electrical math

[blazin_blazer]

anyone know how to figure what amperage breaker i will need for an air compressor that has a running hp of 5.4hp,..w/220V?

i was going to get the I/R 60 gallon single stage compressor, w/12.1/10.8 scfm@90/120 psi, for $899

but, i got my craftsman member ''tool club'' sales paper today, & they had this craftsman professional compressor" its 80 gallon dual stage compressor w/13.3/12.8 scfm@100/175 psi for $899.

i think I'm going to sears tomorrow & get this compressor & I'd like to pick up the correct breaker while I'm out, so i can wire it up....do y'all think 12/3 romex would be big enough to wire this up,....4' of wire at the most, or should i step up to 10/3 wire?

heres the compressor i'm talking about regularly $1049.99:

hmmm...sears site is down, i will post link as soon as sears site is back up...

 

[bp71k5]

Just look at what the amp rating is. 14 is usually rated for no more than 15a and the 12 is good up to 20a. Dunno about 10g but make sure the wire can handle 20% more than the motor is rated for.

Edit: that advice is for 120V equipment. 220V I cannot help with but it usually requires less current than 120V don't they?

 

[apache]

The motor on the compressor will state on the data plate or tag or even on the website showing the specs the FLA or fulll load amps in both high and low voltage if its able to run both. A 5hp motor in 220 V shouldent need much really,under 15 amps im sure,and yes the higher the voltage the lower the amp draw. If it was a 440 V motor or it could be wired/paired as such the amp requirement would be about 1/2 that of 220v.

 

[cdoggwsu]

In other words, pop a 20 amp breaker in the box and go!

^^^ If you're running the wire externally I'd go MC (Metal Clad) over Romex.

 

[blazin_blazer]

u think lowes would have that greenfield/metal sleeved wire or i need to get it from an electrical supply house?

 

[cdoggwsu]

I would think so...I've always picked it up at Home Depot so one would assume Lowe's would carry it as well.

 

[Blue85]

You don't have to size the breaker for the compressor. You match the breaker to the wiring and socket that you put in (whichever will handle less). You just have to choose the next standard size (or bigger) up from what the compressor needs. If the equipment needs a different kind of protection, it should be built into the equipment.

If you knew the real HP rating of the motor, this would work to estimate the current requirements, but a lot of compressors rate the pump capability, not the real motor power. The best way is to get the information from the motor tag. If you can't do that, see the owner's manual or contact the manufacturer. You don't want to go small with wiring for a motor becuase the surge currents can be very high.

 

[3 on the tree]

I would run 10 gauge, and 40 or 50 amp breaker. That way, you have the capability of running a 220V welder off the same service.

 

[79BRUISER]

I would run 10 gauge, and 40 or 50 amp breaker. That way, you have the capability of running a 220V welder off the same service.

I ran my welder and compressor seperately. I have found that running high amp draw equipment runs better with dedicated lines. Especially welders.

 

[blazin_blazer]

i already have a circuit ran for my welder & don't want to piggy back my compressor on that circuit, b/c if i'm welding and compressor kicks on, it makes the welder ''brown out'' and go cold at the arc for a second.

so the amperage on the motor plate is what size breaker i need or 20% higher as mentioned?

 

[bigblock72]

You might be able to get away with 12/2 and a 20 amp breaker but I'd just step up to to 10/2 and a 30 amp breaker and be done with it.

 

[chosen(1)]

I would run 10 gauge, and 40 or 50 amp breaker. That way, you have the capability of running a 220V welder off the same service.

As an electrician I can't let this one go. Please don't ever, ever do this. 10awg wire is rated at 30 amps for a reason. This is the type of thing that can burn down your house and kill your whole family.
As was said before you need to find the full load amperage (FLA) off the motor plate and size your wire and breaker accordingly, and yes the 20% that was stated before needs to be figured in as a circuit breaker will trip with a continuous load over 80% of it's rating.