Electricity Board Fuse

[Shaneyboy]

In an effort to improve my electrical knowledge, I have been reading some of the books featured on previous threads. In relation to consumer units, I recently read the following:

You will need to specify the trip rating for the main power switch on the CU. It will usually be 80 or 100 amps depending on the size of the electricity boards fuse. You must check the fuse size (electricity board), which is printed on the casing. The trip rating of the main power switch fuse must not be greater than the fuse size, because otherwise the main electricity board sealed fuse could overload.

My main power switch on the CU is rated at 100 amps. My electricity board fuse has Type II 60 amp 415 v printed on it.

Should this be cause for concern?

Regards.

 

[Aragorn84]

no, its perfectly fine.

I should point out that the "Main Switch" is often just a Double pole isolator, and the 100A rating is simply its maximum current carrying capacity. It doesnt have the ability to "trip".

More recently RCD's are sometimes used as a Main Switch, but again, these wont usually trip with overcurrent, only earth faults.

 

[DetlefSchmitz]

You will need to specify the trip rating for the main power switch on the CU. It will usually be 80 or 100 amps depending on the size of the electricity boards fuse. You must check the fuse size (electricity board), which is printed on the casing. The trip rating of the main power switch fuse must not be greater than the fuse size, because otherwise the main electricity board sealed fuse could overload.

'main power switch fuse '

I'm finding it hard to make sense of that. Surely this is one of the books BAS has been recommending?

Sorry: supposed to say surely this isn't

 

[flameport]

You will need to specify the trip rating for the main power switch on the CU.
It will usually be 80 or 100 amps depending on the size of the electricity boards fuse. You must check the fuse size (electricity board), which is printed on the casing. The trip rating of the main power switch fuse must not be greater than the fuse size, because otherwise the main electricity board sealed fuse could overload.

Utter tripe.

Main switch is just that - a switch. No 'trip rating'.
Electricity board - just how old is this piece?
Fuse size will NOT be printed in the casing, that is just the maximum for that particular cutout. 100A outside, but could have 100A, 80A, 60A or whatever else inside.
No way that any main switch or other downstream protective device could cause the main fuse to overload.

Shaneyboy - where exactly did you read this? Everyone needs to know, because if that's typical of the information given, the whole publication is likely to be wrong.

 

[Adam_151]

Perhaps it was one of david cockburns books

 

[Shaneyboy]

The passge that I quoted is on page 12 of The Complete Handbook of Home Electrics by Julian Bridgewater.

 

[OwainDIYer]

The passge that I quoted is on page 12 of The Complete Handbook of Home Electrics by Julian Bridgewater.

"Julian Bridgewater is a qualified systems engineer. As a consultant, he travels widely throughout UK and Europe and, a respected authority in the field, he sits on various European boards and committees. " (Ebay author biography)

Doesn't say what sort of systems engineer.

 

[DetlefSchmitz]

Also by Julian Bridgewater: Home Plumbing: The Complete Handbook

 

[OwainDIYer]

I can't wait for "Cushions, Throws and Dangly Bits for Curtains"

 

[ricicle]

A book review is on the cards.....

 

[Shaneyboy]

Another part of the above book that has me confused is in relation to installing a smaller CU in say, a garage, is as follows:

You must ensure that the total fuse ratings of the existing and the new circuits do not exceed the rating of the main electricity board fuse.

In my house I have an MK Sentry split load CU with a 100-amp DP isolator switch and an 80-amp RCD. I have two MCB's for the lighting circuits on the non RCD side and four MCB's on the RCD side for everything else. The total amperage for the six MCB's is 106-amps. My electricity board fuse is 60-amps.

Would I not, therefore, be able to consider having a smaller CU put in the garage with another 6-amp and 20-amp MCB on it for lights and sockets for fear of overloading the main electricity board switch?

(Apologies in advance if I have got this completely muddled up.)

Kind Regards.

 

[riveralt]

Another part of the above book that has me confused is in relation to installing a smaller CU in say, a garage, is as follows:

You must ensure that the total fuse ratings of the existing and the new circuits do not exceed the rating of the main electricity board fuse.

Carry on reading because the book should also talk about diversity.

 

[stillp]

Even better, throw the book away and get a real textbook. See Flameport's comments above.

 

[ban-all-sheds]

Even better still - take it back to the seller for a refund on the grounds that it is not fit for purpose.

 

[Shaneyboy]

Sorry boys, the book is obviously rubbish and I will get rid of it immediately and look at some of the Brian Scaddan books. But if someone wouldn't mind explaining it to me. Can I consider having a smaller CU fitted in the garage?

Riveralt, Diversity??

Kind Regards.