Can a Shower MCB cut out for just a few seconds?

Twice this morning in my electric shower (Triton T80), the water flow stopped suddenly as if switched off. I then turned the shower's own switch off as a precaution, and got out of the shower to look at the isolator pull-switch.

Both times, the red neon power light had gone out, but came back on again as I watched in seconds. Both times, I then switched the shower back on again to work normally. All lights, radios, and a mains powered PC remained on throughout, the latter would normally crash in an instant with mains failure. So I can't blame a local power glitch.

So I don't see I can blame the shower, it seems a supply issue. But the MCB (Wylex B40) remained untripped throughout, as did all other MCBs. There are no RCDs in this system.

Can someone explain how the shower supply can seemingly switch off for a few seconds, then return normally without intervention. Can an MCB, perhaps faulty, do this somehow?

 

state it - thanks for the advice, I'll check this as soon as I'm back home (had to nip out).

Would the terminals at the consumer unit be equally suspect, or is it there some reason the isolater pull switch is more prone to overheating or arcing, like Bathroom steam/condensation?

 

So I suppose the lack of space plus the fact the switch has to be pushed back into the pattress after wiring, adds to the strain on the terminals.

But why more often the neutral? That sounds strange?

 

Unphased - thanks for your vote of agreement.

Assuming the shower isolator is to blame, is it normal to find the wires burned up a bit, and in need of cutting back? Or is just tightening or wiring straight into a new isolator ever possible or wise?

 

OK, job done. It was as you all wisely said, the ceiling isolator pull-switch.

The Live (out) wire had clearly overheated insulation for an inch or two coming out of the isolator. On taking the old one off, all wires were still tightly clamped, including the faulty Live (out) terminal, the area around which showed clear signs of overheating/burning/cracking. That screw terminal was especially tight all the way out, as if the thread was partly heat-welded.

If I can't blame loose/arcing screw terminals, I have to assume something just inside the isolator, like a spot welded copper strip, had been the source of the heat and that this slowly cooked the screw terminal and attached Live wire? Is that likely?

Anyway, there was just enough slack, as unphased said, to cut back a few inches to unharmed wire. I just hope I don't have to replace this one!

Cheers again everyone for your accurate help!

 

Any tips for doing this? The problem of course is having to twist the wired-in Isolator to access the far/rear screw terminals likely to be up against a wall. Every time you disturb it to check tightness, you fear it may loosen as twist it all back in place again.

Thinking about it, should I treat this like a car mechanics problem and get a 1/4" drive ratchet handle and screw bit around the far side? As far as tightness of terminals goes, I've always felt I over did it at the risk of causing problem, like damaging threads etc. Is that irrelevant on connections this heavy?

One other daft thought: How about holding a portable AM radio near the isolator whilst under load. I seem to remember arcing causes lots of radio interference?

 

Bazza-spark - interesting what you say, i.e. never turn it off. I always thought it was pretty dim as a safety device. If you're in the shower getting electrocuted, you're probably too busy to pop out and pull the switch. If you're loved one is likewise afflicted, the response time to rush in and pull the cord is pretty hopeless. If it's for maintenance only, how about just throwing the breaker down at the consumer unit? Seems a fair case for omitting the isolator completely, but for the regs.

 

Bazza-spark - yes always have used it. Don't most people? Just assumed it was there for a reason, without considering it much. But yes agree, the shower has plenty of safety disconnects of its own to sit happily live but off.

State-it - your comment made me smile. Half the electricians warn of the dangers of loose connections overheating. The other half warn like you of stripped threads from overtightening. Meanwhile, almost no-one seems to suggest torque wrench use, with many fittings not even having recommended settings.

It's kind of hard to know what to do for best...