Is my electric shower about to fail?

[Dave]

Our Triton electric shower trips the mcb after about 3 minutes use. (Fed via a combined mcb and rcb). The shower is about 12 months old and been working fine until now. I have no way of measuring the actual current. The mcb casing is quite warm so I guess real overcurrent is the problem - rather than a fault in the in mcb? There is no sign of air in the water supply. Is the above a typical failure mode for an electric shower - is it about to go BANG! The cable and double-pole ceiling switch are the only other things in the circuit. Wonder when the guarantee is up (sigh) :-) Thanks

[BigWallop]

Hi Dave,

It sounds like a tired MCB with all the work it's been doing. Check that all the connections are tightened fully and that all the cable isn't damaged or squeezed to tightly anywhere. If that checks out OK, then try upping to the MCB to the next one up in Amperage and see how that goes. It could just be that you're working that breaker at its full load capacity every time you use the shower.

[Chris Oates]

what's the MCB rate at ? how many kilowatts is the shower ?

[Dave]

It's marker B40 - and shower is 9.6kW. The booklet that came with it says use mcb 40/45A. Think I've found the trouble though. The copper link that feeds into the mcb has cracked through but was still making some sort of contact. The heat generated has melted some mcb case (!) All is isolated now and I'm off to get some new parts tomorrow. I think the copper link cracked as it was folded at quite an angle there.

[Chris Oates]

MCB rating is right on the limit (9.6Kw = 40Amps)

That usually means the MCB wasn't attached to the DIN rail properly. You need to look at the cable, it should be 10mm with a 45Amp MCB While shopping buy an RCD if you haven't already got one.