Outside lighting circuit Question

[sambotc]

Which would lead me back to the question 'why have the fuse at all?'

It seems daft having a fuse there but then not taking it into account for its sole purpose?

personally, I think as long as the disconnection times are met, regardless of which device, it should be fine. Whether or not that is how the regulations were mean't be perceived remains a mystery i guess? The disconnection times are there for a purpose after all, so I think I would be happy if the times are met as it would obviously seem that the hierarchy who compiled BS7671 would be happy from a safety point of view?

I'm getting assessed on this job for CPS so I will ask the inspector on his views as well.

 

[Barry Rathbone]

Please don't tell the inspector about your thoughts on second thougths do!
The fuse is there to protect the cable is it not(FIRE!), surely you haven't just said you would connect a 1.5mm cable to a ring circuit to a light via a socket on a ring( 2nd FIRE )??
Saying that are you now happy with the outcome of the Max Zs being the 1362 fuse in the BS7671? 3A or 13A.
As I said the reading is high it is not not a complete failure it works, ok so it won't blow your fuse atm but it would if you placed in a 3A and labelled up as 3A only.. Making recommendations in report as this fuse could be replaced with a 13A and never blow with the readings you give......
But you HAVE to check out the wiring as you have a high ELI and leave it safe or as said before rip out renew.
Forget calculations( use when required to design ) use your calibrated ELI tester( your calcs say theory do they not your meter doesn't), it says what it says....BS7671 backs you up...
Oh and for me I WOULD add it on a report as Outside light etc etc....remarks/FCU at back door on downstairs ring

Thats just me sorry ...

COVER your arse at all time, miss it someone won't... written down is your only case for your defence in a court god help us all!!!

 

[brman]

brman......"No, because the regs only deal with fixed wiring. Anything beyond a socket doesn't count"

According to the regs, fixed wiring is still fixed wiring regardless of whether it is connected via a plug and socket or an FCU. The old get out clause of outbuildings "plugged in" doesn't work any longer

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when does it change from being portable and go to being fixed? Does my extension lead for my computer (that is screwed to the wall) count as fixed wiring then? Sounds like another can of worms :lol:
anyway, I don't think it changes my arguement. I would definitely treat any extension lead (whether fixed or not) as a seperate circuit and only consider things like Zs (in the unlikely event I actually tested it!) back to the plug fuse.....

How could I ignore you laid up in bed. Nothing worse than twiddling you thumbs and not being able to move around.
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You are too kind

RFC's are peculiarly a British invention aimed to satisfy the reduction in the use of copper, and so require a peculiarly British solution of testing. I think providing a separate EIC for a fused spur to a socket being even more peculiar.....
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Are you calling me peculiar?
it wouldn't be the first time someone has done that.... :lol:

Actually, I don't think a seperate EIC is required. The form is after all just a guideline and can be modified as long the required information is included. So nothing wrong with modifying it to add sub circuits like fused spurs along the main curcuits like the ring.
eg.
1. Ring final......
1.1. Fused spur to garden......
2. light radial....
etc
You would just need to be clear what the Zs as origin of the fused spur was as there isn't an obvious place for that. Could put in the comments box though.

I'm getting assessed on this job for CPS so I will ask the inspector on his views as well.
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I'll be interested to hear what he says!

 

[Barry Rathbone]

I want to be a rather large fly on the wall in the conversation.

1. Ring final......
1.1. Fused spur to garden......
2. light radial....
etc
Yes, but each to his own as I say written down.
The origin is what the rings Zs is so thats covered.

 

[sambotc]

Not what I was implying Barry, sorry if I have confused my posts!! :biggrin5:

I am definitely NOT going to just let it go. I will search for the fault to the best of my ability. If it is found to be the cable itself, all I can do is notify the customer BUT I would walk away knowing that the RCD is still going to be effective as per the 1667 rule or even better the fuse, after all I can't force the customer into lifting the patio?

I'm not a corner cutter, and if you read my post at the top of the page, you'll see that I object to effectively falsifying the results by changing the fuse for a 3A, thats not the way I operate personally.

The comment above was aimed more at the theoretical/logic explanation of the regulations. I can't see why they have BS1362 listed in the look up table's if it is to be ignored in a situation like this though.

I presume there may be a time where I come across a similar installation (with no faults apparent etc) which exceeds the disconnection times for the MCB, but would comply with the disconnection times of the rated fuse at the spur. In this sort of instance, my personal assumption (rightly or wrongly, but until I can see a logical argument against it) I would be happy to walk away knowing that the disconnection times have been met for the BS1362

At the end of the day, we don't write the reg's but we have to adhere to them. The disconnection time for the OCPD would have been achieved and satisfy BS7671 so I would be happy to sign my name on the line?

Does this seem logical?

Otherwise, we will have to make an assumptions on the situation which is the cable in question will never have a load higher than whatever the rating of the fuse is, but lower than the MCB rating. In which case, why have the fuse at all?

Its an interesting conversation and I can see both sides of the argument, but as of yet nothing which makes any sense for using the MCB rating for disconnection time. I am also very willing to see the evidence for it, but preferable a logical explanation rather than dissecting the terminology of BS7671, logic overrides assumption in my mind!

