Correct Wire Size for Heat Pump

[snorky18]

Yesterday I was under the house working a minor plumbing job, and I happened to run across the electrical wire supplying our heat pump. It seemed a bit small, so I started looking for the label on the Romex jacket, which was really hard to read (faint yellow dots/writing on black pvc jacket, and it was dark). The wire is 8/2, and it is currently fed from a 60-amp breaker (and has been for the last 7 years since the house was built).

The heat pump is 3 ton with 10kW of strip heat. According to the nameplate, minimum circuit ampacity is 74 amps, and maximum overcurrent protection device is 80 amps. So it would seem, at least to me, that this wire is GROSSLY undersized. By the way I’m out in the boonies, so the only permit for the whole house is the state septic permit.

I dig out an (02) NEC handbook, look at article 440, and when I size the wire based on what I see there, I get 3AWG for CU or 2AWG.

Somebody stop me right here if I’m heading down the wrong path (or feel free to tell me I’m on the right one), but I think what needs to be done before there’s any chance of the strip heat kicking on this winter is to upgrade the wire size, as well as the breaker and disconnect.

My current plan is to install an 80 amp breaker feeding 2AWG-2 conductor with ground SER cable (I’m assuming I don’t even want to know how much 50’ of 2-2 copper would cost) that runs to a 100 amp disconnect, then a liquidtight PVC whip containing 6' of 2 -#3 THHN hot conductors and a #8 THHN equipment ground connector. AL wire connections will have noalox.

A few questions

1. Is my wire size correct? Seems like I hardly ever see wire this large used on a residential unit.

2. Any reason that I should not use SER cable?

3. Am I right that once you go over a 60 amp disconnect (~$7) the next step up is 100 amp disconnect (~$70)

4. Does anyone sell a whip with #3 Cu conductors, or will I just need to put one together? (Seems like most of the whips I see are #10 or #8) What size liquidtight conduit would I need to use for this?

 

[pattenp]

The 10kw strips will need about 43A, so a 60A circuit is all that's needed. A 60A circuit will need #6 Cu and a 60A breaker. I don't see that you need to push it to 80A. If you do the 80A then the #2 Al SER is fine and you can get 80A breakers.

I believe you'll need 1" Liquidtight for the #3 Cu.

 

[snorky18]

The 10kw strips will need about 43A, so a 60A circuit is all that's needed.

True, but the strip heaters and compressor can run at the same time.

The compressor pulls ~24 Amps on top of the 43A strip heaters, 67A total, and according to the nameplate, Minimum circuit ampacity is 74 amps.

At any rate, the 60A breaker has been running the load without tripping, my concern is the #8 wire it has been fed through.

(Admittedly the strip heaters are very rarely used).

 

[frankzlt1]

The 1 true way of knowing if the wire is undersized is to turn you're system on and amp probe the circuit with the electric heat secondary and compressor running at the same time. A lot of times the name plate may be a higher rating than the system really is. When amp probe you my find the system will be around what its fused at. If you find that the name plate is close then i bet you have a ge breakers.

 

[wyliesdiesels]

I would at least upgrade the wiring! That's a fire waiting to happen! And before pulling new wire, perhaps u could call the manufacture and see if they recommend upgrading the circuit to 80a!

 

[pattenp]

True, but the strip heaters and compressor can run at the same time.

The compressor pulls ~24 Amps on top of the 43A strip heaters, 67A total, and according to the nameplate, Minimum circuit ampacity is 74 amps.

At any rate, the 60A breaker has been running the load without tripping, my concern is the #8 wire it has been fed through.

(Admittedly the strip heaters are very rarely used).

Yeah.. I was thinking emergency heat. Didn't think about supplemental heat for when the HP can't keep up. It's hard to believe with the nameplate stating 74A minimum circuit that the installer put it on a 60A circuit using #8.

 

[brewchief]

Is the heatpump original to the house is was it replaced in the past? If it's a replacement I wonder if the original only had 5kw in heat strips.

Are the strips one or two stages? It's possible if they are two stages that only one stage is hooked up, this would account for never tripping a breaker.

 

[sberry]

Got an installation manual or can look one up?

 

[bassman]

It says all it has to say rite on the nameplate, 74a minimum ampacity, out away the amprobe and upgrade you're circuit

 

[jbberns]

It says all it has to say rite on the nameplate, 74a minimum ampacity, out away the amprobe and upgrade you're circuit

Agree. Always go with the nameplate

 

[wyliesdiesels]

Yeah.. I was thinking emergency heat. Didn't think about supplemental heat for when the HP can't keep up. It's hard to believe with the nameplate stating 74A minimum circuit that the installer put it on a 60A circuit using #8.

