Circuit breaker size for compressor

[smalltown]

I've got a standalone Husky compressor that I am finally wiring up. I have pulled in about 35' of 10 AWG THHN wire: 2 hots, and a ground.

What I am wondering about is the in rush current since none is listed on the motor. Here is a picture of the motor, the compressor decal, and a copy of the manual instructions.

Since the instructions call for a time delay fuse, and I have a standard non time delay breaker I was wondering if you would use standard non delay 30 amp 240 volt breaker?

lastly while I have your eyes what are they talking about in the lower section of the motor picture. "line to ungrounded side of supply when grounded supply is available" with the numbering 4 or 1. I am bringing over 2 hots, and a ground to the compressor.

 

[Fixin'Stuff]

Circuit breakers can handle the inrush current. Breakers don't trip instantly unless the overload is way above their stated rating. It says right on your 3rd pic that you need a 20-amp service.

 

[md21722]

A regular 30A will be fine.

 

[matt_i]

The 15A on the motor plate * 1.25 factor for motor inrush = 18.75A. Should be OK as recommended for a #12 = 20A circuit.

As above, the time-delay requirement is for classic individual line fuses that are rarely seen outside of industrial equipment. A 20A circuit breaker that is OEM to your panel will work correctly in my opinion, there is no need to look for a special class or type of circuit breaker.

 

[md21722]

The NEC has specific rules for wiring motor circuits. Basically you take the nameplate HP and voltage and look up the Amps in the NEC tables. Nameplate amps are not used. Then size wire to 125% of the NEC table Amps and if thermal protection is present the breaker can be up to a maximum of 250% of the NEC table Amps.

 

[sberry]

It could be 12/30, number 10 wont hurt anything.

 

[alfredeneuman]

The starting current (motor inrush) at the instant you start the motor is the Locked Rotor Current, (LR=93 Amps on the nameplate). That will last for only a fraction of a second.

 

[smalltown]

Thanks to all !

 

[wyliesdiesels]

As has been stated by md21722, motor circuits are wired based on NEC FLC tables using the motor nameplate HP.

Your motor is labeled SPL aka special so u take the FLA and compare it to table 430.148.

15a puts it at about 3HP which = 17a.

17a * 125% = 21a. U need #12 THWN or #10 NM-b. Breaker can be max 250% or 43a. Start with the 20a and increase if it nuissance trips.

Does the motor have integral thermal overload?

Will u be hardwiring it or did it come with cord and plug?

If hardwiring, u will need a disconnect IF the breaker panel is more than 50' away and not within sight.

 

[MushCreek]

My so-called 5 hp compressor has the same motor specs, and I have been running it on a 20A circuit for 20 years without issue.

 

[CompressorPros.com]

From the guys at BelAire and Chicago Pneumatic...they suggest 1.78 x Full Load amps, so that is what we always suggest

 

[mike93lx]

From the guys at BelAire and Chicago Pneumatic...they suggest 1.78 x Full Load amps, so that is what we always suggest

the NEC makes it nice and clear. why would you make a suggestion that deviates from that?

 

[Aceman]

the NEC makes it nice and clear. why would you make a suggestion that deviates from that?

The NEC is NOT a design guide, it only gives the minimums for a safe installation.

The NEC allows a single phase motor breaker to be anywhere from 125 to 250% of the full load amps from the NEC tables. His suggestion of 178% is not wrong.

 

[smalltown]

All good questions.

Wylie yes the motor has thermal protection.

I am going to hard wire it using a non metallic whip from a wall box.

I am adding a safety disconnect switch http://www.homedepot.com/p/Square-D-30-Amp-240-Volt-2-Pole-Indoor-General-Duty-Fusible-Safety-Switch-with-Neutral-D221NCP/100164967 and have a question about that.

My question is about the ground in the safety switch. Drawing for switch states " all neutrals-insulated groundable" And the product info states a neutral bar is included. Does that mean that I can use the neutral bar for my ground connections provided I can bond the neutral bar to the switch case ? I will be running only 2 hots, and a ground through this switch. Or maybe I should pick up a small ground bar, and install that.

Can I ask about horsepower ratings for safety switches? Do I need to worry about that?