DIY Home Improvement Forum banner

2x100a sub on service main

5K views 17 replies 4 participants last post by  jrclen 
#1 ·
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
 
#2 ·
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
 
#7 ·
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.
 
#13 ·
#15 ·
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?
 
#17 ·
Theres a 8-3 romex run that was used for a range but no longer used or energized. Its right behind the subpanel and coming from the 200 main. Could i just use that wire for the ground since it goes to the main? Or does the ground have to be in the same conduit as the feeders?
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top