Using Stranded 10AWG Wire in EMT

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Old 11-01-07, 04:20 AM
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Using Stranded 10AWG Wire in EMT

I'm running a 20 amp circuit with ten duplex receptacles in 1/2" EMT in my detached garage. The first receptacle will be a GFCI with the rest being 20 amp rated duplex receptacles.

I was given some stranded 10 AWG thwn and was wondering if this would be okay for code? If this is okay for code do I need to add a eyelet to the green ground wire to attach it to the receptacle electrical box as it would seem to be the proper way. I was also wondering how I would connect the four grounding wires together in my run at the receptacles as I do not see any wire connectors that can handle four 10 gauge wires. Thanks for your help.
 
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  #2  
Old 11-01-07, 08:34 AM
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Yes, the #10 stranded is okay for a 20A circuit. It would be a good idea to mark the circuit clearly in the panel so that a future worker doesn't see the #10 and assume it's for a 30A circuit.

The easiest way to ground the boxes with stranded wire is to buy grounding pigtail assemblies. It's basically a short piece of wire with an eyelet and screw on one end and a big green wirenut on the other end that will accept #10 wire. They come 10 in a pack for a few bucks.

http://www.idealindustries.com/prodD...=0&l1=twist-on

You'll also want to use "back-wire" receptacles. You insert the wire into a hole and turn the screw to compress the wire with a pressure plate. They're usually sold as commercial-grade or something like that and should accept #10 wire as it is very common in commercial/industrial settings.
 
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Old 11-01-07, 08:45 AM
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If you don't want the pre-wired ground wire nuts, you can always use wire nuts and a piece of 12 gage bare wire. Make it long enough to loop around the ground screw in the back of the box and then hit the receptacle.

Note that the less expensive receptacles with screw terminals may not accept 10 gage wire on the screw terminals. That is why Ben is suggesting back wire receptacles.

You may also want to consider if 20 amp receptacles are absolutely necessary. I don;t know your intended plans, but there are very few devices that actually need 20 amp receptacles. In the US, 15 amp receptacles are allowed on 20 amp circuits.
 
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Old 11-01-07, 08:45 AM
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You will need a White #10 THWN conductor for the Neutral, and a Green #10 THWN conductor for Equiptment Grounding. The use of any other colors is a Code violation.

I suggest you terminate the #10 conductors in a panel with a single-pole 20 amp breaker,and extend from the breaker with #12 conductors to avoid termination problems at devices and boxes.
 
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Old 11-01-07, 10:52 AM
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If using #10 for hot & neutral, and IF the circuit is marked/designated as 20A max and protected with a 20A breaker, is it not acceptable to use a #12 green wire for ground?
 
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Old 11-01-07, 11:04 AM
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Yes, he can use a #12 green for the ground.

The OP didn't say what color this wire was, but it's likely he can only use it for the hot, since the neutral will need to be white.

My guess is that, when all is said and done, this "free" wire is going to be pretty expensive. It may be cheaper and easier to throw away this free wire, or recycle it for the copper.
 
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Old 11-01-07, 04:37 PM
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See 250.122(B).

If he uses #10 for hot and neutral, then he has to also use #10 for the ground.

There are certainly splices that will hold 4 #10 conductors; see for example http://www.idealindustries.com/media...mbinations.pdf
(Note that most allowed wire combinations permit either solid or stranded, but some are specific as to one or the other, read carefully)

You've seen advice to use 'back wire' receptacles that will accept #10 stranded conductors directly into the holes. Many of these receptacles are 'self grounding', meaning that there is a bonding spring that will ground the receptacle if it is screwed into a properly grounded metal box. This might save a couple of fat pigtails.

-Jon
 
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Old 11-01-07, 07:10 PM
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Thanks for the help everybody.

I just checked my receptacles that I bought and they are the back wire type for 10 gauge wire and they have a thin copper wire on one end where the screw is. The box is labeled "backwire grounding duplex receptacle' and on the back it states:

"This device has a special yoke and mounting screw to establish the grounding circuit between the device yoke and the metalic flush type box installed in the wall without the use of a bonding jumper As permited by exception No. 2 NEC 250-74"

I think I'm okay to run just the three ground wires to the wire nut with one going to the box. If anybody sees any issues doing it this way please let me know.

By the way, my ground wire is green and my neutral is white and the hot is black.
 
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Old 11-01-07, 07:18 PM
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Sorry, forgot to mention that all three wires, hot, neutral & ground are 10 guage and are the appropriate colors being black, white & green.

Thanks
 
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Old 11-01-07, 08:16 PM
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If he uses #10 for hot and neutral, then he has to also use #10 for the ground.
Agreed. I was wrong.
 
