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Discussion Starter #1
Hi, I'm trying to get an old air compressor going again, but when power is applied, it just hums. I've checked power and 220 is on all 3 legs at the switch box. I can easily rotate the pump and motor by pulling on the belts so I don't think I have any bad bearings. I'm thinking the centrifugal switch is bad and wondering if someone can tell me if it is located on the end in the attached picture. If so, will removing the 4 screws around the round cap allow me access to it? I'm afraid if I take the cap off, I may end up with more problems... The specifics of the old motor are:
Peerless, 5 hp, 1750 rpm, 40 c(?), 3 phase, 200-440 volt, 60 hz, 13-6.5 amp, CON duty, Frame PH254, Serial 403257.

I'd greatly appreciate any help. Thank you in advance! Pat
 

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E2 Electrician
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Hi, I'm trying to get an old air compressor going again, but when power is applied, it just hums. I've checked power and 220 is on all 3 legs at the switch box. I can easily rotate the pump and motor by pulling on the belts so I don't think I have any bad bearings. I'm thinking the centrifugal switch is bad and wondering if someone can tell me if it is located on the end in the attached picture. If so, will removing the 4 screws around the round cap allow me access to it? I'm afraid if I take the cap off, I may end up with more problems... The specifics of the old motor are:
Peerless, 5 hp, 1750 rpm, 40 c(?), 3 phase, 200-440 volt, 60 hz, 13-6.5 amp, CON duty, Frame PH254, Serial 403257.

I'd greatly appreciate any help. Thank you in advance! Pat
Where is this pump located that you have 3 phase? This really isn't DIY... best call in an electrician.
 

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You do now your house is not going to have 3 phase power, right?
If you really do have 3 phase where your trying to get it to run are you sure the motors not wired to run with 440?
Open up the cover where the wires are and there should be a wiring diagram telling how to switch back to 220.
 

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Lic Electrical Inspector
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Hi, I'm trying to get an old air compressor going again, but when power is applied, it just hums. I've checked power and 220 is on all 3 legs at the switch box. I can easily rotate the pump and motor by pulling on the belts so I don't think I have any bad bearings. I'm thinking the centrifugal switch is bad and wondering if someone can tell me if it is located on the end in the attached picture. If so, will removing the 4 screws around the round cap allow me access to it? I'm afraid if I take the cap off, I may end up with more problems... The specifics of the old motor are:
Peerless, 5 hp, 1750 rpm, 40 c(?), 3 phase, 200-440 volt, 60 hz, 13-6.5 amp, CON duty, Frame PH254, Serial 403257.

I'd greatly appreciate any help. Thank you in advance! Pat
3 phase motors do not have centrifugal switches. Will the motor start and run if you spin it in either direction by hand? If it does then you have a missing phase.
 

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Discussion Starter #5
The pump is located in an old automotive restoration shop that my uncle had. It is an old DeVilbiss compressor that is probably 40-50 years old. I know my uncle took care of it through the years. I'm guessing it hasn't been running in 10 years or so now... Power is controlled by a heavy duty 3-pole on/off switch (similar to an AC lockout switch by an HVAC compressor).

I measured voltage between the 3 pairs and I get 230 and 247 readings between the pairs. Holding one lead on the left most incoming wire, I get 230 to the center wire, 247 to the right most wire. Moving my one lead to center wire, I get 230 to left wire and 247 on the right most wire. Moving my one lead to the right wire, I get 247 on the left most and center wire...

I've got a guy coming over tomorrow that is smarter than me and hopefully can figure it out... I'll let you all know what happens. Thanks!
 

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Your voltage readings certainly indicate 3 phase. If there are fuses between where you took the voltage readings and the motor, one of them is likely blown. Only one, not two or all 3.

Another possibility is the controller. There's a chance it is closing only two of the 3 phases to the motor. It could also be the motor itself, or the connections in its terminal box.

The voltage readings show a pretty serious imbalance. It's possible there's a failing (but not completely failed) component anywhere from the supply all the way to where the readings were taken. Take the voltage readings under load, but be careful; don't let the motor just hum without actually running for longer than a few seconds.

Rob
 

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Semi-Pro Electro-Geek
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Measuring current draw on each of the phases will be much more informative. That will narrow it down a lot.
 
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had saw dust in a contactor once. amazing what some compressed air and installing the cover correctly will do in a wood shop. my bet is a blown fuse.

bernie
 

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UAW SKILLED TRADES
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Your voltage readings certainly indicate 3 phase. If there are fuses between where you took the voltage readings and the motor, one of them is likely blown. Only one, not two or all 3.

