I don't think so. A switch can be ON but have no power.
If the fuse is before the innards of the RCD FCU then, presumably, the RCD has no power to work the test button.
I think upstream would be the situation. Why would it be otherwise?
How to fix an RCD fused spur that wont reset
- Thread starter ZeroTools
- Start date
If the fuse is before the innards of the RCD FCU then, presumably, the RCD has no power to work the test button.
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Sorry, I am perhaps being dim, but I still don't understand.
As I said, I would expect that the 'indicator' (red/black) would be downstream of both fuse and RCD, indicating whether or not power was coming out of the fuse/RCD combination - witness the fact that, as the OP says, what should happen is that it changes from red to black if one presses the test button. Do you agree?
If that is the case then if the device is working correctly, if the indicator is showing red this must mean that the fuse is intact and the RCD is in the 'on' state - the OP could see if this is the case by ascertaining whether power is getting to the socket(s) supplied by the RCD FCU. In that state, pressing the test button should cause the RCD to operate and for the indicator to go black. If that's not happening, then I can think of no explanation other than that the RCD is faulty, can you?
As I said, that's what I have been assuming.
Kind Regards, John
Yes.
Well, it would/does indicate that but it only indicates the position of the mechanism.
With no power going in past the blown fuse, obviously none can come out.
Yes, but he can't switch off the RCD part because it is not receiving any power.
It might as well still be in the box.
No, the fuse has removed the power.
Physically, yes, but it is receiving no power.
Yes, above.
It is no different than an RCBO which is switched on - with the Main Switch off. It won't do anything.
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Ah, that's probably been my problem - I was not thinking of it as a 'mechanical indicator' but, on reflection, that's almost certainly what it is.
Fair enough. All of that obviously assumes that the fuse has blown. I recently suggested to the OP that, in view of what had been suggested, the most obvious thing for him to do next (assuming he does not have the means of doing any testing) would be to replace the fuse - albeit there is the possibility that the replacement would immediately blow if there is a persisting fault.
He really needs to have a means of at least testing whether or not the present (and replacement, if necessary) fuse has blown - which, if he has no other means, could I suppose be done by putting the fuse into the plug of something else appropriate.
Kind Regards, John
Fair enough. If the theory about the fuse having blown is correct, then you will obviously find no power at the supplied sockets. If that's the case, then please see what I've just written (to EFLI) about fuse replacement and testing.
Kind Regards, John
What is its rating, then?
Oh the perils of replying without reading through the rest of the posts...
Just my 2p's worth - I've come across a damp connection causing a 13A fuse in a FCU to blow before. It was powering a gate motor in a box in the ground. I would not have expected it either and it caused me to replace a motor stator at over £130, assuming it had gone short circuit before I found the issue.
I eventually found the controller side of the supposedly IP67 connector had become contaminated with muddy water. The mud and proximity of the terminals seems to have caused a build up of burnt carbonised material which was evidently acting like an arc lamp inside the connector.
The terminals were very close and it had mud / silt from the soil in it not just rainwater, but maybe something similar has happened here?
I've also seen some quite unhappy 3-phase 415V equipment in a pit that flooded, so it was underwater, still live, but not very happy. Industrial setting, no RCDs and big MCCBs that just kept the power flowing...
I eventually found the controller side of the supposedly IP67 connector had become contaminated with muddy water. The mud and proximity of the terminals seems to have caused a build up of burnt carbonised material which was evidently acting like an arc lamp inside the connector.
The terminals were very close and it had mud / silt from the soil in it not just rainwater, but maybe something similar has happened here?
I've also seen some quite unhappy 3-phase 415V equipment in a pit that flooded, so it was underwater, still live, but not very happy. Industrial setting, no RCDs and big MCCBs that just kept the power flowing...
Interesting. I obviously cannot argue with your experience, by I'm very surprised, given that it needs a minimum of something like 22A to blow a 13A BS1362 fuse.
Kind Regards, John
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.
The flooded motor will take longer to run up to normal speed and the prolonged start up current can trip the breaker.
That makes sense but, as I understand it, in WhydidIstart's case, the water was in an FCU, not the motor it supplied.
Kind Regards, John
then contact corrosion creating intermittant connection could have resulted in slow acceleration of the motor. Starting current intermittant but with an average high enough to trip the brealer.
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