Yeah, its hard to believe installations like this happen but some contractors are cons and skimp on this or that to make a few xtra bucks. Just like its hard to believe all the crappy electrical I found in McD restaurants when I was doing electrical inspections for NCR- #12 connected to a 50a 3 pole breaker that was also populated with #6! Or ground and neutral bonded together in subpanels. Or arcing wires cause someone skinned the insulation!

The OP might be able to go after the contractor who put it in and make them fix it!

 

[snorky18]

The OP might be able to go after the contractor who put it in and make them fix it!

I'm in rural AL, no building codes enforcement. I'm 2nd owner, original install was in 2005 by a guy who is apparently (in)famous for being the low bidder on HVAC jobs for the entire area, and he apparently still makes a living doing work "like this".

Quite frankly a lot of people (and contractors) around here are far too "laid back" for my liking when it comes to building standards like this, especially those with such a direct and severe impact on safety. This is not the first electrical issue that I had to clean up.

It makes selecting a contractor lots of fun, and suffice it to say you would be laughed at for trying to go after the slimeball who did this in the first place. There's not any path to do such a thing, or in local dialect, "Ya caint get there from here."

It does help explain why my homeowner's insurance is sky high, despite being 150 yds from the hydrant and ~3-4 miles from the FD.

 

[wyliesdiesels]

Not so fast! Is the guy a 'licensed' contractor? If so, you may be able to file a complaint with the SLB(State Licensing Board) regardless of the code enforcement standard in your locale! I'm not sure of the laws in your state, but in California, u can do this! You file a complaint and you can have the state force him to remedy the situation! I've seen it happen many times here! It may be worth looking into. And maybe if you fix all the dangerous code violations in your house, u may be able to get your insurance lowered. Also, there's always the option of suing him in 'Small Claims' Court! Just make sure to take pics and document everything! Have a third party inspector come in and do a documented inspection to use in court!

 

[sberry]

Not so fast! Is the guy a 'licensed' contractor? If so, you may be able to file a complaint with the SLB(State Licensing Board) regardless of the code enforcement standard in your locale! I'm not sure of the laws in your state, but in California, u can do this! You file a complaint and you can have the state force him to remedy the situation! I've seen it happen many times here! It may be worth looking into. And maybe if you fix all the dangerous code violations in your house, u may be able to get your insurance lowered. Also, there's always the option of suing him in 'Small Claims' Court! Just make sure to take pics and document everything! Have a third party inspector come in and do a documented inspection to use in court!

I actually did that, asked the agent out, said do I get some brownie points for being neat? He brought out the underwriter about 4 months later, I asked, we got any lines where we slain the general condition of matters, he said,,, you get a big atta boy.

 

[Charles (in GA)]

The air handler and the compressor/condenser outside should have separate breakers. I have a heat pump with back up strips, and there are two breakers, one for the outside and one for the air handler.

I have a 60 amp supplying my air handler, and a 40 amp supplying my compressor/condenser unit.

Charles

 

[Full Throttle]

Is your heatpump a package unit or split system?

Either way 90% of the time we pull 2 circuits 1 for the comprrssor and 1 for the strip heat, yes even package units.

So please chexk and make sure you dont have another circuit.

 

[brewchief]

The air handler and the compressor/condenser outside should have separate breakers. I have a heat pump with back up strips, and there are two breakers, one for the outside and one for the air handler.

I have a 60 amp supplying my air handler, and a 40 amp supplying my compressor/condenser unit.

Charles

I took it as the unit being a package unit, everything combined in one box with just ductwork going into the house.

 

[snorky18]

The air handler and the compressor/condenser outside should have separate breakers. I have a heat pump with back up strips, and there are two breakers, one for the outside and one for the air handler.

I have a 60 amp supplying my air handler, and a 40 amp supplying my compressor/condenser unit.

Charles

^^ Charles that's exactaly how my split system for upstairs is set up. But the unit in question is a package unit for my downstairs.

Is your heatpump a package unit or split system?

Either way 90% of the time we pull 2 circuits 1 for the comprrssor and 1 for the strip heat, yes even package units.

So please chexk and make sure you dont have another circuit.

I personally cataloged every outlet, switch, piece of equipment, and breaker in the house... I'm real sure there is not another circuit, though I wish there was.

Question for you full throttle:

So for the 2-circuit method, even for a package unit, I'd have two separate double pole breakers feeding two circuits that go to two separate disconnects outside, two whips to connect the disconnect to the unit, and all 4 hot conductors terminating within a couple inches of each other inside the unit? I'm certainly not saying it's wrong, I even remember seeing the amperage charts for that configuration in the manual, I've just never seen it done in person.

 

[snorky18]

Or could I run the 2-2-2-4 SER to a small outdoor load center and use it as a disconnect at the heat pump, and then run two separate liquidtight conduits from outdoor load center to heat pump?