Maximum Demand exceeded

[Leigh Winspear]

No two EICR's are the same, this time a contactum CU has 11 ways/circuits, it is a split load board with 2 x 80 RCD's. 100A main switch.
MCB's are as follows - 32, 32, 32, 20, 20, 6, 32, 20, 20, 6, 6 amps.
I make the Max demand using diversity, 109.6 amps.
I have made a note on the certificate, unsatisfactory of course, and I am now looking for a way forward as the duty holder who ordered the eicr needs a pass asap.
I wont be rushed into signing off a job and am looking for a solution along the lines of using smaller mcbs if possible.
I am not a circuit designer and would appreciate some guidance.

Cheers n stuff

Leigh

 

[Sharpend]

Did you actually clamp the tails to see what the property was actually drawing in Amps?

 

[SPECIAL LOCATION]

The number of MCB's does not define the maximum demand.
It is the loads connected.

e.g. a house with a single 5A BS3036 lighting circuit.
could be improved by splitting the existing circuit on to 2x 6A 60898's (up/down)
Supplying the exact same lighting load

The Max demand of the lighting has not suddenly doubled because it has been split onto two circuits.

Or a 32A rings suppling a few bedrooms could be split into a pair of 20A radials..
Still supplying the exact same sockets & loads.. (but not suddenly gained an extra 8A of demand.)

Capacity and demand are different things..
Start assessing the actual fixed and portable loads these circuits may or may not be supplying..
and which ones could be in simultaneous use.

Have a read of the second paragraph of Appendix A On Site Guide.. Pg135.
I would suggest your method of evaluating Max Demand is incorrect in this instance.

 

[Murdoch]

The maximum demand calculations are way out of date with reality and need to be ignored.

What is important is what the circuits are used for. So if the installation has electric hob, oven, hot tub , ev chargers and 2 showers then there may be an issue

If not and it’s gas CH then it’s not an issue

Tin hat on

 

[Leigh Winspear]

Did you actually clamp the tails to see what the property was actually drawing in Amps?

Didnt seem much point as the flat is unnocupied and everything was turned off apart from fridge/freezer. OK. IS it normal to turn everything on and to max in a dwelling before doing such a test?
Used calculations as per regulations.

 

[Fleeting]

You don't need to find a way forward the chances of the loading in a flat reaching your figure of 109.6A is all but zero.

 

[Murdoch]

Used calculations as per regulations.

Reg number?

FWIW I add up the breakers and divide by 4 ..........unless its all electric

 

[kerching]

FWIW the local "leccy board" used to use a value of 15A for each property (semi or detached) and 8A for a bungalow or flat!

 

[SPECIAL LOCATION]

Used calculations as per regulations.

The calculations that I suspect you are using are described as "guidance". by BS7671..

which then goes on to state:- "because it is impossible to specify the appropriate allowances for diversity for every type of installation"

also any values given in the tables "may be increased or decreased by the installation designer".

As I said previously Have a read of the second paragraph of Appendix A On Site Guide.. Pg135.

There are NO fixed one-size fits all diversity calculations given in BS7671..

Its no good skipping pages to a table, without reading the text that puts the tables into context.

 

[binky]

Didnt seem much point as the flat is unnocupied and everything was turned off apart from fridge/freezer. OK. IS it normal to turn everything on and to max in a dwelling before doing such a test?
Used calculations as per regulations.

Nope, not a standard test, but you need to apply common sense, it's a flat. My entire house never exceeds the 60A main fuse.

I abandoned the diversity calcs years ago, when I rewire a house I install lots of small circuits, sockets on 20A radials, external light separate to internal, shed separate from house etc etc. This means I end up with a large board and lots of MCBs, ergo the diversity calc would look horrendous. The calculation is for guidancce only.

 

[Andy™]

addings MCB values etc is pretty much useless

you can have a house with a 5a lighting circuit, 30a sockets and 30a shower. rewire it with multiple 6a lighting circuits, 32a kitchen sockets, 20a upstairs sockets, 20a downstairs sockets, 40a shower etc. adding them up and dividing by whatever you now have a completely different number to before yet nothing has changed

and why is it 'unsatisfactory of course'. historical evidence of the fact it isn't blowing fuses every other day would suggest the actual max demand is well within the capacity of the supply and the only problem is the one doing the I&T...

