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.
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.
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.
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.
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:
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...
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?
No way. The grounding conductor needs to be run with your other conductors and terminate in the service panel. You can use a #8 copper wire for the grounding conductor. Yes, keep the neutral and ground separated in the sub panel.
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?
In the same conduit as the feeder circuit per code. The conductor you mentioned would work of course. But it would not be code compliant. And who knows what might happen in the future to that old circuit. I recommend just doing it correctly and be done with it.
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