Oversized wire, or is it ok?

[Tommy1010]

I have a Carrier 5 ton package water cooled heat pump rated for 15A. Why is it wired with 10 gauge wire??? The service disconnect is 3 ft away, then has an additional 10 gauge wire run to a fused disconnect about 25ft across the room. Its been running OK like this, but I had to move the unit and when I rewire it can I just use 12 or 14 to go from the unit to the service disconnect, and leave the 10 gauge feed as is? Everythings telling me yes it'll be fine, but verification feels better!:callpro:

[BamaCool]

Over sized wire is never a problem as long as you still get good firm connections and the circuit breaker is sized correctly.

[ga-hvac-tech]

You need to check what size breaker is on that wire...

The purpose of a breaker is to protect the wire from carrying too many amps... and generating heat. If it were me, I would just use the same 10 G wire.... maintain conformity in the circuit. And the whip... they probably used a pre-made whip... WAAAY cheaper and easier.

If you changed the breaker to, lets say, 15A, and used 14G wire it would work if it is indeed a 15A load. However later down the line someone that does not know about your 14G wire might change the breaker back to 30A and overheat the wire...

I am not up on elec code, but I think one needs to stick with the wire size.

Someone that is up on elec code might be able to answer this.

[Tommy1010]

This was entirely IN HOUSE job initially. My former boss put it in from the service disconnect to the unit. I asked the electrician that ran the feed, he pretty much said "I guess he (my boss) only had 10 gauge with him". I went with 12. It IS indeed a 15A fused disconnect. Got everything done except i gotta re run the Tstat wire. Only be a few minutes, then ill test and amp it out.

[btuhack]

I've never looked it up but I have been told that 14 GA. on commercial work is a No No.

[bjones]

I've never looked it up but I have been told that 14 GA. on commercial work is a No No.

You were told wrong. There is nothing in the National Electrical Code (NFPA-70) that says, "Using 14 GA. on commercial work is a No No".

[gevans]

15 amp on a 5 ton unit does not sound right. It should be more.

I don't use 14 gage solid on ANYTHING.

[maintenanceguy]

It's fine for wire to be too big. It's bad for wire to be too small.

Big wire can carry more amps than it needs to. Small wire can't carry the amps and overheats.

I think I'd check the specs on a 5 ton heat pump to see if it's really calling for a 15A circuit.

[Tommy1010]

Well I got it all up and running. Pressures, 68/210....comp. amps= 4.2 rated at 4.8, IFM amps= 1.1 rated @ 1.7, I still have to clean the evap coil though. Good airflow, but its been sitting for quite a while so i know theres alot of dirt in there.

[jemawalton]

I think I'd check the specs on a 5 ton heat pump to see if it's really calling for a 15A circuit.

Depends on the voltage. Most of the 5 ton units I see are 460V 3ph and 15 amp service sounds about right.

[Tech Rob]

Circuit breakers should be sized for the equipment MOCP. The wire should be sized for whatever the circuit breaker is.

If in doubt, consult the NEC guidelines.

[klrogers]

Circuit breakers should be sized for the equipment MOCP. The wire should be sized for whatever the circuit breaker is.

If in doubt, consult the NEC guidelines.

Technically the wire only needs to sized for the MCA (Minimum circuit amps) of the equipment, but yes sizing it for the circuit breaker is best.

Kevin

[pecmsg]

Technically the wire only needs to sized for the MCA (Minimum circuit amps) of the equipment, but yes sizing it for the circuit breaker is best.

Kevin

Don’t you mean Max Circuit Amps?

[jayguy]

You were told wrong. There is nothing in the National Electrical Code (NFPA-70) that says, "Using 14 GA. on commercial work is a No No".

is there anything in the NEC that uses the term: No No? perhaps this term is too technical for me.

[BamaCool]

is there anything in the NEC that uses the term: No No? perhaps this term is too technical for me.
No, not in the NEC. That term is reserved for inspectors. You know, the same inspectors that wire manufactures had to color code Romex wire for.:eek2:

[coolerinfrederick]

on large scale jobs for electricians that cost some serious $$$ when wire is oversized just cause

[klrogers]

Don’t you mean Max Circuit Amps?


