AIR COMPRESSOR

[jap]

I have an air compressor to hook up that the label is gone off of the motor.
The plastic cover says 7 Horsepower 60 gallon yet on the other end of the plastic cover it says 15 Amp 240v.

This don't add up to me.

 

[jap]

Not sure what to pull to it or what to size the OCP at.

 

[suemarkp]

Air compressor HP values lie big time. Perhaps they have a legal way of lying using a different HP measurement (kind of like Sears and their table saw ratings). I'd go by the nameplate rating otherwise you'll be more than doubling the size of everything. I'd use #12 on a 20A breaker, or maybe a 30A breaker if you hard wire it.

 

[jap]

I guess my question would be aside from cost if the overload protection is in place can you ever really oversize the short circuit protection to a motor? Say a 60 amp feed to a compressor that only reauires 15 amps?

 

[Sierrasparky]

I guess my question would be aside from cost if the overload protection is in place can you ever really oversize the short circuit protection to a motor? Say a 60 amp feed to a compressor that only reauires 15 amps?

I would go with what the manufacture requires. Those compressors usually have a unique motor . SPL designation. They never operate at full load until the end of the cycle.

If they are used on a continuous duty they will overheat.

 

[kwired]

I guess my question would be aside from cost if the overload protection is in place can you ever really oversize the short circuit protection to a motor? Say a 60 amp feed to a compressor that only reauires 15 amps?

430.52 does set limits, but you are allowed to increase those amounts if the device doesn't allow starting still have a cap on how much increase is allowed though.

The 15 amp motor in this case can have 250% of full load for an inverse time breaker - 15x2.50= 37.5>>can round up to next higher standard device so a 40 amp breaker shouldn't be out of the question here unless it will not allow starting. Never seen one of those motors not start on a 20 amp breaker that I can recall though.

 

[jap]

430.52 does set limits, but you are allowed to increase those amounts if the device doesn't allow starting still have a cap on how much increase is allowed though.

The 15 amp motor in this case can have 250% of full load for an inverse time breaker - 15x2.50= 37.5>>can round up to next higher standard device so a 40 amp breaker shouldn't be out of the question here unless it will not allow starting. Never seen one of those motors not start on a 20 amp breaker that I can recall though.

They wanted to just put a 50 amp male cap on the #12 cord and plug it into an existing welding outlet and that's what started this whole dilema. I thought about letting them do that but changing the 2p 50 in the panel out to a 2p 30 but then I'd be short changing a welder should they happen to want to unplug the compressor and plug in a welder.

 

[kwired]

They wanted to just put a 50 amp male cap on the #12 cord and plug it into an existing welding outlet and that's what started this whole dilema. I thought about letting them do that but changing the 2p 50 in the panel out to a 2p 30 but then I'd be short changing a welder should they happen to want to unplug the compressor and plug in a welder.

I've seen such items plugged into 50 amp circuit many times, never seen any major problems from it, but is still not really code compliant.

 

[Sierrasparky]

I've seen such items plugged into 50 amp circuit many times, never seen any major problems from it, but is still not really code compliant.

The welder will normally have a larger size wire, The compressor will probably have 12 or 10ga.

 

[kwired]

The welder will normally have a larger size wire, The compressor will probably have 12 or 10ga.

There are welders out there with factory installed cord/cord cap - 50 amp cord cap, 12 AWG cord.

Duty cycle is a big factor into why this works without overheating the cord.