Contactors tripping RCD
Contactors tripping RCD
(OP)
Hi,
I have an old resistive starter that has been overhauled. We installed 8 new 250A contactors, all with 240VAC coils. When we were testing the starter the main RCD to the board would trip when the third contactor turned on. It should be noted that we did not have the motor connected at this time - we were simply testing the starter to see if all the contactors came in at the right time.
Well, we didn't really know why this was happening so we jacked up the settings on the RCD temporarily (up to 1000mA for 3 seconds). Now we can get the 7th contactor to come in before the RCD trips.
This has me baffled. Why is the RCD tripping? Everything runs fine when the RCD isn't connected. We have to leave the RCD connected though because of a directive from the mines inspector (I won't get into that now though).
I have an old resistive starter that has been overhauled. We installed 8 new 250A contactors, all with 240VAC coils. When we were testing the starter the main RCD to the board would trip when the third contactor turned on. It should be noted that we did not have the motor connected at this time - we were simply testing the starter to see if all the contactors came in at the right time.
Well, we didn't really know why this was happening so we jacked up the settings on the RCD temporarily (up to 1000mA for 3 seconds). Now we can get the 7th contactor to come in before the RCD trips.
This has me baffled. Why is the RCD tripping? Everything runs fine when the RCD isn't connected. We have to leave the RCD connected though because of a directive from the mines inspector (I won't get into that now though).





RE: Contactors tripping RCD
Do the contactor coils have suppressors by any chance?
RE: Contactors tripping RCD
"Will work for (the memory of) salami"
RE: Contactors tripping RCD
Bill
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"Why not the best?"
Jimmy Carter
RE: Contactors tripping RCD
I am an engineer, so the glass is twice as big as it needs to be.
RE: Contactors tripping RCD
After looking more closely I suspect it may be related to a bad installation. Because they had to fit this to an existing board, they have used a huge CT to fit around the busbars, and one of the phases is much closer to the inside edge of the CT while the other two are in the middle.
At this point we have just turned the RCD off. It's actually not in our standards or regulations that we need to have it on this circuit.