New MCB will not re-set

[bernardgreen]

They normally fail because of their location and debris falling into mechanism or a loose connection!

But frequent switching of a load is also a factor in why they fail. There is good reason for them being described as an isolator and not as a switch.

I cannot find quoted life times for isolators ( can't be bothered to spend time looking )

but as an example this is the quoted lifetime of a MK switch ( Logic Plus™ plateswitches that comply with BS EN 60669-1: 1999

Operational testing (all plateswitches ):
tested to 100,000 operations for mechanical life
tested to 40,000 operations at 10 amp rating
tested to 10,000 operations at 20 amp rating

 

[Taylortwocities]

A picture may help!

Need to see what it is that has tripped. Pop a photo on here, it may be an easy fix!

 

[JohnD]

In the circumstances described, I have a feeling the heating element(s) may have boiled dry often enough for the sheath to have cracked, which would trip the RCD. Can't see why it won't reset, though, if the isolator is off. Perhaps it's SP. A photo will help. Otherwise, what are the words and numbers on the thing that has tripped?

MEM RCDs, for example, have to be pushed fully to the "off" position before they can be turned back "on"

 

[Doggit]

It won't reset John because the Showers still turned on; it's being turning on and off at the pull cord.

 

[JohnD]

, if the isolator is off.

 

[Taylortwocities]

It won't reset John

but we do not know what the "it" is

the OP has an

additional Mcb unit

in this there may be a single RCBO, or there may be an RCD and/or an MCB

we need to know what it is that has tripped and cannot be reset.

 

[PrenticeBoyofDerry]

But frequent switching of a load is also a factor in why they fail. There is good reason for them being described as an isolator and not as a switch.

Please read carefully the transaction between what I said and what Midas Man said.
I never mentioned or indicated that the iso should used as a switch, only that it is common practice that after showering with shower flow turned off, that people including my family remove power at the isolator. Whether this be that they feel safer or feel they are saving money or not wasting electric, is a question for each individual!
This procedure would not dramatically reduce the lifespan of the isolator, in fact it could be argued that it would keep contact cleaner and prevent them from seizing up!
My argument/debate is not about it being used to switch the shower, while a load demand is in use.

So I stand by my claim/opinion: "Complete Tosh"

 

[bernardgreen]

So I stand by my claim/opinion: "Complete Tosh"

Isolators do have a quoted life time of how many operations before the mechanism becomes un-reliable and that life time has nothing to do with errosion of contacts due to arcing when breaking a load current. Because it is classed as an isolator it has to ensure that operation to the OFF state will break the contact so the construction is somewhat different to a normal switch. If a normal switch on an appliance fails in the ON position then the appliance can be ( or should be ) isolated by un-plugging or switching OFF the MCB or, in the case of a shower ,operating the isolator.

The other reason why frequent operation of a domestic shower isolator can result in premature failure is that the vibration generated when the isolator operates can affect the screw terminals leading to reduction of pressure and subsequent heating of the terminals. This is more prevalent in high current isolators due to the stiffness of the 6 or 10 mm² conductors

 

[JohnW2]

Isolators do have a quoted life time of how many operations before the mechanism becomes un-reliable and that life time has nothing to do with erosion of contacts due to arcing when breaking a load current.

Indeed - that's obviously true of anything mechanical, but I suspect that the mechanical life is likley to be of the same order as the 100,000 (off-load) operations you mentioned for MK plate switches. At, say, four operations per day for a shower isolator, that would amount to around 70 years' life.

Kind Regards, John

 

[PrenticeBoyofDerry]

So I stand by my claim/opinion: "Complete Tosh"

Isolators do have a quoted life time of how many operations before the mechanism becomes un-reliable and that life time has nothing to do with errosion of contacts due to arcing when breaking a load current.

Everything has an expected lifespan (even Bruce Forsyth!)

The operation of a shower isolator from the on to off position when off load after showering, will not dramatically reduce that and is not "the very reason pull cords fail prematurely"as quoted by Midas Man!

 

[EFLImpudence]

I agree with PBoD.

Isn't it only us who are calling them 'isolators'?
Are they not just described as 'switches' by the manufactures?

Whilst not actually required by the regulations as an 'isolator', if people want to switch them off, that is up to them.
Switching them on-load may be detrimental to the shower and so the problem should not really arise but, again, if the owner wants to do it and have it replaced more frequently, that is up to them.

 

[JohnW2]

Isn't it only us who are calling them 'isolators'? Are they not just described as 'switches' by the manufactures?

Indeed so. AFAICS, nearly all manufacturers describe all their high current DP switches as 'Switches'. Ironically, one of the few accessories which is widely described as an 'Isolator' is the 3-pole 'fan isolator' (maybe because, as normally wired, it could not be used as a functional switch?).

Kind Regards, John

 

[garash]

As said earlier, when you switch off an electric shower (a modern one at least) they'll run the cold through for a few seconds to cool down the heating unit. By turning off the shower from the pull cord, this isn't happening, so it may well have killed the shower prematurely, hence the MCB won't reset whilst the shower is still switched on. Have you tried turning the shower itself off, then then resetting the MCB yet.

If the shower has failed, then replacing it with a digital shower that has the control switch outside the shower may be the way to go next.

Thanks - that could be the answer. We have tried turning the shower

 

[garash]

Hi Everyone, just to let you all know the shower is now working again. It turned out to be a blown 30amp old cylinder type fuse in the old fuse box. We thoiught that the new 45 amp
RCB/MCB fitted was going straight to the shower unit but apparently that was not the case. Thank you all again for your replies.

 

[Taylortwocities]

Hi Everyone, just to let you all know the shower is now working again. It turned out to be a blown 30amp old cylinder type fuse in the old fuse box. We thoiught that the new 45 amp
RCB/MCB fitted was going straight to the shower unit but apparently that was not the case. Thank you all again for your replies.

Thatnks for the update.

What steps are you taking to stop this happening again? If the 30A fuse has blown it sounds like the circuit has not been sized properly for the shower.
Do you know how many KW the shower is rated for?