electric shower tripping rcd

IR test shower engine

 

Disconnect the heater wires inside the shower unit and then do an ins. test between live and neutral and the earth connection of the element or to it's casing if metal, anything less than 50 megohms or so means a duff element.
Just remembered you said a "cheap" multimeter, this probably won't have an insulation test range but might show a fault using it's resistance range, anything less than about 10 megohms will indicate a duff element.

 

Far too much stuff inside an electric shower now to prompt tracking down faults. .simply not cost effective, more than likely its the Baked Bean can inside

Remove and replace, no spark will bother with nailing a fault down on a lecky shower

Better still ditch the whole idea and get the hot water off the Immersion or Combi, electric showers are a waste of time

Sorry bud

 

Ben, I think that RCDs will trip when the cumulative leakage in yer hoosie reaches 30mA or so?

So it might be the case that there's little wrong with your shower, but the extra few mA of leakage in the cans is enough to push your RCD over t'edge.

Is that possible?

Bottom line - for a paltry 9m run, just buy some new 10mm cable and redo it. (Use the old cable to pull through the new). New isolating switch too.

If it still trips, get a sparky in to look at your house's wiring without too much delay.

 

Without having a clamp meter to hand,if the op wants to check for cumulative leakage then there's an easy way,if he isolates all the other circuits then tries the shower this would prove or disprove your theory.If it was cumulative then with other circuits isolated then it shouldn't trip.

 

Not a mission of pulling in 10mm cable using the 6mm as a draw wire, but at least the holes will be drilled and the relevant floorboards already have been lifted and put down again

 

Interesting,

This can be several things, one being a faulty shower which you seem to have ruled out.

Next is faulty wiring, you could upgrade the 6mm2 cable to 10mm2 cable and rule that out seen as you don't have a insulation tester.
You could get a spark in to test cable for insulation damage if you are so inclined.
RCD's do fail and trip well bellow their rated current so the RCD will need testing, this of course needs a RCD tester to ramp up the current until it trips so you know what it is doing in human readable terms.

You could have a fault elsewhere like @Devil's Advocate has mentioned when turning the shower on it is pushing close to the RCD's rating by adding to the residual current already existing from something else in the property. This is really only valid if you have a Split load type of CU.

I had an RCD trip issue this weekend, turned out to be a Sony phone charger that had a fault. Still worked fine in the consumers eyes but was in fact breaking down and overheating causing the RCD to trip constantly.

Goes to show why one should UNPLUG chargers when you are not charging devices.

If you want to measure a cable short circuit fault then disconnect the terminals at the shower and make sure they are not touching anything, disconnect the wires from the breaker in the CU and test with your meter probes set on continuity test(buzzer) if the buzzer sounds your cable is screwed. Do the test between brown and blue, blue and earth, brown and earth.
For the resistance of the cable you need disconnect the wires from the breaker and the showers terminal block. Use a chocblock and connect the blue and brown together(short circuit) at the shower and measure resistance back at the CU between the blue and brown you shorted out at the showers location. If the value is greater than 2 Ohm you have a cable issue due to high resistance. Do the same between neutral and earth and live and earth.

For an insulation test you need a tester capable of 500v testing. Both ends of cable need to be disconnected and not touching anything. You then apply the tester to the conductors at the consumer unit which are also disconnected and measure the value the tester gives you. It should be in MegaOhms as in above 2 MegaOhms preferably several hundred megaohms. If not your cable is poofed.

To measure residual current in the appliance earth conductors you need a clamp ammeter. This is placed around the earth conductor so one can observe how much current is actually flowing in the earth conductor. This is rarely done by a spark as electrical appliances are not something the tinker with, that is the job for the TV repair man so to speak, omitting PAT testing of course.

You can buy cheap insulation testers, they are by no means accurate but they do provide you with a reasonable value to accurately ascertain where a fault exists.

All this said, the fault may well be with the pull-cord isolation switch. They are known to melt, corrode terminals from the moisture and so on. Check the shower pull-cord and the terminals and wires connecting into it... If you don't have one then well, urm, why don't you have one?

Of course it goes without saying, i am not responsible for any of the above work you decide to attempt. You carry it out at your own risk, if in doubt get a spark to do it.

 

Absolutely brilliant advice, that's how to test without an MFT and just a multi meter.
Apart from IR of course.