Craftsman Compressor

Status
Not open for further replies.
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician (retired)
Here is a problem I've been having with a compressor in my shop. The unit came with a 15 amp plug and in the literature that came with it, it states that it should be connected to an individual 15 ampere circuit. So I installed an individual 15 amp circuit with #12 AWG THHN. The problem is that it trips the 15 ampere circuit on start up. So I installed a 20 amp circuit breaker with a single 20 amp receptacle, plugged in the compressor and it now trips only sporadically (usually when I'm wedged under my truck with an air ratchet).

To correct the problem I thought about installing a 25 or 30 amp circuit breaker, but now that creates a problem because the receptacle is rated for 20 amps and someone could unplug it and use the receptacle for something else which is protected by a 25 or 30 amp breaker. I've also considered hardwiring the unit to eliminate the receptacle issue altogether but then I would lose the portability of the compressor. Any thoughts?
 
Re: Craftsman Compressor

Find out what's wrong with the compressor. All compressors use some sort of unloader scheme to prevent the motor from starting under load. See where the problem is.

And, no you definately do not want to hard wire that thing to a 30A circuit!

-Hal
 
Re: Craftsman Compressor

Why couldn't the compressor be hard wired with a larger circuit breaker? Doesn't the NEC make allowances for larger overcurrent devices when motor cannot start with a smaller device?
 
Re: Craftsman Compressor

Why couldn't the compressor be hard wired with a larger circuit breaker?

Because there is a problem with the compressor or, as Dave points out, what are we talking about on terms of voltage drop?

That compressor is portable and made to operate on a 15A circuit. Find out why it won't. If you don't and just supply it with more current it will burn up.

-Hal
 
Re: Craftsman Compressor

Voltage drop causing it to draw too much current?

Edit: With 12 AWG it would take 120' to drop 8% at 20 amps. It, seems like most cases it should be ok with 12 AWG.

A funky wire nut somewhere could add voltage drop.

[ April 02, 2005, 04:46 PM: Message edited by: physis ]
 
Re: Craftsman Compressor

Voltage drop is what I was getting to. #12 might be way too small.
Need the length from outlet to panel and accurate voltage reading AT the panel.
Also while your taking a voltage reading in the panel, sometimes switching phases can help! (Sometimes their voltages vary a little) could be just enough to make a difference.
Could be a voltage drop at the panel itself, is it the main panel or sub?

Need more info!
:)
Dave
 
Re: Craftsman Compressor

I agree with Hal on both his points.

Don't keep up sizing the breaker, the unit was made and designed to run on a 15 amp breaker. If it does not work with a 15 amp breaker there is an issue that should be fixed.

Do check on the unloader valve.

On a typical home compressor this unloaded valve is incorporated into the pressure switch.

When the receiver reaches the set pressure the switch should open and at the same time you should here a distinct 'leak' of air from the unloader valve.

No compressor starts well with full tank pressure against the piston.

Another possible problem would be the check valve between the compressor and the receiver.
 
Re: Craftsman Compressor

Originally posted by davedottcom:
Voltage drop is what I was getting to.
Click to expand...
Funny thing is many times the voltage drop helps to keep the starting amps down.

Think of a reduced voltage motor starters.
 
Re: Craftsman Compressor

It depends completely on the motor and how it's used. The possibility exists for increase as well as decreased current.
 
Re: Craftsman Compressor

Originally posted by physis:
It depends completely on the motor and how it's used. The possibility exists for increase as well as decreased current.
Click to expand...
I will bet you the starting current is less on this motor with reduced voltage.

A fine example of this was a question posted here a while ago about a chop saw.

It would run fine on a 14 AWG cord, when used with a 12 AWG cord it would trip the breaker.

Voltage drop 'softened' the inrush current and let it start with out tripping.

Motors do not always draw more current when run with less voltage. Instead of the current increasing, the torque is reduced.

Here is a link that will help explain this.
 
Re: Craftsman Compressor

Maybe thats why my compressor does better on a 100 foot cord.It has a hard time starting if under pressure and pluged straight in.Solution was a hard start cap
 
Re: Craftsman Compressor

Excellent site Bob, I've posted from it before. :D One of the better places to read up on motors, at least that I've found.

We actually don't disagree I don't think (sorry).

The starting current will be lower. Locked rotor current isn't dynamic and will decrease with lower voltage.

