Hi Folks,

New to forum, though I have been viewing for ages. I am a recently qualified sparkie, and would like some guidance for NIC DI assessment.

I have changed a DB, upgraded Earthing and banged in a new rod (TT system). Fitted a split load-dual RCD board with 3 additional unprotected ways, all main Earthing/bonding Conductors in 16mm, Rod in plastic pit with a Ze of 61Ω. Goes to around 30Ω with parallel paths from utilities.

I would obviously prefer to pass assessment 1st time and avoid having to pay £300+ for a 2nd visit. I have a few points of concern though:

1) There is a small section of rubber cable (approximately 7ft in length) with no CPC (radial cct).. I have replaced a large part of this cable but this last section would involve massive disruption. I have IR'ed the rubber section and got >299MΩ. All the cct has a CPC bar this small section (and I do actually get a R1R2 due to earh path through pipework).

2) Should I install a Type S 100mA front end RCD for discrimination, or can this be omitted?

3) There is a shared N between lighting ccts so have put both these ccts on RCBO's.

4) The upstairs power cct appears to be a radial, though have not had a chance to fully investigate this yet. Was this ever common practise in an install approx 40 yrs old?

5) PSCC is 1.4kA. Can equi-potential bonding be omitted due to 17th? TT is not likely to meet Dis.Times, though not checked this yet. Is there an equation for calculating this? Sorry, being a bit lazy here!

Overall the install is much much safer than it was, so would I be ok to list 1), 2) & 5) above as departures on EIC. Or will assessor likely insist otherwise.

All thoughts welcome and appreciated.

Thanks,

Dave

Just some initial thoughts there....

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Experience can sometimes show that cost prevails over quality and safety, such little self-value that people hold.

1. What's the circuit for? The only circuits that you could argue for a cpc to be omitted are for lighting where all the fittings and accessories are class 2. If it is another type of circuit then I would say you need a cpc .see the ESC guide on this. ESC Best Practice Guide No.1

2. Discrimination for what? If all the circuits are protected by 30mA RCDs a time delay RCD not going to do anything

3. "Shared", "Borrowed" or "Stolen" neutrals not allowed. The wiring of each final circuit is required to be kept electrically separate from every other final circuit.

4. Radial circuits are found in all types of houses,

5. Main equipotential bonding is an essential part and required in the majority of electrical installations. Supplementary bonding can be omitted in bathrooms see Reg 701.415.2

Cheers Test it:

543.2.2 (vii) seems to point that an extraneous conductive part can be used as long as it is not gas, oil, etc (543.2.1). So I guess this being a water pipe it should satisfy?

RCBO's on 2 unprotected ways, work fine. See your point about other unprotected way then making the 100mA necessary. Could I label the unprotected ways to say that only RCBO's should be used and not MCB's?? Just a thought.

So do need to cross bond water pipes and boiler then. But see at bottom re: 701.415. I'm confused!
Guess what I was trying to say is under the 17th I seem to remember that sometimes equipotential bonding can be omitted (mainly TN-S TN-CS). Is there a general equation to work this out? Seem to recall something that involved PFC and Ze.....May be wrong though.

Only plastic is in my head!!

Mike:

"2. Discrimination for what? If all the circuits are protected by 30mA RCDs a time delay RCD not going to do anything"

That's exactly what I thought! Though with unprotected ways will need to do now. Or I may put in another cct on last spare unprotected way with a RCBO instead!!

And "Main equipotential bonding is an essential part and required in the majority of electrical installations. Supplementary bonding can be omitted in bathrooms see Reg 701.415.2"

Had a look at 701.415.2 which says that if a protective equipotential bonding system is in place then if RCD protected then bonding can be omitted as you say. And bonding is not required in kitchen anyway!

Thanks fella

Nope...No 3rd party utility service pipes can be used. The only time pipework can be used if I remember correctly, is something like pipework from a borehole on the consumers property.



In 701.415.2 the second set of 3 numbered points detail the three criterion which must be met in order to omit SEB. So for TT, it needs 0.2 s disconnection (though refer to note at bottom of table 41.1 in BS7671, which allows 0.4s disconnection in certain circumstances). All circuits in the location require RCD protection. All extraneous conductive parts require there to be adequate main earth bonding in place (protective equipotential bonding).

Yooj

Reason for editing: thought of something else to add

But don't confuse CPCs with earth electrodes - the 542.2.4 is talking about electrodes.


But 543.2.2(vii) says you still need to comply with 543.2.6 - what precautions have been taken to prevent the pipe being removed (e.g. plumber replacing with plastic).


