Clarification on additional sockets on a spur

[radiohead]

Thanks radiohead is there any scenarios then you would be comfortable doing what I proposed....2 double sockets off 4mm from ring.

Absolutely not. Bs 7671 permits a maximum of 1 double outlet to be on an unfused spur from a ring.
The only theoretical reason I can see for wanting to put two double sockets on a 4.0mm spur from a 2.5mm ring would be because it was anticipated that these two sockets would be heavily loaded. That would create an unacceptable load potential on one point of the ring.
Where a number of lightly loaded outlets are to be installed then a 13a FCU spur for ease of installation would be sensible, but where more than one outlet is required and load is unknown always incorporate on the ring.

 

[Pretty Mouth]

In the case of an unfused spur feeding a twin socket then potentially a load of 26a could be drawn at that point on the ring.

Potentially it could be 52A at that point on the ring, assuming the spur feeding the twin socket has been taken from the terminals of another twin socket.

 

[JohnS888]

Potentially it could be 52A at that point on the ring, assuming the spur feeding the twin socket has been taken from the terminals of another twin socket.

Can you clarify that for me. Seem to suggest even with one double socket being supplied from another double on a ring could be 52 amps on one leg of the ring?

 

[TJ Anderson]

Potentially it could be 52A at that point on the ring, assuming the spur feeding the twin socket has been taken from the terminals of another twin socket.

Anything over 32A for whatever reason will then be covered by the fuse or circuit breaker in place. The potential issue is long duration overload overheating and damaging cable insulation but It's not really such an issue anymore in my experience and certainly nothing like the level it is talked about. It was more of a problem with the 3036 fuses which would stay intact for long periods significantly over their rated current. The worst case of it where it was really an issue and had caused damage was in an office with 30A 3036 fuse in place. Panel heaters as well as the computers etc. It was pulling 47A when I clamped it at DB. Running for hours on end like this. 60898/61009 has far better characteristics.
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Can you clarify that for me. Seem to suggest even with one double socket being supplied from another double on a ring could be 52 amps on one leg of the ring?

You can easily overload any ring final circuit with the sockets available but it is designed to be limited by the overcurrent protective device and with realistic diversity it is not an issue to 99.9% of them that are in operation .

 

[radiohead]

Potentially it could be 52A at that point on the ring, assuming the spur feeding the twin socket has been taken from the terminals of another twin socket.

Yes of course, I stand corrected.

To the OP..... a ring with 10 double sockets could potentially be loaded at 260a. but as above, thats why Bs7671 stipulates a 32a OCPD to protect the conductors from prolonged overload.

 

[Pretty Mouth]

Can you clarify that for me. Seem to suggest even with one double socket being supplied from another double on a ring could be 52 amps on one leg of the ring?

At the terminals of the double socket spurred from, there could theoretically be 52A (26A from the spur, 26A from the spurred-from), but this would be divided up between the 2 legs of the ring, with more of it going down the shorter leg. While this overload is taking place, the circuit breaker is working toward disconnection, could take up to 10 mins for a 32A 60898. So if the spur was taken from a socket very close to the CU on a very long ring, then a cable rated to perhaps just 20A could indeed be getting the majority of that 52A for 10 minutes.

Highly unlikely though, and to design a circuit like this would be breaking 433.1.204