No it is Minimum, see 440.35 in NEC(2005)

[bob_scheel]

This was entirely IN HOUSE job initially. My former boss put it in from the service disconnect to the unit. I asked the electrician that ran the feed, he pretty much said "I guess he (my boss) only had 10 gauge with him". I went with 12. It IS indeed a 15A fused disconnect. Got everything done except i gotta re run the Tstat wire. Only be a few minutes, then ill test and amp it out.

If the total draw on the circuit is more that 15.0 amps ie 15.1 then you should be #10 to allow for the compressors start up. Motors are never wired with the bare minimum. Keeping the voltage up as the motor / compressor starts prevents overheating and minimizes the time the motor spends getting up to speed. This prolongs the life of the motor/compressor and other components like the contactor.

[printer2]

Good thing you went with 12, 14 is only rated for 12 amps continuous.

While length comes into play, having a larger wire size reduces the voltage drop going to the load. Motors are not partial to being operated under full load with reduced voltage (exactly what happens under full load), you increased the service life going larger.

[Paul Bee]

N E C article 440.6 (A) Hermetic Refrigerant Motor-Compressor. For a hermetic refrigerant motor-compressor, the rated-load current marked on the nameplate of the equipment in which the motor-compressor is employed shall be used in determining the rating or ampacity of the disconnecting means, THE BRANCH CIRCUIT CONDUCTORS,the controller,the branch-circuit short-circuit and ground-fault protection,and the separate motor overload protection. An electrical CIRCUIT is a SYSTEM and everything is sized and rated to work together as a system!! YES bigger wire will work but some of the safety built into that engineered system is now gone. Do it right or don't do it!!!!! If you are not going to do it right, you might as well let the customer do it himself!!!!! Tommy1010 Get yourself an NEC code book I know you can read. Answers from reference books tend to be accurate not BS. BIGGER WIRE IS NOT BETTER!!!!!!

[btuhack]

N E C article 440.6 (A) Hermetic Refrigerant Motor-Compressor. For a hermetic refrigerant motor-compressor, the rated-load current marked on the nameplate of the equipment in which the motor-compressor is employed shall be used in determining the rating or ampacity of the disconnecting means, THE BRANCH CIRCUIT CONDUCTORS,the controller,the branch-circuit short-circuit and ground-fault protection,and the separate motor overload protection. An electrical CIRCUIT is a SYSTEM and everything is sized and rated to work together as a system!! YES bigger wire will work but some of the safety built into that engineered system is now gone. Do it right or don't do it!!!!! If you are not going to do it right, you might as well let the customer do it himself!!!!! Tommy1010 Get yourself an NEC code book I know you can read. Answers from reference books tend to be accurate not BS.
Bergermech Rob's makes more sense to me and is more accurate for this circumstance I think. The heatpump in question is a "listed device" that has it's own electrical rating-MOCP. If the issue was with a stand alone compressor, say your typical open drive set up, then I think your quoted interpretation would be accurate. Perhaps I misunderstood your interpretation, or perhaps my NEC knowledge is even worse than I thought.

[crab master]

There is nothing wrong with going with larger wire size, as long as that wire size doesn't put you over on the conduit max fill rating. Wire sizing is basically based on heat dissipation based on how many amps will be going through the wire. Conduit max fill ratings are also based on that same heat dissipation. Larger size wire costs more, so typically wire is pulled at the min. gauge wire needed to handle the maximum unit amp rating. The circuit breaker/fuses are sized to protect the wire and the device(s) downstream. You are not going to have a problem with a 20 AMP circuit breaker not tripping when it hits 20 AMPs just because your wire is bigger than 20 AMP 'rated' wire.
Now to reverse that situation and have undersized wire with over sized fuses/breakers, your wire is likely to melt down/degrade before the fuse/breaker blows.
Voltage drop is a serious issue on long runs, and up sizing your wire will help prevent that voltage drop. It becomes extremely apparent when running low voltage runs (24V AC/DC) as the +/-10% shows up in a hurry at only 2.4 Volts. Lower than expected voltage at a device increases the amp draw of the device.

