Need Electrical Help

Fri Mar 25, 2011 7:55 pm

I just picked up a new to me air compressor. When I was cleaning the dust off it I noticed that there was a bare red wire sticking out of the end of the power cord. The cord has 4 wires (white,red,black and green). The red wire that is bare is on the end where it goes into the pressure switch.
My question is does this wire need to be connected? The compressor runs great! It is a 80 gal. Porter-Cable with a 6 hp motor. It puts out 17.3 scpm at 100 psi. My brother bought this a couple years ago and only used it to inflate his car tires so you could call it lightly used.
This should run a sandblaster I would think!
Thanks for any advice!

Re: Need Electrical Help

Fri Mar 25, 2011 9:06 pm

Your power cord may have an extra wire you do not use, since it will only require 3 to operate, 2 for the 220 and one for ground. If you go to their website http://www.portercable.com/ you can click on support, and put in your model number to download a manual. That should tell you what you have.

Re: Need Electrical Help

Sat Mar 26, 2011 5:14 am

I agree that it was most likely a spare cable that had an extra conductor.

Re: Need Electrical Help

Sat Mar 26, 2011 6:07 am

It would only need that 4th wire if it were a 3 phase unit, which it ,obviously, is not. I suspect that if you check out the other end of the cord, you'll find the same wire that is not connected to anything.

Re: Need Electrical Help

Sat Mar 26, 2011 8:42 am

Thanks for the great info. I suspected that it may have been a extra wire but wasn't sure! I knew that you guys would steer me in the right direction.

Re: Need Electrical Help

Sat Mar 26, 2011 10:21 am

I should have posted this earlier, but never thought to until reminded, new 220 outlets and cords have 4 conductors, as opposed to the 3 we have always seen. You can still get the 3 conductor ones, but I believe the 4 wire is now the standard according to new electrical regulations.

Re: Need Electrical Help

Sat Mar 26, 2011 1:07 pm

Papermaker:
Red & Black - Hot wires
White - Neutral
Green - Ground
Should be wired that way!

John

Re: Need Electrical Help

Mon Mar 28, 2011 11:34 am

John *.?-!.* cub owner wrote:I should have posted this earlier, but never thought to until reminded, new 220 outlets and cords have 4 conductors, as opposed to the 3 we have always seen. You can still get the 3 conductor ones, but I believe the 4 wire is now the standard according to new electrical regulations.

yup, when there is a 120vac motor light or timer the neutral has to be covered beecause as the return it is considered a current carrying conductor. not so sure about the air compressor though, a few voltage checks should clear it up.

Re: Need Electrical Help

Wed Mar 30, 2011 9:36 am

I assume this is a 220 volt motor. As others have said, in the USA, red and black are the 220 legs, L1 and L2, they are needed for the 220 part to work. White is the groundED conductor and is needed as a leg to get 110 volts. Your compressor may not need 110 volts for anything and therefore will not have a spot in the box for the white wire. The green wire is the groundING conductor or the safety ground and needs to be attached to the frame of the motor or the ground screw. If it was working with the red wire not connected, this means something is wrong somewhere. Is the plug a molded plug or one of the add on plugs?

Re: Need Electrical Help

Wed Mar 30, 2011 9:43 am

Landreo wrote:.......... Is the plug a molded plug or one of the add on plugs?
Even if it is a molded plug, the wiring in the receptacle the previous owner had it plugged into may have been incorrect, necessitating the odd wiring. My suggestion is to rewire the cord to code and then wire your receptacle properly, regardless of how it was wired when you got it.

Re: Need Electrical Help

Sat Apr 02, 2011 1:18 am

The cord is a made up cord. The receptacle is one that I wired in. Let me see if I have this correct,The black wire is one leg and the red is the other 220v leg. The green wire is grounded to the frame .The white wire goes ?
In the box on the compressor there are two lugs on the pressure switch and a spot on the frame for the green ground.
Would the red and black wires be connected to one of the lugs on the switch and the white to the other lug.

Re: Need Electrical Help

Sat Apr 02, 2011 7:30 am

papermaker wrote:Would the red and black wires be connected to one of the lugs on the switch and the white to the other lug.
Halt. Wait one. I have read this sentence 6 or 7 times. Not sure what was intended in the sentence.

For 220 Volts both the red and black wires are seperately switched. The green and white wires are not switched. Some switches have an unswitched terminal for a ground wire.

Could the electric motor be 120 volts or 120/220 volts? If it were wired for 120 volts the red wire would not be used.

At this point. Either research the manufacturers material for the correct wiring diagram - - - - or obtain professional help.

Edit: 20.45 amp draw for 220 volts. Almost certainly a 220 volt motor.

Re: Need Electrical Help

Sat Apr 02, 2011 10:01 am

Remember, these power cords are universal. Assuming that your pressure switch opens both sides of the power line (not all do, some only one side), the normal wiring would be black on one lug of switch, red on other lug, green to ground screw, and white either not connected or also to ground screw. Of course your receptacle also has to match this pattern. The reason for the 4 wire cords is that some 220 volt equipment also has 110 volt items built in, such as monitor lamps, timers, control relays, etc. and white is a neutral for those items. An example of this is both your clothes dryer and electric range. The heating elements are 220, but on the dryer, most motors are 110, and on the range, the timer and digital display, etc. are 110 so they need the white wire.

Re: Need Electrical Help

Sat Apr 02, 2011 12:23 pm

For safety's sake, and probably code, both legs of a 220 device must be switched. Otherwise the motor stays energized, although it won't run with one leg switched open.

Re: Need Electrical Help

Sat Apr 02, 2011 5:01 pm

As I am typing this, the only time I can think of that a neutral, white, wire is connected to the ground is at the service entrance of the house. Never at a motor. Place some tape or heat shrink tubing over the end of the white wire and leave unconnected. Since it is a made up cord make sure the other end, plug, is correct. You should have 220 volts between the two phases when plugged in, i.e. 220 volts on a voltmeter between the red and black wire.


Connect the red to one switch lug, black to the other, ground wire to the green screw or frame ground.