?
THHN describes the type of insulation on the wire. THHN is a PVC/Nylon insulation suitable for use in dry areas. Your spool is probably THHN, look for it printed on the cable.

There are dozens of insulation types for all sorts of different applications.

Considering I have #8 green, can I run that instead of #10? Can a ground be too big?
That would be okay.

Also, if I can run a 45 amp circuit and utilize the #8 green I have, can I also use it for the hots if I tape the ends black/red?
I don't believe that is okay. Green must always be ground and cannot be redesignated. Someone else please confirm that.
 
  #12  
Old 07-07-05, 12:24 PM
ally68
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Using a big amp breaker is not going to give you more power but if the breaker is to big it may not tripp soon enuf to avoid damage to your unit. Maybe I am incorrect. but if this is just to the outside unit I would think a 30 amp with #10 wire would fine. but if it is for your inside furnance or something then 50 amp sounds ok. But I dont know a whole lot.
so dont go by what I say.
 
  #13  
Old 07-07-05, 01:15 PM
sklett
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Panel Upgrade Needed? (round 2 w/ images)

OK, I'm a bit confused again. The So. Cal. Edison guy just left and he said that I already have a 200 amp supply from the pole, I'm assuming that's 220v 200 amp, which would effectively be 400 110v amps, correct?

Anyway, that's not the real confusion. The real confusion is about my existing and old panel. I don't want to upgrade if I don't need to. I have tried to determine what amp rating my current panel is, I don't see anything on it to indicate what it's rated at. Here are some facts, links to pics will follow.

-----The Facts-----
-supply lines from the weather head are #8 (2 hot and a neutral)
-supply lines form the pole to the house are #4 aluminum
-the combined amperage of the installed breakers is 230 amps
-I need to add an additional 60 amps of circuits(220 @ 45amp and 110 @ 15amp)
-There doesn't appear to be a central disconnect(is this what they call a "split bus system"?)

pic of the outside(why? I don't know...)
http://www.pmddirect.com/temp/p7060142.jpg

pic of whole panel
http://www.pmddirect.com/temp/p7060143.jpg

pic of upper panel
http://www.pmddirect.com/temp/p7060144.jpg

pic of lower panel
http://www.pmddirect.com/temp/p7060145.jpg

I know there aren't currently any open spots, but a couple 15amp double slims should free up what I need.

Also, the 3 wires coming into frame at the bottom are a 220 cord (temporary) out to the garage.


What I'm hoping is that by changing the wire from the weather head to the panel to something bigger (#4?) I can breathe some more life into this thing.
 
  #14  
Old 07-07-05, 01:20 PM
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There are two issues with a motor like an air conditioner compressor. Short circuit protection and thermal protection. If the motor has built-in thermal protection, then the associated circuit breaker is more flexible as it only needs to account for locked-rotor current in rush and short circuit protection.

If the motor does not have built-in thermal (overcurrent) protection, then the breaker size becomes much more important. That is why the precise specs from the manufacturer are important before planning the circuit. Either way, you can't go wrong with larger-than-required wire; just don't buy the breaker yet. You'll just end up spending a little more upfront on wire, but it may pay itself back in the long run with regard to voltage drop. However, installing wire that is too small is an expensive mistake.
 
  #15  
Old 07-07-05, 01:31 PM
ally68
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Do most motors have thermal protection like a.c. (carrier) how about attic fans I have often wondered it those motors have thermal protection they run for like 8-10 hours straight sometimes.
 
  #16  
Old 07-07-05, 02:26 PM
sklett
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I've got some specs:

PhaseFrequency (Hz)Voltage (Volts): 1-60-208/230
Rated Load Amperes(RLA): 14.1/14.1
Locked Rotor Amperes(LRA): 68
Fan Motor Full Load Amperes(FLA): .75
Minimum Circuit Ampacity Amperes: 19/19

Fuse or HACR Circuit Breaker
Minimum Amperes: 20/20
Maximum Amperes: 30/30


Does that give you a better idea? If I'm reading this correct, I only need a 30 amp 220 circuit? If so, wow, neat!

I can run #10 for 30 amp, can't I?
 
  #17  
Old 07-07-05, 05:37 PM
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The NEC only requires a #14 AWG conductor for this circuit, with a 20 to 30 Amp HACR breaker.

Feel free to exceed the NEC minimum wire size, but the breaker must be HACR rated and can only be 20, 25, or 30 Amp.
 
  #18  
Old 07-07-05, 05:40 PM
sklett
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Wow, thanks for the info!
I can't believe it went from #8 or #6 to #14, that's tiny! 30 amps on #14.... crazy.

Thanks again, I will wait for the unit to show up and verify the details are the same as what I was supplied with today.
 
  #19  
Old 07-07-05, 06:57 PM
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sklett, first of all, your best bet is to keep your posts on this subject in the same thread to allow for continuity. Perhaps one of the moderator's can move them....

Yes, generally a 200A service translates to 200A at 240V. You should not try to equate that with 400A at 120V.

Service through the weather head and mast is #8? I don't think that #8 CU is good for more than 40A, AL is even less. Are you sure about this?

