help wiring Campbell Hausfeld 7.5 hp compressor

on the motor its self it says it draws 21 amps but on the tank its calling for 35 anyway so i got a 40 amp breaker and 8 gauge wire but when i took the pressure switch cover off i was going to but my black wire on L1 and red wire on L2 but on L2 they have a white wire going to the motor dont they follow color code or am i just not looking at it right also there is no where for the neurtal to go hope this makes a little sence if it helps at all the wires are conected to a square d pressure switch

I'm not an electrician, but you shouldn't need a neutral. Just two hots and a ground for a 220 compressor.

splashofred said:

on the motor its self it says it draws 21 amps but on the tank its calling for 35 anyway so i got a 40 amp breaker and 8 gauge wire but when i took the pressure switch cover off i was going to but my black wire on L1 and red wire on L2 but on L2 they have a white wire going to the motor dont they follow color code or am i just not looking at it right also there is no where for the neurtal to go hope this makes a little sence if it helps at all the wires are conected to a square d pressure switch

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Usually, all the wires inside the peckerhead are white, and no they don't follow any color code. Put one hot to L1, and the other to L2, and connect the ground.

If your going to wire it that way I would sujest an additional ground wire bolted directly to the frame and then grounded with a ground rod,,,,,safety thing

Why do you have the cover off the pressure switch??? The pressure switch is being used to open close current to the Motor starter coils and should be prewired to the starter box. No need to mess with it. All you will need to do is come thru the side of the motor starter housing and go on to the lugs on the starter relay. You only need two hots and a ground (green) to do this.

The pressure switch cannot handle the kind of current the motor draws, that is why you use the motor starter box.

Is this used? sounds like someone has swapped the motor for a smaller one. I have a Husky 7.5 that is made by C-H and is the same unit, different paint. All true 7.5 motors (and mine is) should say 31 to 33 amps on the data plate. A true 7.5 motor will draw more than 21 amps (sounds like a 5 hp)

Charles

Sorry if my post sounded a little too agressive, it was way early in the morning. Anyhow, Magnetic Starter is the word I was searching for. A true 5 horse, or a true 7.5 horse compressor should have a Magnetic starter. That is the large black box with the reset button on the front that is mounted on the compressor, and is connected to both the pressure switch and the motor.

Here is a pic of my 7.5 HP Husky (made by Cambell-Hausfeld and the same as theirs at the time it was made. Its three years old and they have changed them since it was made). I removed the cover to the mag starter so you can see how it is connected (sorta). I used #6 wire.

The NEC 430 requires that on motor branch circuits, that you size the conductors to 125% of the standard values given in table 430.247 (rather than actual motor amperage) for a 7.5 hp motor at 240 volts, that would be 29 amperes. Sizing a conductor for this would mean taking 29x1.25=36.25 or 37 amps.

Looking at conductor sizing charts you will find that THHN (commonly used in conduits) at 90c is good for 55 amps in #8 so you are more than good there.

For circuit breaker MAX capacity, you take that 29 amps found in the table in the NEC and mutiply by 250% (ref. NEC 430.52) to get 72.5 amps. You would use the next higher standard breaker than this. This would be the largest breaker you would be allowed to use, to avoid tripping during starts.

Yes, I know, its alot. I have a 50 amp on mine, and never have a problem.

The pics show the magnetic starter. #6 incoming power cables and a #10 ground come in from the right in the blue flexible conduit, and the two hots attach at the top, the ground goes 3/4 of the way around the inside to end up at the terminal on the lower right. Wires from the Left are to/from the pressure switch, and the wires to the motor leave via the very bottom of the unit. There is no neutral just two hots and a ground. One hot to L1 and one hot to L2 of the magnetic starter, doesn't matter which goes where, and a green ground to the appropriate terminal block.

Charles