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Head Grunt
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Discussion Starter · #1 ·
Got a service call from a fella i had done work for in the past asking me to wire in a new air compressor in his garage. He tells me it takes a 60amp 2-pole breaker so i know to bring one with me. I am curious of this so i decide to drag my trailer with me just in case we are looking at rewiring this circuit. He removed his old 60gallon compressor "sears" and installed a new 80gallon compressor "sears" and had it all plumbed in. He was comfortable with removing the wire but not reattaching it. So i am curious of this breaker spec and read through the manufacturers directions and sure enough it states to run a 10ga circuit on a 60amp 2-pole breaker. The old compressor was operating off a normal 30amp 240v 10-2 romex circuit with a knife switch hung on the wall and a 10-2 MC whip to the compressor. I reattached the whip and wired it in, swapped out the breaker to 60amp and fired it. It started and i made the pressure switch adjustments he wanted and was done. I let the owner know i was not comfortable with the 60amp breaker on a 10ga circuit but that was what the manufacturer required and i told him to keep the paperwork in his home separate from the building in case of any problem.

Have any of you fella's ran into this type of situation before? The utility room this was in also had finished walls with a hot water heating system and oil tank inside too so rewiring would have been out of the question with the HO.
 

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60 amp OCD on AWG 10 may be perfectly legal for a motor application. But without more details it's impossible to say at this point.

I've put 14 on 50a breakers before.
 

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Head Grunt
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Discussion Starter · #3 ·
I should have taken a pic of the page with manufacturers specs/directions. The only reason why i did it was required by manufacturer. I gave it some thought of trying a 30amp breaker to see if it would run on it without tripping but last thing i need as a call back for a tripping breaker or the breaker/buss getting hot.
 

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Head Grunt
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Discussion Starter · #4 ·
This is the compressor that he bought through Sears, it is identical except the control box was on the right side and not the left.
 

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Compressors pull a lot more current the first couple seconds they start up, especially when it's cold. That's why you need the 60A breaker. You warned him the circuit is for the compressor only right? You can't run a continuous load on it.
 

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What if the comp seizes up and you get a high amp draw greater than 30 amps ? Unfortunately I was involved with 2 new IR each failed within 6 months. One new, One the repl.

Maybe there is a thermal reset on the motor ? Check the manual.

Also put an amp probe on the wire ?
 

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What if?

Are you aware of the old table 310.16? How about 240.4(D)?
Everything should be wired to 15a breakers and use 500 kcmil copper. :laughing:
 

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The NEC allows oversizing the breaker on dedicated motor circuits to prevent tripping on start-up. I installed one of those Quincy 120gal compressors in my friends shop, it's a thermally protected motor.
 

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Head Grunt
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Discussion Starter · #11 · (Edited)
Compressors pull a lot more current the first couple seconds they start up, especially when it's cold. That's why you need the 60A breaker. You warned him the circuit is for the compressor only right? You can't run a continuous load on it.
Certainly, most any motor has a larger load when starting than normal but this is the 1st time where i have seen a manufacturer required a larger breaker. Take most any deep well submersible pump. They most commonly require a 20amp 2 pole breaker but i have checked amp draw readings upon start up as much as 32amps yet the breaker did not trip so this is why i was asking about this being such a large breaker. It is a dedicated circuit for the compressor only or would not even had installed the breaker otherwise. I did notice a thermal overload reset button on the motor but i did not bother with checking the amp draw. The lights in the building did flicker upon start up but that is pretty much a normal reaction to most any air compressor regardless of size. So far the owner has had no issues and i hope it stays that way. I was merely curious if anyone else had run into this type of situation. I have seen where large motors with large amp draw used a smaller wire but being a different type of load the size wire used by the manufacturer was considered the norm. This is a 1st for me using such a large breaker to protect a smaller wire than the norm. Thanks for the replies fella's.
 

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60 amp OCD on AWG 10 may be perfectly legal for a motor application. But without more details it's impossible to say at this point.

I've put 14 on 50a breakers before.
I just glanced at the NEC for motors, motor circuits, and controllers. Never again - that is a complicated part of the code.
 

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Code

The motor conductors have to be sized a minimum 125% of motor FLA from tables in the NEC.

The circuit breaker rating (inverse time) is allowed to be a maximum of 250% of FLA. Plus you can go to the ext higher size breaker if the FLA does not correspond to a standard size.

Additionally,the manufacturers installation instructions are required to be followed.

Often a large circuit breaker feeds conductors that seem too small to the uninitiated. But for motors, AC compressors and similar items this is permitted by the NEC.
 

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Head Grunt
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Discussion Starter · #15 ·
The gray box contains the relays and reset button but i remember seeing a red button on the motor also. Maybe it has two thermal resets? Again, thanks for the info and replies.
 

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gray box contains magnetic starter and an overload relay. The red reset on the motor is the motor's thermal protection.


this is pretty typical for compressors...

"Overload Relay

An overload relay monitors the compressor motor electrical current and turns
the compressor motor off when an overload is sensed. It is mounted on the
bottom of the motor starter. The overload relay is designed for motors with a
1.15 service factor. The overload relay setting should be adjusted to the motor
nameplate amp rating. If the motor has a service factor rating other than
1.15, the overload relay setting must be adjusted to compensate. Contact your
Quincy distributor for assistance."



I've installed 2 similar compressors with 60AMP breaker / 8AWG





2008 NEC


430.21- wire shall be 125% of full load current.
Table 430.52- Inverse Time Breaker (standard breaker) not to exceed 250% of full load current.
28 amp (FLA OF THIS PARTICULAR MOTOR) x 125% = 35 amp wire
Table 310.16- #10 copper THWN = 35 amp
28 amp x 250%= 70 amp max fuse
The motor is protected by the thermal overload installed in motor (reset button)

60 AMP BREAKER
 
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