Need help settling a dispute......

[golfincock]

First off I know very little about HVAC. But my HVAC guy and my electrician are have a dispute about the wiring of a heat pump. It is a four ton Goodman split unit with 3 12 w heat strips. Hvac guy says 10 AWG wire with a 60 amp breaker is ok. Elec. says you should never have a #10 with anything over 30 amp. Hvac guy says wiring HVAC is different. He even showed me in the manual of the system and in the UGLY book. Both seemed to show that it was fine. Could this be right?

[jim reynolds]

My first suspicion would be HVAC guy saying that air conditioining is different. A qualified Electrician should know exactly what size wire and breakers you need.

[operator]

with wir e i would go with sparky, its his job to know the code on all elec.

[tecman]

My suggestion is to find a new HVAC guy. Doesn't matter if it's AC or a stove, the electrical code (NEC) clearly spells out the ampacity ratings for wire. The breaker is to protect the wiring (not the device) and at 60 amps you could nearly use the 10 ga wire as a toaster. The code calls for a #4 or #6 wire for 60 amps, depending on if it is 60c or 75c insulation rating.

The other thing that doesn't make sense is you say there are 3 12KW strip heaters. That is 36KW, and 150 amps at 240v. Perhaps it is 1 12KW heater (about the normal size for a 4 ton) which requires 50 amps at 240. Breaker at 60 would be about right for such an air handler, allowing for the blower power as well. The compressor is usually on a separate circuit, 4 tons about 30 amps. Maybe it is the compressor circuit that he wants to run with 10 ga wire. That would be okay.

Be sure to check out the facts and follow the code, unless you don't like your house, and you are well insured.

paul

[golfincock]

Thanks for the replies, guys. I am treading lightly here because I am pretty good friends with both of these guys. And going in to this, I would have trusted the HVAC guy more. He's been in the business for a while. But what I don't understand is why the UGLY book and the manual showed it as acceptable. Maybe I just didn't understand what I was looking at.

[ralphtheplumber]

My square D calculator says #10 copper wire is good for 35 amps.

#8 - 50A
#6 - 65A

[Wild Leg]

This is probably a resistive vs. inductive load confusion.

NEC allows a larger breaker on a given wire size, if it is the outdoor unit's circuit.
This is done to avoid nuisance trips of the breaker while the motor is starting.
The installation guide or rating plate may have the tie-breaking information, under "Minimum circuit ampacity".

For resistive loads, (heat strips, lighting, etc.), breakers are matched more critically to the size of the wire.

It is better to have too large a wire, than too small.

If you doubt, go with the larger recommendation.

[Jultzya]

You were probably looking under the motor section for HVAC. Motors can be wired this way for starting issues.
(However, I wouldn't recommend it)

The resistance heat strips requires the larger wiring. No questions about it! Go with the electrician.

[wormy]

There is also a slight difference between stranded wire (THHN) and Romex (what the electrician probably runs the most).... don't have my notes in front of me (or in my head on this one hehe)


I'd go with the electrician, but if all else fails...
oversize the wire. Bigger is OK... smaller is not.

[beenthere]

If he's talking about the outdoor unit, your hvac guy is right, if he's talking about your strip heaters he's dead wrong. Resistance is sized at 125% of load.

[amb4081]

Shouldn't the manufacturer have some information about this? I know Carrier, Bryant, and Payne list the minimum breaker size and wire size for their equipment; especially air handlers with electric heat.

[hvac guy1075]

10 awg and a 60 amp breaker, i hope you have very good fire insurance. the hvac guy is wrong wrong . i pick the electrician

[Midwest]

I think we discussed the hell out of this one last summer here in this site. Now, I'm refering to the condensor and not heat strips - heat strips will be on different circuit and overcurrent protrection. When it comes to HVAC, the NEC shows it's true colors. That is not only being the National Electrical Code, but the "National Exceptions Code". Get your hands on a copy of the NEC, read and study section 440 which details wiring for HVAC. Next review the rating plates on the HVAC equipment. Compare the min. required conductors vs. maximum overcurrent protection. Ignore table 310-16 (table of max. ampacity of general circuit conductors) if you wish, because 440 is the real rule in HVAC wiring. Then, you will be able to come to the right conclusion. Some electricians are not tuned to section (440) and use their customary methods. This will exceed min. requirements and it is always OK to exceed minimums. That causes no problem, other than a little extra expense.

