Installing a subpanel

[Aaron Fude]

Hi,

In an earlier post, I described my kitchen project and my need for a subpanel. I'm now ready to undertake the project. So here's my algorithm, is there anything wrong with it.

1. Install a 70 amp breaker in the main panel.
2. By #4 wire and connect it to that breaker as it if were just another circuit.
3. Run that wire to the subpanel where, I assume, there will only be one self-explanatory way of connecting it. (Will it be connected in the same way as the cable that comes from the street is connected to the main panel.)
4. Connect circuits to the subpanel.

Many thanks in advance,

Aaron

[RBM]

The only difference is that in the main panel, there will be a bonding jumper that attaches the neutral/ ground buss to the panel. In the sub panel you won't use that jumper and you may have to purchase and install a separate ground buss. The neutral conductors will go to the insulated buss, and the ground conductors will go to the buss directly attached to the panel

[Kevin Ricks]

In my area sub-panel disconnects are required. Either by installing a main breaker kit in the sub-panel OR what I did was to back feed the sub-panel through a standard breaker (60A in my case). Much cheaper than the main breaker kit, but it uses up 2 slots in the sub-panel. IOW I put a 60A breaker in my main panel and ran that to a 60A breaker in my sub-panel, leaving the main lugs empty.

Kevin

[Wayne Whitney]

That seems odd--shutting off the main breaker in a subpanel doesn't render it safe to work on, as the incoming feeder conductors are still energized. To deenergize the panel, you have to kill the feeder itself.

This configuration requires an additional holddown bracket on the backfed breaker.

Cheers, Wayne

[Kevin Ricks]

I was told the local inspector would require the disconnects where there are 2 columns of breakers in the panel? With one column you can turn everything off in one sweeping hand motion...with 2 columns your all confused in a panic emergency ..... It was just a store employee that said that... , but it may be that the NEC would require disconnect anyway in my situation. It's an 8 slot sub in a detached shop building. I believe NEC requires disconnects for subs in detached buildings. Actually, I am not sure if my shop is classified as attached or detached? It's separated from the house by a breezeway but attached at the roof. I treated it as detached.

Thanks I didn't know that. Kevin

[Jennifer Eden]

Hi,

This is a very valuable discussion for me, I was wondering if you could define some of the terms that you were using, since I am still at the point where I know hot/neutral/ground/breaker/panel/subpanel/ main breaker. What are:

Disconnect - Lug - Main Lugs Holddown Bracket - Back feed - Main breaker KIT -

Thank you in advance!

Aaron

[RBM]

The NEC does require a disconnect in a sub panel in a detached building, but it also allows up to 6 disconnects in the panel, which is probably where the single column of breakers comes from

[RBM]

Hi,

This is a very valuable discussion for me, I was wondering if you could define some of the terms that you were using, since I am still at the point where I know hot/neutral/ground/breaker/panel/subpanel/ main breaker. What are:

Disconnect - switch or breaker to turn off electricity Lug - connector in panel to attach wires Main Lugs lugs where the wires feeding the panel are attached Holddown Bracket - bracket that holds a main circuit breaker to the panel Back feed - Back feed circuit breaker connecting the main panel wires to a circuit breaker plugged into the panel, as opposed to attaching to an installed main circuit breaker , or lugs Main breaker KIT - some panels that come with lugs only, can be furnished with main breaker kits. You can purchase a panel either way

Thank you in advance!

Aaron

[Jennifer Eden]

Thank you.

So - what are the pros and cons and having a main breaker on the subpanel. (I noticed that it is a little more expensive to have the breaker, but not enough to affect my decision.)

Thank you in advance.

[RBM]

Thank you.

So - what are the pros and cons and having a main breaker on the subpanel. (I noticed that it is a little more expensive to have the breaker, but not enough to affect my decision.)

Thank you in advance.

I don't see any advantage to having a second disconnect if the sub is in the same building as the main panel. If it's in a detached building, it is a requirement

[Steve Barker]

being in the same building brings up another question i had the other day. I've got a sub right next to the main panel ( to add spots) . Does it still have to have the ground and neutral seperate and fed with 4 wires in this situation?

steve

[Wayne Whitney]

Yes. In any building, there is to be only one point in an electrical system in which the ground and neutral (grounding system and grounded conductor) are interconnected**. That point is at the main disconnect; anywhere downstream of it the grounds and neutrals are to be kept separate.

Cheers, Wayne

** If you have, for example, a generator in which the transfer switch switches the neutral conductor, then that is called a separately derived system (SDS), and as a separate electrical system it has its own ground-neutral bond.

[RBM]

[Steve Barker]

and each of these six panels would be fed how? to qualify for this scenario?

thanks

steve

[RBM]

[Steve Barker]

so obviously never from one box to the next?

s

[RBM]

[Tom Horne]

That depends on how the additional panel is supplied. If it is supplied from a breaker in the cabinet that contains the "Service Disconnecting Means" then you will need to separate the neutral conductors and the equipment grounding conductors as already described. If it is supplied by service entry conductors then you wire it exactly the same as you would the first panel.

-- Tom Horne

[Tom Horne]

of a gutter trough where they would be

Not quite never but rarely, Some panels have multi barreled lugs for use as the main lugs and there are kits available from some manufacturers that will add such lugs to an existing panel. These allow you to run service entry tap conductors from one main lug to another. Additionally some panel cabinets have sufficient room to house separate lugs, split bolt taps, and so forth. Were the panel cabinet has enough room you can avoid the need to install a trough.

-- Tom Horne