Shower EICR Code- 9.5kW- 40amp mcb!. De rate MCB to 32 or rewire cable to 10mm

[CM 1]

Argument at work!
on an EICR its common to find a 9.5kW shower wired in 6.0mm T/E with a 40 amp MCB.
obviously a code 2 unless short run and clipped direct?
Our argument is whether to down rate MCB to a 32amp or rewire the circuit in 10mm?
I say ok to down rate the MCB as

cable is 32amp IEE say must take 1.45 times rating for 1 hour and not exceed 60 deg C also 32amp mcb will take this current
others say rewire shower in 10mm, I would agree if new install, but on an EICR it would reduce the coding to a C3 and I would note " Circuit derated and a shower rewire desirable?

 

[KEV 1 N]

The 32amp mcb will likely trip on overload as 9.5kw is 39amps at 240v or 41amps at 230v. Advise a down rate size of shower to suit cable or they need to upgrade it to 10mm2 for the 9.5kw
Is there any signs of over heating at all the terminals?

 

[Ian1981]

The mcb may never trip depending on the time taken in the shower however overloading the mcb at regular intervals during different days will eventually lead to heat/damage to the mcb and a possible fire risk.

As a shower is a fixed load, overload protection shouldn't be an issue or necessary if the circuit and protective device are designed and installed properly

 

[CM 1]

The 32amp mcb will likely trip on overload as 9.5kw is 39amps at 240v or 41amps at 230v. Advise a down rate size of shower to suit cable or they need to upgrade it to 10mm2 for the 9.5kw
Is there any signs of over heating at all the terminals?

32amp mcb will run at 39 amps for an hour easily , no sign of overheating at terminals.
We come across lots of these as we do a lot of local authority work, i always down rate the MCB and have never been back to one tripping MCB !
The cable is covered by the MCB

 

[westward10]

There are installation methods where the existing set up could be considered acceptable however, doing an EICR you can rarely verify the full extent of the cable route to assess this so I tend to consider worse case scenario and Code it appropriately.

 

[CM 1]

There are installation methods where the existing set up could be considered acceptable however, doing an EICR you can rarely verify the full extent of the cable route to assess this so I tend to consider worse case scenario and Code it appropriately.

Ah yes but you missing the point? No doubt it’s a code 2 to me unless can verify the installation method for the entire cable run, but I would put a 32amp MCB to protect the cable , the shower won’t trip the MCB for over an hour and would advise on the cert that the shower needed rewiring when possible

 

[kingeri]

Simplest answer is to advise fitting a lower powered shower!

 

[CM 1]

We would never justify fitting a lower powered shower as many properties tested have this problem , and we may have fitted the showers previously lol

 

[kingeri]

Would surely be a cheaper/quicker fix than rewiring though? And a better option than down rating and therefore overloading a breaker (lets be honest this would be poor design!).

 

[Ian1981]

Not to mention the regulations specify that even a small overload shall be avoided on a circuit

 

[KEV 1 N]

Not sure on what long term effects will have on the protective device operating on over maximum load? Particularly if someone decides to have a long shower....like my sister did once and nearly set fire to the DB with a 30amp fuse wire!

 

[CM 1]

I would say it’s safe on the 32 though as we do say if the shower trips we would rewire the circuit?

 

[CM 1]

Not sure on what long term effects will have on the protective device operating on over maximum load? Particularly if someone decides to have a long shower....like my sister did once and nearly set fire to the DB with a 30amp fuse wire!

Lol! Definitely not safe on fuse wire , but on an MCB I think it’s ok as the only problem would be possible tripping if a V long shower was taken

 

[buzzlightyear]

Ah yes but you missing the point? No doubt it’s a code 2 to me unless can verify the installation method for the entire cable run, but I would put a 32amp MCB to protect the cable , the shower won’t trip the MCB for over an hour and would advise on the cert that the shower needed rewiring when possible

answer. change the shower or change the cable .

 

[CM 1]

answer. change the shower or change the cable .

No need for either in my opinion , as cable needs to be able to take 1.45 rated current without exceeding 60deg C, also MCB will take the current for over an hour