Feed-Through Panel Size

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graham85

Member
This is a calculation and code question.

I am working on designing a 400A 3 phase service upgrade for a large residence. I have determined that it will require 60 circuits total. Section 408.15 states that there can be no more that 42 overcurrent devices in one panel. Therefore I need to use a feed-through lug panel. I will be using a 42ckt (1st) and a 30ckt (2nd) panel

My question is this, do I need to match the amerage rating of the 1st panel with the 2nd panel? Or can I size the 2nd panel for the calculated load on that panel (70A)? Because it seems that Sq.D only makes 225A & 600A feed-through panels. I would like to minimize the cost to my client.

Thank you in advance for your assistance.

Keith
 

iwire

Moderator
Staff member
Location
Massachusetts
Re: Feed-Through Panel Size

You would be using a 225 amp bus protected by a 400 amp main, 408.16 would prevent this.

IMO use the same size panels for true feed through or get a 225 amp main breaker panel for a sub panel and use the tap rules to feed it from the outgoing lugs on the 400.
 

ryan_618

Senior Member
Re: Feed-Through Panel Size

Originally posted by graham85:
This is a calculation and code question.

I am working on designing a 400A 3 phase service upgrade for a large residence. Keith
Hello Keith. Does your power company have three phase in the area? I know that here they typically don't have it in the middle of a subdivision. Maybe something to think about...

[ July 08, 2003, 06:27 PM: Message edited by: ryan_618 ]
 

graham85

Member
Re: Feed-Through Panel Size

Thank you both for your responses.

I was hoping we would be able to do something like that iwire.

Yes, I have already coordinated with the power company and they are going to run a new 3 phase service for us.

Thanks again.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: Feed-Through Panel Size

Remember that when you use 3 phase you have 208 and not 240 hot to hot and this will require different electric heating elements for any equipment that uses electricity to create heat. Operating 240 volt electric heat elements on 208 results in 25% less wattage.
Don
 

bob

Senior Member
Location
Alabama
Re: Feed-Through Panel Size

Don
You are correct about checking with the utility about voltage. Many times the utility will provide 3 phase service using an open delta bank which give you 240 volts. The 3 phase is used for the A/C units only and 120/240 volt single phase for the remainder of the load. It needs to be verified.

[ July 09, 2003, 12:55 PM: Message edited by: bob ]
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Re: Feed-Through Panel Size

Back to the original question.

If you use feed-thru lugs then your additional panel must have the same ampere rating as the original, unless it has a main breaker in which case you would feed it using cables sized per the "tap rules".

If your load is only 70A, how about putting a 125A breaker in the mani panel and then feeding a second panel? This way you do not have to get a special "main" panel.
 
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