I'm pretty Ok with understanding Inspection and Testing concepts but today have been asked a question which I'm unsure of the answer and hence would like some thoughts.

If you consider a ring final circuit for example and a fuse spur is incorporated rated at say 13A, if this spur feeds say three sockets the furthest socket will have the highest Zs obviously, however the protection device is a BS1362 Fuse, so do you add this as a seperate entry on the schedule of test results as the remaining ring is proteced by a B32 breaker.

The complication continues when a boiler/timeclock/thermostat circuit is connected to a spur from a ring, is it the responsibility of the tester to stop at the spur, if so the wiring downstream doesn't get a R1+R2 measurement or IR Test! I understand the importance of taking care doing an IR test on electronics and appricate it could be removed from ciruit and linked out.

But the issue remains how far do you go downstream from a spur, any ideas would be greatfully recieved.

To answer the question about the spur from the ring, then it would be highly unusual that the Zs would be greater than that required for the ring protective device anyway.

That said, it can happen (bad design or installation) so it is possible to reference the Zs to the 13A fuse.

It comes down to the definition of circuit in essence, so I would first check index point Zs against the ring CPD and if it complies then no extra line in the schedule required, if it doesn't then add a new line and refernce to the 13A fuse

As for testing cablingdownstream of a spur then I guess there is no right or wrong anwer - it needs testing for sure but for all practical purposes it can't be recorded in a conventional fashion. many sparks just exclude it (either with or without the agreement of the client)

Regards

OMS

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Failure is always an option

I think you have to look carefully at the wording;

A PIR is an inspection that covers the fixed wiring of an installation from the company meter to the end of a circuit???, upstream of the company meter and any equipment connected by a flexible cord to a socket or spur is subject to different regulations, although they are unable to warrant a code on the PIR if any defects that need attention are spotted then note on a seperate piece of paper attached the the PIR form for action by the person ordering the work if they wish to do so.

Or would you want to get in bed with the lady of the house and test the electric blanket!

regards.

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"Take nothing but a picture,
leave nothing but footprints!"
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"Oh! The drama of it all."
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"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
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I suspect that the 17th have a slightly wider scope than earlier versions perhaps did - the prohibition of flex for fixed wiring is long gone and 110.1 specifically says that the regs include requirements for "wiring systems and cables not specifically covered by the standard for appliances". So CH wiring for instances, could well be within scope, even if it's fed via flex from a plug & socket to the wiring centre.
- Andy.

Many thanks for the advice, I think the concept is you can't test too much!

I think you should consider the purpose of the FCU in question.
In the 3 sockets scenario, it is acting as overload and fault protection for a reduction in the current-carrying capacity of the conductor. As such, I would view the 3 sockets to be a continuation of the ring circuit.
Where the FCU is used to connect an appliance or item of equipment, I would view that the circuit ends at the FCU in the same way as the circuit ends at a socket-outlet, and the appliance or item of equipment is not part of the circuit.

If the OP was asking with respect to a PIR then it is really between himself and the person that commissioned the report and the 'Extent of Report' section should be used to make clear what is and isn't covered.

For reasons of practicality I usually stop at the spur for the central heating and attached appliances, but would certainly check sockets/cables etc. downstream of fused spurs.

Slightly different for the purposes of an EIC, as fixed wiring for stats etc. which has been installed should be included - but at least you have the opportunity to complete IR tests etc. before connecting any electronic equipment if you plan ahead.

Isn't that a contradiction in terms Spin - either the sockets spurred from theh ring via a FCU are refrenced to the Ring Final Circuit CPD or they are referenced to the device that provides overload and fault protection (at least in terms of how they are recorded)

I think the problem really arises when the FCU 13A fuse does really need to offer fault (as opposed to overload) protection. In this case the circuit may well be safe when the characteristics of the 13A fuse are refrenced but not when examined against the ring final CPD.

By definition, the spur off the ring controlled by a FCU is a new circuit - whether you choose to treat it as such is a matter for the designer/tester - as I mentioned it's rarely a problem - but that's not always the case

Regards

OMS

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Failure is always an option

I don't want to go back down that road again OMS, but it is your opinion that a spur controlled by an FCU is a new circuit.
Not however the opinion of BS7671.

Only if you ignore the definitions and take the guidance out of context

- Andy.

And treat Appendix 15 as the final word on all matters, whilst ignoring the rather crucial word 'Informative'.

- Sorry Spin, but whilst I haven't much work on it is fun taking you down this road again.

Not just my opinion Spin - it is the de facto definition in BS 7671

Let's ask the question - if you loop tested a socket outlet knowing it was a spur off a ring via a FCU and teh measured Zs was higher than that allowable for the ring final CPD how would you code it - would you then reference it to the 13A fuse and perhaps change the coding accordingly - you might even introduce a seperate "line" on the schedule to note this

Regards

OMS

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Failure is always an option

To my mind, it's a choice between taking note of the guidance which clearly states where the origin of a circuit is.
Or using a definition which doesn't state where the origin is.
To then disregard such guidance because it is only informative, seems ridiculous, especially when there are Regulations that require you to refer to or comply with some of the informative Appendices.
It's your choice, your opinion.
I'm quite happy to use BS7671 when making my opinion.

So what is your opinion on my question then Spin

Regards

OMS

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Failure is always an option

If this was written as 'taking note of guidance which states where the origin of a circuit can be'

and



this was 'Using a definition which clearly states that a circuit is defined by its overcurrent protection only'

then you may start to come over to the dark side

Excepting that the guidance does not use the phrase 'can be', instead it uses:
"A ring final circuit starts and finishes at the distribution board, where it is connected to a 30 A or 32 A overcurrent protective device."
or:
"An unfused spur may be connected to the origin of the circuit in the distribution board."
There is no abiguity in the statements in Appendix 15, whereas the definition of a circuit refers to the assembely of electrical equipment being supplied from the same origin and being protected by the same overcurrent device(s).
If a circuit starts at an overcurrent device, why place an 's' in brackets? Surely according to you each overcurrent device would be the start of a new circuit.

Quite simple really, specify the correct size of cable to allow for Zs to be within acceptable limits when designing the circuit.

'cos 3-phase circuits need more than a single fuse?

- Andy.

Not really no - that just allows you to use seperate devices for overload and fault protection at differing points in the same circuit.

Take a motor circuit - fault protection is usually offered by the CPD at the circuit source end but overload protection is usually offered at the circuit load end. This complies with BS 7671 and is a single circuit by definition - thats why we have a (s) in the definition.

and of course we still have polyphase systems that use fuses

OMS

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Failure is always an option

Edited: 24 February 2010 at 05:38 PM by OMS

What, as in 3 separate FCUs?