 

[Barry Rathbone]

No confusion sorry, light humour!
It ain't being ignored and DONT ignore it the inspector will slap ya! and hard....lol

All tests done on 1.5mm cable ? ins res, r1 + r2 ,after you found the high Zs? Any problem jump at you,condition of cables both ends?.
Falsifying records? Don't agree you ARE making it SAFE.An inspector would pat you on the back for a thorough job IMO...

It will blow in 5s according to the regs why the confusion, fixed equipment?Would be nice to get it below 16 ohms though at least for a .4 Disconnection time..And below the 2.42 for a 13A with a .4 disconnection time! All happy Good look..
The mcb on the ring is not your issue its the high Zs on the outside light/s circuit.You know if the ring gets a fault it WILL trip the mcb due to the max Zs of 1.44 and your good readings.

"I presume there may be a time where I come across a similar installation (with no faults apparent etc) which exceeds the disconnection times for the MCB, but would comply with the disconnection times of the rated fuse at the spur. In this sort of instance, my personal assumption (rightly or wrongly, but until I can see a logical argument against it) I would be happy to walk away knowing that the disconnection times have been met for the BS1362" Woo HOO!!

Walks away happy.....

 

[sambotc]

I see your point and if all else failed then I guess it could be considered, but then with that attitude why not just leave it and sign it off under the 1667 RCD rule?

Is there a right or wrong in this instance? probably not as far as the reg's go as there are multiple ways of meeting the disconnection times depending on how you want to look at it, it's more of a moral high ground I suppose? Why leave something (compliant) in a condition that could be improved for a little more effort?

I'm going to have another look tomorrow as i couldn't get back today so I will see if I can find the culprit and report back.

I'll take a 3A fuse just in case . . . :tongue3:

 

[soulman]

That's interesting, fixed wiring now extends to extention leads. Are you sure about that one, I would not test or check the wiring within a shed if was fed via a 1363 plug. I think you need to find the reason why zs is so high, An rcd protecting the circuit doesn't mean that you shouldn't be investigating a high ELI value on a TN installation

 

[Guitarist]

That's interesting, fixed wiring now extends to extention leads. Are you sure about that one, I would not test or check the wiring within a shed if was fed via a 1363 plug. I think you need to find the reason why zs is so high, An rcd protecting the circuit doesn't mean that you shouldn't be investigating a high ELI value on a TN installation

Fixed wiring now covers any installation where the cabling is fixed. It used to be an old way of avoiding testing to simply "plug in" an outbuilding. No longer allowable.
An extension lead which you can reel up is still an extension lead

 

[sambotc]

OK UPDATE:

This has really been a bad day today, and i'm not sure if I have overlooked something here and starting to doubt myself so here goes.

Went back to re test, Zs on loop on my metrel = 18 ohms. Using line function on the metrel = 0.60 ohms. Figured as before, must be a poor earth.

Went back to the spur, and carried out Zs on supply side, 0.55 ohms. Tested on load side 0.80 ohms, a bit high but not causing the problem.

Decided to do end to end, so got the wander lead out. R1 = 0.39 ohms (if I can remember readings now!) Rn = similar readings R2 = >2000 ohms.

Baiscally quadrupole checked leads, connections, everything. Nothing.

IR test all great across all conductors.


So, how is this possible? Has the loop test on my metrel measured a path through neutral and back from earth which would explain the high readings?
I'll be honest i got lost when trying to figure it out and couldn't explain it but had to stick to my test and decide that with no earth it had to be disconnected as the fitting is metal.


Would appreciate some of your thoughts as it's really annoyed me today and my head feels frazzled trying to work it out. I may have missed something really obvious which is why I ask. The customer surprisingly wasn't bothered and just asked me to take it all out, but until I can understand what happened its going to really bug me.

Cheers in advance

 

[telectrix]

R2 = >2000 ohms.
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if that,s correct, you've got an O/C cpc.

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[sambotc]

Yep, which is why I have disconnected it, but how did I get a Zs ?

 

[sambotc]

The penny has just dropped, there must have been a path back to earth from the cable underground which was in a duct/pipe/conduit.

This was full of water,mud and muck,so I am guessing it would have tracked back to earth and would explain the high resistance?!

Thoughts welcome ....

 

[sambotc]

Anyone, does this seem like a logical explanation? Defiantly open circuit end to end, so unless my 3 lead metrel has been playing funny games, the only way I could have got the MFT to work at all, would have been to get a path to earth some how? Would you expect 18ohms though from the 1.0mm CPC effectively buried in mud and water?

Would just be good to draw a line under it, figure out what wa going on, and know that I haven't cut their outside light off for no reason!

In hindsight, could I have left it operational on this retro TT installation lol? It was RCD protected, ,but surely knowing it wasn't connected to the MET means it is wrong?

Cheers in advance

 

[polo1]

Sorry, don't know the answer to the Zs question, but think you were absolutely correct to disconnect an external fitting having no effective earth, RCD or not!

Regards