Sub-panel w/ main breaker

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prattz99

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Long Island NY
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Electrician
Hi all,

I'm a young electrician and I'm getting a little confused with some code requirements pertaining to sub-panels and "main breakers" on the sub-panels. I think the NEC is confusing at times with too much "lawyer talk". I have a job that is a residential single family dwelling that has an existing 200 amp main breaker panel as the main electrical service and a small 10 circuit 60 amp sub-panel fed from the main panel. Both are located in the basement. I need to upgrade the size of the sub-panel so I've run a 4/3 copper romex and plan to fuse it with a 90 amp dp breaker, all good.

Here's where I get confused, can I install a 100 amp 20/40 main breaker load center or does it have to be a main lug? There will be more than 6 handles installed. I'd prefer to use the 100 amp main breaker panel, if it's a violation would somebody please explain why.

Thank you so much,
 
The code does not require your new sub panel to have a main, but it also does not prohibit you from using a sub panel with a main.
 
Thank you Don!! So it's just a preference then? Okay, I'll go ahead and plan to install the 100 main breaker panel and hopefully, hopefully the AHJ won't give me a hard time about it. :angel:
 
prattz99 said:
Thank you Don!! So it's just a preference then? Okay, I'll go ahead and plan to install the 100 main breaker panel and hopefully, hopefully the AHJ won't give me a hard time about it. :angel:
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In addition to what Curt wrote, make sure your neutrals and grounds are separated in the subpanel and the bonding strap is removed.
 
I think it was about a 70' run and kind of tricky in an old basement with duct work around. I'll keep SER in mind for the next time and see if it's a cost effective option.
 
prattz99 said:
I think it was about a 70' run and kind of tricky in an old basement with duct work around. I'll keep SER in mind for the next time and see if it's a cost effective option.
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There is not even a question about that, AL-SER is less much less expensive than copper NM.
 
Once instance where a main breaker in a sub is not just a matter of preference is in a detached building. The code requires a disconnecting means for the feeder at the building. Technically there are multiple ways to do it but a main breaker sub will usually be the most cost effective.
 
prattz99 said:
Hi all,

I'm a young electrician and I'm getting a little confused with some code requirements pertaining to sub-panels and "main breakers" on the sub-panels.
Click to expand...

Here is what I come up with for when main breakers are required (note the "main breaker" doesnt have to be integral to the panel so really a MB is never actually required, but we will assume that is what will be done most of the time because it is generally simplest and most cost effective).

1. Disconnecting means needed for service or a detached structure
2. To meet 408.36 where supplied by (most) transformers or feeder taps.
3. To meet the conductor protection requirements in 240.21.

That is all I can come up with. I have heard of some panelboards that require a main breaker (per manufacturer) if they are to be used as service equipment, even if 6 or less branch breakers are installed.
I have heard 240.24(B) mistakenly cited as requiring a main breaker, however note a MB does not gain you anything toward meeting the requirement.
 
jumper said:
Oh yeah, wide margin.:happyyes:
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If this is a competitive situation then price it to be apples to apples as per the minimum code requirement.
Otherwise I prefer including a main breaker so that if it was urgent to shut off the power it is a lot quicker to throw a single main than to quickly read the list of branch breaker labels in an emergancy to determine which one to throw if that is the correct breaker.
 
templdl said:
I prefer including a main breaker so that if it was urgent to shut off the power it is a lot quicker to throw a single main than to quickly read the list of branch breaker labels in an emergancy to determine which one to throw if that is the correct breaker.
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Please explain the situation that would require that.

Breakers are not intended to be manual emergency shut offs, they are often behind locked doors or panel covers.
 
templdl said:
If this is a competitive situation then price it to be apples to apples as per the minimum code requirement.
Otherwise I prefer including a main breaker so that if it was urgent to shut off the power it is a lot quicker to throw a single main than to quickly read the list of branch breaker labels in an emergancy to determine which one to throw if that is the correct breaker.
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Er tempy, I was agreeing with iwire that AL SER is much cheaper than CU NM-B.
 
iwire said:
Please explain the situation that would require that.

Breakers are not intended to be manual emergency shut offs, they are often behind locked doors or panel covers.
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I'm a bit surprised that you would ask. Are you assuming that breakers are now not intended has a manual emergency shut off? Really? If so by what means do you suggest that power be disconnected if there is a need to so in a hurry? Take a pair of linemans pliers and cut the wire? According to the UL489 tests breskers are perfectly capable of the task and come back to do it hundreds of times.
If there were any electrical emergency such that could hurt or kill someone or an arcing fault that is not of a great enough magnetude to trip a breaker or another event that may result in a fire any bright ideas? With all the panels as you say are behind locked doors and all the panel doors are locked, yes, if that is normslly the case then there is an issue. So what you are saying is trying to disconnect a main breaker shouldn't even be considered then.
Wonderful.
 
jumper said:
Er tempy, I was agreeing with iwire that AL SER is much cheaper than CU NM-B.
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Yes, big time cheaper. To be politically correct though from a sales perspective it is less expensive as cheap often is viewed as of lower or poorer quality and we never want those to think that we are using a cheap or poor quality product. ? Kind of got away from a main breaker in a subpanel though.
.
 
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