Replacing 32a mcb with a 40a

[EFLImpudence]

The only consistent and true advice in this thread is that an electrician (or anyone who knows what to do) should inspect the circuit.

Whilst it may have been non-compliant in the first place with a 32A MCB, 4mm² cable in method C would have been acceptable.
The current drawn is and has been the current drawn and the cable is still there.
The replacement with a 9.5kW shower should not have been done.

As it stands now, if inspected and found to be 6mm², method B or C, then the MCB rating can be increased.
Obviously 40A would be used - but subject to fault current being acceptable it does not matter if it were higher.



To be pedantic, 8.5kw @ 240V = 34A @ 230V and 32A x 1.13 = 36A.
Allowing for the time factor, the original installer may have considered this compliant and indeed used 4mm².
This would be far less onerous for the 32A MCB than a large cooker circuit which is perfectly compliant.


So, we don't know. Someone knowledgeable must inspect.

The only definite fault is the replacement with a larger a shower.

 

[securespark]

I suspect that even 'cowboys' probably don't often wire showers in 4mm² cable

There are a large number of showers out there (or at least the original cabling) installed in the days when 6-7kW was the norm for a shower: they are wired in 4 milli.

And as we all know, over the years, the unit gets swapped out, each installer failing to notice (or care) what size the cable is.

 

[JohnW2]

I suspect that even 'cowboys' probably don't often wire showers in 4mm² cable

There are a large number of showers out there (or at least the original cabling) installed in the days when 6-7kW was the norm for a shower: they are wired in 4 milli.

I'm sure that's true. However, I was talking 'in context'. We're talking about an (8.5kW) shower which was installed 3 years ago in a then newly-built extension (not about 'ancient history') and one imagines that it was a new circuit at that time. I still doubt that, 3 years ago, anyone would have installed a 4mm² shower circuit, even if it were adequate for the shower installed at the time - but maybe I'm wrong!!

Whatever, we are all agreed that the circuit needs to be investigated, particularly in relation to determining what cable has been used.

Kind Regards, John

 

[scousespark]

In answer to John

I first saw this when Eric posted his advice and meant to reply then, but was too busy. Your posts were added after I saw the thread.

I don't have it in for you or anybody and my post was made only to point out that there were not enough facts in the thread to lead to any assumptions.
You have said that you write or have responsibility for reports in the the health sector and I would assume you get 'all' the facts before you make assumptions. The only known fact is that here was a 32A MCB and the shower installer has upped the elements to 9.5Kw. He then told Rob his 32A MCB was probably shot and he should get a 40A MCB. The cable may be 6mm, but there's nothing known to back up your assumption that this is likely to be the case.

JohnW2 said: ↑
That may well be true, but I'm not sure that we should be advising (or even suggesting) that anyone should deliberately overload an MCB (even if the cable is adequately protected) - not the least because it is non-compliant with regulations.
... and I'm a little surprised that even you should criticise me for any of that!

Read more: //www.diynot.com/diy/threads/replacing-32a-mcb-with-a-40a.455568/#ixzz43kDdL0wy

The above was buried in your last reply and I had posted a similar reply to Eric. Sorry for the confusion.

I don't understand your apparent need to always be right. If Rob had called me with what he's posted, my reply would have been "I will come and have a look", and definitely not "the shower guy is probably right and the cable will likely be 6mm, so I just need to fit the 40A MCB and switch it on for you"

 

[endecotp]

I don't understand your apparent need to always be right.

Have you discovered the Ignore button yet?

 

[scousespark]

I come across 2 approaches to shower installs.
1 The standard design is applied and the MCB/Cable are selected directly in relation to the load.
2 The rule of thumb is applied with 40A MCB/6mm cable (up to 9.5Kw) or 50A MCB/10mm (up to 10.5Kw) and these combinations allow for future shower upgrades.

Given Rob has said he's not strong on electrics, it is possible that the original shower was rated at 7.5Kw (as we are playing guess what I have).
I'd also say the first check should be an IR test, rather than measuring the size of the cable, as Rob has said the MCB trips instantly.

 

[JohnW2]

You have said that you write or have responsibility for reports in the the health sector and I would assume you get 'all' the facts before you make assumptions.

It's true that some of the work I do relates to "the health sector", but a fair bit isn't. No matter what the field, my opinion is often sought on what I feel is the likely interpretation on the basis of "all available information" - and the nature of things is such that amount of information which is 'available' is often sadly lacking, leaving me to make the best judgement I can on the basis of what is available (what you call 'guessing and assuming')

The cable may be 6mm, but there's nothing known to back up your assumption that this is likely to be the case.