 

[Bruspark]

A history of overheating or blown main fuses would be unsatisfactory. All-Electric House with 2 showers, massive ovens/hob and an EV charger on a 60A fuse maybe also so . .
Otherwise you are
a) Guessing
b) Making unsafe assumptions that Breaker Ratings somehow reflect maximum demand rather than just their Cable ratings . I've seen doorbells on their own 6A breaker

 

[Leigh Winspear]

Nope, not a standard test, but you need to apply common sense, it's a flat. My entire house never exceeds the 60A main fuse.

I abandoned the diversity calcs years ago, when I rewire a house I install lots of small circuits, sockets on 20A radials, external light separate to internal, shed separate from house etc etc. This means I end up with a large board and lots of MCBs, ergo the diversity calc would look horrendous. The calculation is for guidancce only.

A history of overheating or blown main fuses would be unsatisfactory. All-Electric House with 2 showers, massive ovens/hob and an EV charger on a 60A fuse maybe also so . .
Otherwise you are
a) Guessing
b) Making unsafe assumptions that Breaker Ratings somehow reflect maximum demand rather than just their Cable ratings . I've seen doorbells on their own 6A breaker

Not unsafe assumptions at all.



I think you should get GSH removed from Youtube as he obviously is teaching his 119k subscribers wrong too.....................

Learning loads, Don't pardon the pun, due to this thread but also, I will admit its a learning curve which you lot are unfortunately part of.......

 

[Leigh Winspear]

addings MCB values etc is pretty much useless

you can have a house with a 5a lighting circuit, 30a sockets and 30a shower. rewire it with multiple 6a lighting circuits, 32a kitchen sockets, 20a upstairs sockets, 20a downstairs sockets, 40a shower etc. adding them up and dividing by whatever you now have a completely different number to before yet nothing has changed

and why is it 'unsatisfactory of course'. historical evidence of the fact it isn't blowing fuses every other day would suggest the actual max demand is well within the capacity of the supply and the only problem is the one doing the I&T...

Just looking for guidance as outlined in my original post. If im over safe isnt it better to be than not giving a shit and ignoring a possible safety issue?

 

[Leigh Winspear]

FWIW the local "leccy board" used to use a value of 15A for each property (semi or detached) and 8A for a bungalow or flat!

interesting when was this?

 

[Leigh Winspear]

A history of overheating or blown main fuses would be unsatisfactory. All-Electric House with 2 showers, massive ovens/hob and an EV charger on a 60A fuse maybe also so . .
Otherwise you are
a) Guessing
b) Making unsafe assumptions that Breaker Ratings somehow reflect maximum demand rather than just their Cable ratings . I've seen doorbells on their own 6A breaker

I didnt install the system im just testing it without any design characteristics or previous certification. All most posters on here want is guidance. We are not all perfect are we?

 

[binky]

Not unsafe assumptions at all.



I think you should get GSH removed from Youtube as he obviously is teaching his 119k subscribers wrong too.....................

Learning loads, Don't pardon the pun, due to this thread but also, I will admit its a learning curve which you lot are unfortunately part of.......

Couldn't give a toss what some prat on YouTube thinks. I've been at this game a very long time, long enough to be retiring very soon.

 

[Fleeting]

interesting when was this?

Back in the 90s I knew someone who was involved in distribution and they allowed 6A for every dwelling on a new estate.

 

[Fleeting]

Not unsafe assumptions at all.



I think you should get GSH removed from Youtube as he obviously is teaching his 119k subscribers wrong too.....................

Learning loads, Don't pardon the pun, due to this thread but also, I will admit its a learning curve which you lot are unfortunately part of.......

The chances of that installation peaking at 88A is slim to not at all. There is nothing wrong it what he is demonstrating but in practical situations it will be well above the realistic maximum demand.

 

[Leigh Winspear]

Couldn't give a toss what some prat on YouTube thinks. I've been at this game a very long time, long enough to be retiring very soon.

Ok, Perhaps a non prat youtube channel beckons for you? I would subscribe, as I have learned much from your input on here and you clearly have bags of experience to show us all...........a forum is one thing but a You tube channel is a challenge only the brave seem to take on in the right way. Or those with plenty of time on their hands............................