Choosing first mains electricity supplier.

[Markblox]

4 hours ago, Ed Davies said:

 

This comment is off the main topic here (which is about stuff before the meter tails) and also fails at basic logic; it's not true that ∀A, B: (A => B) => (B => A). Yes, if you comply with BS7671 you'll be deemed to comply with the relevant building regs but it doesn't follow that if you comply with building regs then you must have complied with BS7671. There are other ways to comply with BRs though they'd be hard work to prove and just complying with BS7671 is by far the simplest and easiest solution in almost all cases.

I didn't mention building regs, just said court of law, as in what might result from a fire or electric shock. Just saying that although the regs are not law themselves, compliance with them will be deemed  to be within the law. More of a health and safety thing.

 

Anyway, as you have pointed out it is off topic a bit but is related to what EpsilonGreedy was insisting on.

[Jeremy Harris]

Compliance with the law when it comes to electrical work is fairly complex, as unlike gas work there is no requirement to adhere to any standard in order to ensure a safe installation.

 

BS7671:2018 isn't law, and doesn't have the backing of statute, and whilst adhering to the guidance within it may be deemed to absolve any individual from liability in the event of an accident, it would not constitute a complete defence, and it's quite possible that someone who has followed the letter of BS7671:2018, and then been prosecuted for negligence as a consequence of an incident arising from the work they have done, could still be found guilty.

 

I must have dealt with several dozen cases where proving negligence has been involved, and none of them have ever been clear cut.  Thankfully 99% of them never get to court, but if they did then I can pretty much guarantee that just adhering to guidance would not be enough, on its own, to get someone off the hook.  BS7671:2018 is full of incomplete advice, as well as the occasional bit of conflicting advice.  For example, BS7671:2018 mentions that the total demand should be taken into account when inspecting/testing an installation, but is silent when it comes to the detail as to how to do this.  Clearly this is a critical safety issue, as it's well known that running the cut out fuse at close to, or in excess of, its rated current for long periods of time will cause it to overheat.  There are also examples where such overheating has cracked and damaged the fuse holder and housing, such that live parts are exposed.

 

The OSG (again, just guidance, not law) has some advice about calculating diversity, as ONE way of estimating the likely maximum load, but it's common knowledge that this isn't either foolproof, or even that applicable today.  For example, lighting circuits are most probably far less lightly loaded than the (very old) diversity calcs in the OSG might suggest, due to the widespread use of low energy lighting.  Equally, we now have some high power loads that aren't yet specifically included in the latest OSG guidance on diversity (or at least aren't yet in my 2018 copy of the OSG).  A common approach taken to try and estimate maximum demand is to fit a clamp meter to the tails and leave it switched on in peak hold mode for a day or two.  This works well enough, but nowhere in BS7671:2018 does it state that this is an acceptable method for ensuring that the maximum load is within the supply rating.  In fact, pretty much all that BS7671:2018 has to say on this is:

 

Quote

311  MAXIMUM DEMAND AND DIVERSITY
311 .1  For economic and reliable design of an installation within thermal limits and admissible voltage drop, the maximum demand shall be determined.  In determining the maximum demand of an installation or part thereof, diversity may be taken into account.