New light added to circuit

[too old to learn]

Hi Guys,

wondered if anyone could give me advice on hypothetical question.

You go to a customer who wants an additional light added onto a lighting circuit. lets say they want 2 lights in there sitting room instead of one.

How would you go about carrying out a Zs test if all the other ceiling roses had been painted in. therefore you can not get to the end of the circuit?

Just wondered this as obviously you would need to do a MWC but I wouldnt want to say I need to add additional cost of 7? new ceiling roses as have to smash them off to complete test?

Or would you just fit the lights and not do a MWC?

Thanks

 

[holmslaw]

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[too old to learn]

thanks holmslaw,
I just thought if you were modifying a circuit though you took responsibility for that circuit.

so what if after this joint there were (totally exaggerating) hundreds of meters of extra lights and therefore a fault on the circuit at the end would not trip the breaker. would this not be down to you not testing it correctly?

I appreciate the answer though as this is what I thought ).
I also thought I would just write on the limitations section that tests were carried out here due to not been able to identify the end of the circuit

 

[holmslaw]

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[ban-all-sheds]

What if at the end of the existing circuit Zs was only just OK, and by adding a new light, and extending the loop, your addition pushed it over the limit?

 

[holmslaw]

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[ban-all-sheds]

True - I was thinking more of the general case - might there be occasions where the location of a new light in relation to others and to existing cable runs made extending it the most obvious solution?

I'm can't think of an example though, so maybe I've answered my own question....

 

[too old to learn]

if i added to the end of the circuit then i will be able to get my Zs reading and as long as it passes then all is fine. If it didn't pass i guess I would have to fix the problem, or remove the light and state that I cant extend and remove the joint.

I still believe though that if you work on a circuit then you take responsibility for it? as you have stated you need to check the main bonding. as this is part of your responsibility. You cant say, it wasn't there before hand so its not upto me to put right? as long as my little extra light is done correctly then im all right?

Even tho, in the real work i would suspect that 90% (random high figure lol) of sparkies would carry out the work but point out they need the bonding done

 

[ban-all-sheds]

if i added to the end of the circuit then i will be able to get my Zs reading and as long as it passes then all is fine. If it didn't pass i guess I would have to fix the problem, or remove the light and state that I cant extend and remove the joint.

I was thinking about extending it in the middle, thus making the end point further away, but as I said I can't postulate an example....

I still believe though that if you work on a circuit then you take responsibility for it?

But you can't.

What if you were adding a light but no new switch drop on a circuit with no RCD? Would you insist on installing an external RCD/an RCBO/moving the circuit to the RCD side?

How would you ensure that the existing circuit had no cables run out of zones, no concealed JBs, no lack of cpc continuity somewhere, no sections wired in telephone cable?

Would you expect to check the other lighting circuits for borrowed neutrals?

If you were adding a socket to a circuit which somewhere had a spur running off to a pond pump would you want to dig up the patio to check that it was the right sort of cable/properly protected/at the right depth?

Would you lift floors/drop ceilings to check that cables through joists were far enough from the surface?

The list goes on and on - "taking responsibility for the entire circuit" is a chimera. Why beat yourself up by taking the illogical and inconsistent position of "well I could decide that I have to ensure that what's already there complies with some of the regulations but not all of them"?

 

[too old to learn]

Well i was taught (rightly or wrongly) that you modify a circuit then you are responsible to ensure that circuit is safe.

Yes, I understand that doesn't mean lifting floors / smashing floors etc to ensure safe runs etc.

still, it has made me think and I guess what the real case is that you don't make the circuit any worse then it all ready is? which goes to cover some of the aspects of cables that are ran outside of zones.

So, lets say that there is no main bonding done. you are only adding a extra light to the circuit. Your not really making the installation any worse then it is.

would you still carry on with the job?

 

[GaryMo]

So, lets say that there is no main bonding done. you are only adding a extra light to the circuit. Your not really making the installation any worse then it is.

would you still carry on with the job?

131.8 Additions and alterations to an installation

No addition or alteration, temporary or permanent, shall be made to an existing installation, unless it has been ascertained that the rating and the condition of any existing equipment, including that of the distributor, will be adequate for the altered circumstances. Furthermore, the earthing and bonding arrangements, if necessary for the protective measure applied for the safety of the addition or alteration, shall be adequate.

411 Protective Measure: Automatic Disconnection of Supply (ADS)
411.1 General

Automatic disconnection of supply is a protective measure in which:

(i) basic protection is provided by basic insulation of live parts or by barriers or enclosures, in accordance with Section 416, and

(ii) fault protection is provided by protective earthing, protective equipotential bonding and automatic disconnection in case of a fault, in accordance with Regulations 411.3 to 411.6.

 

[too old to learn]

i luv it when ya get regs numbers quoted lol.

Problem been though, how many people would turn down an easy job because they knew the bonding weren't upto scratch?
guess it is all down to your own conscience!


and as previously mentioned, if you cannot trace the end of a lighting circuit to carry out the Zs test due to painted in ceiling roses what course of action would you carry out.? or would you just carry out the work regardless?

sorry for all this, just on a quiet day!

 

[GaryMo]

Regarding the addition of a lighting point then I agree with the others - install your new extension or branch to the existing radial and measure R1+R2 at your new point along with Zs (or calculate with the addition of Ze).
As long as Zs is low enough to ensure disconnection of the protective device within the allowed time then all is well and no need to crack open other roses.

Replacing fittings on a like for-like basis is one thing but if installing new cabling and fittings then I would want to see that Protective Bonding Conductors are present (if required).

 

[holmslaw]

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[GaryMo]

If a rewireable fuse is it the correct size fuse wire, and if it is an rcbo or an mcb then fully test them.

How do you fully test an MCB apart from switching it on and off and checking its output? Or is that what you mean?