[Paul Bee]

My point was to use the correct size of wire, taking into account the length of run etc. I believe the situation we were talking about was a heat pump and my point was to use large enough wire but not too large. They don't print all those sizing tables in the NEC just to kill trees.

[acjourneyman]

Look, you can use 500MCM to run a heat pump if you can get a big enough lug to get on the contactor. It doesn't matter how big it is, the NEC dictates the minimum size you can use, not the maximum.DId you take into consideration it might have been #10 because of its location. You need to derate for ambient conditions, length of run etc, you don't technically just go off of nameplate.

[printer2]

In our hospital complex we always go up one wire size, if it is a 15 amp circuit we use #12 rather than #14 gauge wire and it is not because we have too much money.

I tried to find a good simple explanation of why a larger conductor is acceptable but I could not find less than a 10 page example (Not as bad as could be, half charts).

This is more for plant calculations but it still holds true for residential.

For those not interested in doing the reading the last page is of interest.


CONDUCTOR SHORT-CIRCUIT PROTECTION

Circuit Breaker Systems
In the previous example a 30A, Class RK1 fuse was protecting a 10 AWG conductor. If the 30A
fusible device were replaced with a 30A, molded case circuit breaker with a clearing of 1/2 cycle would the
10 AWG conductor be protected?

Since the I2t let-through of the circuit breaker is not known, Tables 2 through 4 must be used. If the 30A circuit breaker is current limiting, at a 40,000A fault, with a clearing time of 1/2 cycle, per UL 489, the let-through current could be as high as 40,000A RMS symmetrical and still be marked current limiting. If the device was not current limiting, the let-through current could be as high as 40,000 X 1.3, or 52,000A.
The short-circuit current rating of 10 AWG conductor is 6,020A for 1/2 cycle (per ICEA).

Since the let through current of either the current limiting or non-current limiting circuit breaker could be much greater than the short-circuit current rating of the conductor, protection can not be assured for either the phase or equipment grounding conductor.


http://www.cooperbussmann.com/pdf/afa010b0-160c-4794-86ec-5c41057056bf.pdf

Normally #10 AWG is thought to be OK for 30A. In a short circuit condition that may not necessarily be the case. A larger size wire would be needed.

[finest]

you must protect that 12gauge wire that you put in with the properly sized breaker

[printer2]

you must protect that 12gauge wire that you put in with the properly sized breaker

And the 15A breaker will do it.

[NOBULL3]

I am shocked at the amount of quibbling over such a simple question. I may just be really stupid or just tend to try to simplify things. General rules of thumb, size the breaker according to either minimum or maximum RECOMMENDED circuit ampacity (meaning the smallest or biggest breaker size for the slower of us), Size the wire by taking into account a. circuit amps b. line length. RLA is generally much lower than min circuit size, the start up surge is already factored into the the equation by the engineers and the lawyers at the factory. It is kind of hard to mess that one up. Agreeing with the comments below, there is absolutely no harm in going bigger in line size as long as the breaker is properly sized, if you go the other way and reverse it you got problems. Moral of the story, minimal amount of knowledge or homework, job well done. BASIC STUFF certainly not three pages of stuff.

[jayguy]

I am shocked at the amount of quibbling over such a simple question...BASIC STUFF certainly not three pages of stuff.

he's funny cause he's new here:argue:

[acjourneyman]

Actually you don't have to resize the breaker for larger wire, you could put #2 wire on a 15 amp breaker and conversely I could put in 250 MCM feeding a 5 ton heat pump with a fused disconnect and pick a breaker size of 400 amps if I wanted, the breaker is to protect the branch circuits to the unit, not the unit itself.

[bob_scheel]

I am shocked at the amount of quibbling .

If you don't quibble you are missing half of the fun!:playing:

[VTP99]

AC
Lets just hope there is a fused disconnect of the right amperage at that unit in this case.

[finest]

And the 15A breaker will do it.

sorry i didnt read 15 amp breaker anywhere, only 15 amp fused disconnect

[printer2]

sorry i didnt read 15 amp breaker anywhere, only 15 amp fused disconnect

I like fuses better than breakers when it comes to safety.