lighting contactor

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kwired said:
My bet is on this being OP's troubles. Perhaps OP needs undervoltage relay wired into the control circuit so the contactor coils are isolated when there is not full voltage.

Fuses as initially suggested might protect the coils, but will still be left with equipment not working just as frequently because of blown fuses. Find the problem, don't just treat the symptoms.
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Ding ding ding... We have a winner! :thumbsup:

Something else to look at: if you have mechanically latched contactors, the coils are typically NOT rated to be energized continuously, they are intended to be momentary pulses to open or close. Take a look at your controls to make sure someone didn't screw up.
 
Jraef said:
You're probably thinking of MV breakers, which sometimes people use as contactors. But that's not a good idea.
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standard practice in mining worldwide
a circuit breaker uses the exact same vacuum contactor as a starter
the only difference being the controls

in fact in the starter it serves dual purpose
protection and starting
 
Jraef said:
Ding ding ding... We have a winner! :thumbsup:

Something else to look at: if you have mechanically latched contactors, the coils are typically NOT rated to be energized continuously, they are intended to be momentary pulses to open or close. Take a look at your controls to make sure someone didn't screw up.
Click to expand...
Finally! This is my thought also but the OP provided just enough information to csuse guessing. If the contactor is marginally energized not enough to pull the contactor in and disconnect power to the coil as normally happens with a magnetically latching contactor the coil will fry.
 
Jraef said:
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Something else to look at: if you have mechanically latched contactors, the coils are typically NOT rated to be energized continuously, they are intended to be momentary pulses to open or close. Take a look at your controls to make sure someone didn't screw up.
Click to expand...
There are some mechanically held contactors on the market which the terminals are the same as and energized, de-energized exactly like a basic electrically-held relay. Internal electronics develop the pulses for the change of state. Don't recall make and model, but I do recall having run across them in research for a design-build project.
 
GoldDigger said:
A typical contactor's AC coil will draw more current when energized in the open position than it will once the armature has moved and the magnetic circuit is complete. .
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Are you sure on that?

I have had AC coils burn out because the contactor was mechanically stuck.
 
Jraef said:
Something else to look at: if you have mechanically latched contactors, the coils are typically NOT rated to be energized continuously, they are intended to be momentary pulses to open or close. Take a look at your controls to make sure someone didn't screw up.
Click to expand...

Every latched contactor I have wired had internal contacts that open the coil circuit once the contactor changes position.
 
iwire said:
Why would the coil burn up if drawing less current?
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It would burn up while drawing less current if it was intended to be momentarily energized and the break contacts failed.
But if it was stuck in the open or partially closed position it would be drawing *more* current not less.
 
GoldDigger said:
It would burn up while drawing less current if it was intended to be momentarily energized and the break contacts failed.
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It was made to be energized, it was an electrically held contactor.

But if it was stuck in the open or partially closed position it would be drawing *more* current not less.
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That is what I would expect but seems to be the opposite of what you said above.


Edit, I believe I misread your post. :)
 
I think OP needs to post some part #'s or pictures and give us some voltage readings.
All we know is his contactors are burning out coils.
Being there's more than one, I'd first guess someone put something together wrong.
As someone previously stated, fixing the problem is better than treating the symptoms.
 
coils

coils

mgookin said:
I think OP needs to post some part #'s or pictures and give us some voltage readings.
All we know is his contactors are burning out coils.
Being there's more than one, I'd first guess someone put something together wrong.
As someone previously stated, fixing the problem is better than treating the symptoms.
Click to expand...
I know that it is the surge burning them out when power comes back on its the only time it happens!!!
 
fuses

fuses

kwired said:
My bet is on this being OP's troubles. Perhaps OP needs undervoltage relay wired into the control circuit so the contactor coils are isolated when there is not full voltage.

Fuses as initially suggested might protect the coils, but will still be left with equipment not working just as frequently because of blown fuses. Find the problem, don't just treat the symptoms.
Click to expand...
we're ok with replacing fuses,no problem
 
iwire said:
I find it pretty common when only one ungrounded line is dead.

I assume it is because they end up with a under voltage backfeed of sorts through other equipment.
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Exactly correct. Undervoltage kills AC-coil contactors. If the coil is L-L, and one line is dead, the coil will see ~50% voltage by backfeeding through other loads connected to that phase. It's enough voltage to heat up the coil, but not enough to pull the armature in. Until the armature pulls in, the coil draws significantly more current with its poles open than it does when the magnetic circuit becomes "sealed." The coil typically melts, smells funny, and burns out.

Fusing won't help in this situation at all. Your two options are to use a L-N contactor; if the phase feeding it is dead, it won't work, but it won't burn up. If you must use a L-L contactor, an undervoltage release relay will protect it.

I faced this exact situation a few years ago, albeit with 3-phase power, but the protection concept should be the same:
http://www.plctalk.net/qanda/showthread.php?t=75605



SceneryDriver
 
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