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DrP 05-22-2006 05:56 PM

Adding new circuit breakers to 100 amp sub panel
New to this forum. Have searched archives for answer and got no results so.....
Recently a professional electrician added a new 200 amp service and a main service panel now located in the garage. Presently the only breaker in this panel is for the "sub panel" located in a bedroom closet. Note: the "sub panel" was previously the "main panel" and contains twelve circuit breakers (some 15 amp and several 20 amp) each servicing respective areas of the old part of the house.

My dilema: 1. I'm adding one 15 amp circuit for a floor heating unit with thermostatic control and this requires a dedicated circuit.
2. I also intend to seperate an existing light and plug circuit currently located in the master bedroom from the present "old" configuration where it is wired in with the 2 bathrooms circuit. The intent is to have the master bedroom on a seperate 15 amp circuit of its own.

My question: Can I go to the to the old sub panel (only 15 feet of wire required) and install an additional two new 15 amp circuit breakers and connect each of "new" circuits there OR, must I pull 80 ft of wire accross a low roofed attic to the main panel and connect to circuit breakers I would have to add to that panel?


jbfan 05-22-2006 08:35 PM

If the subpanel has room for more breakers, then you should be able to add them. If there is no room, then you must pull back to the new panel.

DrP 05-23-2006 05:07 PM

Adding new circuit breakers to 100 amp sub panel
Tnx jbfan. The sub panel has three more slots for additional breakers. My big concern is that adding more breakers may risk putting added load on the main cable connecting the sub panel to the new main panel. Is this possible? Could it cause "overloading" and tripping the main panel breaker?
Buffet's song "He Went to Paris" is such a great poem/story. Love it.


darren 05-23-2006 06:54 PM

Of course you could overload the cable and have the sub panel breaker pop(i assume that is what you meant). But a 100A is alot of power so my guess would be no you won't pop it. Of course this all depends on what you have connected in the subpanel.

I run my whole house off of a 70A breaker, but i do have natural gas furnace and H20 tank.

Let us know what else you have connected in the subpanel and we can give you a better answer.

Hope this helps.

DrP 05-24-2006 06:07 PM

Adding new circuit breakers to 100 amp (Oops! it's a 125 amp) sub panel
Tnx Darren
First I need to correct the amperage rating of this panel. According to the manufacture's info it is a 125 Amp service panel. BTW, it's a Zinsco unit. I've read that Zinsco is not such a hot (no pun) breaker panel system.
Here's the list of breakers presently in the sub panel and they are running the 3 bedroom, 2 bath house:
1 ea 20 AMP single pole dedicated to refrigerator/freezer
1 ea 20 AMP single pole for circuit supporting approx 3 wall plugs + 100 watt lighting
1 ea 15 AMP single pole for circuit supporting 5 wall plugs for computers + 150 watt lighting
1 ea 15 AMP twin (two toggles), single pole "space saver" for circuit for 6 wall plugs for living room
1 ea 15 AMP twin (two toggles), single pole "space saver". One for garage circuit, one for the two bathrooms and master bedroom wall plugs. (THIS IS THE CIRCUIT I WANT TO DIVIDE ADDING ANOTHER BREAKER)
1 ea 20 AMP single pole dedicated to garbage disposal/dishwasher
1 ea 20 AMP single pole for kitchen plugs and lights
1 ea 20 AMP twin (two toggles but locked together) don't seem to operate anything
1 ea 20 AMP to wall plugs and lights in bedroom
There are three, double knock outs remaining in the panel.

Any comments or suggestions whether I should continue to pull wire for two additional circuits down to this sub panel would be greatly appreciated.

jbfan 05-25-2006 06:18 AM

Even though the panel is rated at 125, what is the breaker feeding the panel? This will determine the amout of power you have. Base on what you have listed, I think you will be safe to add 2 other circuit.
I would suggest that you consider replacing the zinco panel. The breakers may be hard to find, and they do have a bad rep.

DrP 05-25-2006 10:02 AM

Adding new circuit breakers to 100 (125) amp sub panel
Again, tnx for your help.

The "new" main panel is a Siemens rated at 150 amps. Yes. I agree the Zinsco should be replaced as, not only does it have a bad reputation but, it is in the closet of a bedroom. I'm told this was a common installation at the time the house was built-1971. Zinsco breakers are available at Home Depot at $30 each. We are planning a major remodel within the next year including taking off the roof and adding a second story. So, that will be the time we can re-route the old circuitry to the Siemens main panel. Meanwhile we need to make the hook ups as I described. It sounds like the hook up to the sub panel with two added circuits with 15 amp breakers will work satisfactorily. This'll allow less wire pulling through the dusty, low clearance attic.
My hat's off to you guys who do this kind of work every day. You really earn your pay.
One last "stupid" question if I may: Should I get a space saver double toggle breaker with twin 15 amps and could I hook up one circuit to each? OR, should I get two seperate 15 amp breakers? I have available slots for either way.

darren 05-25-2006 05:25 PM

Thats a choice of preference.

It probably doesn't matter since you are doing a remodel in the near future. I would do what ever is cheaper for you.


DrP 05-25-2006 10:05 PM

Adding new circuit breakers to 100 amp sub panel
TO: jbfan and darren

Thanks a lot for your help and guidance. What goes around comes around. So....maybe there'll be a day.............

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