Section 701 only applies rooms containing a bath or shower only - it doesn't apply to the rest of the installation and the bonding it's talking about omitting is only the supplementary bonding (usually within the bathroom) - not main bonding to services entering the building.

Surely both "circuits" would need to be on the same single RCBO (or RCCB) to avoid nuisance tripping???

- Andy.

Ahh yes...cheers Andy

Yooj

Just on the point of the pipework.. yes it can be used, making note of prevention of removal of any pipework...

I did this once about a year back when the upstairs lights were unearthed on a CU change, no trunking or cabling on the downstairs walls wanted so I utilised the CH pipework with trunking in the landing corner to run cables as well as interlink alarms...

Prevention of pipe removal is a difficult one, however what I did was to have solid labels made about the size of a single gang socket and placed this right above the boiler switch, namely because anyone doing plumbing changes would need to go to that switch to disconnect boiler and also placed one at CU incase of being switched there... they cost about £8-50 each when buying three and warned of any pipe changes made to confirm earthing due to pipework being used as the earth... on the cert I noted the reg number and usage of pipework for earthing... job done... actually the property I decided to use as one for my soon assessment and I'm happy with the decision and resolution found which can be supported with BS7671.... likely I will need to explain it again though...

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Experience can sometimes show that cost prevails over quality and safety, such little self-value that people hold.

Er Downtoearth Dave.
Can't ya pick another job for your assessment..
My assessor would throw a big red book at you.

just a thought
Ady

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Resistance is futile.

It appears the OP is not yet quite ready for the world within the 'registered contractors' club.

"Can't ya pick another job for your assessment." sums the current situation up neatly.

Never mind, I ain't registered either, so it's not the end of the world.

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Norman

Hi again, SORRY for delay in replying, and thank you all for input.

Interesting to see different interpretations of the regs. Just goes to show how confusing they can be!

But anyway the consensus is NO, NO, NO! Fair enough!

How about if I sorted equi-bonds to bathroom and replaced small section of rubber cable.

The stolen, crossed, borrowed, naughty neutral is a common occurrence on lighting ccts isn't it after all. So SURELY this can be listed as a departure, and a notice put near CU to warn of this situation for future??

My argument would be that the installation (with above alterations) is much safer than previously. In an ideal world then yes this would also get sorted, but tis not a land of make believe we live in. Is it not part of the remit of the scheme providers to allow a smidgen of reasonable (and warranted) give and take? If not, I believe this is truly counter productive to what the NIC/ESC are ultimately trying to achieve; "sorry householder, due to the possibly dangerous state of your electric's I will either rewire or walk away. If you do not accept a full rewire, then I cannot change your DB and upgrade your Earthing, which YES, would make your installation that bit safer, but its all or nothing I am afraid....."

SO for initial assessment all the criteria have to be fully satiated. Do you reckon they would still throw the red book at me for the odd (borrowed N) departure!?!?

Norm, I feel I am ready. Have full 2330, 2382 and NVQ3. Just lack a bit of experience of what the NIC Et Al will allow in terms of departures. Hence my OP.

Thanks again

As i say, I've got none of those, so you should be OK.
I haven't killed anyone in 35+ years although it took me two goes to get on the approved list of the NICEIC, so it looks like standards have risen considerably.

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Norman

have you maimed or injured someone though?

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Nope! (AFAIK)

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Norman

A departure is something that does not comply with BS7671, yet offers the same degree of safety.
120.3 Any intended departure from these Parts (1 to 7 of the Regulations) requires special consideration by the designer of the installation and shall be noted on the Electrical Installation Certificate specified in Part 6. The resulting degree of safety of the installation shall be not less than that obtained by compliance with the Regulations.
120.4 New materials and inventions Where the use of a new material or invention leads to departures from the Regulations, the resulting degree of safety of the installation shall be not less than that obtained by compliance with the Regulations. Such use is to be noted on the Electrical Installation Certificate specified in Part 6.
A defect on the other hand is something that should be rectified if it is in the part of the installation, covered by the EIC. Or it should be noted under comments on the existing installation.

Two lighting circuits each on their own RCBO, with a borrowed N isn't so much an issue for a departure from standards as a departure from actually working! (as soon as the borrowed N connection is used, both RCBOs will trip).


There are several options short of a complete re-wire of the entire property - depending on circumstances: fix just the borrowed N, or perhaps merge both into a single circuit; or (maybe with the case of the landing light on downstairs L and upstairs N - arguably a borrowed L rather than N) transfer the offending light to the other circuit (e.g. run a cable from the downstairs lighting circuit, via somewhere convenient like the airing cupboard, to the landing rose to reconnect the landing N to the downstairs circuit).

- Andy.