Quick question?

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justin

Senior Member
What would you guys run to a residential AHU rated 10KW (60A)? This is new construction. I am aware of what should be run, I am not a DIYer, when some replies come in I will explain the reason for the question further, Thanks.
 

mdshunk

Senior Member
Location
Right here.
I'm confused. 10KW is only around 42 amps. Maybe there's a 60 amp QOU type disconnect in that AHU, but 10KW is still 10KW. The blower will add a couple amps. I'd be upsizing 1.25 since this is heating and running #6 copper.
 

mdshunk

Senior Member
Location
Right here.
I assumed that he was talking about a heat pump type AHU with a 10KW resistance heat pack installed. I don't think too many residential installs will have 10 ton AHU's. Normally, they'll have several smaller systems rather than to have one that big. An AHU with a 10 ton DX coil won't draw near the 60 amp he proposed anyhow, since it will only be (about a 3hp) blower.
 

justin

Senior Member
Correct, heat pump with blower(Florida), 10 KW heat strips. Also would you run 6-2 NM or SER or something different and why?
 

justin

Senior Member
No pop quiz, this is a question of practice versus code. I am just curious what's done in the field. In other words I have been doing things one way for a long time and have been made VERY aware of what should be done and I would like to know if I'm being held to the same standad as other contractors, if I give the reason behind the question up front there could be biased responses.
 

justin

Senior Member
Also what do you run for your Range ckt and what size OCP do you use? Come on, there has to be thousands of you guys that do this every day, you have to have some answer, this isn't "NECSI" interrogating you or anything!!
 
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justin

Senior Member
emahler, awesome response!!! but no!! this is a simple AHU with 10KW heat strips. The rating on the unit would read for example 57 A. No trick question here. If you were to wire this simple unit in a house what would you use?
 

emahler

Senior Member
the nameplate FLA is 57A?

I'd probably run #6cu. But to be honest, growing up in NJ, I've never seen a heat pump. It there a blower motor on this circuit? What's the motor load?

Does it list Min and Max fuse size like an A/C condensor does?

I'm just guessing here.
 
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mdshunk

Senior Member
Location
Right here.
justin said:
The rating on the unit would read for example 57 A. No trick question here. If you were to wire this simple unit in a house what would you use?
Hang on a sec... that's not how a heat pump AHU data plate reads. It might state a max amp draw with max heat installed, but there's a whole table that you have to pick a "check box" for what you have installed in that unit. You can install a variety of accessories and different amounts of heat packs. I'd like to see a pic of that data plate.... something sounds fishy to me.
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
Look on the ahu they should have circled what was installed and it should say max /min breaker sise .60 is about normal for an ahu with 10 kw.#6 copper is fine,for years i ran 6 seu alum .amd never failed.
 

justin

Senior Member
Well what I have always seen run and have run to a 10 KW 60A max AHU was 6-2 NM and 8-3 NM for a range with 50 A OCP for the range. I was told that I was unable to run the 6-2 NM for the 60A max AHU and the 50 A breaker for the 8-3 NM range cicuit was against code. The inspector is not wrong, I was eventually able to find the NEC reference, since he did not offer one on his failure notice, but I have to admit it caught me off guard and we have completed hundreds of homes this way. So are any of you familiar with the rule that makes this illegal or have any of you experienced the same issue before?
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
10kw of heat is 42 amps at 240V single phase. But that is a continuous load, so the circuit that feeds it should be rated for 42*1.25 = 52 amps. Rounding up, that gives a 60A circuit with #6 wire.
 

RB1

Senior Member
The range circuit violates Section 240.4(B) where NM cable is used. I don't see anything wrong with the AHU based on the information given.
 

paul32

Senior Member
Location
Minnesota
I haven't done a heat pump, but use 8-3 NM for 40A ranges. Yes I agree 50A is against code. I assume the reference you just discovered is 334.80 (maybe it isn't well known in some areas, on another site I pointed this out to someone that didn't know it).
 

dahualin

Senior Member
Are we discussing the wire size for 60 amps circuit (AHU with heater) and 50 amps circuit (range)?
Please check 110.14.(C).(1).(a) Termination provision of equipment for circuits rated 100 amps or less shall be used for conductors rated 60 degree.

We select wires for 60 amps circuit and 50 amps circuit shall based on temperature rating of 60 degree in Table 310.16. So 60 amp circuit needs #4 wire and 50 amp circuit needs #6 wire.
 

Rockyd

Senior Member
Location
Nevada
Occupation
Retired after 40 years as an electrician.
Temperature range under a 100A has you hostage.

As a note of interest, you may want to go to Table 210.24.
 
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