Another possibility is the controller. There's a chance it is closing only two of the 3 phases to the motor. It could also be the motor itself, or the connections in its terminal box.

The voltage readings show a pretty serious imbalance. It's possible there's a failing (but not completely failed) component anywhere from the supply all the way to where the readings were taken. Take the voltage readings under load, but be careful; don't let the motor just hum without actually running for longer than a few seconds.

Rob
Rob did a great job summarizing your issues. With three phase motors about 90% of the time it is single phasing if all it does is hum and barely rotates. Only thing I will add to Rob's reply is that what he is telling you is troubleshooting a motor problem involves isolating where the probelm is ... in the motor or in the supply and devices. It sounds like your starting the motor across the line or in other words just closing a switch from the supply to the motor terminals. You do not mention any starters with contact and overloads. So I'm visualizing protection for the wiring being a 3 pole breaker or fuses in a panel, 3 phase wiring to a 3 pole saftey knife blade type switch, then to the motor.
It looks like you have all three phases to the switch, though you have close to 5% change with one phase, that is somethong that is not quite correct as it is just outside what would be considerd an bad imbalance. I am assuming your taking the voltage readings line side of the switch terminals. Do not close that switch and then take voltage readings .. that is way too much time to let the motor hum and heat up. I do not like 3 phase motors that do not have motor starters with overloads controlling and protecting them.
Anyway your motor just hums and doesn't rotate. I'd disconnect at the motor terminal box and recheck voltages a L1 L2 and L3. If you get the same results your not single phasing from the supply, though an imbalance is apparent. Still though if your motor is good it should run. Next would be possible wiring error to the motor leads.

Has anyone reconnected the wirng to the motor?

Hopefuly if that is the case you haven't damaged your motor. If the name plate is still attached to the motor check the wiring diagram for proper connections. That being ok it is almost certain you have a bad winding(s) causing the motor to single phase. There are ways to check for a bad winding but if that is the case might as well get a new motor which really should not be that expensive.

If the motor has been reconnected and no wiring diagram exists then we might be able to show you how to check winding continuity to reach the correct connections based on the number of motor leads ..ie..9 or 12 leads etc.
 

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Your voltage readings certainly indicate 3 phase. If there are fuses between where you took the voltage readings and the motor, one of them is likely blown. Only one, not two or all 3.

Another possibility is the controller. There's a chance it is closing only two of the 3 phases to the motor. It could also be the motor itself, or the connections in its terminal box.

The voltage readings show a pretty serious imbalance. It's possible there's a failing (but not completely failed) component anywhere from the supply all the way to where the readings were taken. Take the voltage readings under load, but be careful; don't let the motor just hum without actually running for longer than a few seconds.

Rob
Duplicate post ...sorry ...problem with posting reply
 

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Discussion Starter #11
Progress...

Looks like we have identified the problem of one of the 3 poles (left most) not being connected at the meter. The meter was replaced a year or so ago with a digital meter. It looks like the proper meter (4W), but it is cocked where the bottom sticks out, so one pole is probably not connected...

The configuration is power from the meter through a box where fuses are in series for each of the 3 poles, then to the switch box where it connects to the 3 knife blade sockets on the non-movable contact side. The moveable contact side of the 3 pole switch has a fuse in series with each pole that goes through the pressure switch and to the motor.

Troubleshooting showed the middle and right knife blades significantly arcing when making/breaking the switch, but not the left most pole. Measuring voltages with an analog meter showed the left most leg dropping out when the load was applied. This was all the way back to before the first fuse coming in from the supply/meter. The 230 vac on the left pole that I was measuring before must have been a floating voltage. I wanted to re-measure from the right most pole to the other 2 poles, because both of the previous readings showed 247, but when I tried to measure, I had a problem with my meter... :(

Anyway, I'll follow-up after the city comes out and checks their meter...
Thank you all for the great feedback. This was my first problem post to this DIY group and you all have been great! I hope I can give back what you all have given me.

Thanks,
Pat
 

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Discussion Starter #12
Progress...

Looks like we have identified the problem of one of the 3 poles (left most) not being connected at the meter. The meter was replaced a year or so ago with a digital meter. It looks like the proper meter (4W), but it is cocked where the bottom sticks out, so one pole is probably not connected...

The configuration is power from the meter through a box where fuses are in series for each of the 3 poles, then to the switch box where it connects to the 3 knife blade sockets on the non-movable contact side. The moveable contact side of the 3 pole switch has a fuse in series with each pole that goes through the pressure switch and to the motor.

