single phase motor
- Thread starter hilltop
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One-eyed Jack
Senior Member
- Location
- Scotland Neck, NC
Contactor not rated for 20 amps. Contact points burnt. Loose connection at terminal.
good possibilities
I was told they pulled new # 10 THHN to new motor [ ona 30A breaker had #14 originally, not sure who planned that out???]...thinking voltage drop and/or faulty motor...hooked everything back up and same issue...nuetral is cherry red at contactor.
I asked if they checked nuetral to ground voltage at panel source..no one looked at that yet. The nuetral carries the unbalance of the line so why would the nuetral heat to this extent????? Assuming that there are no loose connections.
I asked if they checked nuetral to ground voltage at panel source..no one looked at that yet. The nuetral carries the unbalance of the line so why would the nuetral heat to this extent????? Assuming that there are no loose connections.
- Location
- Logan, Utah
#14 AWG wire and a 30 amp breaker providing short circuit and ground fault protection is most likely just fine in this circumstance. For motors 240.4(D) does not apply.
In a 120 volt motor situation as you have described the neutral conductor will carry the same load as the ungrounded "hot" conductor.
Chris
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- Location
- Logan, Utah
Your welcome.
I would first check for loose connections in the motor and any juction points between the motor and the contactor.
Chris
Cold Fusion
Senior Member
- Location
- way north
Why would any loose connections anywhere other than at the contactor affect this? OR how would a loose connection in the motor affect the conductor temP at the contactor?
cf
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Once the connections at the contactor became 'red hot" the contactor was most liekly ruined, so it must be replaced.
Is the contactor 20A resistive rated or 20A motor load rated?
Is the contactor 20A resistive rated or 20A motor load rated?
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I wouldn't assume that. You could try substitution, such as swapping poles, so the one that switches the neutral will switch the hot.
Or, since the line giving you trouble is the grounded conductor, just connect the line and load wires together, bypassing the contactor.
One-eyed Jack
Senior Member
- Location
- Scotland Neck, NC
If the red hot heat is at the contactor this is the most likely source of the problem. ie where there is smoke there is usually fire.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
The red-hot wire is a symptom, and you need to find the cause. Mother nature has a way of finding the weakest link. By design, that's a fuse or breaker. If it was simple overload, the heat would be spread out among the equally-weak links. If the wire was too small, it would all be warm. You have a hot spot.
You need to find what's making the wire so hot at one point. Maybe a loose screw or termination, a worn contact, or something else at that one terminal. It's only happening at one of four supposedly-identical terminals, and didn't happen when it was new. Something has changed at that one termination.
Several points come to mind:
One, why are they even bothering to switch the neutral? Totally unnecessary in any event. Perhaps the equipment was originally designed for 240 volts?
Two, simply replacing the contactor isn't gonna cut it. ANYTIME a wire is overheated, it will oxidize and become high resistance. The heat has ruined BOTH of the wires attached to that side of the contactor.
Only way to repair this is to:
First, quit switching the neutral, totally unnecessary. Splice it after cutting back or repull it.
Second, replace ALL of the wire connecting to the contactor, including the neutral and hot. (If space permits, cut the wire back at LEAST 8 inches and splice on new wire, otherwise repull it.)
And finally, replace the contactor again, no matter how the existing one looks.
Anything less and you'll keep having problems.
This is a common event on my cinema lamp rectifiers and the fix above is the only sure cure.
If the current measured on the hot and neutral are the same, quit trying to over-think the problem, because there isn't a problem. :grin:
Edited to add: If the neutral current is higher than that on the hot leg, then throughly check for another load bootlegged onto that neutral.
One, why are they even bothering to switch the neutral? Totally unnecessary in any event. Perhaps the equipment was originally designed for 240 volts?
Two, simply replacing the contactor isn't gonna cut it. ANYTIME a wire is overheated, it will oxidize and become high resistance. The heat has ruined BOTH of the wires attached to that side of the contactor.
Only way to repair this is to:
First, quit switching the neutral, totally unnecessary. Splice it after cutting back or repull it.
Second, replace ALL of the wire connecting to the contactor, including the neutral and hot. (If space permits, cut the wire back at LEAST 8 inches and splice on new wire, otherwise repull it.)
And finally, replace the contactor again, no matter how the existing one looks.
Anything less and you'll keep having problems.
This is a common event on my cinema lamp rectifiers and the fix above is the only sure cure.
If the current measured on the hot and neutral are the same, quit trying to over-think the problem, because there isn't a problem. :grin:
Edited to add: If the neutral current is higher than that on the hot leg, then throughly check for another load bootlegged onto that neutral.
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Cow
Senior Member
- Location
- Eastern Oregon
- Occupation
- Electrician
I agree with Mxslick. That's just weird to switch a neutral plus it's one more splice in the run. Unless it's a fuel pump, that's the only time I switch 'em.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Dual-voltage motors such as these often switch both conductors in case the higher voltage is used.
Which brings me to: Can this unit be switched to 240v? Doing so would halve the current.
Which brings me to: Can this unit be switched to 240v? Doing so would halve the current.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
and help balance the load (on single phase supply) voltage drop is also less.
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