Service from the pole to the weather head is #4? 4/0 AL is appropriate for a 200A service. Are you sure about this?

Combined value of breakers isn't a factor in determining circuit capacity or needs. Not everything is used at the same time. Branch circuit breakers are rated to protect the branch circuit wiring, nothing else. A main breaker (if there is one) is rated to protect the buss in the panel, nothing else. You need to do an electrical load calculation to determine your actual requirements. Do a google search on the term.

Sorry, but I can't speak to the split buss situation you mention. I know what it is, but I've never experienced one.

Overall, as a fellow DIY guy not wishing to sound condescending, it appears to me that you may want to study up a whole lot before you undertake this project.
 
  #20  
Old 07-07-05, 07:28 PM
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Originally Posted by Bolted Fault
The NEC only requires a #14 AWG conductor for this circuit, with a 20 to 30 Amp HACR breaker.
No. this wire is for his house.
You can NOT use # 14 ga wire with a 30 amp breaker.
I think he is talking about the cord that comes with some units
============
First-First you should go by the instruction that come with the unit.
Don't go any smaller then # 10 wire


This is for your house.
NEC book states.
14 ga wire with 15 amp breaker
12 ga, 20 amp breaker
10 ga, 30 amp breaker

if you have a long run you should go up one wire size to avoid voltage drop.
Motors start better with larger wire.

Look at your # 8 ga wire. tell us what is printed on the insulation ?
 
  #21  
Old 07-07-05, 07:53 PM
sklett
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OK, got it. Thanks for the clarification.

The wire is 8awg stranded green, oil & gasoline resistent
THHN and THWN
600v

It's green though, so I'm still waiting for someone to clue me in if I can wrap the ends in black tape to use as my hots.

Thanks again for the post!
Steve
 
  #22  
Old 07-07-05, 08:00 PM
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Guys this is a piece of equipment covered in article 440. This A/c condensor of sklett's is considered to be a combination-load.. ie .. Hermetic motor and condensor fan. He has provided us with the name plate info. Notice it says "minimum circuit ampacity 19 amps". When a nameplate provides that information the manufacturer has already taken into account the 125% of the Hermetic motor plus the condensor fan to calculate the wire ampacity. In this case he would need 14 awg miniumum as Bolted Fault suggests. Table 310.16 shows 14 awg good for 20 amps with 60C terminations. Motor circuits are not treated the same as house wiring. In this case the nameplate data is telling you that a 30 amp HACR breaker can be used as the maximum overcurrent protection. The minimum is 20 amp breaker. The mimimum meaning that is the smallest breaker that will allow the hermetic motor to start without nuisance tripping. So you can legally use a 30 amp HACR breaker on 14 awg wire.

I came back to edit this reply as I noticed that for some reason I had 12 awg as the minimum wire size for this application in the original reply.... I guess I need to get some sleep.
 

Last edited by Roger; 07-07-05 at 10:00 PM.
  #23  
Old 07-07-05, 08:37 PM
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Noticed you asked about the green #8 awg. You cannot use green insulated wire for your conductors. Green is ground only....article 310.12(c) and 250.119. You cannot reidentify it.

You also need a disconnecting means located in sight of the outside condensor unit.

Sometimes the nameplate specifies a BCSC (branch circuit selection current) it is prudent in these cases to use this value for your branch circuit conductor ampacity instead of the mimimum circuit ampacity as shown on the nameplate.
 

Last edited by Roger; 07-07-05 at 11:04 PM.
  #24  
Old 07-08-05, 01:50 AM
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Bolted Fault, Roger.

After reading an updated book I see where you come up with 14 ga wire.
So I now disagree with the NEC Book.

I can see the lawyers having a field day with this one.
----------------------
I believe it was meant, that 14 ga wire would be ok from the AC unit to a service disconnect located close to the AC unit.
The wire from the service disconnect thru the house to the main panel should go by the standard guide lines of the NEC book.

The fuses at the service disconnect may help protect the AC unit.
The circuit breakers in the house are to protect the house wiring not the AC unit.
Underrating the wire in the house contradicts safety.

That's my point of view.
-----------------------
Trying to start a 1 hp motor or larger on 14 ga wire over 25 feet long is a Gamble (it may not start).
In this case its about 2 hp.
Using that small 14 ga wire can shorten the life of the motor.

I can see someone tapping a Dryer or welder off this line thinking its good for 30 amps.
-------------------------
Go by the instruction manual but use larger wire.

What's the distance you need to run the wire ?

If it a long run you must use larger wire to avoid voltage drop.
That voltage drop prevents the motor from getting its full starting horse power needed.
Maybe that's why your HVAC man suggested a 50 amp run, then maybe 30 amp fuses at a service disconnect at the AC unit.
 
  #25  
Old 07-08-05, 06:48 AM
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.

I believe it was meant, that 14 ga wire would be ok from the AC unit to a service disconnect located close to the AC unit.
-----------------------
My understanding is that 14 awg as specified by the minimum circuit ampacity spec on the nameplate is for the branch circuit feeders from overcurrent device to the unit. I cant recall ever seeing a requirement for this to be only from outside disconnect to the unit.

