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-   -   2x100a sub on service main (http://www.diychatroom.com/f18/2x100a-sub-service-main-18094/)

jambud 03-06-2008 11:31 AM

2x100a sub on service main
 
Is it possible to feed 2x 100A subpanels on a 200A service main?

The subs are one 6space mainlug...6=20A circuits, and the second 24space mainlug... 15=20A circuits and two 30A circuits not connected as of yet.

The 200A service main panel has 14=20A and 2=30A existing circuits that are powered.

Or do I need a new service main for the second subpanel? Thanks

InPhase277 03-06-2008 12:25 PM

Quote:

Originally Posted by jambud (Post 104790)
Is it possible to feed 2x 100A subpanels on a 200A service main?

The subs are one 6space mainlug...6=20A circuits, and the second 24space mainlug... 15=20A circuits and two 30A circuits not connected as of yet.

The 200A service main panel has 14=20A and 2=30A existing circuits that are powered.

Or do I need a new service main for the second subpanel? Thanks

Well this is a little advanced for the DIY forum, but you can feed the two panels using a little gem of Code known as the "Tap Rules". This comes in both 10 ft. and 25 ft. flavors. You have a specific set of rules that must be followed in order for it to be safe and legal.

10 ft. Rule:

The conductors must terminate into a 100 A circuit breaker
They must be enclosed in conduit. You CANNOT use a cable for this
The conductors must be rated for the load you serve, and in no case shall they be smaller than 1/10 the capacity of the main.

So, if you install the panels within 10 ft. of the main, you can tap that with an approved method, and feed the two 100 A panels. Each 100 A panel must have a 100 A main of it's own, and you can use #3 copper with a #8 ground.

25 ft. Rule:

All of the above rules, except the capacity of the tap conductors shall not be less than 1/3 the size of the main.

So, if you can do the exact same thing as I suggested above except you cannot exceed 25 ft.

InPhase277

jrclen 03-06-2008 12:34 PM

Quote:

Originally Posted by jambud (Post 104790)
Is it possible to feed 2x 100A subpanels on a 200A service main?

The subs are one 6space mainlug...6=20A circuits, and the second 24space mainlug... 15=20A circuits and two 30A circuits not connected as of yet.

The 200A service main panel has 14=20A and 2=30A existing circuits that are powered.

Or do I need a new service main for the second subpanel? Thanks

Yes, you can feed 2 sub panels from your 200 amp main panel. You will need to connect the feeders to 2 100 amp circuit breakers in the main panel seeing as the sub panels are lug panels. Other code articles may apply but this is your short answer.

chris75 03-06-2008 04:36 PM

YOu can have as many panels as you want. As long as the load is under the calculated service load.

chris75 03-06-2008 04:39 PM

Quote:

Originally Posted by InPhase277 (Post 104812)
Well this is a little advanced for the DIY forum, but you can feed the two panels using a little gem of Code known as the "Tap Rules". This comes in both 10 ft. and 25 ft. flavors. You have a specific set of rules that must be followed in order for it to be safe and legal.

10 ft. Rule:

The conductors must terminate into a 100 A circuit breaker
They must be enclosed in conduit. You CANNOT use a cable for this
The conductors must be rated for the load you serve, and in no case shall they be smaller than 1/10 the capacity of the main.

So, if you install the panels within 10 ft. of the main, you can tap that with an approved method, and feed the two 100 A panels. Each 100 A panel must have a 100 A main of it's own, and you can use #3 copper with a #8 ground.

25 ft. Rule:

All of the above rules, except the capacity of the tap conductors shall not be less than 1/3 the size of the main.

So, if you can do the exact same thing as I suggested above except you cannot exceed 25 ft.

InPhase277

He didnt want to tap anything, he just wanted to know if he can add another subpanel off his existing 200 amp panel.

InPhase277 03-06-2008 06:07 PM

Quote:

Originally Posted by chris75 (Post 104895)
He didnt want to tap anything, he just wanted to know if he can add another subpanel off his existing 200 amp panel.

Oh, I took him to mean different. OK. I had a discussion similar to this on another forum, where the fella wanted to add a set of lugs to his panel and pull a 100 A tap from there. I guess it is still bouncing around my head.:laughing:

He did say "on a 200 A service main"...

