# Breaker Size for a Single Phase 5 HP Saylor-Beall Compressor



## Steinbierz (Jan 9, 2018)

Hello,

I have seen a lot of discussions over the years on how big of a breaker and what gauge wire to run for a 5 HP air compressor and, although a lot of answers are somewhat consistent, there is some variation.

This topic became relevant to me recently when I purchased a 5 HP Saylor-Beall and went back to the nets to look for answers and still found the same variation. I contacted Saylor-Beall and this is what they said:

"Electrical Spec as Follows:

FLA= 28

Rec breaker = 60 Amp"

Not trying to start another long thread on this topic but didn't see a more recent thread to post what I had gotten from the manufacturer…which, btw, recommends a higher breaker than pretty much any info I have found on this and other forums.


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## TopamaxSurvivor (May 2, 2008)

The manufacturer's specs are what you should follow.


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## Steinbierz (Jan 9, 2018)

That is my intention.


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## AlaskaGuy (Jan 29, 2012)

10 gauge wire, 30 amp breaker. 240 volt


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## AlaskaGuy (Jan 29, 2012)

Deleted


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## Vuddha29 (Apr 3, 2021)

The large breaker is to account for the inrush current, which can be many times the FLA.


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## TopamaxSurvivor (May 2, 2008)

> 10 gauge wire, 30 amp breaker. 240 volt
> 
> - AlaskaGuy


What are the Full Load Amps? Should be FLA on the motor nameplate.


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## WhyMe (Feb 15, 2014)

To be NEC compliant a true 5HP motor needs to be hardwired. 28A x 1.25 = 35A, so wire size needs to be either #8 NM or #10 THHN in conduit. The 60A breaker can be used only if the compressor is hardwired and 60A is fine because the compressor has its own overload protection. Follow NEC article 430 for wiring requirements.


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## WhyMe (Feb 15, 2014)

Deleted duplicate…....


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## ibewjon (Oct 2, 2010)

My 5 hp Baldor compressor motor is nameplate rated at 25 amps, 208/240 volts, single phase. No different amperage listed for the higher or lower voltage. The magnetic starter is Allen Bradley. I run it on #8 thhn wire, and a Square D 40 amp QO breaker for the last 45 years. No problem. I would not cheap out and use the # 10 wire. The additional cost of #8 is less than the cost of a replacement motor.


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## squazo (Nov 23, 2013)

I was at the BORG the other day and the 8 gauge romex was cheaper than the 10 gauge for the same length, I dunno why,


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## WhyMe (Feb 15, 2014)

> ....... I would not cheap out and use the # 10 wire. The additional cost of #8 is less than the cost of a replacement motor.
> 
> - ibewjon


Seriously, you're suggesting that using #10 thhn will not be good for the motor?


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## Steinbierz (Jan 9, 2018)

> My 5 hp Baldor compressor motor is nameplate rated at 25 amps, 208/240 volts, single phase. No different amperage listed for the higher or lower voltage. The magnetic starter is Allen Bradley. I run it on #8 thhn wire, and a Square D 40 amp QO breaker for the last 45 years. No problem. I would not cheap out and use the # 10 wire. The additional cost of #8 is less than the cost of a replacement motor.
> 
> - ibewjon


It so happens that I have plenty of #8 and would have to go buy #10 so it is an easy decision for me.


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## TopamaxSurvivor (May 2, 2008)

> ....... I would not cheap out and use the # 10 wire. The additional cost of #8 is less than the cost of a replacement motor.
> 
> - ibewjon
> 
> ...


Voltage drop is higher with the unlimited starting current. That puts more stress on the motor insulation. It can become an issue over time.


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## WhyMe (Feb 15, 2014)

> ....... I would not cheap out and use the # 10 wire. The additional cost of #8 is less than the cost of a replacement motor.
> 
> - ibewjon
> 
> ...


In general that's true where the wire is undersized. But to say its an issue in this case is a stretch and is a non issue.


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## TopamaxSurvivor (May 2, 2008)

It is an accumulation of insulation stress over time. A table saw starting under no-load conditions it would be irrelevant.

This is a compressor starting under load. Assuming this is a residential installation it will probably have a relatively small capacity transformer. The starting spike could easily be 140 amps, maybe higher. Considering the power factor ( amperage out of synchronization with voltage) and voltage drop creating higher amperages adding more heat and stress in the motor windings. Puget Power Company in this area will install a larger transformer if they know there will be a 5 hp motor starting on a residential service to cover the voltage drop issues. My bet is the neighbors will see when this motor starts with a dimming of their lights. The 3 to 5-voltage drop difference between #10 and #8 could very well make a difference over the life span of the motor depending on numerous unknown factors including the motor service factor.


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## ibewjon (Oct 2, 2010)

On the job, with engineered drawings, the wire was often upsized one step. A very common practice. Maybe it won't hurt the motor, and maybe over time it will. And new motors are built cheaper for energy efficiency and selling price. In my experience these are more sensitive to voltage drop and heating than older motors. And if it is a long enough run to warrant it, I would jump to #6 awg.


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## TopamaxSurvivor (May 2, 2008)

> On the job, with engineered drawings, *the wire was often upsized one step.* A very common practice. Maybe it won t hurt the motor, and maybe over time it will. And new motors are built cheaper for energy efficiency and selling price. In my experience these are more sensitive to voltage drop and heating than older motors. And if it is a long enough run to warrant it, I would jump to #6 awg.
> 
> - ibewjon


Lots of specs here size a 20 amp circuit up to #10 if the home run is 100 feet long.

I used to see most motors with a 1.15 service factor and an occasional 1.25, recent years 1.0 is the standard. That is the percent of overload they are built to withstand; ie, 1.15 =15% overload.


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## Steinbierz (Jan 9, 2018)

> It is an accumulation of insulation stress over time. A table saw starting under no-load conditions it would be irrelevant.
> 
> This is a compressor starting under load. Assuming this is a residential installation it will probably have a relatively small capacity transformer. The starting spike could easily be 140 amps, maybe higher. Considering the power factor ( amperage out of synchronization with voltage) and voltage drop creating higher amperages adding more heat and stress in the motor windings. Puget Power Company in this area will install a larger transformer if they know there will be a 5 hp motor starting on a residential service to cover the voltage drop issues. My bet is the neighbors will see when this motor starts with a dimming of their lights. The 3 to 5-voltage drop difference between #10 and #8 could very well make a difference over the life span of the motor depending on numerous unknown factors including the motor service factor.
> 
> - TopamaxSurvivor


Residential 7.5 acres in the country but is for a business with a separate metered 400 amp service.


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## rwe2156 (May 7, 2014)

> 10 gauge wire, 30 amp breaker. 240 volt
> 
> - AlaskaGuy


This ^^^^

Forget about start up surge amps. Common cause for breaker trip is bad capacitor.


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## Knockonit (Nov 5, 2017)

hire an electrician and be doen with it, if wrong his/her dime no harm no foul,


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## WhyMe (Feb 15, 2014)

> 10 gauge wire, 30 amp breaker. 240 volt
> 
> - AlaskaGuy
> 
> ...


So what kind of #10 are you agreeing with?


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## TopamaxSurvivor (May 2, 2008)

> Forget about start up surge amps. Common cause for breaker trip is bad capacitor.
> 
> - Robert


All the wiring factors increasing heat, higher amps, voltage drop, etc that can shorten motor life also cause capacitor failures.


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