problem with electic shower

[Richardp]

HI! I have a shower which has been working fine for years on a 6mm cable from a 32amp fuse no probs until now, it keeps tripping on the mcb so I changed the wiring to 10ml and replaced the msb (another 32amp} and put in a new 2pole switch for good measure but it still trips?? I've ordered a 40amp mcb which should solve the problem but still have one in another room just the same as this one ( 32amp 6mm cable) working fine. so what do you think the problem is????p.s I've checked the earth connections no probs there, the cable run is 4mtrs.
any advice will be gratefully received

 

[BR]

There are many possibilities here. Replacing the cable was probably not required, a simple test could have confirmed this. The problem most likely lies with the shower unit itself. If this is the case it needs to be replaced, servicing/repairing these units is uneconomical. Please answer the questions below in order to help diagnose the problem.

Up rating the breaker to 40A, although reasonably safe to do so with 6mmsq, is not the solution.

When exactly does the MCB trip? Does it trip when the pull cord is at off or only when at on. Then does does it only trip when the shower unit itself is switched on?

What is the rating of the shower (if known)

Does the breaker trip immediately (possibly with a flash inside the breaker when it is reset) or do this sometimes take a period of time.

 

[Richardp]

OK , I've put a new 10kw shower unit in and its still trips, its lasts about 10mins before it trips, its got a 2pole switch inline and trips on the mcb, the unit has 2 setting high and low, I can get a shower out of the low setting without it tripping.

 

[BR]

What is this? A joke? It was a 9.5KW 5 minutes ago that had be there for "several years".

What you speak of here sounds very much like an overload. You should really have 10mmsq cable protected with a 45A MCB.

BUT, you really need to clarify all this, and do it HERE, in THIS topic PLEASE

 

[Richardp]

OK tonight whilst posting these messages I have been working on my shower, I put a new unit in which happens to be a 10kw one whilst the one I removed was 9.5kw, I have also put in a new 10mm cable the old one was 6mm hope this clears things up!!!
In another room in our house we have another 9.5kw with a 6mm cable into a 32amp Breaker which works well.

 

[BR]

Now were getting somewhere Your on the right track just one more question. Did the shower which you removed, the 9.5KW work properly

 

[Richardp]

It would work for about ten minits and then throw the trip but the new one also trips so I guess the old one was possible still good (its only a couple of years old)

 

[BR]

OK, You have a 10KW shower and 10mmsq cable from the CU to the DP ceiling switch and another run of 10mmsq from this switch to the new shower.

I immagine your problem here is that the MCB is simply underrated (too small) You should have a 45A MCB installed here for your new shower and your old one should have had at least a 40A.

for TEST PURPOSES ONLY you could switch the cable at the CU to another breaker rated at 45A or above. This will confirm that the problem is that the breaker is simply underrated and all you need to do is replace this for a 45A.

It is very important with such a high energy circuit that ALL terminals are fully tightened (as much as possible without getting a vice grips!)

 

[securespark]

I think the problem here is one I see many times.

Scenario: an old 7kW shower wired through a BS3036 (re-wireable fuse) is replaced.

The fuse allows an overload, as 3036 fuses do, but now you've changed to an mcb which is far less tolerant of such a large overload (it takes a 3036 fuse approx 2x its rated current to blow instantaneously).

Hence the mcb is tripping quite quickly.

I cannot guarantee that you don't have a fault somewhere, but from where I'm sitting it looks like as I have outlined above.

9.5 showers should not be run through a 32Amp breaker as the current is 41.3Amps If it has never tripped, then either it is welded into the on position, or you are using a reduced power setting.

 

[Richardp]

Well your almost right! the original shower was 7.5kw which at the time recommended a 32amp fuse and 6mm cable, since then the unit has changed twice to higher amps but the cable and fuse has remained the same which no problems until now, as I said, the one in the other room with 9.5kw and 6mm cable to 32amp is still working fine??.
so if I now acquire a 40 amp mcb that should solve the problem, thank you all for your advice.