Electrics tripping

[John D v2.0]

So that's probably added about 0.3 ohms to the loop thus possibly halfing the current. Although even with 1.2 ohm total it should still trip a b40, and I assume your ring is on a b32.
Not conclusive but my money's still on the toilet. Is the heating element removable? Did you check it when you dismantled it? Does the dimming happen when it's heating or pumping? What happens if you disconnect the pump/heating element as applicable and run it (safety first - make sure the unplugged cables are unable to touch anything and wrapped with insulating tape, and the unit is closed up)

 

[m0t]

The heating element isn't removable as far as I could see. There wasn't anything obviously wrong with it although it's in water so I assume the bit I can see is not the actual element but a coil that it sits in.

It was causing the flickering in use so both the heating and pumping were going on. Not flickering when on but not in use.

I'll try and disconnect the pump and heater tonight.

 

[John D v2.0]

Just before that, normal your vac will affect the lights a little, or any powerful motor, or even a kettle. Try switching them on and off and see if the light is affected a lot.
The toilet power level will be reasonably high, and it could still feasibly be just a high power appliance combined with faulty wiring.
Try plugging other high power devices into the toilet socket as well, see what effect it has. For precaution don't touch any metal while you're trying the item that's plugged in.

 

[Taylortwocities]

Whatever, the fault is large enough to trip a 40A MCB! A loose connection means less current, not more.
A loose connection usually doesn't trip an RCD.

My bet is not on the seat. Don't mess with it. Leave it connected to the extension lead for a couple of weeks. If all is OK it's time to look at the fixed wiring.

 

[John D v2.0]

@Taylortwocities I was meaning the flickering specifically, but agreed there is another issue. I don't think any loose connection would explain the trip, but I'm happy to believe there are two faults.

So far we know the problem is with the toilet or its wiring upstream up to the fuse that blew in the fcu, but what I don't understand is how faulty wiring would only cause a trip when an appliance is in use?
Is there a small heating of the cores causing them to move closer together? If it's not the toilet Perhaps the OP should check the wiring between the waterproof socket and the fcu?

 

[dobby1]

I would like to see a pic of the FCU wiring if possible. Do you happen to have a clamp meter laying around by any chance? That could aid in establishing current flow during operation.

Also, why don't you get a spark in to diagnose it? We're all throwing stones in the dark as it currently stands.

 

[m0t]

I had my kettle plugged into the socket last night and made a few cups of tea without issue.

I found some 'damage' to several of the solder points on one of the pcbs in the toilet last night. It looks like some brown liquid has started seeping out of them. I tried to get a photo but the pcb is inside a waterproof plastic bag and it is proving tricky.

I wasn't allowed to do much other testing as we had someone round so not really a good idea to try and plunge the place into darkness.

Both times it tripped were after a shower. Although there's no water leak I can't help but wonder if the moisture in the air is somehow impacting it?

I'll try and get pictures of the FCU wiring. I think we are leaning towards pulling the t&e cable and replacing it at this rate.

 

[Taylortwocities]

What else does this 40A circuit also power? The shower, maybe?

 

[John D v2.0]

I can't see the brown but it could just be flux residue from when it was soldered. Especially If they didn't clean the board after soldering a manual component at the end, that would explain it. If it were black/sooty marks it would be noteworthy.
After shower would be significant if it were just the RCD tripping, but I just can't imagine what's happening with water otherwise. Others will be along with more suggestions I'm sure!

 

[m0t]

What else does this 40A circuit also power? The shower, maybe?

Nothing. The shower is not electric.

 

[m0t]

I can't see the brown but it could just be flux residue from when it was soldered. Especially If they didn't clean the board after soldering a manual component at the end, that would explain it. If it were black/sooty marks it would be noteworthy.
After shower would be significant if it were just the RCD tripping, but I just can't imagine what's happening with water otherwise. Others will be along with more suggestions I'm sure!

The big problem with inspecting anything is that most of the electrics apart from that board are encased in a jelly like substance for waterproofing. I can't see the back of the board where the power supply connects and most of the rest of the components can't be got at without destroying things.

 

[stillp]

There is no point in inspecting the innards of the toilet seat. The fault is almost certainly in the wiring at the socket or between the socket and the FCU.

 

[m0t]

I think I got sidetracked by the flickering lights when the seat was on.

I've bought a new FCU and will try to fit tomorrow afternoon. I needed one anyway because I managed to crack the faceplate at the weekend when investigating it.

I've got quite a lot of t&e in the loft so might just replace the cable. I'm not sure I'll be able to get the old one out and inspect it. I think it might be clipped to the joists and I wouldn't be able to get to it without pulling the tiles.

I can route the replacement by taking up some boards under the bath.

Total cost to hopefully fix is about £15.

 

[m0t]

 

[stillp]

That looks more like a probable cause! Where was that?