Conclusion- your HVAC guy may be right, but it won't hurt anything to go with the electrician. If he just simply can't sleep nights following rating plate min./max. then let him exceed them. It takes the same labor to run a big wire vs. a little one. Greg

[Freezeking2000]

If the wiring you are talking about is contained within the Air Handler i believe your HVAC guy is 100% correct. Open wires in a controll panel are not rated the same way as the wiring that is to be covered. I notice that panels wired from TYLER for supermarket racks use #10 for 60 amps. As crazy as this sounds i uven called the factory to confirm it was the proper size and they said all ok. As for the size between the air handler and the panel i would error on the side of safety.

[contactor]

Let sparky wire the unit. Thats his job & his ratings seem ok ,Hvac guy seems questionable.(No wrong).
10 awg at 30 amp circuit is correct.
Why is HVAC guy arguing with sparky?

[glennwith2ns]

" Elec. says you should never have a #10 with anything over 30 amp"




Originally posted by contactor
Why is HVAC guy arguing with sparky?



Cause sparky is wrong!

[cem-bsee]

NO wire of any size nor voltage rating has an AMPACITY rating!!!!

Wire MAY have a voltage rating. Wire WILL have a maximum conductor temperature rating.

Lots of wire has no voltage rating = most service drop cable, street lighting cable, lots of welding cable, etc.

ampacities are derived from the installation environment and the conductor temperature rating.

the use of ONLY the 60C conductor temperature ratings equates to the cheapest everday operating costs, but not the wire cost.

[tecman]

True there is not a "current rating" per se, but for a given insulation temperature rating, NEC defines a maximum allowable current. Article 310 has a series of tables titled "Ampacity Ratings of Single Conductors..."

It's the NEC definition.

paul


[Edited by tecman on 05-05-2005 at 10:55 PM]

[rsmith46]

Look at the data sticker on the condenser, if the minimum ampacity is 30 amps or less you can run #10 wire. The maximum overcurrent rating gives you the largest breaker to use, if it says 60 your HVAC guy is right. I'm sure he is, but if the electrician already bid the job let him put in a larger wire if he wants.

[docholiday]

If Sparky pulled the electrical permit, you better listen to him. If the HVAC guy did.... Listen to sparky anyway.

[woowoo]

Remember
The NEC states the minimum requirements.
Run the bigger wire......

[golfincock]

Thanks for the discussion, guys. Now I'm more confused than ever. I think I'll just tell them to run the bigger wire. Oh by the way, its not really an argument. There actually kind of working hand in hand, which is how this came up. We all know each other. Its a small town. Its really more of a discussion. I just want to be sure its safe. So, it CANNOT hurt to have the bigger wire, right? I think I'll just have them run it.

[Jax]

Goodman heat strips come in basic 5, 8, 10, 15 and 20 K.
The electrical requirements are very clearly stated by Goodman.
5k is a 30a service, 8K is 40A, 10K is 60A, 15K is one 60a and one 30a. And 20k requires two 60a services. The actuall run amps are also provide. The electrical usage in each case is well in line with NEC.
Jax

[du mech eng]

Originally posted by rsmith46
Look at the data sticker on the condenser, if the minimum ampacity is 30 amps or less you can run #10 wire. The maximum overcurrent rating gives you the largest breaker to use, if it says 60 your HVAC guy is right. I'm sure he is, but if the electrician already bid the job let him put in a larger wire if he wants.


this is exactly right. the mca is typically 1.25 x the full load running amps of the unit. mocp is typically around twice the full load amps. both should be readily availible from the manufacturer though. as rsmith said, wires are sized for mca, breaker is sized for mocp. bigger wires will not hurt however, just cost you more $$$.

[ct2]

I am looking at UGlys and it shows 60 amps for FEP FEPB and PFA

for THHN it shows 40 amps and the footnotes for Welders and for motors says 30 amps for #10

I have never used FEP FEPB or PFA. THHN is the rating I would use

[tecman]

Originally posted by ct2
I am looking at UGlys and it shows 60 amps for FEP FEPB and PFA

for THHN it shows 40 amps and the footnotes for Welders and for motors says 30 amps for #10

I have never used FEP FEPB or PFA. THHN is the rating I would use

Those ratings are the insulation material...THHN is hi-temp thermoplastic with nylon overcoat. Normal romex is type NM, 60 deg rating. THHN is 90 deg rating, so higher current rating. THHN is single conductor so you would need to run it in conduit or sealtite.

The others are different insulation material and are alos rated at 90 deg.

paul