wire size for these 60 amps?

[Richard W. Washington]

thanks.

[Speedy Petey]

If that label is correct it is feeding an A/C.
Depending on the actual wire size and unit specs it is likely fine.

[kgreeson]

Several things should be verified by what I'm seeing in this photo, The wire size does not look to adequate for a 60 amp breaker, it looks to be 10awg or 8awg, it should be 6awg or sometimes local codes will allow #8 stranded (check your local codes, if none use the national electric code). The other issue is the color index (white being used as a power leg). A certified electrician should do an evaluation and recommend any upgrades or repairs as needed.

[Speedy Petey]

Kieth, it's NOT always so cut and dry.

For an A/C install the old rules of "#6 for 60A", and so on, DO NOT APPLY.

Also, in this older installation re-identifying the white was NOT required. There are millions of safe and legal 240v installations with the white wire on a breaker.

I agree, call it out if you want, but don't be upset when the electrician comes back with an "all OK" report.

[Mike Whitt]

Originally Posted by kgreeson

it should be 6awg or sometimes local codes will allow #8 stranded (check your local codes, if none use the national electric code).

Kieth,
I am not trying to pick on you personally but you made a statement here that I feel needs to be addressed.

Looking at the picture in the original post I see bare equipment grounding conductors leading me to believe that the conductors in question are part of NM cable.

If these conductors are in fact part of NM cable then #6 would only be good for 55 amp and #8 40 amps. Using 240.4(B) one would be allowed to install a 60 amp breaker on the #6 as long as the load did not exceed the 55 amp rating of the conductor.

When dealing with motor driven equipment such as air conditioners the breaker will need to carry the inrush of the motor starting. This amperage draw at start up can be as much as 6 times the rating of the motor.
An example; A 5 hp 240 volt single phase motor draws 28 full load amps.
This motor can legally be installed with a #10 AWG conductor and protected with a 70 amp breaker.
This motor will draw 168 amps when it starts.

[James E. Braun, CMI]

Originally Posted by Mike Whitt

When dealing with motor driven equipment such as air conditioners the breaker will need to carry the inrush of the motor starting. This amperage draw at start up can be as much as 6 times the rating of the motor.
An example; A 5 hp 240 volt single phase motor draws 28 full load amps.
This motor can legally be installed with a #10 AWG conductor and protected with a 70 amp breaker.
This motor will draw 168 amps when it starts.

Can you elaborate on this. I always understood the startup draw on a single phase motor was so short that the breaker would not have time to react.

[Richard W. Washington]

maybe i'm just not getting this. the whole premise for the question was which one is correct since there are two different wire sizes feeding the same size breaker?

[Jeffrey R. Wicklander]

maybe i'm just not getting this. the whole premise for the question was which one is correct since there are two different wire sizes feeding the same size breaker?

Both of the wire sizes will probably be correct. Did you, by any chance, read the info on the A/C unit nameplate. It will give the info that is needed for the correct sizing of wire and OCPD needed. For example... the plate might say
AMP 27
MAX BRKR 50

This will tell you that #10 wire is suitable for the unit and that it can be connected to a 50 amp breaker.

If it says 50 amp breaker and it is hooked up to a 60 amp breaker, check the disconnat of th A/C unit. If it is a fused disconnect and the fuses are rated at 50 amps, it's fine. If it is not a fused disconnect, write it up.

[Mike Whitt]

Originally Posted by jbraun

Can you elaborate on this. I always understood the startup draw on a single phase motor was so short that the breaker would not have time to react.

Let’s stay with this 5 hp 230 volt single phase motor for this discussion as it is what I have already referenced.

This motor straight out of the box with nothing connected to the shaft will need enough current to overcome the static state or in other words to start the shaft turning. I will take approximately six times the rated current to start this motor in motion.
This motor is rated at 28 full-load amps by Table 430.248 of the NEC.
430.22 requires that the conductors supplying this motor to be sized at 125% of the FLA (full-load amps) or 28 x 125% = 35 amps.

If the conductors are in a NM cable then from the 60 degree column a #8 would be required but if installed as one of the conductors outlined in 310.13 and installed in a raceway the from the 75 degree column a #10 will work.

Per Table 430.52 an inverse time circuit breaker is allowed to be sized at 250% of the FLA of the motor and should this not allow the motor to start then this inverse time circuit breaker can be increased to not more than 400% of the FLA.

Under normal circumstances a 70 amp breaker would be used but it could have a 110 amp breaker installed on the same #10AWG conductor.
This motor without any load (straight out of the box with nothing connected) is not the norm for motors as most will start under some sort of load. This load will prolong the time that the startup current will last.