InPhase277

jambud 03-06-2008 09:39 PM

Thanks guys! yeah I wanted to feed out of the 200A service main, so Ive got #3 thhn stranded copper going to run to the farthest sub 24-space(40ft. from the 200 service main) fed with a 100A breaker. And #4 thhn stranded copper gonna run to the 6-space sub ( 4ft. right behind the 200 service main) fed with a 100A breaker(or should I use a smaller breaker?). All one building no detached rooms.

InPhase277 03-06-2008 10:41 PM

Quote:

Originally Posted by jambud (Post 104986)
Thanks guys! yeah I wanted to feed out of the 200A service main, so Ive got #3 thhn stranded copper going to run to the farthest sub 24-space(40ft. from the 200 service main) fed with a 100A breaker. And #4 thhn stranded copper gonna run to the 6-space sub ( 4ft. right behind the 200 service main) fed with a 100A breaker(or should I use a smaller breaker?). All one building no detached rooms.

You need #3 for both, because that is the smallest copper allowed on a 100 A breaker. Or use a smaller breaker.

InPhase277

jrclen 03-06-2008 10:44 PM

Install 4 wire feeders. No main bonding jumper at the sub panels (keep ground and neutral separate). Stay below a 85 amp breaker on the #4, an 80 amp would be good.

jambud 03-06-2008 11:37 PM

Thanks yeah I will run 4wire feeders in 2" pvc and use an 80A breaker for the #4 wire. Could you enlighten me on how to calculate the amps used in the panels to make sure it doesnt go over the main breaker Amp?

jrclen 03-07-2008 09:50 AM

Quote:

Originally Posted by jambud (Post 105015)
Thanks yeah I will run 4wire feeders in 2" pvc and use an 80A breaker for the #4 wire. Could you enlighten me on how to calculate the amps used in the panels to make sure it doesnt go over the main breaker Amp?

To tell you the truth, load calculations are beyond the scope of a DIY project. You're close to the edge just installing your own sub panels. :whistling2:

jambud 03-07-2008 10:09 AM

I agree but I would just like to know and hear your explanations on load calculations.

jrclen 03-07-2008 10:19 AM

I understand. Maybe this will help. Thanks to a nice feller who calls himself Celtic. :whistling2:

Branch-Circuit, Feeder and Service Calculations


Branch-Circuit, Feeder and Service Calculations, Part II


Branch-Circuit, Feeder and Service Calculations, Part III


Branch-Circuit, Feeder and Service Calculations, Part IV


Branch-Circuit, Feeder and Service Calculations, Part V


Branch-Circuit, Feeder and Service Calculations, Part VI


Branch-Circuit, Feeder and Service Calculations, Part VII


Branch-Circuit, Feeder and Service Calculations, Part VII


Branch-Circuit, Feeder and Service Calculations, Part IX


Branch-Circuit, Feeder and Service Calculations, Part X


Branch-Circuit, Feeder and Service Calculations, Part XI


Branch-Circuit, Feeder and Service Calculations, Part XII


Branch-Circuit, Feeder and Service Calculations, Part XIII


Branch-Circuit, Feeder and Service Calculations, Part XIV


Branch-Circuit, Feeder and Service Calculations, Part XV


Branch-Circuit, Feeder and Service Calculations, Part XVI


Branch-Circuit, Feeder and Service Calculations, Part XVII


Branch-Circuit, Feeder and Service Calculations, Part XVIII


Branch-Circuit, Feeder and Service Calculations, Part XIX


Branch-Circuit, Feeder and Service Calculations, Part XX


Branch-Circuit, Feeder and Service Calculations, Part XXI


Branch-Circuit, Feeder and Service Calculations, Part XXII


Branch-Circuit, Feeder and Service Calculations, Part XXIII


Branch-Circuit, Feeder and Service Calculations, Part XXIV

chris75 03-07-2008 06:26 PM

Quote:

Originally Posted by jambud (Post 105106)
I agree but I would just like to know and hear your explanations on load calculations.


This is something you cannot just explain in a text, this is why our job is what it is, years of experience and training... some things are just not DIY...

jambud 03-11-2008 09:18 PM

Thanks...One more question..on that 100Amp subpanel, I ran three wires of #3 thhn for the two Hots and Neutral from the Main 200A to the Subpanel.

Can I run the ground separate (not to the main panel) outside to a ground rod which is a shorter run with the remaining # 3 wire that I was short? If so, do I still separate the neutral and ground at the Sub?


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