Troubleshooting showed the middle and right knife blades significantly arcing when making/breaking the switch, but not the left most pole. Measuring voltages with an analog meter showed the left most leg dropping out when the load was applied. This was all the way back to before the first fuse coming in from the supply/meter. The 230 vac on the left pole that I was measuring before must have been a floating voltage. I wanted to re-measure from the right most pole to the other 2 poles, because both of the previous readings showed 247, but when I tried to measure, I had a problem with my meter... :(

Anyway, I'll follow-up after the city comes out and checks their meter...
Thank you all for the great feedback. This was my first problem post to this DIY group and you all have been great! I hope I can give back what you all have given me.

Thanks,
Pat
 

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Discussion Starter #13
Problem solved!

Well the problem wasn't at the meter, but up at the transformer. There was a blown fuse at the transformer. After replacing the fuse, the compressor ran like a "top".

One thing I learned from this is that I intend on rigging up a light bulb socket with test leads. If I had checked each phase to gnd with a 150W light bulb, I probably would have gotten the answer a lot sooner...

Anyway, thank you all for your help!
Pat
 

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Well the problem wasn't at the meter, but up at the transformer. There was a blown fuse at the transformer. After replacing the fuse, the compressor ran like a "top".

One thing I learned from this is that I intend on rigging up a light bulb socket with test leads. If I had checked each phase to gnd with a 150W light bulb, I probably would have gotten the answer a lot sooner...

Anyway, thank you all for your help!
Pat
If you had check each phase to ground with a light bulb, you would get a burned out light bulb! One of those phases is 208V to ground.
 

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Discussion Starter #15
If you had check each phase to ground with a light bulb, you would get a burned out light bulb! One of those phases is 208V to ground.
I thought all 3 phases were the same, about 110-125, with respect to ground. I was measuring 230-247 between phases, which is double a one phase measurement. I guess I'm a bit 'corn-fused'...
 

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I thought all 3 phases were the same, about 110-125, with respect to ground. I was measuring 230-247 between phases, which is double a one phase measurement. I guess I'm a bit 'corn-fused'...
It's not possible to have a 3-phase system with 240V between phases and 120V from each phase to ground. The voltages don't add up. If you have 120V from each phase to ground, then you have a wye system, and the voltage between phases must be 208V. This is a common type of system, but isn't what you have. If you have 240V between phases, then you have a delta system and the voltage from phase to ground is either 120-208-120, or 240-0-240, depending on whether it's a high-leg delta service (most common, and what you have) or a corner-grounded delta (very uncommon).
 
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If you had check each phase to ground with a light bulb, you would get a burned out light bulb! One of those phases is 208V to ground.

To get around this problem your test lamp should be
rated for 240v !
Either use a 240v lamp or use 2 x 120v lamps in series.

This is common practice in Australia,
but we use 2 x 240v lamps
incase we find 415v.

But because you use 120v,
then you would use 2 x 120v lamps
incase you find 220v.

Test lamps are a simple but very effective tester.
You can put them in a clear acyrilic tube
for protection.
 

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Discussion Starter #18
It's not possible to have a 3-phase system with 240V between phases and 120V from each phase to ground. The voltages don't add up.
Now that the 3rd phase is connected again, I will re-measure.

If you have 120V from each phase to ground, then you have a wye system, and the voltage between phases must be 208V. This is a common type of system...
I don't understand why each phase can be 120V to gnd, but going across two phases is only 208V and not 240V. Maybe the addition that I'm missing has to do with rms, avg, or peak readings?

I'm pretty sure that I have a 4 wire wye config and maybe my high readings earlier of 247V across two phases was due to one phase not connected? I will re-measure tomorrow because I would like to understand this better.

Thank you for your help AND patience! :)

To get around this problem your test lamp should be... ...a 240v lamp or use 2 x 120v lamps in series... You can put them in a clear acyrilic tube
for protection.
Great ideas! Thanks much!
 

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I will give you a quick drawing what the typical 3 phase 4 conductor service look like so you will get the idea.

The upper one is WYE connection and the lower one is DELTA connection with wild leg.



Hope that clear up on that one but beware the drawing letters are not the excat the same as it supposed to be but the key item is you find the netural on B-C then you know the A is wild leg per picture in real life normally B phase is wild leg if connected to the netural.

Merci,
Marc
 
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If you had a 4-wire wye service and phase-to-phase voltage of 247V, then the phase to ground voltage would be 143V (by definition - there's no room for variation on this) and that's way too high for things to work normally. If you had 247V between two phases, you must have a high leg delta service.
 
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