Air Conditioner O/C protection

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rwreuter

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here is something that has puzzled for me for some time. air conditioner unit overcurrent protection.

when i wired houses it was oh so common to see a name plate rating of a unit and then we would put a cb on it that was higher. why and was it correct.

i am now about to place a disco on my unit and the name plate states 40amps, but as it sits now i have it fed with a 6-3 w/ground copper and the breaker is a 60amp.

believe it or not, i am not sure if what i (we) did was right, just dumb ignorance on my part, doing what we were taught without knowing the how or why.

is a 60amp breaker good, bad or ugly and/or should i just place a 40amp in there and it will work fine. i am sort of assuming the name plate is taking into consideration the motor start up.

advice or a place to look would be great here.


rw
 
What number are you 'exceeding'? The 'Maximum Overcurrent Rating'? If so, you're creating a violation. If the nameplate states a MOR of 40 amps, installing a 60 should result in a red tag.

Replacing it with a 40 is only part of the potential problem. Another thing to check is the wire size.
 
wire size should not be an issue, i can go over but not under.

i just remember reading somewhere that air conditioners have "funny" rules that apply to them and their over current protection devices and odly enough their wire size.

just can't remember where i read it and whether or not it was a valid article or statement.



rw
 
for example....i just went over 440.22 (a)

"a protective device having a rating or setting not exceeding 175 percent of the motor compressor rated-load current or branc-circuit selection current, whichever is greater, shall be permitted provided.........."


if i understand this right (not sure if i do) then if the max ocpd is 40 and i multiply 40 * 175%, i get 70....so by this reasoning the 60amp ocpd is good.


make good or bad sense, or am i completely off of my rocker?



rw
 
rwreuter said:
when i wired houses it was oh so common to see a name plate rating of a unit and then we would put a cb on it that was higher. why and was it correct.
Click to expand...

This is correct because a/c units usually need a higher amp. breaker to help it with the startup. The a/c unit has overload protection built in so the wire is protected from overload. The higher breaker will have no problems clearing a ground fault or short circuit.
 
rwreuter said:
wire size should not be an issue, i can go over but not under.

i just remember reading somewhere that air conditioners have "funny" rules that apply to them and their over current protection devices and odly enough their wire size.

just can't remember where i read it and whether or not it was a valid article or statement.



rw
Click to expand...

The 'funny' rule is 240.4(G).
 
ok, lets look at 440.22 (c)

how do you all interpret that, comparing it to 440.22 (a)....

seems to contridict, or am i reading it incorrectly?



rw
 
rwreuter said:
ok, lets look at 440.22 (c)
how do you all interpret that, comparing it to 440.22 (a)....
seems to contridict, or am i reading it incorrectly?
Click to expand...

I don't see it as a contradiction but rather as a trump of 440.22(A) &(B). Basically it limits you to what the manufacturers has marked on the unit for the maximum overload setting.
 
ok, now i am back to where i started

name plate: 40amp with a 60amp ocpd

just curious what is 440.22 (a) for then if the other paragraph trumps it? just an obviouse common sense question is all. oh wait, i can't ask that, dumb me....:(



rw
 
rwreuter said:
ok, now i am back to where i started

name plate: 40amp with a 60amp ocpd

just curious what is 440.22 (a) for then if the other paragraph trumps it? just an obviouse common sense question is all. oh wait, i can't ask that, dumb me....:(
rw
Click to expand...
It probably doesn't trump it very often. I have never seen an a/c unit whose max OCP was less than 175%. I guess they exist for some specialized equipment.
 
Steve Beranek said:
We went over this today already in the morning. http://forums.mikeholt.com/showthread.php?t=126009

I'm still confused/unsure about feeder vs branch circuit.
Click to expand...

What does feeder vs branch circuit have to do with this discussion.:-?

Branch Circuit. The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).
Click to expand...

Feeder. All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device.
Click to expand...
 
This is very simple. Look on the unit and it says min. circuit amps and max. breaker size. You can not go over the breaker limit. That is why they stamped that number. Now to select the wire size look at the min circuit amps. It never hurts to over size the wire and just might help in future when the unit is replaced and often for a larger unit or heat pump. The numbers are there so use them. Here the inspector will be checking and if your over you deserve a prize ,a nice red tag
 
some older units will only have the FLA, and maybe the LRA, when this occurs I just apply 125% to the FLA for my circuit conductors and then apply the 175% for the breaker, this is of course if the label also stated the compressor has overload protection.

With newer units the 125% and 175% is built into the max and min. figure
 
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