Article 440

[g-and-h_electric]

I need a bit of help . HVAC crew at the shop installed a new heat pump system. condenser was "size for size" btu wise.

Existing unit was 4 ton wired with #10 THHN in EMT with (get this) a 20 Amp breaker. New unit wants a a minimum 42 Amp circuit, maximum breaker 45 Amp.

Now for my problem The #10's wont pull out of the pipe (best guess is a buried box). It is in a finished basement, so there is no easy way to repipe things without the obvious drywall removal.

Here is my question..... With a condenser load of 23 Amp (before any 125% factors), am I code compliant with the #10's on the 45? My interpretation is that I am, but I would like another opinion .

Thank you.


Howard

 

[infinity]

The MCA is 42 amps? Then your minimum conductor size is #8 if in conduit. Do you have a photo of the nameplate on the unit?

 

[LarryFine]

Now for my problem The #10's wont pull out of the pipe (best guess is a buried box). It is in a finished basement, so there is no easy way to repipe things without the obvious drywall removal.

I suggest de-energizing the circuit and push a steel fishtape (with the hook bent and/or taped closed) in and out from either or both ends while having a helper listen for the bang of hitting a box.

 

[hbiss]

Before you even waste your time doing that, will the existing conduit size allow for two #8s?

-Hal

 

[electrofelon]

. With a condenser load of 23 Amp

Where is this 23 amps from? IS this what you actually measure when you clamp it? Unfortunately the code doesnt care what it clamps at.

Sounds like there is no way to do it code compliantly if the MCA is 42A. In practice it would work fine and safely, as the MCA has an extra 25% built into it, and in reality, I find actual draw is almost always around 66% of the MCA. You could splice on some #8 and use the #10 at its 90 degree rating which gets you to 40A, still not 42, but closer

 

[LarryFine]

Before you even waste your time doing that, will the existing conduit size allow for two #8s?

Two 8s and a 10 will fit in a 1/2" EMT.

 

[mtnelect]

What are the most common questions asked on this Forum:
a. HVAC
b. GFCI/AFCI

I think it is a draw !