Correct MCB ???

[srl-8]

Hello guys. I am new on here and wanted to get involved.
Firstly, I am on route to becoming a domestic installer and now becoming very inquizitive when I see other peoples installations.. And for the record, I know i have a LONG way to go before I would consided myself competent !

At my parents house, they have had a new electric shower put in, but I am unsure if the electrican has used the correct rated MBC...Can someone clarify the below

Taken a new feed from the Hendy Block and feed a Small 2 way C/u (Just for the bathroom)
The new Cu has a 63A / 30ma RCD main switch, and then 6A MCB and a 32 A MCB which the shower is on.
The shower Cable is 10mm.
The shower is rated at 9.8kw / 9800 watts

I think this MCB is underated and should be a 45A MBC, however it have never tripped??

Can someone explain what is happening here

Thanks!!

SRL-8

 

[TPES]

Would you of coded this on a PIR?

 

[Deleted member 26818]

It doesn't comply with the requirements of 433.1.1(i), as such an EIC should not have been issued untill the MCB had been replaced.
However it is not particuarly dangerous, and to my mind would only warrent a code 4.

 

[Zeno]

A 32A B type MCB will run at 38A for ever, so it will cope with 42.6A for average shower use, which is why it has not tripped.


Although shower manufacturers go for a continuous rating for MCB ratings, a lot of showers do not have a continuous duty rating, many are just 20min on 20min off, or variations of that but that is hidden away in the instructions.

In which case a 40A MCB will do even at the lower end of the supply voltage when the current drawn by the shower will be 47.3A, insulation derating factors and installation methods, then start to become a problem!

 

[malcolmsanford]

A 32A B type MCB will run at 38A for ever, so it will cope with 42.6A for average shower use, which is why it has not tripped.


Although shower manufacturers go for a continuous rating for MCB ratings, a lot of showers do not have a continuous duty rating, many are just 20min on 20min off, or variations of that but that is hidden away in the instructions.

In which case a 40A MCB will do even at the lower end of the supply voltage when the current drawn by the shower will be 47.3A, insulation derating factors and installation methods, then start to become a problem!

Not according to ABB whose low current test on page 14 on their data sheet is 1.13 In. Which would make a Type B 32amp MCB trip at just over 36amp on continuous load. But a shower that is on for less than an hour will not trip the MCB as the high current rating is In X 1.45.

http://www05.abb.com/global/scot/scot209.nsf/veritydisplay/e5a4baa7eed9b492c1256a49004a812e/$file/gsk0400701s0201.pdf

As this is a British standard for all Breakers I would say that no Type B 32amp MCB would "run forever" at 38amps

 

[platty1005]

Design basics
Load current equal or less than protective device and cable current carrying capacity equal or greater then protective device so start with load current 9800/230 = 42.6 MCB equal or greater so B45 MCB
Cable 45A or greater see Table 4D5 BS7671 column 6 method C for 10mm cable 64A
Ib 42.6, In 45, It 64 The original B32 MCB is too small repeated overheating may damage the MCB
You did the right thing and changed it