Circuit breaker question
 

When i opened my box last night i noticed that some of the breakers have 2 black wires running to them while others only have 1. Are there 2 circuits running off of 1 breaker. These are Square D QO breakers and are also not tandems. The breakers do have a slot on each side of the screw for wire to be connected.

If it is 2 circuits on 1 breaker would i be able to add a new circuit to an existing lightly used breaker?

Thanks

Yes, this is 2 circuits running off one breaker.
Yes, as long as the other breaker has the same type of lug (slot on each side of the screw).

Welcome M McVicker:
The first wires doubled up on breakers were not legal (if my memory serves me correctly) and the new one won't be either. But then, that's why we use circut breakers; if you overload the breaker by using it on 2 circuts it will kick out.
I love the Square D QO's; one saved my son-in-law's life when the GFCI in the circut didn't detect him standing in a puddle of water using a power saw.
Glenn

What you have and what you propose IS perfectly legal.
Glennjanie, these particular breakers are designed for a two circuit setup.
Of course you'll want to be prudent about overloading it.

for all practical purposes, the 2 circuits become 1. Really no different than branching out after the first gang box, except here it's branching out immediately from the breaker.

Double breaker
 

If im Think of the right Square D they make a double breaker with 2 15 amps switches that fits in one slot. (each wire has its own switch and amps )Then you would have nothing to worry about. Like not having enough wire to move circuits to other breakers.

This works ONLY IF your panel accepts this type of breaker. Not all do.

If it's two VERY light loads, then pigtailing or (legally) doubling up is fine.

We have decided to upgrade the service to 200amp. It just seems like the right thing to do and will allow us for expansion in the future if needed. Thanks for all of the input.

That is a great decission, even increases your property value. :cool:

Im sure no one will agree with me but upgrading to 200 is over kill for 95% of homes. I have electric heat, electric hot water heater, and every electric device you can think of. my electric bill get up to $500 in the winter. Only have 100 amps. Even if i did ever trip my 100 amp breaker. i still wouldnt want to upgrade because if i was using more than 100 amps at a time i would want my electric to turn off. It would be like my house giving me a slap in the back of the head telling me to use less electric.