But after it's moving you have to start treating it like an individual. When it gets up around 85% or better low voltage can cause less power to get to the rotor, increasing slip, putting it into the higher current part of the curve.

Now I'm still learning these induction motor thingies, so if I'm a little off it's ok. :D
 
Re: Craftsman Compressor

A motor is allowed to be supplied from a time delay circuit breaker that is 250% of motor nameplate rating. If your motor has a nameplate rating of 12 amps you can refit with a 10 gauge cord and 30 amp receptacle and breaker.

One of your problems is that your motor is operated in the deliblerately overloaded state. This lasts about as long as the kind of aircraft engine tuneup that is good for 2 years penal servitude in Leavenworth. You probably need a heftier motor.

When I use my air powered electrician's drill with so and so's air compressor with a 12 amp 230 volt single phase motor the motor trips its internal overload relay if I am drilling enough holes in 1 session of hole drilling. I also have to allow the air compressor time to catch up even if I have to move the ladder once every 5 holes.
 
Re: Craftsman Compressor

Originally posted by mc5w:
A motor is allowed to be supplied from a time delay circuit breaker that is 250% of motor nameplate rating. If your motor has a nameplate rating of 12 amps you can refit with a 10 gauge cord and 30 amp receptacle and breaker.
Click to expand...
Sure, if you built this unit yourself.

A Craftsman compressor will be UL listed and labeled as a complete unit / appliance.

You can not rewire any appliance for use with a larger overcurrent / short circuit / ground fault devices.

110.3(B) Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.
Click to expand...
If it came with a 15 amp cord it must stay with a 15 amp cord. :)

[ April 03, 2005, 05:54 AM: Message edited by: iwire ]
 
Re: Craftsman Compressor

I agree with iwire
It should run off 15 amp circuit. There's either a problem with the unit or the circuit. If the compressor has belts on it to drive the compressor, pull the belts and run just the motor. If it trips your motor might be the problem. There could be several things to try. If your checking wire length for voltage drop, make sure you firgure distance x2. Feed and return on the 120 volt run. Let use know if you find the problem.
Jim
 
Re: Craftsman Compressor

Thank for all of the responses. In answer to some of the questions raised here the circuit conductors are about 40' of #12 THHN so I don't think that voltage drop is an issue. A quick voltage test with my Fluke 87 yielded a voltage of 124VAC at the receptacle supplying the unit. I looked at the motor on the compressor and the nameplate states that it draws 15 amps @ 120 volts, yet it only has a 15 amp plug on a #12 flexible cord. Would it be required to have a 20 amp plug if it draws more than 12 amps?

I'm also curious as to why a compressor with a plug couldn't be hard wired? Would this really affect its listing? This particular unit has provisions to mount it to the floor if you choose to make it stationary, so why couldn't it then be hard wired? Does the listing really go as far as saying it must only be used with the cord and plug that was attached to it then it came out of the box?
 
Re: Craftsman Compressor

40' of #12 copper would only cause a voltage drop of less then 1.9% IF the reading you took was taken while the "Load" was applied (Compressor running) 1.9% VD of 124v is 2.35 volts. 124 - 2.35 = 121.65 volts. No Problem.

If the voltage reading was taken while No load was applied it doesn't tell you much of anything!

Dave
 
Re: Craftsman Compressor

You beat me to it Dave. You'd want to try to get a measurement while your motor's trying to trip the breaker. The current draw is what makes the voltage go down.

I agree with Iwire though, leaning towards something else being the problem.
 
Re: Craftsman Compressor

Originally posted by infinity:
I'm also curious as to why a compressor with a plug couldn't be hard wired? Would this really affect its listing?
Click to expand...
It depends on what the listing and labeling on the unit says.

If it gives you an option to hardwire it (I doubt it) it will also tell you the MCA (minimum circuit ampacity) and the Maximum overcurrent protection.

Originally posted by davedottcom:
If the voltage reading was taken while No load was applied it doesn't tell you much of anything!
Click to expand...
I agree but will add unless you take a look at the breakers trip curves knowing the load will not help much either.

A 15 amp breaker should hold with more than 15 amps for the length of time start up takes.

Again this compressor should start with the intended breaker.

If it does not there is an issue that needs to be fixed and up sizing the breaker is not 'a fix' it is a hack.
 
Status
Not open for further replies.
Top