Shower MCB question after electrician installed new Consumer Unit

[DPG]

I've read above and some are saying it's not ok to leave as is, and another answer was it was safe as is.
The MCB's will protect for short circuit faults.

Remember, I am just an end user here and the installation in 2016 was completed by an electrical contractor (with, from what I can see, has a good reputation), so in all honesty I am no further on now than I was before I started this thread

Which post number said it was OK to leave the 32A MCBs in place?

 

[Julie.]

How many MCBs does the shower have then?

HV Approved person, what is that Julie? is that the same as a HV Authorised Person?

Yes, my error, it autocorrected when I first posted it, never noticed!
[automerge]1595501246[/automerge]

I've read above and some are saying it's not ok to leave as is, and another answer was it was safe as is.
The MCB's will protect for short circuit faults.

Remember, I am just an end user here and the installation in 2016 was completed by an electrical contractor (with, from what I can see, has a good reputation), so in all honesty I am no further on now than I was before I started this thread

It is safe, but the MCBs are likely to trip or fail prematurely given that it is actually overloaded.

They should be changed, this does not mean it is dangerous if they are not.

 

[Plantman2000]

Which post number said it was OK to leave the 32A MCBs in place?

Without wanting to get into a blaming game post number 6 seemed to give me assurance:

"that looks good to me."
Presume the setup of what is currently installed is good?
Maybe it was my pictures that were good

"both those showers should be on 40A for the upstairs shower, as long as the cable is nowhere covered in insulation, and a 40A or even a 50A for the downstairs shower. simple job to get him back to swap out the MCBs."

So, should be on higher amperage rating but not has to be for safety?

"as a side note, though, 32A MCBs will withstand the 4A t0 8A overcurrent for far loger than it takes to have a shower, so even as it is, it's safe. might get the occasional trip on the 9.5kW shower, but unlikely. the lifespan of the 32A MCBs may be shortened somewhat as they are running at their rated limits."

The wording here states it is safe.
We've never had a trip.
This setup has been in place for 4 years near enough with daily use.

I guess, all the answers point to that the setup is "safe", though perhaps not ideal.
At the end of the day, as I mentioned, this was all put in by a competent electrician as far as I know.
[automerge]1595501565[/automerge]
So, yea, I think we are there - sounds safe, though probably not correct, especially for long term use.

I will approach the company that installed the system to see what they say as to their decisions for what MCB ratings they chose and whether they would offer swapping these out for free, else, I will look to swap these out in due course.

Good discussion all, appreciated the feedback.

 

[Julie.]

Without wanting to get into a blaming game post number 6 seemed to give me assurance:

"that looks good to me."
Presume the setup of what is currently installed is good?
Maybe it was my pictures that were good

"both those showers should be on 40A for the upstairs shower, as long as the cable is nowhere covered in insulation, and a 40A or even a 50A for the downstairs shower. simple job to get him back to swap out the MCBs."

So, should be on higher amperage rating but no has to be for safety?

"as a side note, though, 32A MCBs will withstand the 4A t0 8A overcurrent for far loger than it takes to have a shower, so even as it is, it's safe. might get the occasional trip on the 9.5kW shower, but unlikely. the lifespan of the 32A MCBs may be shortened somewhat as they are running at their rated limits."

The wording here states it is safe.
We've never had a trip.
This setup has been in place for 4 years near enough with daily use.

I guess, all the answers point to that the setup is "safe", though perhaps not ideal.
At the end of the day, as I mentioned, this was all put in by a competent electrician as far as I know.

Ah OK, I think it was the wording rather than meaning, the issue when you first posted was that we had no idea of the size of cables, if they were smaller, then it would be unsafe to increase the size of the MCB, and you would either need to have the cables and MCB replaced or just use it with overloaded MCBs - not dangerous but as you say not ideal.

Once you posted the table of readings, then it was clear the cables are of sufficient size to allow upgrading to correct size MCBs - this is by far the best situation hence I think the response "looks good to me".

Again within that post is the common theme: safe - but should be changed

 

[Plantman2000]

This makes sense. I am learning a lot so thank you all for the education

 

[Julie.]

This makes sense. I am learning a lot so thank you all for the education

As a bit of background there are number of factors involved in sizing the cable/MCB.

Firstly there is the cable’s physical size itself, this determines the maximum cable rating – cable size is on the table/extract you provided.

Then there is the installation method, all cables get hot when used, but if it’s run in very good thermal insulation for example it would get too hot, therefore we have to downrate the cable rating from maximum to one suitable for the installation method actually used – this is also indicated on the table/extract you provided (Combination of cable type and reference method).

Then, we must ensure the larger MCB would trip in a sufficiently quick time to be safe in the event of a fault – this is available on the table/extract you provided (Earth loop impedance)

(there are some more such as voltage drop and so on – actually we can estimate them from the same extract and it all looks ok - I appreciate the raw information on the form looks meaningless - but it is possible to calculate most things from it. )

Since this is all provided on a well filled out form, it’s clear that the actual work appears OK, it’s just strange that they chose to fit undersized MCBs

 

[Lucien Nunes]

There is a 'no-mans land' between the rated current of a circuit breaker and the lowest current at which it will trip. A 32A MCB will not trip at 34A, but neither should it be used to carry that current by design, as it will run hotter than it should and the normal safety margins and tolerances will be disrupted.

The rule is that the breaker rating (In) should never be less than the load (Ib), and the cable rating (Iz) once adjusted for the installation method should never be less than the load (for a fixed load) or In otherwise. That ensures everything has its normal safety margin and nothing gets stressed.

There does not seem to be any reason not to up the rating to 40A and if that is so, I agree it should be done.

 

[telectrix]

if you can't get the original installer back to do it, it's approx. 1 hour's labour and the cost of 2 MCBs inluding a quick test of the circuits and production of a MWC, should not cost over £80 - £90 all in, assuming no problems are found.

 

[Plantman2000]

Thank you all, this makes for very interesting reading.

The electrical contractor did come back to me just now, so a credit to them, and said those MCB's were chosen to protect the cable considering the shower ratings.

They did offer to come out to take a look but did stop short on offering to swap the MCB's out for higher rated ones, which would be expected else it would look like they may have installed incorrect ones initially.

 

[telectrix]

all he's go to do is say "my bad, should have fitted 40A for one and maybe 50A for other. we'll freplace as a goodwill gesture, don't tell anyone".

 

[Plantman2000]

all he's go to do is say "my bad, should have fitted 40A for one and maybe 50A for other. we'll freplace as a goodwill gesture, don't tell anyone".

Sadly I don't think that happens any more these days

 

[Markyd]

View: https://www.youtube.com/watch?v=2Ng4ylZrFVs
still think you should have one of these as well

 

[DPG]

View: https://www.youtube.com/watch?v=2Ng4ylZrFVs
still think you should have one of these as well

Or do it like I did in my house - one combi fed and one electric. If you have a fault in either the boiler or the shower you can still get a wash.

 

[telectrix]

the biggest problem with showers is that you can't lie down with a smoke in 1 hand and a Jack Daniels in the other. give me a bath every time.