I see no harm, the prospective fault current is mainly determined by the impedance of the DNO supply. Simultaneous faults on two or branches of a radial circuit shoud be no worse than a single fault very close to the consumer unit.

Who told you this ? Do they understand electricity and can they point to any credible  reference? Films on Youtube do not count !

 The fault current is highest and most damaging to the breaker when the fault is as near as it credibly can be to the breaker.The breaker needs to match the supply PSSC, or perhaps slighty less if suitably de-rated by the energy limiting action of any up-stream fuse.

The idea of time synchronized  faults somewhere off down branches is a red herring, even if you could lay the two cables one over the other and fire a nail through both together, the breaker will already have begun to unlatch due to the first fault, before the nail shorts the second and fault current comes on .  And if they are not co-located how exactly are the two faults to be synchronized to well within the breaking time of the breaker - i.e. within perhaps a fraction of millisecond of each other....

15 B does not imply that at all. It is just an advisory drawing of one sort of circuit, Does this person also have an issue with ring spurs direct from the CU as well because they are not shown ?

It's the same.

EDIT

Rather like the cable installation methods in the annex, these are not the only wiring methods you can use of course - just the only ones that have been measured or calculated for which ratings are published. For other situations/ layouts one just has to interpret which standard case it is nearest to or do the design calcs yourself.

Mike

PS that nail gun thing...

*Assume the nail gun nail does as good as the best recorded here and shoots at 134 feet/second  that's 40 proper speed units (in technical works speed should be in m/s for any Americans reading)  this is  40mm per millisecond so perhaps it takes 1/4 millisecond to pierce the first T and E, - assuming no loss of speed in doing so. In reality it will be slower.

Compare this to the effective pseudo-speed of a 32A B type breaker  at 6kA fault ( assume an I2t of 29000 A2seconds from this Hagar datasheet)

time is 29000 / (6000.6000) = 0.008 seconds to break . By the time the nail hits the second cable the breaker has already started opening and is about 1/4 of the way through and once contacts begin to open the current is limited by the arc impedance.

This is not a real time, as really breaking completely takes a lot longer, but for most of the time the fault is not the current limiting factor.

Northern Spark said:

I have been informed that we can no longer terminate two or more branches of a radial circuit into the DB/CU. Because of increased fault currents potentially exceeding the breaking capacity of the protective device, if there were two simultaneous faults on the two branches.

Interesting, BS 7671 (for the most part) considers only single fault conditions. Which (specific) Regulations in BS 7671 have been quoted by those "informing" you?

More to the point, though, as Mike will have attested ... how can two simultaneous faults draw more current (and.or for more time, but in energy terms it's the current that's dominant, but in terms of breaker operating time, things get complicated) than other fault combinations in any ring or radial final circuit, regardless of where branches or spurs are made?

Not from YouTube! It was on an annual assessment. The circuit in question was a 20A radial supply socket outlets and the like, wired with two branches into the circuit breaker. The only reference cited was Fig15B. Maybe I misunderstood what was being said, but I don't think so. 

That is rather worrying!

Suppose that two appliances on consecutive sockets shorted simultaneously. Would that make a difference?

I might worry about the assessor to be honest. Ideally anyone doing inspection of any kind needs to be a notch or two above the chaps at the coal face whose work they are looking at. This is because they  need to be able to pick stuff up and run with it very quickly, in any situation, and could be faced with almost anything at zero notice, while the installer may specialise and only do alarms, or never do heating or something.. 

Here however I am confident  your doubts are right, and the assessor is not.

Mike.

Northern Spark said:

The only reference cited was Fig15B.

Interesting ... Figure 15B is "informative" not "Normative".

Are we to understand that we can only wire radials in BS 6004 Flat T&E because that's all that's in the Note under the Figure? Well ... no, that's not the case.

OR perhaps the fact you can't "spur off a spur" in a radial ... well, no, that's not he case either!

Fig 15B is used to illustrate a principle, not provide every permutation possible for a radial circuit.

quite so. And a bit of a worrying attitude from an 'Assessor'

Mike.