Guess the fault

[p11jor]

Had a call out late last night, everytime the shower comes in it's blows the whole house.

The set up of the board is duel rcd. 2 mcb either side.

Cooker/shower on left

Lights/sockets on right



So the power to the shower switch is fine, again this can function fine and send power to the shower, bit as soon as the shower is pressed is wipes both rcds straight out after 2seconds.

I did a insulation resistance test, was getting 0.25megohms.
Removed tge switch and was getting 459megohms. So thought new switch, put new switch on and still wiping the whole board out, but obviously were not getting a dead short as the power to the shower is fine untill pressed.

Quite interesting this one. But such a obvious one which I will always look out for on my future PIRs

 

[Octopus]

What has the customer been meddling with?

 

[miner69er]

If it's taking out both RCD's then there cannot be any discrimination between them, ie. there is a common point between them. Are the circuits correctly fitted to correct sides of board, more to the point the nuetrals as this would not trip until power runs through the appliance. i know this seems like a daft suggestion but to take out both RCD's there has to be some kind of connection between them.... And the number of customers that try to do their own work without the faintest idea is gobsmacking, always remember they may have been in the board before you..!!

 

[miner69er]

Murdoch, your fingers type faster than mine........

 

[Octopus]

With only 4MCB's its not exactly ideal that the lights and sockets are on the same side is it!

 

[JUD]

If it's taking out both RCD's then there cannot be any discrimination between them, ie. there is a common point between them. Are the circuits correctly fitted to correct sides of board, more to the point the nuetrals as this would not trip until power runs through the appliance. i know this seems like a daft suggestion but to take out both RCD's there has to be some kind of connection between them.... And the number of customers that try to do their own work without the faintest idea is gobsmacking, always remember they may have been in the board before you..!!

Agree. Shower neutral connected to wrong neutral bar in CU.

 

[telectrix]

has a plumber fitted the shower?

 

[keefy]

Common neutral somehow? Maybe the bonding in the bathroom not connected correctly?

Intrigued...

 

[Octopus]

Agree. Shower neutral connected to wrong neutral bar in CU.

I thought of that but the inference of the post that a fault had developed and I've yet to see a CU rewire itself!

 

[p11jor]

It's was guys, the bus bar there was only a 6mm separation between them and as soon as my mate pressed the shower the Lecky jumped from one bus bar to another, And wiped the whole board out.

Snipped it back....jobs a gooden!

 

[Octopus]

Can't quite see how that would suddenly become an issue.

Out of interest did you put the sockets and lights on different RCD's while you were there?

 

[Engineer54]

How does 230/240 volts jump 6mm ?? Where is the CU located, must be in dammed humid location?

 

[p11jor]

Don't take that 6mm as a set in stone measurement (as you know diy and poor sparks put them in and they angle slightly, again I taken a measurement from the bottom of the bus bar so it may of been 2mm at the top) I didn't care it was late, dark I found the fault so was made up to fix it and go home without measureing the degree of angle it was on......but whatever it was they were not touching and with it being dark I could see tge jump of 230/240 to the next bar.

I don't kno why all of a sudden this has happened but he had been away and he bought a cooker that was fitted when he was away, there is a 6mm supply for this but the new cooker was just gas range with a ignition, so apparently they swapped the cooker plate behind the over for a fuse spare and ut a 3amp fuse and wired the 1mm flex in the fuse spare.....don't see any reason for them to be in the board though???

Also as tge house is a 2 up 2 down there is only 1 circuit for sockets and one circuit for lights, 12 sockets, 6 lights, I didn't see tge need in swapping these over, as 1 I didn't install it and two it was dark, late, and not my install.

 

[Knobhead]

2000V to jump 10mm, but you need at least 750V for spark propagation in dry air.

 

[pmac10]

i'm no expert but i thought RCDs only protected against earth path faults?