First NIC inspection (electrical domestic installer)

[automationman]

Hi all, looking to you good people for some NIC advice. have been in the industrial electrical/electronics game since 1976 and yes I am older than the pyramids!! business went bad last year and I moved into the brick dust and floorboards of the domestic world. Despite having an electrical engineering degree and two level 3 C&Gs (electronics) I had to take the 5 day EAL level 2 domestic installer training which to be fair did enlighten me in this new world especially the inspection and testing. So I am just 3 weeks away from my first NIC inspection and quite nervous about it! For my two jobs I am just near completion of a full rewire (3 bed terr) and a consumer unit replacement with new 4mm radial feeding 4 double sockets over two rooms.

With the rewire I have a dual RCD split load CU with an additional 6amp RCBO for a class D interlinked smoke alarm system also feeding lower hallway lights as a method to warn if power is off. Main service head is PME so Ze and therfore loop tests are nice and low... However, in the main entrance I have the hallway lights (on the smoke alarm circuit) switched on a double gang switch where the other switch is switching the landing lights on two way switching... So to isolate power completely from that specific switch you would need to isolate two MCBs (actually one MCB and one RCBO) Is the nice NIC man going to kick me for that?

With the consumer unit, it’s also a split load dual rcd unit but supply is TT.
Good Ze (for TT) at approximately 0.9 but I can’t actually find the rod!! I see a 10mm CPC going off in the distance into the ceiling but I would need to tear up the upper floor boards to find the rod and that would be a problem for the house owner. My fear is the NIC man will tell me that despite the relatively good Ze is it really just the rod or the rod and service pipes?? By the way, the water main and gas are bonded with 10mm CPC at the right locations and that is all accesible.


Regarding the other NIC requirements, I have my liability insurance, test equipment (seaward and megger) proving unit, copy of the part P doc, 17ed regulations (the red book) cal certificates.

Have also got the green NIC certificates – completed for the consumer unit but not yet completed for the rewire since that is work in progress.

Sorry for this very long story, I am paranoid that I will fail but have I forgotten anything? Do you think the AWL earth rod or the two gang light switch will get me into trouble?

Will the NIC guy want to take up floor boards etc? How extensive is the inspection?

Thanks and again my apologies for the very long post!!
automationman

 

[1john]

make sure you are on the ball with testing, your switch isnt a problem, you obviously have not got shared neutrals.

 

[electronicsuk]

0.9 sounds extremely low for a TT Ze. I can't see how you can possibly have measured it in isolation without any parallel paths, as if you can't find the earth electrode, how can you confirm which conductor is the main incoming earth to the installation?

I'd suggest the best thing you can do is drive in and test a new rod, then you're covered either way. What you currently assume to be the main earth may be bonding of an old/unused or additional service that enters the property in an unknown location.

Assuming this is a domestic property with 60/80/100A incoming service fuse, running a 16mmsq conductor from the MET to the earth electrode should cover you in the unlikely event that an additional supplier's earth is already present.

 

[RF Lighting]

He will not lift floorboards!

Your switch should have a warning lable on it if you were following BS7671 to the letter, but virtually every house in the land has a switch at the bottom of the stairs with two feeds at it.

It is so common you would expect it to be like that, and it is generally ignored.

If you can not find the earth rod, then never mind your NICEIC inspector, you ought to be kicking your self.

How do you know there is a rod at all if you can not see it? it is most likely that the reading you are getting is from a service pipe if it is as low as 0.9Ω, and this is not allowed.

You must disconnect all main protective bonding and test at the rod in isolation to record an accurate Ze value.

 

[automationman]

Thanks 1john, thats good to know about the switch. I would have kicked myself for failing on that. Of course I could have changed it for two seperate switch plates but the customer would not be too impressed with that anyway.

Regarding the earth rod on the other installation, I did measure more than 50 Ohms (cant remember the exact reading now but I can re-measure it) between the 10mm CPC that I think goes to the earth rod and the water main (with its bonding and the gas bonding removed for the sake of the test) I think this strengthens my case that the Ze reading (0.9) is really from the earth rod alone but I can't be sure of that. All the plumbing is a mix of lead and copper (no plastic at all as far as I can see) so I'm sure I would get a much lower reading between the main earth rod CPC and the pipework if they were connected even at a distant point.
What I did not do and I am just realising that it would be useful is to do a loop impedance test between phase and the unbonded pipework!! I suppose if that yields a high Ze then I'll be pretty sure that my 10mm CPC is a connected to a reasonably good earth rod........ I did a full inspection and test on the existing wiring including earth leakage between phase-earth and neutral-earth and that was all > 200M @500Vso I'm as sure as I can be that my Ze is not being fooled by a convenient neutral return instead of earth. Also, when I did the Ze I had the same reading (allowing for noise) with both phase and neutral completely isolated from the CU and the house wiring.

 

[SparkyNinja]

As RF has pointed out, if you cant find the electrode then install a new one. How else can you test the ze and assure connections are satisfactory throughout?

 

[RF Lighting]

It doesn't matter how you try and dress it up, and how you try and convince your self that there must be a rod and it must be ok. If you cant see the rod then there isn't one as far as you and your inspector are concerned.

If there is no means of earthing, the installation is unsafe, and you will fail your inspection.

 

[automationman]

thanks electronicsuk and RF Lighting, Yep, I must admit the 0.9 seems like wishful thinking for an earth rod and I did not consider an older service that might be providing an illegal earth. I did seperate out all the existing bonding but I take on board that can be sure of nothing without actually seeing that rod and measuring the Ze at that point.

I should have folowed the main CPC and was going to but the nice fitted carpets put me off (not the work, just putting them back as they were) I did check extensively outside and with the people next door and they do have an earth rod under the main entrance floorboards less than two meters from the incoming service cable but I could not find the same on my installation. I did not see any earth at all on the incoming service but I'm going to have another look. I did measure more than 50 Ohms between the incoming water supply and the main CPC with all bonding disconnected but admitedly that does not prove very much if there are other older services that might be proving the primary earth.

Looks like I'll be running out to purchase a rod tomorrow!!

 

[SparkyNinja]

thanks electronicsuk and RF Lighting.....

Looks like I'll be running out to purchase a rod tomorrow!!

errr...

then install a new one.

Your welcome.

 

[automationman]

and thanks to you too Widdler

 

[automationman]

Got permission from the house owner today to lift the carpet and floorboards!! Will be doing that tomorrow and will keep you posted.

 

[securespark]

The lowest reading I've ever had for the Ze of a rod on TT is 43 Ohms.

 

[nozspark]

You only need a label at the switch if there isn't a single point of isolation, which in this case there is.... the main switch!

and just whack another rod in; it's the easiest, cheapest and least disruptive option

The lowest Ra I've ever had on a TT is 15 ohms.. most are <100, but my latest was 143ohms

 

[electronicsuk]

You only need a label at the switch if there isn't a single point of isolation, which in this case there is.... the main switch!

I think it's still good practice to label things properly in this situation, as Average DIY'er could easily see the landing light go off and think they've isolated everything at the switch. For the couple of minutes it takes to attach a label (even if it's somewhere inside the backbox that's visible when the switch is pulled away) then it could save someone from a nasty shock in the future.

 

[holmslaw]

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