Maximum Demand

[m4tty]

Hi,

Im filling a Certificate out for the board change ive just done and am having problems with maximum demand. Its got a 60A BS1361 Type 2B Mainfuse.

Circuits are:

RCD1

Downstairs Ring 32A

Shower 32A

Upstairs Lights 6A

Kitchen Lights 6A

Alarm 6A

RCD2

Kitchen Ring 32A

Upstairs Ring 32A

Immersion 16A

Downstairs Lights 6A

Loft Lights 6A

This is a 2 Bed Mid Terraced house.

Ive worked it out as the biggest one 32A + (the remainder x 0.4) which i get 88.8A which is more than the 60A Mainfuse.

I know that 6A for the loft lights will actually be a maximum of 240W which is 1.04A and kitchen lights on 6A breaker is 3 flourescent tubes only so probably about an amp tops.

Can i put down max demand of 88.8A on a 60A Mainfuse or is there a better way of working it out.

Ive got regs osg etc so will check through these now.

Thanks in advance for any help

CheersGuinness

Edit: Or do you recon I should turn everything on and clamp the tails?

 

[Riggy]

I'd go for 14kVA (230V x 60A rounded up!).

Is it a critical value in terms of condition of installation?

 

[springcrocus]

Since you haven't previously blown the 60A fuse, then your max demand has not exceeded 60A. Therefore, put down 60A on your cert.

 

[batty]

Since you haven't previously blown the 60A fuse, then your max demand has not exceeded 60A. Therefore, put down 60A on your cert.

But it could have easily gone over 60 amps for short periods without blowing main fuse.

 

[springcrocus]

I quite agree, Batty, but the only people who are interested in the max demand figure are the people supplying the service fuse. Since Matt has only changed the CU and not increased the existing demand, they wont be wanting to uprate the fuse just because he has worked out that the max demand MIGHT be higher than previously thought.

 

[steptoe]

<80A

havent been to a standard domestic yet that realistically needs more.

 

[batty]

<80Ahavent been to a standard domestic yet that realistically needs more.

Most domestics are easily catered for with a 60a main fuse my whole road has them and the whole estate. Only time I recommend they are upgraded if people want a 10.5 kw shower or other serios high load appliances.

 

[Andy™]

Since you haven't previously blown the 60A fuse, then your max demand has not exceeded 60A. Therefore, put down 60A on your cert.

^ what he says

simply adding up figures & times that by a random, unproven number, is not much of a help. for a standard house, unless you have much bigger loads that what could be reasonably expected, then i would just go with either 60 or 80, depending on fuse rating

in my house it has a 40A fuse. its never blown. even with an electric cooker, electric shower, and everything else. and there have been many times of both shower & cooker on at same time.

 

[steptoe]

how do we know what size fuses are fitted folks?

I have seen cartridges pulled that has stated 60a on the side, and it has actually been a 3/8" copper strip inside (loads of old TNS were temped this way and never changed!)

if I dont physically see the fuse I state NOT VERIFIED.

NICEIC are more than happy with this on my certs.

and I put my normal domestics as <80A , again more than happy, its a realistic maximum

 

[Andy™]

depends if the seal fairy has been

either way, even if i have seen the fuse, i still mark cert as 'sealed', or 'not verified'

 

[green-hornet]

how do we know what size fuses are fitted folks?I have seen cartridges pulled that has stated 60a on the side, and it has actually been a 3/8" copper strip inside (loads of old TNS were temped this way and never changed!)

if I dont physically see the fuse I state NOT VERIFIED.

NICEIC are more than happy with this on my certs.

and I put my normal domestics as <80A , again more than happy, its a realistic maximum

Good point, I have just replaced 3 main fuses on a 3 phase board which I managed to blow 2 of the fuse holders had 80amp fuses the other was 60 amp.

Yes I was working live and yes it was my fault and yes I know I am a numpty, but I learned a very good lesson,besides working live and shorting out a 3 phase board, that not all fuses are what you think they are.

Back to the OP, I can honestly say that I always remember Special Locations explanation of maximum demand. The gist of which is this.

You start off with 1 lighting circuit at 5 amp, 1 socket circuit at 30 amp and one cooker circuit at 30 amp. You then put in a nice new cu with rcd and led warning lights linked to the national inteligence service via the local tax office.

The lighting gets split into two circuits each with a 6amp mcb, the sockets get split into 2 or 3 circuits each at 32amp, then the cooker gets its own 32 amp. The actual installation still has its original demand but if calculated we now must "presume" the demand has changed.

I still use the add all and times by method. Perhaps we should really use the testing method, turn everything on high and clamp the line, I doubt it would go above 60amp.

 

[Andy™]

Good point, I have just replaced 3 main fuses on a 3 phase board which I managed to blow 2 of the fuse holders had 80amp fuses the other was 60 amp.Yes I was working live and yes it was my fault and yes I know I am a numpty, but I learned a very good lesson,besides working live and shorting out a 3 phase board, that not all fuses are what you think they are.

what went wrong?

 

[green-hornet]

I moved a mcb down to balance the phases and shorted across two, its one of those cheap CEF boards, so I should have expected it

 

[Andy™]

you certinly balanced it!