Definition of 'electrical installation' and requirement to upgrade existing to current regs?

Wasn't there a time when all sockets were on 16 A radials?
Nominally 15A or 5A radials, one per socket, BS3036 style hot wire fuses.

Even by the 1929 9th edition, that had gone..

 could  have more sockets, Not much later, then earths were also required on new socket circuits, since just after the war - its been a verylong while since one wire one socket, and all that sort of stuff was being taken out from the 1970s onwards.

Mike.

mapj1 said:

If we really believed a fuse or breaker could never ever be used as a load limiter, then all socket circuits  would be limited to supplying a maximum of 2 and a bit 13A sockets, and or  we should dispense with the 32A breakers as they are superfluous.

Yes.

Wasn't there a time when all sockets were on 16 A radials? In those days, there were no spurs.

acceptable to down rate the ocpd for a ring final to 20 amps,

Agree, and quite common when the ring has lost its ring and become 'crab claws' or Christmas Tree spurs or similar. This reduces a risk of burning the house down to a risk of getting a bit hacked off because it trips occasionally, and if that encourages a more careful use pattern, that avoids the overload and tripping,  that outcome is very good. If it encourages a call back for a rewire, also good ;-)

If we really believed a fuse or breaker could never ever be used as a load limiter, then all socket circuits  would be limited to supplying a maximum of 2 and a bit 13A sockets, and or  we should dispense with the 32A breakers as they are superfluous.

I suspect neither interpretation is what the author intended however.

Mike.

Spurs from spurs, are quite common in practice (go back far enough and two single sockets where permitted on a spur, undoubtedly many of those singles got replaced by doubles over the course of time). Not to mention the usual total botches. The worst I came across was most of the kitchen sockets fed from a 4mm or 6mm cable (lollipop style) - presumably originally the cooker circuit but made redundant when the hob was changed to gas - but then it looks like the old cooker fuseway was pinched for a new shower, so the old cooker cable was redirected into the back of a convenient socket ... which happened to be on a spur. So you had in effect an entire kitchen, including a 2kW oven, washing machine and all the usual kitchen appliances, plus the socket usually used for the ironing, all on one 2.5mm2 cable. It had been like that for years apparently - but had it burned the house down? was it frazzled to a crisp? was it looking a bit distressed? not at all - it all looked fine. (it did get changed all the same though). Has anyone else seen a domestic spur cable looking distressed from overload?

  - Andy.  

gkenyon said:

Any starting point could be considered an assumption, because the socket-outlets could be used for any purpose by any "ordinary person", but generally, perhaps the kitchen given the "usual loads" plus any "odd loads selected by any ordinary person".

And of course, different households do things differently, so what suits the current occupier may not suit the next.

Chris Pearson said:

gkenyon said:

I think, though, there's a difference between the "kitchen sockets" vs the "upstairs sockets" when taking this into account ... clearly one usually has more propensity for accidental overload due to anticipated loads involved.

Which one?

I doubt that electric heaters are used as much in kitchens as bedrooms.

Moreover,

MFr said:

the other big load devices (hob, oven, washing machine) are on separate rings or radials

So in this case, the dishwasher may be the biggest load in the kitchen, but it will not be heating water for long.

Any starting point could be considered an assumption, because the socket-outlets could be used for any purpose by any "ordinary person", but generally, perhaps the kitchen given the "usual loads" plus any "odd loads selected by any ordinary person".

This discussion proves that there is no "guarantee of safety", only a "likelihood of safety" that's possible with an electrical installation - the same holds true for discussions about protection against electric shock.

broadgage said:

Portable electric heaters with a single phase loading of more than 3Kw are very rare. In many years of experience I have seen just one !

They weren't that rare in the 1970s (3-bar fire) ... probably a hang-over from the 1960s ... but since the move towards, and later achievement of, harmonization, agreed ... 

True.

I was suggesting a hopefully easy to grasp hypothetical situation to help give an example that could help with understanding the 'rule' about fuses and circuit breakers for control of 'stupid' [aka uniformed] users.

Portable electric heaters with a single phase loading of more than 3Kw are very rare. In many years of experience I have seen just one !

It has 4 radiant elements, each of 750 watts, and 3 settings of convector heating with a maximum output of 3Kw, so a total of just over 6Kw, allowing for the improbable number of 60 watt lamps in the decorative fuel effect. It remains in use, and is on a dedicated 30 amp circuit, with final connection via a 32 amp  ceeform plug.

I believe that one 'plans' the expected/typical value of n (number of sockets) for the n single bar fires and ensures that the circuit's cables are capable of that level of current.

So in that sense the trip is for 'fault' detection, and that normally the user would not have overloaded the circuit.

The user would have to work hard to create the problem, while in an N+1 way switch case it's easy for a user slip-up to select the overload case warned about in the extract.

A good read is Reason's "Human Error" book to see the distinction between slips, lapses and mistakes and their different protection/safety approaches.