would it affect for example an insurance claim? If something was to go wrong?

From an electrical safety point of view, it would be hard to imagine what insurance implication there might be. There should still be adequate overload protection whatever the MD had been assessed as - underestimating MD should at worst (other than a small reduction in the serviceable lifetime of the installation) just lead to undesired disconnection - there should be no significant increase in fire hazard for example. Buildings with overloaded conductors may well burn down, but normally that's a result of loose connections and the like - which would have been almost as likely without an overload.

At a stretch I could perhaps see some indirect consequences - e.g. DNO fuse blows because demand significantly exceeds supply rating so freezer contents thaw, and there's an insurance claim for the spoiled food, but I suspect that sort of thing is way down the list of things to worry about.

   -  Andy.

HI Andy, thanks for the response - I accept the point re the overload issue, however my main concern and subsequent ask would be the non compliance between an ENA  and a certificate - if there were any discrepencies there. I am seeing more and more issues where insurers regardless of the cause flagging up non compliance as a way of geeting out of payment in a claim. 

Interesting CPD opportunity with NICEIC on this subject. About 90minutes of material that ends up with equally as may ways in establishing maximum demand. However, according to the presenters, NICEIC inspecting engineers will be expecting contractors to be able to justify how they determined MD for certification purposes. What spiked my interest was the requirement for those carrying out periodic inspection to be able to do the same.

perhaps they have just bought a batch of data loggers from the back of a yellow van from someone in Peckham!

What spiked my interest was the requirement for those carrying out periodic inspection to be able to do the same.

That will give rise to some random numbers, there are some that seem quite unable to estimate the number of light fittings or even rooms in a flat correctly, let alone how much current it all takes.

Mike.

Realistically in many installations estimating maximum demand is pretty much impossible. The "Official" maximum demand is the rating of the supply fuse, because any sustained significant overload will cause failure. The "real" maximum demand all depends on the diversity applied in the DESIGN, and may well be more than the fuse rating. The fact that the NIC is suddenly interested is strange, I suppose it is all to do with some Green push, or perhaps they have a new booklet which gives some magic formula for calculation! Using a "sum of breaker ratings" in my own house for example would give a silly number because I have a lot of circuits. The actual real load is usually less than 6kW and that includes all electric cooking. Space and water heating is all gas, but even so our total energy use is considerably less than the nonsense Government "average" figure, probably because the estimates for maximum demand are ridiculous! All this can probably be traced to car charging and DNO panic. Don't forget the potential £3 Trillion cost to make the electricity supply resilient in an all electric world, this is conveniently ignored everywhere now.

The legal view of such a number is very dubious, one could get two experts in court who would offer entirely different opinions, and the Jury would have no idea who to believe. I suggest that if the NIC ask you, you say "I don't know and care less, the installation DNO fuse is the final arbiter". That should keep them quiet!

David Stone said:

The "Official" maximum demand is the rating of the supply fuse

Which is not necessarily the same as the after diversity maximum demand which has been agreed with the DNO.

I wonder how many people know what their ADMD is. Mine is 30 kW, but the fuses are 100 A.

I wonder how many people know what their ADMD is.

Very few I suspect - after all in this virtual supplier world, where would you look if you have had no correspondence with the DNO for the last 20 years  - it is the sort of thing that could be on the electricity bill, as I presume it is decided per MPAN. However, I'd be surprised if the suppliers know - all they seem to do is take meter readings. On the other hand the DNO might know what it was once upon a time I suppose, but they have precious little direct contact with customers or the kit they have a responsibility for when things change.

Plenty of houses will have sprouted a new electric shower or bigger cooker since they were built and the bit about notifying the DNO when there is a load increase of  or more than 13A  is long  forgotten.

Mike

In our new all electric world, the ADMD number must have gone out of the window, because we must all fit car chargers and heat pumps. If it actually meant anything, the DNOs would say not likely to both upgrades and the Government policy would look very silly indeed. In reality not many can have both of these (or even one) before there is trouble with the system, which only supplies 1-2kW per house on average. If the peak gets too far from the average, large fuses start popping with a good crack, also known as trouble at the substation (not Mill?) and hopefully in Westminster too!

If it's a complete new install ask the designer. If you're adding some new circuits check the meter.

It seems odd that the NIC have begin to comment on this issue. When I did a 9 moth contract as an inspector for a LA, we were informed that max demand was indeed the rating of the DNO fuse. When I questioned this with the LA supervisor he said was 'Because the NIC says so'.

So I gather that because of all this extra green nonsense, that the NIC have now changed their tune.