Adding a sub panel for Central A/C

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  #1  
Old 06-10-09, 07:35 AM
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Adding a sub panel for Central A/C

Hi All,

I want to see if there's anything we should be considering on this next project.

We have a Cutler Hammer 4040 panel, that's only has two spots open. I need 4 for the AC, 2 for the condenser, and 2 for the air handler. And since it's a 4040 panel, I can't use (to meet code anyway), tandem breakers with the rejection tabs.

So my only real option, I think, is to add a small sub panel next to the main panel, for the A/C circuits. At least I have the two spots available in the main panel for the breaker to feed the sub.

What we're thinking (the electrician and I), is a 100amp 16 circuit sub panel. It would have the 50amp DP breaker for the condenser, and the 15A DP breaker for the air handler, and that's it.

I assume the main panel breaker would be a 100A breaker.

Anything else I should consider?

Thanks.
 
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Old 06-10-09, 08:24 AM
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It sounds like you're pretty well set. 100A subpanel is a good idea since it will be right next to your main panel and wire cost won't be an issue. (if it was 100' away, you might want to try to get away with something smaller).

You should consider though moving some smaller loads to the subpanel and keeping the AC and other large draw items in the main panel. With a 100A feeder and only a few feet of wire, it won't make a huge difference, but you generally want to keep the larger draw items in the main panel to reduce any voltage drop when the large appliances startup.

In your case, it's probably 50/50 either way.

It's also a good plan to stick with the same manufacturer and model of panel so the breakers are interchangeable between the two. Again, not a big deal, but it helps ensure you have the correct breakers down the road.
 
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Old 06-10-09, 09:36 AM
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We talked about that, moving smaller stuff. But the box is so full, moving stuff seems like a bigger pain, plus, it's all balanced for my generator.

Literally, the new panel will be within 24" of the current panel, so we figured since the A/C is only used 3-4 months out of the year, we'd just have the subpanel be for the A/C. So that's ok? Figure the total length of wire is less than 48".

I was doing what you say too, getting another Cutler Hammer BR panel.

Sound ok? The draw of the condenser is 33A, with a 50A breaker, and the air hanlder draws 7.8 with a 15A breaker.
 
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Old 06-10-09, 09:43 AM
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Originally Posted by steveg_nh View Post
So my only real option, I think, is to add a small sub panel next to the main panel, for the A/C circuits. At least I have the two spots available in the main panel for the breaker to feed the sub.

What we're thinking (the electrician and I), is a 100amp 16 circuit sub panel. It would have the 50amp DP breaker for the condenser, and the 15A DP breaker for the air handler, and that's it.
That's exactly what I would do.
 
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Old 06-11-09, 10:18 AM
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Perfect, thanks Guys. That's what we'll do then. Keep it simple.
 
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Old 06-11-09, 05:40 PM
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Originally Posted by steveg_nh View Post
What we're thinking (the electrician and I), is a 100amp 16 circuit sub panel. It would have the 50amp DP breaker for the condenser, and the 15A DP breaker for the air handler, and that's it.
That I will go that route as well keep it simple and quick due your exsting box is allready about full now.

And that way if in the future you add a circuit you can go from subpanel that way.

Merci,Marc
 
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Old 06-14-09, 03:08 PM
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Thanks again.

I do have one follow-up question if I could. I bought the sub panel today. It's a cutler hammer 8 space, 1 circuit 125A panel, with main lugs only. It doesn't have a main breaker, which would be in the main panel. We're putting a 100A breaker on the sub panel. I assume this is the right type of a panel for an add-on.

On the sub panel, it says the ground bar is not included. I will ask my electrician, but do I need to get one of these before we start, or is it all tied into the main panel with the existing neutral bar in the sub panel?

Thanks.
 
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Old 06-14-09, 03:43 PM
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You will need to buy the ground bar. All subpanels require a bonded ground bus and non-bonded neutral bus.
 
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Old 06-14-09, 05:46 PM
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Thanks. Wonder why they don't just include it then.
 
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Old 06-14-09, 06:08 PM
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Originally Posted by steveg_nh View Post
Thanks. Wonder why they don't just include it then.
Some times it isn't needed.
 
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Old 06-14-09, 06:09 PM
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I'm confused then. Above you said all subpanels require both. So when would it not be required? Thanks!
 
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Old 06-14-09, 06:17 PM
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The panel could in certain cases be used as a main panel. A main lug panel can be used as a main panel if there are 6 breaker or less even though there isn't a main breaker. In certain cases to a main lug could be back fed through a breaker (with approved hold-down) and used as a main panel.
 
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Old 06-15-09, 05:43 AM
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Boy, literally, you learn something every day.

Thanks.
 
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Old 06-15-09, 08:55 AM
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Originally Posted by steveg_nh View Post
Thanks. Wonder why they don't just include it then.
How could they charge $8 for it if it was included?

You do need to buy it for probably 95% of projects with a subpanel, but it is not always needed so they don't include it.
 
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Old 06-15-09, 12:36 PM
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A 240v only subpanel would not need it either as the "neutral" bar could be used as a ground bus since no neutral used. One of the other 5% Ibpooks was referring to.
 
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