The trip curve for an inverse time circuit breaker is outlined in the attachment below. As can be seen a 20 amp breaker can hold twice its rating for a couple of minutes and even more. This breaker can hold five times its rating for a period of up to close a half a minute.

Cutler Hammer’s trip curve information shows a 20 amp breaker holding under a load of 200 amps for a period of 90 cycles or in time that would equate to 1 ½ seconds.

On a side note I would like to ask who it was that said that breakers are safer than Edison Base fuses?

[kgreeson]

After doing some checking, I stand corrected. Thanks Mike, age does play a roll and I over looked that.

Richard, to answer your basic question, the wire size looks the same to me, are you sure it is different?

[James E. Braun, CMI]

Originally Posted by Mike Whitt

The trip curve for an inverse time circuit breaker is outlined in the attachment below. As can be seen a 20 amp breaker can hold twice its rating for a couple of minutes and even more. This breaker can hold five times its rating for a period of up to close a half a minute.

The 5hp motor should not have that load more than a half a minute so why use a 70 amp breaker?

Thanks for your answer in advance.

[Mike Whitt]

Originally Posted by jbraun

The 5hp motor should not have that load more than a half a minute so why use a 70 amp breaker?

Originally Posted by jbraun

Thanks for your answer in advance.

Sorry for the time lapse between my post but I am hard at work and just checking in as time will allow.

If the motor is not loaded it will reach its FLA in a mater of seconds but if the motor is under a load or is producing work then this inrush current can last from a few seconds to several minutes depending on the amount of load.

A garbage disposal is a good example to look at when thinking about motors. The disposal in nothing but a motor with some sort of contraption connected to the shaft that grinds up garbage so it can easily go down the drain.

Let’s use the tables in 430 and a ½ hp disposal for this discussion. According to the table a ½ hp motor at 120 volts draws 7.2 amps.
The conductor supplying this disposal must be capable of carrying 9 amps and should be installed on a #14 conductor and a 15 amp breaker. The disposal will come with a factory installed integral overload device as outlined in Part III of 430.
This integral overload device must be set at not more than 156% of the FLA for the disposal, 430.32(A)(2)
This means that the integral overload device will trip out when the motor reaches an amperage of 11.32 for any period of time (approximately 10 seconds)
The 15 amp breaker could possibly hold a load of 30 amps for a period of 2 ½ minutes.
The locked rotor amps for this disposal would be 58.8 amps according to Table 430.251(A).


Motor driven equipment such as air conditioners have a fuse or breaker that protects against such things as one leg shorting out against the case or other metal and one of the other conductors as well as the windings of the motor should they short out. It does not protect against the motor drawing too much current.

The running overload protects the motor against drawing two much current due to carrying to much load. This running overload also protects the conductors supplying the equipment. An air conditioner or heat pump is going to come from the factory with an integral overload device which will protect the compressor motor as well as the conductors supplying the compressor.

A table saw is another good example of a motor that comes with an integral overload device.
An ammeter connected to the conductors supplying a table saw will show the inrush current needed to start the saw and the current will settle down in less than two seconds.
Start ripping an 8 foot long piece of ¾ inch plywood and the meter will again show a high amperage draw and the amount of draw will be proportionate to the speed the plywood is being fed into the saw. Send the wood in to fast and the overload will trip out before the job is done.

When dealing with motors the overcurrent device (fuse or circuit breaker) protects against short circuits or ground faults and the overload device protects against overloads.

Remember that;
Overcurrent = fuse or circuit breaker
Overload = reset button which can be integral with the motor and automatic as with most air conditioners and heat pumps.

[Greg Fretwell]

We really have two issues here. What is code legal and what will work.
I have one of those "6.5HP" air compressors with a 120v 1HP motor (measured 12-13.5a draw in a bell curve as the tank comes up to 150 PSI).
It is labelled 13a FLA
This thing works on a 15a breaker but I have it on a dedicated 20a (12ga) circuit. The code would let me put it on a 14ga circuit (per 310.16, not 240.4(D)) with a 35a breaker.
(250% of FLA = 32.5a, rounded up to the next standard breaker size)

AC condensers get to use a similar rule.
Mike pointed out that if this is Romex,AC or MC cable you have to use the 60c column to size the conductor, even if the condenser has 75c lugs.
Now if you want to throw another monkey in the wrench, how much do I need to derate that conductor when it feeds the condenser through the 130-140 degree attic???