A/C max. breaker and required breaker size

Status
Not open for further replies.
A

allenwayne

Senior Member
Just to go along with a running thread I ask.If the data plate on a unit has a max breaker size of 40 amps and the min. is 20 amps what is the required breaker that has to be installed.Sized between 20 and 40 or 40 since the max. breaker is listed at 40.This has been a running argument between myself and inspectors for years.They want the breaker to match the max. but I say it is allowed to stay between the two listed amperages.Sometimes a 40 might not be there to get an inspection I say it is allowed to go lower but not higher and stay between the listed amperages is permissable.
 
Re: A/C max. breaker and required breaker size

I agree with you. From what I understand, the unit is tested under certain conditions & the ocp is based on that. So, if the nameplate allows 20a min. & 40a max, IMO, you can go with any in between. I would pass your install.
 
Re: A/C max. breaker and required breaker size

The maximum is just that a maximum. Some units will list a minimum circuit breaker or fuse and a maximum. If they don't than the OCPD can be any size between the MCA and Maximum listed on the unit. However, if the OCPD were sized very close to the MCA than the unit might trip it on start up.

[ February 25, 2006, 10:48 AM: Message edited by: infinity ]
 
Re: A/C max. breaker and required breaker size

I would check the RLA (running load amps)and the FLA (full load amps)to determine what wire and breaker to install.
 
Re: A/C max. breaker and required breaker size

Originally posted by b connection:
I would check the RLA (running load amps)and the FLA (full load amps)to determine what wire and breaker to install.
Click to expand...
This is not required when sizing conductors and OCPD for AC units. All of the information is provided by the manufacturer on the unit nameplate and is required to be used when sizing the conductors and OCPD's.
 
Re: A/C max. breaker and required breaker size

I have seen that most of the HVAC units data plate or dead on with NEC requirements AS to min circuit and max OCPD
 
Re: A/C max. breaker and required breaker size

I ask because the inspectors in this area want it sized to the max breaker size,like I said this has been an argument for along time.Thier argument is that if the manufacturer wanted it to be in between then they wouldn`t list the max breaker and would list the breaker to be within a certain range.I admit to stop the argument I am guilty of caving in but if I had something to show that it can be between A and B,I would not give an inch.
 
Re: A/C max. breaker and required breaker size

I would not give an inch.
Click to expand...
If you add 100% of the fans, plus 125% of the compressor FL amperages, you'll end up with almost exactly what's on the plate for the 'branch circuit ampacity.' Other than using the plate rather than a table (i.e. 430.150), this is the same as for an MCC, and the idea is reinforced by 440.8. At that point, AC manufacturers actually test their eqiupment with UL, to verify that specific fuses or circuit breakers pass. And yes, any of the listed circuit protection devices fulfill the UL requirements.

What those inspectors are probably thinking, even if not consciously, is a related case from Edison fuses. It's now an old unit with every bearing and valve worn, low on refrigerant, a real dog which pulls more than the new one UL tested at the factory. If that breaker opens, whether due to low voltage or whatever, the first thing joe homeowner does is hop down to HD and replace it - what does he put in there? The inspectors are probably thinking that it's best to avoid any nuisance trips whatever, even years from now. Does this make sense? Whew I had to spell check all that
:eek:
 
Re: A/C max. breaker and required breaker size

Originally posted by peteo:
a real dog which pulls more than the new one UL tested at the factory. If that breaker opens, whether due to low voltage or whatever, the first thing joe homeowner does is hop down to HD and replace it - what does he put in there?
Click to expand...
That old unit can not 'pull more than the new one UL tested at the factory'. If the unit did start using more power the factory installed motor overloads will open the circuit.
 
Re: A/C max. breaker and required breaker size

Allen,

I agree with you.

Lately I've seen a lot of condensing units which have the same minimum and maximum breaker sizing. I guess this is what they do when they want a specific size. :)
 
Re: A/C max. breaker and required breaker size

You all seem to be lucky enough to get the privileged "name plate" information up front. During construction all I can manage to get from the GC or AC contractor is the tonnage of the units (at least on residential installations). So, I've been figuring 10 amps per ton and so far I've been safe with that format. I'd rather err on the side of caution and install a larger size wire. As far as under sizing the breaker, you can always bump it up to coincide with the wire size if you start to have problems but you can't always run new wire if you undersize it.
 
Re: A/C max. breaker and required breaker size

The wire size isn`t a problem I agree that if the unit specs are not there then bigger is better in that case.I use 6/2 for all A/C units when the actual required size is not known (residental)It`s just the breaker installed at trim out.Sometimes in a pinch to get an inspection if lets say a 45 amp breaker isn`t handy but there is a 40 amp breaker,we will get shot down by this.
I feel as long as between the listed amperages is maintained then it should pass and not have to be recalled.Now on the electric heat side well that`s a given max breaker so as not to underfuse the unit but on the a/c unit well this is really a stupid situation. :confused:
 
Re: A/C max. breaker and required breaker size

Allenwayne,

For what it's worth I agree with you. As long as you have installed an OCPD that is between the max and min. rating as listed on the unit nameplate then you have an installation that is NEC compliant. As far as nuisance tripping is concerned (with respect to sizing by the Min.)..... I think 90.1(B) says it quite well.

Pete
 
Re: A/C max. breaker and required breaker size

Allenwayne,

Maybe you could buy him a small dictionary and just happen to highlight the word MAXIMUM?
 
Re: A/C max. breaker and required breaker size

If it was only that easy I`d put salt on it that way it didn`t taste so bland. ;)
 
Status
Not open for further replies.
Top