Is this allowed

Merry Christmas

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
HVAC has rating of max circuit protection of 45Amp. With current supply situation, the 45A breaker not available and on back order with no time frame for availability. Can I instead use a fused disconnect at the units that is rated at 60A install a 45A fuse and with the wiring sized, rated and protected at panel box to 50A, that breaker is currently available. Would such meet the requirements of both the HVAC max and the wiring size protection up to the fused disconnect.
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
Currently got the call because one of the 4 units literally melted down the disconnect, the other 3 are starting to show signs of heating up. The original installer put on a 30A nonfused pullout disconnect onto a 50A circuit breaker on #8 wire for a unit that labelled for 36.3A min circuit ampacity, 21.1A RLA compressor, and 105 LRA, and a few other associated loads on name plate.
This is a commercial installation not residential.
Is a 40 amp CB available?
40's are more readily available but don't want to have callbacks "breaker keeps tripping", not sure if there would be issue given how close the min circuit ampacity is to a 40A breaker size and the length of wire run.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I never have had a call back on a unit that was 40 vs 45, 30 vs 35, etc.

The CB & fuse solution would work.
I agree, IMO the callback thing when using a CB slightly smaller than the Max OCPD is more urban legend than a real world problem.
 

edward

Senior Member
Location
CA
Occupation
Electronologist
Name plate looks to give 2 options max fuse size time delay 45A or max circuit breaker HVAC type 45A.
OK. Sounds good you are not restricted to one over the other.

What is the RLA on the fan motor? about 4-5 amps? Just curious for my understanding.
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
I agree, IMO the callback thing when using a CB slightly smaller than the Max OCPD is more urban legend than a real world problem.
Just not sure, given a 40A would only be slightly larger than 36.3A min circuit size, but guess a 40 would be "next standard size up".
Given that the one unit did have enough draw to melt down the 30A disconnect, would you think the 40A breaker would hold?
Or would it be better to go smaller than the max 45A listed because of the melt down, or at least for testing reasons? (Meltdown occured on the original with someone putting on a 50A breaker that from reports didn't trip.)
Replacing all 4 unit's 30A pullout disconnects with 60A knife throw ones.
OK. Sounds good you are not restricted to one over the other.

What is the RLA on the fan motor? about 4-5 amps? Just curious for my understanding.
Name plate has the following values:
208/230V 1PH 60HZ
Compressor 21.1 RLA. 105 LRA
ID Blower 1.5 HP. 7.6 FLA
OD Fan. 0.5 HP 2.3 FLA
Comb Blower 0.05 HP .78 FLA
This is a combo unit that also has heating w/nat gas.
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
HVAC has rating of max circuit protection of 45Amp. With current supply situation, the 45A breaker not available and on back order with no time frame for availability. Can I instead use a fused disconnect at the units that is rated at 60A install a 45A fuse and with the wiring sized, rated and protected at panel box to 50A, that breaker is currently available. Would such meet the requirements of both the HVAC max and the wiring size protection up to the fused disconnect.
Not only legal, often necessary. Most manufacturers don't make 45A breakers in higher AIC ratings, so you have to do what you are proposing.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Just not sure, given a 40A would only be slightly larger than 36.3A min circuit size, but guess a 40 would be "next standard size up".
Given that the one unit did have enough draw to melt down the 30A disconnect, would you think the 40A breaker would hold?
Or would it be better to go smaller than the max 45A listed because of the melt down, or at least for testing reasons? (Meltdown occured on the original with someone putting on a 50A breaker that from reports didn't trip.)
Replacing all 4 unit's 30A pullout disconnects with 60A knife throw ones.

Name plate has the following values:
208/230V 1PH 60HZ
Compressor 21.1 RLA. 105 LRA
ID Blower 1.5 HP. 7.6 FLA
OD Fan. 0.5 HP 2.3 FLA
Comb Blower 0.05 HP .78 FLA
This is a combo unit that also has heating w/nat gas.
What voltage are you using?
 

norcal

Senior Member
The panel is showing a 240/120 highleg delta, but haven't metered it. If this is right, got to watch for the highleg. Probably should check if the original installer put the unit on the highleg.
Nothing wrong with a 240V 1Ø load using the high leg, as long as a 120/240V rated circuit breaker is not used, for that application a 240V breaker has to be used, downside is they are more costly & not real common.
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
Nothing wrong with a 240V 1Ø load using the high leg, as long as a 120/240V rated circuit breaker is not used, for that application a 240V breaker has to be used, downside is they are more costly & not real common.
Only works for a no neutral load application. If there is a neutral load it's got 208 L-N on the highleg. These hvac units all have a neutral load.
 

Buck Parrish

Senior Member
Location
NC & IN
I never have had a call back on a unit that was 40 vs 45, 30 vs 35, etc.

The CB & fuse solution would work.
I have. Every now and again the 30 would trip . Changed it to the MOP of 35 , no more problems.
I did not wire it originally. It was a close by good customer. First couple times I just flipped it back at no charge thinking a surge or lightning caused it to trip.
Maybe now a days the motors do not pull as much on start up.
 

curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
These hvac units all have a neutral load.
Not according to the nameplate info you posted. They are straight 208/230. If they required a neutral there would be a 120 shown on the label.
I have never seen a package HVAC unit that required a neutral. For split systems the furnace/air handler may be 120 but this would be a completely separate circuit.

I would also normally install that 40 amp breaker for this unit even if I could get 45's. I trypically don't use 25's, 35's or 45's unless the units minimum and max OCP happen to be the same and require the odd size breaker.
 
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