Isolator on Ring circuit

333rocky333 · 2 Apr 2021

Went to a job and noticed someone has spurred from a socket on a 32a 2.5mm ring, with 2.5mm cable to feed a rotary isolator.

The isolator is for a Fire system that has a built in motor, not found the relevant data sheet yet but a similar model suggests a 20 amp supply.

Did not seem right to me but is it actually wrong and contravene any regs.

As it is a safety system I have recommended it put on own circuit, though this will not be an easy task.

RF Lighting · 2 Apr 2021

433.1.204 accessories to BS 1363 may be supplied by a 30/32A ring circuit using 2.5mm² cabling. The rotary isolator is not a BS 1363 device so may not be supplied by a ring circuit using reduced CSA conductors.

EFLImpudence · 2 Apr 2021

We (used to) have the same argument with 20A switches; such a prohibition would be ludicrous.

Are switches "supplied"?

Also, the 'ring' regulation (433.1.204) does not apply to spurs.

RF Lighting · 2 Apr 2021

The spur and what ever accessory it connects is supplied by a ring circuit so 433.1.204 does apply.

EFLImpudence · 2 Apr 2021

I disagree.

RF Lighting · 2 Apr 2021

Which part of the regulation(s) says that a spur supplied by a ring is not governed by the regulation about things supplied by a ring?

EFLImpudence · 2 Apr 2021

Well, for a start, if T&E it doesn't have to be a minimum of 2.5mm².

chivers67 · 2 Apr 2021

I wonder what the Start up current for the motor is, probably ok but worth finding out if there's other current carrying equipment being used at the time if it's needed?

JohnW2 · 2 Apr 2021

RF Lighting said:
433.1.204 accessories to BS 1363 may be supplied by a 30/32A ring circuit using 2.5mm² cabling. The rotary isolator is not a BS 1363 device so may not be supplied by a ring circuit using reduced CSA conductors.

If we're talking about "what the regulation actually says" (or does not say), as BAS often used to point out, the regulation does not say that "only accessories to BS 1363 may be supplied by a 30/32A ring circuit using 2.5mm² cabling".

Apart from anything else, as EFLI has said, that interpretation would mean that, for example, the 20A grid (or plate) switches commonly connected to kitchen rings would be non-compliant.

Kind Regards, John

333rocky333 · 2 Apr 2021

chivers67 said:
I wonder what the Start up current for the motor is, probably ok but worth finding out if there's other current carrying equipment being used at the time if it's needed?

Still waiting to here from the suppliers but an internet search suggests it needs a motor rated Mcb, at present its A B32 mcb and that was one concern, will it trip that when its needed in an emergency.
We also need to Rcd protect the sockets, so i feel it should be on its own supply to help maintain continuity of service
http://www.watermist.com/media/filer_public/2019/03/10/f304_-_15apu_data_sheet_iss_1.pdf

333rocky333 · 2 Apr 2021

JohnW2 said:
If we're talking about "what the regulation actually says" (or does not say), as BAS often used to point out, the regulation does not say that "only accessories to BS 1363 may be supplied by a 30/32A ring circuit using 2.5mm² cabling".

Apart from anything else, as EFLI has said, that interpretation would mean that, for example, the 20A grid (or plate) switches commonly connected to kitchen rings would be non-compliant.

Kind Regards, John

When i trained to the 15th regs there was no appendix 15 and it was acceptable i recall to even put a 16a mcb on the Ring and i believe was shown on early diagrams but not on the current one.

20210402_204512

333rocky333
2 Apr 2021

JohnW2 · 2 Apr 2021

333rocky333 said:
When i trained to the 15th regs there was no appendix 15 and it was acceptable i recall to even put a 16a mcb on the Ring and i believe was shown on early diagrams but not on the current one.

Interesting - and I suppose not particularly illogical - after all, the 13A max for FCUs and SFCUs is fairly arbitrary {in relation to a ring final} and probably essentially reflects the fact that 13A is the largest BS1362 fuse available.

At least now, the regulation itself does not say anything at all about the fused spurs (nor, indeed, 'MCB-protected spurs') hence says nothing about the maximum rating of the fuse rating for such a spur, merely indicating that a ring final may be "with or without unfused spurs" - so I suppose that one could probably argue that MCB-protected spurs (analogous with fused spurs) were permissible, perhaps even ones using a 16A MCB? After all, a 16A load applied at one point of a ring final is 'no worse than' (in fact, 'not as bad as') the load which could be applied at that point of the circuit if a double socket were installed there.

Kind Regards, John

SUNRAY · 2 Apr 2021

333rocky333 said:
Went to a job and noticed someone has spurred from a socket on a 32a 2.5mm ring, with 2.5mm cable to feed a rotary isolator.

The isolator is for a Fire system that has a built in motor, not found the relevant data sheet yet but a similar model suggests a 20 amp supply.

Did not seem right to me but is it actually wrong and contravene any regs.

As it is a safety system I have recommended it put on own circuit, though this will not be an easy task.

I haven't tried to look it up but I believe the motor requires a proper motor overload set to the motors FLC.

333rocky333 · 2 Apr 2021

SUNRAY said:
I haven't tried to look it up but I believe the motor requires a proper motor overload set to the motors FLC.

I did not remove the cover but i guess its all contained within the unit.
The systems maintained annually by another company, so you would like to think they knew what they were doing

JohnW2 · 2 Apr 2021

333rocky333 said:
As it is a safety system I have recommended it put on own circuit, though this will not be an easy task.

As I often say in relation to domestic alarms etc., I would personally think it desirable that, if supplied by "its own ('dedicated') circuit", there should be some 'power failure alarm' on that circuit (unless there is already a battery-powered alarm alarm built into the system).

Kind Regards, John

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Isolator on Ring circuit

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