Fuse box tripping after new floor put down

[Notsohandymike]

Put down laminate flooring in two rooms and prior to starting we screwed down a few loose floor boards to secure floor. Now both rooms are all fully completed when the shower is switched on the RCD trips at fuse box. I have clearly a screwed through the shower supply.

here’s the question, how do I find the wire I have shorted out with the screw? Both floors down and not a clue where it could be shorting.

Thanks in advance

 

[MeldrewsMate]

Oh bu**er!

Assuming this is an electric (8kW+) shower.

There is no way that I know of to locate the damaged cable, but there may be a way to estimate how far down the cable the damage is.
Firstly, and with regard to everyone else in the house, do this when there's only you and one other there - someone to isolate the mains if you go wrong!
1. Turn off and disconnect the cable to the shower at the consumer unit (the 'fuse box').
2. Disconnect the same cable at the shower isolator switch.
3. Using a sensitive multimeter measure the resistance between L & N, L & E, and N & E. whichever has the low value (fractions of an Ohm rather than thousands of Ohm) is the pair with the screw in between them.
4. Measure and record this low value.
5. Measure and record the same pair's resistance from the other end of the cable.
6. The distance down the cable is the ratio of these two values x the cable length. As to which route the cable takes, that's anyone's guess, but thick cables (10mm²?) are expensive so as direct a route as possible is expected.

Good luck; aside from lifting the floor it's very much an estimating game.

 

[Deleted member 174758]

Neat solution!

 

[bernardgreen]

I have clearly a screwed through the shower supply.

it may not be the shower cable that has been damaged

the shower is switched on

Which switch are you turning ON when the RCD trips the control on the shower unit or the isolator switch.

If the RCD trips when the control on the shower unit is switched ON then the damaged cable could be a Neutral to Earth fault on any of the circuits that the RCD protects.

If the RCD trips when the isolator is switched ON and the control is still OFF then it is almost certain damage to the cable between the isolator and the shower.

 

[mrrusty]

Isolate the cable. If the fault goes away, you know which one it is. Choice then rip floor up or find a way to run a substitute cable.

 

[Brigadier]

If it's first floor, it might be less problematic to go through the (plasterboard?) ceilings below, and patch and repaint them.

 

[Harry Bloomfield]

3. Using a sensitive multimeter measure the resistance between L & N, L & E, and N & E. whichever has the low value (fractions of an Ohm rather than thousands of Ohm) is the pair with the screw in between them.

He would need an incredibly sensitive instrument, to be able to do that. One able to measure micro-ohms.

Another way, but more labour intensive is to disconnect the cable at the consumer unit, connect L+N+E all to one end of a continuity meter with an audio output, the other you go around and test each screw in turn for one which bleeps the meter.

 

[alex mills]

What about one of those stud/cable detectors to trace the cable's route then it's a matter of trial and error?
Or an electricians screwdriver and check each screw or nail to find the live one?

 

[whall3y]

and test each screw in turn for one which bleeps the meter.

Which means OP needs to take up flooring of course

 

[Harry Bloomfield]

Which means OP needs to take up flooring of course

The only way, it will have to come up anyway, to repair the damaged cable.

Though I might be inclined to try a Meggar first, if the under floor is accessible. One probe connected to cable end, the other on a wander lead with a sharp probe on the end - Perce sharp probe at various points into what ever wood work can be accessed, to trace the lowest value of resistance, which is where the cable has been damaged. There might be more than one such point of damage, if he is unlucky.