Electrical Question

ChrisL

I am working on splitting the heat and a/c on a 10 unit apartment building to individual units. I need power from each apartment. There are main breakers for each apartment in the mechanical room, with a 100 amp line running to each apartment where the subpanel is located.

I have had 2 electricians come out with differing opinions. I would like to run a new circuit from the subpanel in each apartment back down to the maintenance room. This new wire would be fed through the existing conduit that the 100 amp line is in. One electrician said ok, the other not. Something about not putting branch circuit in with a feed. Does this sound right?

Thanks,

Chris

Eric

Current carrying conductors

Its an issue of how many current carring conductors (wires) are in the conduit. The wire must be derated because the extra "warm" wires next to each other increase resistance

Tony_8

branches

the "feed" to ea apt is also a branch in this case as it comes from a disconnect. Branches shouldn't be routed w/unprotected (by breakers/fuses) feeds. Your instance shouldn't be an issue as long as you have proper size conduit for the number of conductors as mentioned in the other post.

Bill NTSG

Wire Size

Maybe the issue. If you have 100 amp cable #2 awg or 1/0 [I'm guessing at size] and then you have a 12 or 14 awg in the same conduit and there is a short or cut in the jacket or insulator the 12 or 14 ga. wire could be exposed to the 100 amps. I know this is clear as mud but do see what I am trying to say ??

Tony_8

yes

I understand exactly what you're saying. I don't have a current NEC book, but I think multiple size conductors can be in the same conduit based on cu.in. available. Think of a panel box, with all the different amps possible to be exposed to. Certainly, you've seen cut insulation there. Besides, amps are drawn, not fed. An appliance wired for 20 amps isn't likely to ever draw 100 for any reason.

MURPH'_2

IF IT WERE SO

THEN WYE would we need overload protection in the first place ??

marc

better read the n.e.c. for a closer look. i dont think you can run branch circuits in same conduit/chaseway as feeders. if i were you i would hire a licensed electrical contractor and make sure there is a permit and inspections done. see n.e.c. 2002 section 230.7 other conductors in raceway or cable. " conductors other than service conductors shall not be installed in the same service raceway or service cable. hope this helps.

ChrisL

Marc brought up the issue I was concerned with. However, I am not sure if the wires that run from a main breaker to a sub-panel are considered "service" conductors.

I guess the person I need to talk to is the inspector.

Thanks guys,

Chris

Tony_8

feeders

I don't believe your 100 amp cables are FEEDERS. They are downstream of the main breakers which makes them branches. Please let us know what your inspector says.

Boilerpro_3

Why not just....

Come off those 100 amp main breakers with a fused disconnect for your load. I believe your not supposed to put two wires under one terminal, so you'll have to wire nut the cables together and then connect to the main breaker.

Boilerpro

Joe_13

220V right?

Is it a double pole 50amp or 100amp (meaning 200amp service) breaker. It's not a single wire 100 amp breaker??? It might be cheaper, easier to run the service feeders to sub-panels and then use an 80 amp breaker for the apartment feed and a single 15 amp breaker for the boiler.

ChrisL

Yes, its a double pole 50 amp breaker. The idea of running to a sub-panel, and then apartment panel is another option. I would prefer to have the breakers in each apartment, but its not necessary.

I'll let everyobe know the outcome.

Chris