3 PH AC motor starter question

[dingo0722]

I have an air compressor that we are hooking up. It runs on 460 3 ph power. The motor starter that I have is rated for 460 on the input/output and the low voltage(on/off) side is rated at 208. I have 240 in the shop, both single and 3 phase. Can I use 240 with this device for the low voltage on off side?

[Al_The_Man]

Please clarify? What do you mean by 'low voltage on/off side'?
Is this a simple 3 phase contactor?
Al.

[dingo0722]

the way it is set up is to use a normal 20Amp switch to activate the relay with the 460 voltage. The relay is alo connected to the air compressor pressure switch. They relay say 208V 60Cy. I was wondering if the relay could operate by using a 240 volt source instead of a 208 volt source. If not I could always by a small 150VA step down transformer

[Al_The_Man]

I am assuming you mean the coil voltage?
If it is presently a 208 coil, you should be OK with 240, if it runs hot, it might be wiser to get the right coil, they can be purchased from any electrical supplier.
Al.

[dingo0722]

thats what I thought. Any idea what the coil goes for. The unit is an allen bradley. Does the brand matter or are they standardized

[lgalla]

You should post a picture orf the rating plate on the motor.You cannot run a 460 volt 3ph motor on your 240 shop voltage.Perhaps the motor has lower voltage taps?
Yes you could run the coil of the starter off your shop 220,but you still need the 480 for the motor.Al could explain much better than I.
Larry

[Al_The_Man]

Larry is correct, the plate may show if it is possible change the motor to 240.
Most motor bring all 6 ends out and can be connected star/delta for 220/480.
Al.

[dingo0722]

I should have mentioned tha I have a step up transformer going from 240 3ph to 460 3ph just for the compressor. The compressor motor, a Baldor, has duel voltage listed on the plate,230/460. When I opened up the box on the motor there were only 3 wires. The previous owner had the unit running on 460V. Dont know if the plate is in error or someone removed the other 3 wires.

So for the high voltage power, I will bringing 460 into the starter and then to the motor. From your comments below, I should be able to use my 240 single phase to power the coil even though the coil has a plate on it that says 208V.

I found coils on McMaster for about $56. But I am unsure if they are the same form factor: McMaster-Carr
listed on the bottom of the page. I can then select 110/240 voltage range

thanks

[Al_The_Man]

AB like many manuf make NEMA and IEC style, the coil has to be for the same frame size of contactor.
You could run the 208 coil for a while on 240 and monitor the temperature.
Al.

[vanjast]

Dingo, try get hold of either a users or technical manual on the compressor.

What you're probably currently looking at is the compressor motor connected for 'Star' 3-phase (you mention only 3 wires and it was set up for 3-phase operation). There are probably configuration links with 6 bolts to connect to. Get hold of a manual before you wire up and switch on power.

Secondly, get hold of a multimeter and measure the voltages across the wires. If they're all in the range of 400+ volts (AC) you're looking at 3-phase power. If it's 3-phase you're missing an earth wire, and possibly a neutral wire as well.

If 2 wires are at 220V(110) AC and one pair around 0V (should be close to 0V otherwise there's a earth problem), then you have 1-phase 220V(110v).

If you get other voltages there's a power/wiring problem
It's advisable to call in a qualified electrician to do a basic checkup as this is cheap compared to a blown motor and possibly a fire, which the insurance will refuse to payout.