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Old 09-16-2008, 06:24 PM   #1
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Wire size for Sub panel


I'm going to be putting in a 60 amp sub panel running off of a 100 amp main panel. The total length of the run is 60 feet from the main to the sub panel. I was curious if I could use 8/3 wire rather than 6/3?? The sub panel will be running nothing more than lights and approx five outlets at any one given time. Any information will be appreciated, thanks.

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Old 09-16-2008, 06:28 PM   #2
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Wire size for Sub panel


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I'm going to be putting in a 60 amp sub panel running off of a 100 amp main panel. The total length of the run is 60 feet from the main to the sub panel. I was curious if I could use 8/3 wire rather than 6/3?? The sub panel will be running nothing more than lights and approx five outlets at any one given time. Any information will be appreciated, thanks.
#8 is good for 50 amps, but if your using NM (aka romex) its only good for 40 amps, I have no idea what your load is, so I have no idea if this is okay.

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Old 09-16-2008, 07:29 PM   #3
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Wire size for Sub panel


As long as the #8 is protected by a 40 amp breaker in the main panel, you can put any size panel that you want at the far end!

Last edited by Wildie; 09-16-2008 at 07:32 PM.
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Old 09-16-2008, 08:42 PM   #4
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Wire size for Sub panel


If your only running a few lights and some outlets, a 40 amp feeder would probably be more than adequate, with a 8/3 feeder cable. This would easily support 4 20 amp breakers no problem.

By the way, is this in a detached garage by chance? The kinda wire and method you run it changes if this is in a detached garage (or any detached structure).
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Old 09-16-2008, 09:48 PM   #5
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Wire size for Sub panel


Yes, this is a detached garage- I know that you must keep the grounds and neutrals separate when you do the panel. Anything else that I have missed???
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Old 09-16-2008, 09:55 PM   #6
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Wire size for Sub panel


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Yes, this is a detached garage- I know that you must keep the grounds and neutrals separate when you do the panel. Anything else that I have missed???
You will have to install some sort of disconnect in the panel, either a safety switch ahead of it, or a main breaker panel (UNLESS it is 6 circuits or less out there, in which case all of the breakers are the "disconnects") to comply with 225.33(A) in the Code.

IF you back-feed a plug-in breaker for the main, you will also need to install a retaining kit [see NEC 408.36(F)]

You will also need to install a grounding electrode, usually a ground rod at the garage connected to the EGC as well.

Last edited by kbsparky; 09-16-2008 at 10:05 PM. Reason: Added code references
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Old 09-16-2008, 10:29 PM   #7
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Wire size for Sub panel


Also, you need to use either UF direct burial cable, and protect it at both ends in the electrical PVC conduit where it exits the ground and enters the building, or run PVC conduit the entire length and pull individual conductors of THWN (must be wet location rated).

6 Circuits max, or a main breaker must be used if more than 6. Typically its just easier to use a main breaker panel, prob a few more spaces than you might need, but it has a main disconnect there (doesn't matter how big) but just so long as you protect the wires at the main breaker box with the proper size breaker.
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Old 09-17-2008, 04:41 PM   #8
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Wire size for Sub panel


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(UNLESS it is 6 circuits or less out there, in which case all of the breakers are the "disconnects") to comply with 225.33(A) in the Code.

Every panel I've every installed always wanted a MAIN if used as a Lighting & Appliance Branch-Circuit Panelboard, so I never offer to use the 6-switch rule as an option.
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Old 09-17-2008, 05:26 PM   #9
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Wire size for Sub panel


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Every panel I've every installed always wanted a MAIN if used as a Lighting & Appliance Branch-Circuit Panelboard, so I never offer to use the 6-switch rule as an option.
Does this include feeders to outbuildings, the topic of this discussion?

We are dealing with Article 225 here., as well as 408.36. Since the feeder cable has proper overcurrent protection at the source, the "Lighting and Appliance panelboard" rules that require no more than 2 main disconnects do not apply.

Last edited by kbsparky; 09-17-2008 at 05:36 PM. Reason: added further code reference information
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Old 09-17-2008, 05:36 PM   #10
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Does this include feeders to outbuildings, the topic of this discussion?

We are dealing with Article 225 here, NOT article 230, which covers "services"
I'm dealing with the instructions on the panel itself. Article 110.3 (B), I've never installed a panel that didn't want a main if used as a Lighting & Appliance Branch-Circuit Panelboard.


And I fully understand article 225 and 230.
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Old 09-17-2008, 07:48 PM   #11
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Wire size for Sub panel


It would be nearly impossible to comply with a 6 disconnect rule in a residential detached garage. If a disconnect is not installed remote from the panel and the panel is mlo it must have a service rated disconnect, and the minute you install a branch circuit 30 amps or less with a neutral connection in the branch circuit for lighting or appliances you now have a L&ABCP. You will find with residential mlo load centers used as L&ABCP's that the panel cannot be used as service equipment without a single throw main breaker installed. the panel will either state a main breaker is required to meet service rating or that 6 breakers or less can be the disconnect if and only if the panel does not meet the criteria for a lighting and appliance branch circuit panelboard. The 6 throw rule is pretty much always concerned with applications where the panel is a power panel and the 6 breakers or less do not have neutral connections at 30 amps or less. You see this often in commercial and industrial applications and residential service equipment at the dwelling where six double pole breakers are generally used but no neutral connections at 30 amps or less. This was as of 2005 and before. In 2008 they did away with the classification of power panels and L&ABCP's so essentially all panel boards will require a main breaker that is single throw unless you can apply the exceptions of 408.36 and I don't see how you can in this situation.