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Old 11-01-07, 09:38 PM
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Why does the ground need to be #10 if it is a 20 amp circuit?
 
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Old 11-01-07, 10:23 PM
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dexwit,

250.122(B) requires that when the circuit conductors are increased in size, the equipment grounding conductor must also be increased in size proportionately.

The assumption is that if you increase the size of the circuit conductors, you are doing this for reasons of voltage drop, and this requirement is supposed to reduce the voltage drop in the EGC.

-Jon
 
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Old 11-02-07, 09:24 AM
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If the reason is not voltage drop, but derating due to ambient temperature or perhaps multiple conductors, does this equal gauge rule still apply?
 
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Old 11-02-07, 09:35 AM
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hondavan,

What the code states as a requirement is a requirement. There are no exceptions unless specifically written.

So if the code states that the conductors must be the same size then they must be. You can't ignore that requirement just because you believe the code is based on an assumption that does not apply in your case.
 
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Old 11-02-07, 09:36 AM
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Yes, it does still apply.

The code is already over 700 pages. To keep it from being even longer, it has a lot of somewhat blanket rules. It probably could have made an exception here, but the exception would be so rarely used as to not be worth the trouble.

Note that the assumption that the rule is because of voltage drop is just that, an assumption. There may actually be other reasons that we don't know about. What I often say about the code is that you should stringently follow it when you know the reason, but you should even more stringently follow it when you don't know the reason. In the latter case, there may be dangers that you can't even imagine, and the code is there to protect you from those.
 
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Old 11-02-07, 09:51 AM
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Honestly, I do not know.

The code rule says "Where ungrounded conductors are increased in size, equipment grounding conductors, where installed, shall be increased in size proportionately according to circular mil area of the ungrounded conductors."

Clear?

What this code rule doesn't make clear is 'increased in size from what?' It could be 'increased in size from what is normally required for the ampacity', or 'increased in size from the minimum that code requires', or 'increased in size from the minimum possible using the highest temperature rating of table 310.16', or something else.

I tend toward accepting the first interpretation, which means that if I use a 10ga conductor on a 20A circuit for any reason, then the EGC is also a 10ga conductor.

-Jon
 
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Old 11-02-07, 11:32 AM
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The purpose of a EGC is to conduct a fault-current from the fault location to the Neutral termination at the Service . The severity of the fault-current is based on the rating of the breaker protecting the circuit . A #10 EGC can be used for breakers with ratings of 30, 40, and 60 amps. ( Table 250.122).

If , because of voltage-drop, a #6 conductor is used for a 30 amp Branch-Ciruit , which is an "increase" from a #10 to a #6 un-grounded conductor, is the EGC requird to be a larger size than #10, per 250.122 ?

If a #10 EGC can a safely conduct the fault-current in a 60 amp circuit , can we conclude it can safely conduct the current in a circuit with only 1/2 of the current-capacity of the 60 amp circuit?
 
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Old 11-02-07, 11:59 AM
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Though the installation of a ground wire is a good idea and I suppose above code it is not a requirement when using EMT... provided the EMT is a complete (metal) system from breaker panel to all devices and outlets and installed with the correct fittings. Also if he is using self grounding receptacles (which it seems he is) that aren't mounted on covers but to the box itself he does not need a connection between the receptacle grounding green screw and the metal box. If he chooses to run a #10 ground wire I only see the need to connect 3 #10's or if using the premade single connection pigtails 2 #10's in that wire nut.
Personnally I think just getting some #12 in all the right colors outweighs using some free #10. If I was doing this and was fortunate to have some #10 in black and white I would use the Emt for ground and run myself a 30 amp circuit to a 4x4 deep 2 1/8" box and cap it there. This would be for some future use. I would then run 12 awg stranded for my 120 volt 15 or 20 amp receptacles. This would be 2 #10's and 2 #12's in half inch EMT conduit you could branch off at a jb if you wanted. I know that a ground wire is recommended by many but in a residential garage I just don't see where you have any huge issue for the emt to come apart and break the ground path.

Edit: Pattbaa....I would tend to agree maybe this in so much as the code is concerned will help explain...http://www.mikeholt.com/newsletters....y&letterID=216

Roger
 
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Old 11-02-07, 01:38 PM
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Thanks for the reference Roger, it's an excellent one, and lead me to detect my mistake, which was ------??

If the un-grounded conductors must be increased because the I X R voltage drop in these conductors would be excessive , the same would apply to the EGC that conducts the fault-current--- excessive IFC X R voltage-drop in the EGC would affect clearing the fault by tripping the breaker.

Hats Off to Roger!!
 
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