Understanding my central HVAC wiring

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Old 07-03-16, 10:10 AM
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Understanding my central HVAC wiring

Okay, so this is going to be a little convoluted. But if it made sense to me, I wouldn't be asking I guess, right? Anyway, the house has dual zone HVAC: upstairs and downstairs. Downstairs is oil burner, forced warm air, with central A/C. Upstairs is heat pump, with an outside compressor and inside air handler. For ease of understanding, I'll break this into A/C and H/P.

In the breaker panel, there is a circuit for the downstairs A/C compressor. It is two, 20A breakers, ganged together (20A, 240V). There a circuit labeled furnace, which is one, 20A breaker (20A, 120V), which seems to control the blower and burner.

Outside, next to the A/C compressor, is a disconnect box with a pull-down lever (on/off). The rating plate inside says it's a 60A disconnect.

The A/C compressor outside has a data plate that states "minimum ampacity 13.7" and "max circuit breaker 20."

So, the data plate and the inside circuit breakers seem to match. 20A, 240V breakers installed, with a max 20A breaker required. Good, yes? But what about that 60A disconnect? Does it matter? Or, because it's just a service disconnect and not overcurrent protection, is it okay as long as it's MINIMUM 20A?

Also, the disconnect box, if you lift the cover up, exposes all the wiring. This is probably something that, to keep little prying fingers out, should have a lock installed on the cover, yes?

Okay, great, now onto the heat pump:

In the breaker panel, there are two circuits labeled heat pump. The first heat pump circuit is two, 50A breakers ganged together (50A, 240V). The second circuit is two 60A breakers ganged together (60A, 240V). I'm not sure which controls the air handler and which controls the compressor. Since they generally work in tandem, is there a good way to pinpoint which is which? Turn one off and try to run the blower in fan-only mode?

And, like the A/C, the H/P compressor outside has a data plate that states "minimum ampacity 13.8" and "max circuit breaker 20." This causes me concern because either way, the circuit breakers are either 50A or 60A. Am I right to be concerned?

Thank you all in advance.
 
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Old 07-03-16, 10:49 AM
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Disconnect

But what about that 60A disconnect?
60 amps is the maximum current the disconnect will handle. Does the disconnect have fuses? If so, the fuses should match the maximum ampacity of the circuit intended to protect the equipment.
 
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Old 07-03-16, 10:51 AM
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Service disconnects are rated for maximum thru current. Many times the 60A devices are less costly than the 30A ones.

It sounds like your disconnect is missing an internal cover plate.

I would not expect that those two large breakers feed the compressor.... just the heat pump air handler. The reason for the large amperage is due to the electric heating coils in them.

The heat pump compressor should be using a two pole 20A or 30A breaker.
 
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Old 07-03-16, 11:38 AM
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No fuses in the disconnect. When you pull the big on/off handle on the outside of the box, it disconnects it inside, kinda like a giant circuit breaker I guess. I can post a pic if that would help.

PJ... I didn't think of the heat strips, that certainly makes sense. Would it be normal for the air handler to need two 240V circuits? I just wonder because all my two pole breakers are accounted for: Generator interlock, whole home surge protector, dryer, water heater, 2x heat pump, and 1x A/C.

I only have two, nonadjacent, single pole 20A breakers that aren't labeled that I've never been able to figure out. Though I just had a horrifying thought of, what if somebody decided to use them instead of moving breakers around to install a proper two pole... I mean, technically it would work, right?
 
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Old 07-03-16, 11:48 AM
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Pictures are always helpful to us. http://www.doityourself.com/forum/el...-pictures.html

It is normal for a a heat pump that heats an entire house to require two large circuits for the heating elements.

Post the model number for that air handler. There should also be circuit info posted there.
 
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Old 07-03-16, 12:48 PM
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Here's the A/C outside disconnect, with the cover open:

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The heat pump air handler is a Lennox CB29M-31-1P. This is the circuit info. Looks like one 45A minimum ampacity and 50A breaker. I see what you mean, though, had one of the other heaters been installed needing two circuits.

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There's also a 60A disconnect above the unit, which as I understand now is fine.
 
