MCB

[Luke1]

At my work im able to get hager Type B MCB's.
The thing is im installing a 9.5kw shower, which is 41amps ...
They only have 40amp and 50 amp breakers, ideally a 45amp breaker would be best, but will i get away with using a 40amp?

Cheers

 

[basic]

firstly check your cable calcs can take 50amps.

a 40amp mcb will be npo good being that it will trip constantly being that its rated for 40amps, also if you decide to use a 50amp mcb and your cable calcs say no, you will overheat your cables and potentially create a time bomb. also an electricianwill not sign it off

 

[Luke1]

Well the cable is a 10mm on about 15meter run. So the cable is ample.
I thought Type B mcb required 3-5 times the operation current to trip, therefore i thought a 40 amp breaker would be sufficient

 

[basic]

your cooker outlet?

I'm doin some calcs for you.

 

[supersparks]

40 amp breaker will never trip at 41 amps.

also you can get a 45amp RCBO

which is even better

whats the cable run through? clipped to a wall or in insulation ect?

do you have an rcd on your consumer unit?

and btw, if you plone Hager 0207 3293891

they can probrably supply you with a 45amp mcb or give you a reference number to go to an electrical wholesalers with. although one isnt listed in their catalogue

 

[Big_Spark]

http://www.hager.co.uk/files/download/0/201_1/0/New_device_equivalence_chart.xls

Hager do not make any 45A devices anymore...Nice Intelligent thinking there!! The chart above gives a lost of their devices and part Numbers.

 

[Adam_151]

The thing is this is probably not a 9.5kw, 230v shower which is 41A odd amps

it is probably a 9.5kw, 240v shower which is under 40A, but we work in 230 now: so it is a 8.7kw 230v shower which is also less than 40A

check the ratings to make sure it says something like, 9.5kw @ 240v/8.7kw @ 230v

 

[Big_Spark]

Adam, there has been a legal requirment for the last 12 years that all appliances in the UK are sold based on a 230V supply, so stating it has a 240V rating is an irrelevence.

Remember that the supply can vary from +6% to -10%, consequently the actual supply can vary from 207Vac to 243.8Vac, this being the case, you should assume the rating of the circuit is assumed at 230V.

The Breaker that should be installed is a 50A, whilst this is bigger than usually installed, using a 40A MCB would be a bad idea as the MCB would operating above rating everytime the shower is used, this would seriously impede the long term operational characteristics of the MCB.

 

[ban-all-sheds]

Adam, there has been a legal requirment for the last 12 years that all appliances in the UK are sold based on a 230V supply, so stating it has a 240V rating is an irrelevence.

What do you mean by "irrelevance"? It is a fact, easily confirmed by looking at the detailed specs, that most, if not all, shower manufacturers quote the 240V rating as the headline figure, not the 230V one.

Remember that the supply can vary from +6% to -10%, consequently the actual supply can vary from 207Vac to 243.8Vac, this being the case, you should assume the rating of the circuit is assumed at 230V.

Certainly take supply variation into account, but there is no need to assume that the performance of the shower is different to what the manufacturer claims. If his stated specification at 230V is 8.7kW, then that is the figure you should use - there is no possible justification for deciding that the "9.5kW" rating applies at 230V.

The Breaker that should be installed is a 50A, whilst this is bigger than usually installed, using a 40A MCB would be a bad idea as the MCB would operating above rating everytime the shower is used, this would seriously impede the long term operational characteristics of the MCB.

8.7kW at 230V = 37.8A
9.5kW at 240V = 39.6A
~9.78kW at 243.8V ~= 40.1A

I'd be surprised if MCBs from reputable manufacturers would be seriously impeded by a 0.25% overload....

I agree that a 45A or 50A would be a better choice than a 40A, provided that's OK for the cable rating, but that doesn't make a 40A MCB a bad choice...

And what are the implications of ignoring the manufacturers installation instructions? I don't know the answer to this, but would, technically, the appliance no longer be CE approved if it was not installed in accordance with the instructions?

 

[Stoday]

Remember that the supply can vary from +6% to -10%

No, it can vary between 10% above and 6% below 230V, i.e. 216 to 253 V. See section 27 of the Electricity Safety, Quality and Continuity Regulations 2002.