Stupid Question

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This is the kind of information I have taken for granted till now, but what does code say about how many amps can be fed off an 100 amp service. In this case, I need to know exactly how many 20 amp circuits I can put behind an 100 amp breaker.

I know, stupid question, should be load not circuits, but what does code say?

Thanks!
 
Re: Stupid Question

Originally posted by monkey_with_a_wire:
This is the kind of information I have taken for granted till now, but what does code say about how many amps can be fed off an 100 amp service. In this case, I need to know exactly how many 20 amp circuits I can put behind an 100 amp breaker.

I know, stupid question, should be load not circuits, but what does code say?

Thanks!
You can put as many 20 amp breakers 'behind an 100 amp breaker' as you want, 8, 20, 300.

The only thing that matters is the connected load.
 
Re: Stupid Question

Monkey
Next time you take a look a panel, add up the number of overcurrent devices. Say you have a 100 amp panel with 20 circuits, and those circuits add up to 380 amps. As Bob has posted, the overcurrent devices add up to 380 amps, but the connected load to those devices may only total 80 amps or maybe even less, that is why the OCPD that protects that panel does not open. If the connected load should exceed the panel protection, it would open the OCPD that is protecting it. Typically the number of breakers will add up to more than the size of the breaker that is protecting the panel.
 
Re: Stupid Question

Article 408.13 says that the 100 amp rating of the panel cannot be less than the minimum feeder capacity for the load that is calculated per Article 220. Keep in mind also that certain types of panelboards (meaning almost all the ones I ever encounter) have a limit of 42 overcurrent devices. See 408.15.
 
Re: Stupid Question

* This NEC? Forum is for those in the electrical and related industries.
Questions of a "How-To" nature by persons not involved in the electrical industry will be removed without notice.
:confused:
 
Re: Stupid Question

To ?electricmanscott?: The question posed by ?monkey_with_a_wire? was not outside the rules of this Forum. A ?General Contractor? asking about panels and breakers and loads is acceptable, as that type of person might need that type of information in the preparation of a bid. There is no evidence that the question has to do with a home owner performing electrical work at his own home.

To ?monkey_with_a_wire?: If, in fact, you are a home owner performing electrical work at your own home, and if you are not acting in your professional capacity of a GC asking questions about a project, then please be advised that we are not permitted to assist you.
 
Re: Stupid Question

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You can put as many 20 amp breakers 'behind an 100 amp breaker' as you want, 8, 20, 300.
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I don't have my book in front of me, but last I remember, this type of panel would probably meet the definition of a LIGHTING AND APPLIANCE PANEL, which would limit it to 42 over current protection devices. I realize this wasn't the exact intent of the question, but I thought I would mention there is a limit in some cases.
 
Re: Stupid Question

Sorry for the above post, I read through it too quick. I see that Charlie covered this already.
 
Re: Stupid Question

Stud, remember off the 100 amp panel someone could add a sub. panel and maybe add another sub. panel. So now we have alot of 20 breakers. As long as the main is protected, there's not going to be a problem. It sounds like everyone is correct on this.
Bye now,
Jim
 
Re: Stupid Question

Everyone is basically right...However, everytime you add another sub to it you have to calculate the orginal load on the main panel and factor this.

You can't just add to the end of the earth...lol...

As charlie said..most panels I am aware of have a 42 CB limit...but I have also seen some 100A panels with only 20 CB in them.

Either way the factors of 220 have to apply in the calculations and the panel has to be sized to the load being applied.
 
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