Max demand problem

[jimzxcv]

First post - be gentle.

Just changed a consumer unit and am struggling with the "max demand" bit on the paperwork. RCD is 100A, Main fuse is 100A, it has 2 showers (50 A each) no diversity allowed on showers. so, um, not much room for anything else. .....or am I being a moron?
Thanks
Jim

 

[malcolmsanford]

If your main fuse is 100amp, because it might just be the carrier rating, not the fuse inside, then that is what I would put on the certificate

Did a nice DNO chap come put and pull it for you and then look and tell what the fuse was because it might have been an 80amp or even a 60amp, but whatever it was that is what you put down ...........................

 

[jimzxcv]

Thanks, but as I am a newbie I was going through the books to get it all right and the NICEIC book says this is the bit where you add up all the demand , do your diversity calcs and end up with the max demand; which sounds like a hideous amount of sums.
Is it this or do you just go for the main fuse rating??

 

[malcolmsanford]

Do you have a copy of the OSG by any chance?

Well if you do have a look at page 157 and you will see a completed EIC and you will see they have put put as maximum demand 60amps, which is remarkable similar to standard ratings of fuses you will get in a domestic head ........60 80 or 100amp

Then go to page 159 and you will see the SoTR and the circuits that were rewired and you work out and tell me with diversity what the laod is, I bet you a bottom dollar it will not be exactly 60amps.

Also have a read of section 311 in the regsa, and you will see that they mention diversity and "May be used"

As you progress in this industry you will come to see that the NICEIC seem hell bent in re-writing the regulations as per their take on them, and sometimes they get it right and sometimes they don't You maximum demand is the maximum size of the DNO fuse, you can't exceed that can you, if you put another 30 showers in and put the load up to 400 amps then the fuse will blow., and you have exceeded the maximum load or demand

 

[Octopus]

Have you asked your scheme's technical line for their opinion?

 

[dagrat]

Must admit that in this situation, very often I put on as much load as possible and measure the load at the supply after the EICR or cu change. This very often gives a lower value than the fuse rating.
What Malcolm says makes great sense but I struggle with inserting what is in effect the protective device characteristics for maximum demand. Though I could very well be wrong.

 

[Farmelectrics]

Can he not add up the breaker sizes and multiply by 0.4 I thought you could use this for your max demand

 

[Octopus]

Can he not add up the breaker sizes and multiply by 0.4 I thought you could use this for your max demand

With 2 showers?

 

[Farmelectrics]

Ok get your point Murdoch but am I right can you not add the breakers up on a domestic consumer and use that value

 

[Octopus]

Ok get your point Murdoch but am I right can you not add the breakers up on a domestic consumer and use that value

Personally I think the "diversity and max load" calculations need a rethink.

40 years ago houses had 4 or 5 circuits. Now they have 10 plus - more for convinience - yes, we have more plugged in, but most "stuff" isn't energy hungry, unlike 40 years ago when many people used plug in electric heaters. 11KW showers do make a difference!

 

[Lucas123]

the latest niceic certs have done away with the maximum load box.

 

[Farmelectrics]

Any reasons why

 

[malcolmsanford]

Are they allowed to? I thought it was ok for a scheme to design their own cets, but it had to based on the ones in the Regs, and so they could put extras onto it, but omit things

 

[Lucas123]

i thought so aswell malc taking things off but it is gone ive got an eic and eicr in front of me and it is most definitely gone.

farmer - i suppose its purely down to the reason of this OP to much discrepency theyve also added IT system to the type of earthing arrangement section
ill scan it in and post it up

 

[Octopus]

Are they allowed to? I thought it was ok for a scheme to design their own cets, but it had to based on the ones in the Regs, and so they could put extras onto it, but omit things

But Malcolm, I thought that the NICEIC was god of the rules these days.... lol