It may be prudent to upsize these feeders for voltage drop or ambient temp. considerations or the like. That information wasnt given maybe we should have asked??

I offer these for support of the above.

http://www.iaei.org/magazine/99_d/simmons.htm


http://www.iaei.org/magazine/00_d/johnston.htm
 
  #26  
Old 07-08-05, 07:37 AM
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The fuses at the service disconnect may help protect the AC unit.
The circuit breakers in the house are to protect the house wiring not the AC unit.
My understanding is the breakers (HACR type) in the panel or (HACR) fuses at the beginning of the circuit, as specified in the nameplate data blocks, are to protect for overcurrent short circuit, line to line or line to ground in motor circuit designs. The internal overload protection device of the hermetic motor protects the branch circuit conductors from overheating and to protect the motor windings.
In house wiring the inverse time breakers protect for both overheat and overcurrent.
 
  #27  
Old 07-08-05, 08:43 AM
sklett
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The further this thread goes on, the more confused I'm getting.

Just to recap:
I can run #8 to the AC disconnect and that will be fine?
This run should be enclosed in 1/2"+ PVC?
the breaker MUST be HACR @ the panel?
The line from the disconnect to the unit I will determine from the owner's manual

OK, if any of that is incorrect, please straighten me out.

Thanks,
Steve
 
  #28  
Old 07-08-05, 08:52 AM
ally68
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What does HARC stand for?
 
  #29  
Old 07-08-05, 09:00 AM
sklett
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I thought that would be an easy one to google... but man, is it not! Apparently HARC approves all kinds of things from breakers to windows. I couldn't fine a website for them, so I don't know what it means.
 
  #30  
Old 07-08-05, 09:06 AM
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Try looking for HACR instead of HARC. It's a Heating, Air Conditioning and Refrigeration breaker.
 
  #31  
Old 07-08-05, 09:22 AM
ally68
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Did not know they required a special breaker is that new (last 10-12 years) also what makes it different?

Thanks
 
  #32  
Old 07-08-05, 09:22 AM
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>This run should be enclosed in 1/2"+ PVC?<

It may be easier to pull the 3 #8 plus ground in 1".

Bob
 
  #33  
Old 07-08-05, 09:35 AM
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I think we may be trying Johns patience on this thread.

Sklett:

Yes you can use #8 awg, you just cant use green insulated for the hot conductors you can use the green for the ground. #8 awg is overkill for the specs. you posted but it will work.

The breaker must be HACR type....not over 30 amp double pole and not smaller than 20 amp double pole.

My personnal opinion is to use #12 awg unless this is an very long run.

Follow all manufactuers instructions including proper use of the nameplate data.

Depending on where you live it doesnt have to be individual wires in conduit while going from main panel to the disconnect, it can be cable, however when it leaves the outside disconnect it will have to be in some kind of protected weatherproof raceway. This requires running individual wires from the disconnect to the condensing unit inside this raceway.
 

Last edited by Roger; 07-08-05 at 09:53 AM.
  #34  
Old 07-08-05, 09:53 AM
sklett
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I hope we aren't trying John's patience, there is a lot of information going around and at times, things have gotten confusing.

Roger, thank you for your final round up on things, I will be proceeding with your suggestion and advice.

-Steve
 
  #35  
Old 07-08-05, 10:20 AM
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Okay, I wrote up a post about the panel upgrade, posted it here, realized that this was a discussion of wire gage to an AC system, deleted my post, and then realized that it was the _same_ original poster and that the two threads are intermingled.

This is in reference to the questions and suggestions about wire size for the feeders and service conductors to the split but panel that the OP is dealing with.

From the pole to the weatherhead, power company rules apply for rating. #4 aluminium in free air with 90C conductors can carry about 100A on a continuous basis (note: this is a rough estimate from the physics, _not_ the code limited value, which is much lower). Under power company rules, this _might_ be suitable for '200A' service.

From the weatherhead on in to your home, NEC rules apply. For this, #8 is _far_ too small for 200A service. However if the wire from pole to weatherhead is large enough, then an electrician could upgrade the service to 200A by replacing everything from the weatherhead on down.

You may want to check that outside box; it may be that you have your main breaker located there, and that what you think is your main panel is actually a subpanel. If this is the case, then it appears that the panel is not properly grounded.

I would not want to add any circuits to this panel if the feeder is only a #8. It is quite likely significantly overloaded.

I have trouble telling where your main service conductors come in; it appears that they share a conduit with some other conductors, which is a no-no.

-Jon
 

Last edited by winnie; 07-08-05 at 12:19 PM.
  #36  
Old 07-08-05, 03:06 PM
ally68
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I looked at my breakers and they say HACR type series 1 on them
one question all my breakers say this is that ok or are they only supposed to be used on a.c. and stuff.
 
  #37  
Old 07-08-05, 03:28 PM
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Ally68 your breakers are fine. Most molded case breakers today are HACR rated. That simply means they are rated for group motor applications. there are still inverse time breakers in panels and on the shelf that are not HACR rated. This means that they may not be able to handle the in-rush of current created by hermetic motors or groups of motors. Hope this clears things up.
 
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