Resistance / Voltage Drop Across a Contactor
Resistance / Voltage Drop Across a Contactor
(OP)
What is an acceptable level of voltage drop across the line and load side of a motor contactor? Is there an IEEE standard or manufacturer recommendation on this?






RE: Resistance / Voltage Drop Across a Contactor
In the absence of this data, you can derive some useful information from checking like equipment, i.e., you have three contactors, two of which have contact resistance in the 60-70 microohm range and one with readings in the 2-300 range. You'd be wise to suspect a problem with that errant unit assuming it is indeed the same rating for current and voltage. The same goes for each of the contacts in the contactor. If one diverges from the other by more than 50%, then it is suspect.
Lastly, on legacy (read 'so old nobody's seen a manual in decades') equipment, look at the I^2*R loss across the contactor. I always operated on the supposition that if an air-breaker contactor had more than 25 watts loss at rated current, there was going to be an issue due to the equipment's ability to deal with heat in the contact assembly.
Some air-break contactors have a bad characteristic of contacts 'glazing' over with an oxidized layer that renders high readings at the low voltages that test equipment uses. Proper cleaning will often correct this problem.
old field guy
RE: Resistance / Voltage Drop Across a Contactor
RE: Resistance / Voltage Drop Across a Contactor
Note that a brand-new contactor won't meet this on first bang. It's gotta clean itself under load.
Best to you,
Goober Dave
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RE: Resistance / Voltage Drop Across a Contactor
Is it because you are concerned over a 'bad' contact? Or?
Maybe better would be to consider what the RESULT of that bad contact would offer you in clues.....
Assuming you can even find a milliohm spec at YOUR particular voltage and current, why not instead just buy a $25 IR thermal gun and point it at the contact?
I believe this may be the bottom line; if the contact is not 'good enough,' the much higher temp than ambient will tell you there is a 'bad' contact issue.....
www.KilroyWasHere<dot>com
RE: Resistance / Voltage Drop Across a Contactor
"Will work for (the memory of) salami"