Need advice on subpanel options


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Old 03-10-14, 12:13 PM
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Need advice on subpanel options

I am in the process of replacing an electric furnace with a gas furnace. I would like to use the feed currently going to the furnace to feed a subpanel instead. Then I can run the gas furnace off the subpanel. I may also move the water heater and air conditioner to the new subpanel. I would like to have some open slots for future expansion as my main panel is full.

The furnace is fed with armored cable, 3 wire (black/red/white) with ground, and is about 60 feet long. I can't read much on the conductors but I do see #2 gage and the word X-Link. All conductors are copper. The furnace wiring is protected by a 150A breaker.

I would prefer not to have to change the 150A breaker in my current panel as I know these breakers are expensive. I assume this would mean that I would need to install at least a 150A subpanel. Is this correct?

Also I assume that the subpanel would need to have a 150A breaker in it used as a "disconnect".

I haven't priced anything; perhaps I could get by with 100A subpanel but then I expect that I would have to change the 150A breaker in the main panel to 100A or less. Correct?
 
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Old 03-10-14, 12:44 PM
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Number 2 would not be rated for 150 amps under the NEC. I would assume the CEC is similar. Also most electric furnaces are 240 volt only. I don't know why it appears you may have a neutral in the cable.

Are you adding up the breaker handles to get the 150 or does it actually say 150 on the handles?
 
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Old 03-10-14, 04:10 PM
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The furnace is fed with armored cable, 3 wire (black/red/white) with ground, and is about 60 feet long. I can't read much on the conductors but I do see #2 gage and the word X-Link. All conductors are copper. The furnace wiring is protected by a 150A breaker.
Sounds as if you had a single circuit 20 KW electric furnace. It should have been protected by either a 110 amp or maximum 125 amp breaker. Since you have 3 insulated and 1 ground conductor, you could install a 100 amp main lug subpanel, but the breaker in the main panel will have to be changed to 100 amps. As far as I know, the CEC will not require a main breaker as a disconnect in the subpanel.
 
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Old 03-10-14, 04:44 PM
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There are definitely 3 conductors, all the same diameter in the armored cable. The elements in the electric furnace are 240V but the blower motor and transformer are 120V. So they would have needed a neutral for that - of course the neutral didn't need to be 2 AWG for just the motor but it seems like that is how it was done. If they wanted different size conductors then I suppose they would have had to use conduit.

It probably would have been cheaper overall to use a 240V blower and transformer but this works well for me, as without the neutral I wouldn't be able to install a subpanel at all.

The breaker in the main panel for the furnace takes 4 slots and they are ganged with a single folding handle that says 150A on it. The panel itself is a 200A service.

So from what both of you are saying, they goofed by using a 150A breaker in the first place. I don't actually know the furnace rating. So I guess my best bet is to change the main breaker to 100A and use a 100A subpanel. CasualJoe - are you saying that the subpanel doesn't have to have a disconnect to switch off the entire bank of breakers?
 
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Old 03-10-14, 04:53 PM
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CasualJoe - are you saying that the subpanel doesn't have to have a disconnect to switch off the entire bank of breakers?
The NEC doesn't require a main breaker disconnect and I don't think the CEC does either, but I am no expert on the CEC.

The elements in the electric furnace are 240V but the blower motor and transformer are 120V.
That could be because your furnace was made for a market other than the U.S. market. The electric furnaces I am familiar with are 240 volt units with all 240 volt motors and require no neutral in the circuit.
 
 

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