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Old 07-03-16, 01:33 PM
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I don't think that disconnect had or came with a deadfront cover.
 
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Old 07-04-16, 03:11 PM
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Padlock is going on then.

I think I may have answered my question, at least partially. Looking at what comes out of the breaker panel, there's 6-2 NM-B that goes to the H/P air handler. Then there's 8/3 NM that goes to the A/C compressor disconnect, and then 6-6-6 SE from the disconnect to the compressor. And then cables to the dryer and water heater. Nothing else seen coming from the panel that would accommodate a 50A or 60A 240V circuit. I'm forced to conclude that one of the 12/2 NM cables has to be feeding the H/P compressor then, and it's massively over-breakered.
 
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Old 07-04-16, 04:12 PM
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I'm forced to conclude that one of the 12/2 NM cables has to be feeding the H/P compressor then, and it's massively over-breakered.
That is quite possible and deserves immediate attention.

PCB is right about that disconnect. There is no inside cover. A nut and bolt or a lock will work.
 
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Old 07-04-16, 05:51 PM
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Assuming that is the case, the 12/2 NM should be okay for the run to the H/P (Min ampacity 13.8, max breaker 20A), and it just needs the breakers downgraded to a 20A two pole breaker?
 
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Old 07-04-16, 08:40 PM
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Yes..... that is correct.
 
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Old 07-05-16, 10:03 AM
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Okay, so today I decided I'd dig a little deeper and popped the cover off of the breaker panel. You know, to look for which breaker had the high amp ratings and the skinny wires. Yeah. About that...

The 20A, two pole that I told you was labeled A/C... Yeah, THAT's the H/P compressor. The 50A two pole is the H/P air handler. And the 60A, two pole, labeled "heat pump," is actually the A/C compressor.

I suppose this does explain why, a few years ago when I was reconnecting my H/P condensate pump, there was a spark and the compressor fired up, even though "both breakers were off."

So, now it looks like the heat pump is fine. 20A, 240V two pole breaker going to 12/2 wiring to the compressor. And 50A, 240V two pole breaker going to 6/2 to the air handler which is rated for 45A minimum and a 50A max breaker.

It's the A/C that's not right. The wiring for the H/P seems newer, so I theorize that at one point the house had single-zone A/C, with a much larger outside unit that needed the heavier wiring and breakers. They switched to two zone, installed a smaller compressor, and left the wiring as is. Hence the 60A breaker and 8/3 wiring.

So my questions are now really about that. I'll post back in a few minutes with some more pictures.
 
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Old 07-05-16, 10:32 AM
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Okay, so, in this first pic this is a better outside view of the disconnect. What I'm really wondering about here is, why does it look like there's thermostat wire going from inside the box into the ground? It disappears into the ground, and seems to go pretty deep. Could someone have used this as some sort of grounding wire? As you'll see in the next picture, though, it appears to go into the conduit and into the house... What's its purpose? There's other T-stat wire that comes in at the same point, so I can't really discern which is which on the inside.

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Now, here's where I get more confused. In the panel in the house, there is 8/3 wire from the breaker. The green grounding wire and the white neutral are connected to the neutral bar. The red and black wires go to the breaker.

In the disconnect box outside, the green grounding wire is connected to the box. The red and black wires go into the disconnect switch. And the white neutral is just lopped off and left to sit.

And it appears that the grounding wires from the SE cable to the A/C compressor are also connected to the box.

Looking at this, what's up with the neutral? Is it OK to hang out just as it is? Any other problems noticed?

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And, am I going to be able to jam 8 AWG stranded wire into a 20A breaker? I have a CH panel, and I'm not sure how to interpret from their catalog whether or not it will fit.

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Thanks so much everyone!
 
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Old 07-05-16, 02:18 PM
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Air conditioning is a straight 240 volt unit. It does not need a neutral.

The 20 amp breaker will accept up to a #6.
 
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Old 07-05-16, 06:45 PM
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Is it harmful to leave the "neutral" wire connected in the panel if it doesn't go anywhere at the other end?
 
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Old 07-05-16, 08:40 PM
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No but it should be capped off at the disconnect.
 
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Old 07-05-16, 09:43 PM
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Thank you all for your help!
 
 

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