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Old 02-25-2013, 11:09 AM   #1
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New Subpanel feeder sizing


Looking to run a subpanel to our mechanical room due to the need for at least 4 circuits in there. The current expected loads are:

Circuit #1 - Furnace #1 @ 12.5A - 20A breaker
Circuit #2 - Furnace #2 @ 12.5A - 20A breaker
Circuit #3 - Dehumidifer @ 14A - 20A breaker
Circuit #4 - Hot Water Hear Blower @ 2.8A, Recirc pumps @ 1.92A x2 - total 6.64A - 20A breaker

Total max amperage is 45.64. Looks like I would only need a 60A feeder to the sub. Should I go bigger for any possible future needs (humidifiers, lighting, etc). The subpanel I have for the room is a Homeline 6 space with 100Amp max feed.

For a 60amp feed I appear to be looking at 6/3 w/ground. The between the main and sub is approx. 60ft.

Also, if I'm reading the code right I would need to have GFCI protected receptacles since we're in a basement.

The items on circuits #3 and #4 all come with pre-wired cords. Is there anything in the IRC that says that those cords can't be used and they need to be hardwired? I only ask because the install manual for the water heater says some jurisdictions may have this requirement.

We go by IRC here.

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Old 02-25-2013, 01:00 PM   #2
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New Subpanel feeder sizing


If your subpanel is rated for 100A, I'd just wire it for the max. That way, you have space for future upgrades. At that size, AL cable would be fine.

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Old 02-25-2013, 01:13 PM   #3
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You need to say what are 120V and 240V loads. For instance, if they are all 120V loads, properly balanced, one leg would never see more than 26.5A. Only you know what your future loads will be. Whole houses used to run on 60A. Unless you're putting in a three person machine shop, 100A is definitely overkill.
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Old 02-25-2013, 01:19 PM   #4
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You need to say what are 120V and 240V loads. For instance, if they are all 120V loads, properly balanced, one leg would never see more than 26.5A. Only you know what your future loads will be. Whole houses used to run on 60A. Unless you're putting in a three person machine shop, 100A is definitely overkill.
True. 100A may be overkill. Unless, the OP would like to add a welder at some point.

I'm a big fan of overkill.
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Old 02-25-2013, 01:38 PM   #5
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Definitely no welder off of this subpanel. They are all 120V circuits. So it sounds like 60 amps is the way to go then. Thanks.
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Old 02-25-2013, 01:40 PM   #6
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Making connections in aluminum requires a torque screwdriver or wrench with calibrations to match the lug listings on the panel's label. And I recommend a wire brush and Noalox or Penetrox paste, applied as per directions. That said, AL 4/3 w/ ground cable (55A) takes a 60A breaker. That's plenty to add a humidifier and all the lights you could dream of.

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Old 02-25-2013, 03:05 PM   #7
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but copper 6/3 w/ground is ok as well?

Also, what about direct wiring the appliances vs using the attached cords? Anything for or against either method?
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Old 02-25-2013, 05:16 PM   #8
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but copper 6/3 w/ground is ok as well?

Yes. Just much more expensive.

Also, what about direct wiring the appliances vs using the attached cords? Anything for or against either method?
I don't know the IRC. I believe the IRC adopts the NEC. The NEC says make no changes to a listed appliance. If the approved agency (UL) listed it only with a cord, then the cord must stay.
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Old 02-25-2013, 06:07 PM   #9
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I wouldn't run a sub panel at all. Either a piece of pipe, or romex.
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Old 02-27-2013, 07:03 AM   #10
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The number of circuits going to the one place made me believe that one big cable is better than 4 or more this case.

How do you determine finished vs unfinished basement? The room has plaster over brick or stone walls and plaster over wood lathe ceiling. Would I need GFCI outlets or breaker in this case?

Can a MWBC used for the two furnace blower circuits? That is can I run from a 20 amp 2 pole breaker with 12/3 to a junction box and drop a 12/2 to each furnace from there. After typing that I realize that I would have to take down both furnaces if there was an issue in the future so this really just becomes a hypothetical for if there are cases where a MWBC can/cannot be used. The other option would be to use 12/4 and two separate 20 amp single pole breakers, or just use 12/2 the whole way from the panel to furnace.
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Old 02-27-2013, 07:16 AM   #11
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The MWBC would be fine for the furnaces. Each furnace should have a service switch on it to isolate it should ity need to be worked on. You would not need to turn off the breaker.
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Old 02-27-2013, 07:17 AM   #12
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You wouldn't have to take down both furnaces. They each require a service disconnect which you can turn off if there is ever an issue.

You can also install 2 single pole breakers and a handle tie to satisfy the breaker requirement. This will allow one breaker to trip without tripping the other circuit.

You want to install a sub panel, go ahead. As a electrical contractor, I wouldn't suggest it as it would be around a $400 extra expense.

If the ceiling is plaster/lathe, I would run a piece of pipe, unless the joist run in the same direction my romex was running.

Be aware, that you may be required to install a GFI protected receptacle in your equipment room if there is not one there already.
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Old 02-27-2013, 12:45 PM   #13
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Technically speaking with the subpanel in the room I wouldn't need the shut off though right?

Am I reading the code right that I need TR rated receptacles for anything below 5 1/2 feet off the floor?
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Old 02-28-2013, 04:36 AM   #14
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Quote:
Originally Posted by thanh111vuvan
Removed spam from quote.
Mods please delete this garbage.
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Last edited by beenthere; 02-28-2013 at 04:39 AM. Reason: removed spam from quote
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Old 02-28-2013, 04:39 AM   #15
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Please don't quote spam, thank you.

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