No facts relating the the installation in question, I agree (although the OP did say that he 'thought' it was 6mm² cable!). My persdonal opinion remains that it is 'pretty unlikely' that anyone would have installed a 4mm shower circuit just 3 years ago, let alone for an 8.5kW shower.

I don't think that you can really criticise me for the advice that I (and others) have given - that an electrician needs to investigate and determine whether the cable is suitable for an 8.5 kW shower and whether it would be possible to uprate the MCB to 40A. You seem to be fussing only because I added my (possibly wrong) opinion as to what I felt would be the likely outcome of that investigation. Since you seem to like talking about "the health sector" ... if I met someone exhibiting symptoms which might just possibly (but, IMO, not very likely) be indicative of a serious illness, I would certainly advise them to consult their doctor and get 'checked out', but I might well also add my view that the 'checking out' probably would not reveal a serious problem.

The above was buried in your last reply and I had posted a similar reply to Eric. Sorry for the confusion.

I'm not sure what you mean by 'buried in my last reply', and I think you have got the wrong tense when you write "I had posted a similar reply" - your "similar reply" was posted 7 days after mine!!

I don't understand your apparent need to always be right.

And, in turn, I don't understand why you think that is the case. I'm often wrong, and certainly acknowledge that such may be the case. Given the extent to which you apparently scrutinise my posts, I would have expected you to have seen how frequently I add something like "...but I may be wrong" to things I write.

Kind Regards, John

 

[JohnW2]

I don't understand your apparent need to always be right.

Have you discovered the Ignore button yet?

I don't think that would suit him at all. He appears here very occasionally and nearly always finds a recent post of mine to attempt to 'tear to pieces'. If he used the Ignore button on me, he would be denied whatever pleasure or satisfaction he gets by so doing!

Kind Regards, John

 

[JohnW2]

Given Rob has said he's not strong on electrics, it is possible that the original shower was rated at 7.5Kw (as we are playing guess what I have).

My understand of his OP is that the present shower IS the "original" (8.5kW) one, installed 3 years ago in a newly-built extension (which strongly suggests a new circuit). Are you suggesting that he has misunderstood the power rating of his shower?

Kind Regards, John

 

[scousespark]

I don't understand your apparent need to always be right.

Have you discovered the Ignore button yet?

I don't think that would suit him at all. He appears here very occasionally and nearly always finds a recent post of mine to attempt to 'tear to pieces'. If he used the Ignore button on me, he would be denied whatever pleasure or satisfaction he gets by so doing!

Kind Regards, John

Sorry boys, have I upset you. I hardly think I'm tearing John apart and I don't find internet chat a source of pleasure or satisfaction.
Is it a forum rule to only post when you agree with somebody.

 

[JohnW2]

Is it a forum rule to only post when you agree with somebody.

Obviously not, but human nature being what it is, I would obviously feel a bit happier if it was not nearly always me with whom you appear to choose to publicly disagree on the relatively infrequent occasions you visit the forum!

Cheers, John

 

[scousespark]

Firstly, I was critical of Eric and didn't see your reply (which was very similar to mine - and much earlier).
Second, I am not prying into your professional status and was pointing out that you'd get all (or as amany as possible) facts before stating assumptions.
The only way to do this, in the context of the thread, is to inspect/test the circuit. You had agreed with that and I had no comment there.

I made an observation that there is nothing in this thread to support an asumption that the cable will likely be 6mm. The electrician who Rob calls will (most probably) have no knowledge of the circuit. It may be the case that fitting a 40A MCB sorts the problem, but it might not. That was all I pointed out. I am not trying to 'tear you apart' and my interest in this thread came when Eric advised to fit the MCB and replace it when it failed in a few years.

 

[ban-all-sheds]

I made an observation that there is nothing in this thread to support an asumption that the cable will likely be 6mm.

How likely do you think it is that 3 years ago an electrician would have installed 4mm² for a shower circuit?

 

[kai]

Extremely unlikely, as in 2013 the typical shower circuit was run in ten mm cable on a 40amp breaker (most dedicated shower consumer units of that era had a B40 breaker in them).

 

[EFLImpudence]

Extremely unlikely, as in 2013 the typical shower circuit was run in ten mm cable on a 40amp breaker (most dedicated shower consumer units of that era had a B40 breaker in them).

Typical where?