How to fix an RCD fused spur that wont reset

Flooded motors can trip over current devices not because of current through the water but because the mechanical drag of the water in the motor when it starts to rotate.

The flooded motor will take longer to run up to normal speed and the prolonged start up current can trip the breaker.

It makes sense that could happen. Sorry I may have confused things by talking about 2 different things in the same post. The gate motor and flooded industrial 415V equipment were separate events.

In this case the gate motor was a small 270W motor and not direct on line, but fed through a controller that limits power into the motor in order to limit the torque the motor can generate (this is a requirement for electric gates in case someone gets trapped by the gate). Part of the commissioning procedure is to block the gate, stalling the motor and measure the force the gate exerts. So the controller is happy with a stalled motor in this situation.

As JohnW assumed correctly, the motor itself wasn't flooded, just the IP67 connector to the motor which was in the underground box next to the motor. The FCU was inside the house and dry. I went through about five 13A fuses before finding the connector was the problem. Examining rhe connector showed it was full of carbonised material, presumably where an arc had been forming between the terminals.

To me it seems odd the controller could cope with a stalled motor, but not the low resistance of the arcing connector. It’s just a guess but as impedance of an inductor increases with frequency, perhaps the controller runs the motor with a much higher frequency as the motor starts to stall (opposite to what you would normally do, but in this case the point is to reduce torque to stop people being squashed) and perhaps that allows the motor to survive a stall condition without too high a current draw?
 
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Apologies for the slow response, I have tested the external sockets and can confirm there's no power getting to them so will be replacing the fuse in the RCD tomorrow to see if that does the job.
 
So I replaced the fuse on the RCD fused spur today (with power off at the CU), and as soon as I switched on the power at the CU both the MCB and RCD on the CU tripped. I went over to the fused spur and could smell something hot and electrical so I've just popped the fuse out altogether. Guessing I've got a bigger problem on my hands...
 
You should call in an electrician to establish what's going on ,with all due respect .
 
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So I replaced the fuse on the RCD fused spur today (with power off at the CU), and as soon as I switched on the power at the CU both the MCB and RCD on the CU tripped.
That's similar to what you said originally and it wasn't the case.

As Terry says - get an electrician.
 
Sorry to revive an old thread, but similar concern for a recently fitted rcd fcu brought me to this thread. My unit has a red indicator showing, but power is still going to the sockets it serves. Yet like the OPs, mine has printed on it, “If red stays visible DO NOT USE”.
I’ve just realised, after reading through this interesting discussion, that whilst the OP clearly had a problem, I don’t think I do after all?
Presumably the warning only refers to what happens if the test button is depressed, not for the running of the unit.
As JohnW2 clarified earlier on, red just means on!
 

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