Supplies to outbuildings

RF Lighting · 31 May 2020

having just read a lot of posts on this subject, I’m surprised not one person has quoted regulation 433.1.204

“Accessories to BS 1363 may be supplied through a ring final circuit with or without unfused spurs, protected by a 30A or 32A protective device complying with BS 88 series, BS EN 60898...” (remainder of regulation talks about OCPDs and CSAs)

A ring final circuit is not permitted to directly supply anything other than a 13A socket outlet or a fused connection unit.

Adam_151 · 31 May 2020

I think most of us stoped reading that thread before we lost the will to live.....

Anyway, with that in mind, how would you code the following on an EICR:

1) A 20A DP switch directly on the ring, with an unfused spur on the load side supplying a single socket outlet
2) As above, but the feed into the 20A switch is on a short spur from an adacent socket, rather than having the ring looped in and out of the supply terminals
3) A fused spur from a ring supping a number of socket outlets, however instead of a fused connection unit, a 16A 60898 breaker in an DIN enclosure has been used
4) A transformer in a sarel box fed from the ring, instead of a fused connection unit, a DIN rail fuse carrier with 10A Time delay glass fuse is fitted
5) An immersion heater is fed from the ring via a DP isolator, the ring has 30mA RCD protection
6) As above, but no RCD protection to ring (for the sake of argument all sockets are integral RCD types)

flameport · 31 May 2020

1 - no code
2 - no code
No different from a normal spur with a switched socket outlet, other than the switch and socket are separate items.

3 - C3, no selectivity on faults between 16A MCB and 32A MCB

4 - C2, glass fuse has inadequate breaking capacity, likely to explode when fault occurs.

5 - no code
6 - C2 if T&E concealed in walls, no code if steel conduit or similar.
Overload protection not required for a fixed heating load, fault protection is provided by 32A MCB same as for any other unfused 2.5mm² spur.
Fixed heating appliances do not require RCDs.

All above assume 2.5mm² cables used, RCD protection present, no other problems such as signs of overheating, properly connected accessories, etc.

RF Lighting · 31 May 2020

For me, whilst I don’t necessarily agree with it, following the regs to the letter, every single one of Adams scenarios would fall foul of regulation 433.1.204 and would have to receive a code. I think Flameport has taken a very common sense approach and has identified things which may actually impact on electrical safety, rather than just falling foul of some words in a book. This is maybe where the old code 4 would still be useful.

I think this is a case of when the regulation was introduced, it made perfect sense, but as installations have evolved, the regulation has not been updated to recognise the changes in materials and techniques, which whilst they are not compliant, they are perfectly safe.

EFLImpudence · 31 May 2020

RF Lighting said:
“Accessories to BS 1363 may be supplied through a ring final circuit with or without unfused spurs, protected by a 30A or 32A protective device complying with BS 88 series, BS EN 60898...”

It does not say

only accessories to BS1363 may be supplied through a ring final circuit ...

any more than it says

accessories to BS 1363 may only be supplied through a ring final circuit ...

hard-work · 31 May 2020

I believe 433.1.103, Appendix 15, says 20A off a spur. Has that been superseded?

flameport in answer to:

3) A fused spur from a ring supping a number of socket outlets, however instead of a fused connection unit, a 16A 60898 breaker in an DIN enclosure has been used.

"3 - C3, no selectivity on faults between 16A MCB and 32A MCB"

Use different types of mcbs?
No flag on the 16A I see.

EFLImpudence · 31 May 2020

hard-work said:
I believe 433.1.103, Appendix 15, says 20A off a spur. Has that been superseded?

There is no 433.1.101. If you mean .201 it says nothing relevant.
When I find where it says that in the regulations or Appendix 15, I will let you know. Appendix 15 is only informative and not exhaustive.
Out of interest, look at 15B 32A radial circuit and see if you can determine why anything should be different than a 32A ring.

flameport in answer to:

3) A fused spur from a ring supping a number of socket outlets, however instead of a fused connection unit, a 16A 60898 breaker in an DIN enclosure has been used.
"3 - C3, no selectivity on faults between 16A MCB and 32A MCB"
Use different types of mcbs?

Faults does not mean overloads.

flameport · 31 May 2020

hard-work said:
433.1.103

433.1.204 since 2005, which requires the cable to have a current carrying capacity of at least 20A for a ring final circuit.
In most normal situations, that is 2.5mm² cable.

Adam_151 · 31 May 2020

Interesting:

Thoughts were, no.1 has an additional issue over no.2 unless the manufacturer states that the terminals on the 20A switch are suitable for looping a 32A circuit through, so for me, 1 is note it doesn't meet regulations but don't allocate a code, no.2 I'd probably not even mention.
3. I don't beleive the characteristics of a 13A plugtop fuse are actually favourable to a 16 breaker, and if run at nearly full load for extended duration, some fused connection units get a bit hot and bothered, so again note that it doesn't strictly comply but don't allocate a recommendation code.
4. I wondered if anyone would bring up breaking capacity, I think I'd hover between C2/C3 depending on the PFC at the location
5. I'd tend towards a C3 for this.
6. I'd probably upgrade it to a C2 if no RCD protection, I'd class an overload condition as quite unlikely but not impossible with an immersion heater, if it was significantly degraded, but such a condition could only persist if there was no RCD protection, however the suggestion would *not* to be to add RCD protection as that would be a 'very roundabout' way to trying to improve the situation!

JohnW2 · 31 May 2020

Adam_151 said:
... I don't beleive the characteristics of a 13A plugtop fuse are actually favourable to a 16 breaker...

I'm not sure what you mean by 'favourable', but in terms of overload protection they are almost exactly the same. As far as I am aware, to operate in one hour, a 16A MCB needs just over 23A and a 13A BS1362 fuse at least 22A.

Kind Regards,m John

EFLImpudence · 31 May 2020

Not arguing about the EICR aspects; just what you are saying.

Adam_151 said:
Thoughts were, no.1 has an additional issue over no.2 unless the manufacturer states that the terminals on the 20A switch are suitable for looping a 32A circuit through,

Why would a manufacturer state such a thing with no current flowing through their product?

Do socket instructions state it?
It's difficult enough to find out how much can actually flow through a (double) socket being used for its intended purpose.

6. I'd probably upgrade it to a C2 if no RCD protection,

RCD protection is nothing to do with the appliance.

I'd class an overload condition as quite unlikely but not impossible with an immersion heater, if it was significantly degraded

I would say it is impossible.

hard-work · 31 May 2020

Adam_151 said:
5) An immersion heater is fed from the ring via a DP isolator, the ring has 30mA RCD protection

The immersion is a spur off a ring with no spur cable protection, relying only on the 32A mcb in the CU.

EFLImpudence · 31 May 2020

hard-work said:
The immersion is a spur off a ring with no spur cable protection, relying only on the 32A mcb in the CU.

No, it is relying on the fact that an immersion heater cannot cause an overload, and

the 32A is adequate for fault protection; not to mention the stated presence of an RCD.

RF Lighting · 1 Jun 2020

It can cause an overload if the outer housing of the element splits and allows current to flow to earth through the water. This is something I have genuinely seen happen.

hard-work · 1 Jun 2020

Electricity and water do not mix well.

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