The breaker protecting the feeder to the detached garage is located at the dwelling service equipment and is not a service rated disconnect. In order for you to get around 225.36 the mlo would need to be in the same structure with the service equipment for the dwelling and then you could comply with the 6 throw rule with overcurrent protection on the supply side and not in the panel itself.. So 408.36 is IMO talking about such an installation dealing with 230.71 and not a separate building falling under art.225. This is not to say that I am right or wrong or that KBsparky is wrong but it is how I understand the code book.

Example... in order to comply with 225.36 this Siemens mlo requires a main breaker......there are industrial panels that are mlo and service rated in which case you could comply with the 6 throw rule of article 225.


Last edited by Stubbie; 09-17-2008 at 08:45 PM.
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Old 09-17-2008, 09:25 PM   #12
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Wire size for Sub panel


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.... In 2008 they did away with the classification of power panels and L&ABCP's so essentially all panel boards will require a main breaker that is single throw unless you can apply the exceptions of 408.36 and I don't see how you can in this situation....
In reading the text of the Code I can not find anything that affirms your statement here. True, there is no longer any disctinction of a Lighting, Appliance Branch Circuit Panelboard, and any rules pertaining to that particular type has been deleted. But the overcurrent protection does not have to be located at the panel. Otherwise, MainLugsOnly panels would be illegal in most installations.

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The breaker protecting the feeder to the detached garage is located at the dwelling service equipment and is not a service rated disconnect.
This breaker is not intended to be a service disconnect. This particular breaker is there for overcurrent protection of the feeder and subsequent connection to the remote panel as required by 408.36.

It seems we are dealing with 2 different issues here. One is that the (sub-)panel must have proper overcurrect protection. I maintain that this protection can be installed anywhere ahead of the panel, even at the originating point of the feeder. I believe the text of 408.36 backs up this claim.

The other issue is that of whether you are allowed to use a 6-space panel in an outbuilding without having to install a main breaker as the "disconnecting means". Since the rules pertaining to the lighting, appliance branch circuit panels have been removed from the Code, and they also require 6 disconnects or less in a separate building, I also believe that a main breaker would not be required in such a structure.

At least, that is what we were taught in continuing ed classes (2008 NEC) by the electrical inspectors who certify our work.
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Old 09-17-2008, 09:47 PM   #13
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Wire size for Sub panel


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If a disconnect is not installed remote from the panel and the panel is mlo it must have a service rated disconnect
Stubbie, I believe your citing 225.36 here if I'm reading your post right. Curiously, there is an exception allowing snap switches in place of a service rated disconnect for dwelling garages. I believe snap switches max out at 30 amps, anything past that must be service rated.

I have mixed feelings about this exception. Say I want to run a 60 amp feeder, why do I now have to install a 100 amp main breaker panel(it's service rated) to meet code instead of just back-feeding a 60 amp 2 pole breaker? I would sure think that 60 amp breaker is still a better disconnect than a snap switch.

I guess I'm just talking out loud here....
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Old 09-18-2008, 12:28 AM   #14
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This breaker is not intended to be a service disconnect. This particular breaker is there for overcurrent protection of the feeder and subsequent connection to the remote panel as required by 408.36
No its not the disconnect but we are discussing whether the mlo panel in the detached garage can serve as a service rated disconnect under the 6 throw ruling of 225.33. And yes the breaker can be remote from the panel board on the supply side. However the issue here is can 6 breakers or less be the 'service rated disconnect' if a remote service rated disconnect located at the nearest point of entrance of the feeder is not installed. If no service rated disconnect is installed at the structure ahead of the mlo panel then the mlo panel must contain the service rated disconnect. If the panel cannot be used as service rated without a main breaker then 6 breakers won't comply for a service rating. All things considered I agree with KBsparky that the overcurrent protection can be anywhere on the supply side of the panelboard in some applications. My problem here is the service rating requirement of the disconnect in section 225.36. If I'm supplying the panelboard in the detached garage by protecting the feeder with a breaker installed in the dwellings service equipment..... will 6 breakers be allowed to serve as the service rated disconnect for the detached structure?? If the panelboard specifications sheet states yes then you could comply with the 6 throw rule. If it says no and is required to have a integral main breaker to be service rated then 6 throws doesn't work.


KBsparky...the statement you question for documentation is from the 2008 NFPA Handbook in a commentary by Jeff Sargeant. In a nut shell the commentary simply says that with the elimination of the distinction between power panels and l&abcp's all panel boards will need a single overcurrent device that protects the panelboard bus. Only way around it is to be able to comply with one of the exceptions in 408.36. The issue is not that the panels overcurrent can be remote from the panelboard anywhere on the supply side but is the mlo panel with 6 breakers or less service rated to comply with 225.36. You must comply with the manufacturers instructions for making the panel service rated... if it says a integral main breaker is required then I see now way to use the 6 throw rule.


Last edited by Stubbie; 09-18-2008 at 12:33 AM.
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