I need back up!

[Ben Butcher]

Hello all,

I am going to open myself to abuse I think but here goes....

As anyone reading my previous posts will see I am new back to this trade, and am finding it a steep learning curve! I am however trying to install test and leave things in a state that I believe to be safe and persuant with the regs. Today however I need back-up as I think I nearly talked myself onto the dole queue...

I am working for a company installing renewables and we are currently installing a PV system. On arrival to site I discovered that the house is supplied by a 6mm sub main from the garage (1968) with a consumer unit carrying breakers I have never seen before. In the garage is a simple switch fuse with a rewirable fuse (no rating visible)

My immediate response was that I cannot and will not install anything onto the house end of this arrangement as I simply could not even start to claim it would be anywhere near current standards. We then discussed installing a new sub main but when I started talking about digging/RCDs/new CU things became strained to say the least. (the customer had previously been told "all will be easy...")

There is no earth in the house at all, all circuits are wired back to the CU, but from there nothing! not even water pipe.

To solve the immediate problem I have agreed that I will continue with the PV install if I can take it back to the garage (overhead, plastic conduit/catenary) and then install a new mini CU with earth stake and 100mA RCD in it. From there I can wire the PV system (further issues there by the way) safely.

Does anyone think I am being unreasonable, or for that matter not unreasonable enough, I would love to know what you all think! Any suggestions would be helpful, that assuming that tomorrow I still have a job....

Thanks as ever, Ben.

 

[Worcester]

@Ben Butcher, even then you will have a problem completing the EIC as there is no bonding which under a EICR (old term PIR) is a C1 Danger present, Risk of Injury, Immediate remedial action required....

If they insist you carry on, then in order to protect your reputation and maintain your own standards, it;s time to look for another employer.

If you accept their direction, then you have immediately agreed to do other installs just like it, and you will now always accept low quality work as your norm - you've sold out.

 

[Amp David]

Its a C2 coding on an EICR, should be there though

 

[yellowvanman]

@Ben Butcher, even then you will have a problem completing the EIC as there is no bonding which under a EICR (old term PIR) is a C1 Danger present, Risk of Injury, Immediate remedial action required....

Not sure where you get the C1 category, according to ESC best practise guide No.4 its a C2 for no bonding (page 12).

 

[BruceB]

I think you might be being unreasonable. Just because it is not up to current standards does not mean every aspect is unsafe. Your sub-main from the garage might not need an rcd. Is it buried in walls? Presumably the sub-main has an earth wire in it? Is that connected at the garage end? To what? Is it TT/TNS/TN-C-S or what. A 6mm sub main could adequately carry the PV depending on its size. I have installed on a smaller existing sub-main. Not ideal, but depending on local supply voltages might work adequately as long as the customer/your boss understand the tripping risks. What is the point of putting a new catenary on an rcd (is it TT)? Will the new catenary be larger than 6mm2? I have no doubt there are plenty of issues and any new solar stuff I would put in a separate CU with henleys or equivalent. But you need to be sure you understand what to die in a ditch over and what to just make work.

 

[Gavin A]

IMO we'd do the following.

1 - fully test the circuit to the garage - if it passes the continuity, and IR tests as well as visual inspection, then we'd consider using the existing circuit once an earthing arrangement is put into place so that Zs can be tested.

2 - Install an earth spike, 100mA RCD, and bond water and gas pipes (or potentially use the water pipe for the earth IF there is sufficient private pipework before it reaches the public pipes, which is allowed as long as it is suitable, and you put tags on to ensure that it's clear that the pipe can't be replaced without sorting out the earthing arrangements.

3 - go back to 1 and check Zs, if it fails then cry.

4 - Redo the CU arrangement in the garage, or put in a separate unit splitting the cable between the garage CU and the main house CU. At the house end you would then need to ensure that the feed from the garage isn't on a shared RCD (other than the 100mA main RCD you've just fitted), and that the rating on the MCB to protect the cable is low enough that it will still protect the circuit between the new supply and the garage CU - ie if it's a cable that can take 40amps, you'd need to replace the MCB with a 20amp MCB for the garage, (40-16amp pv = 24amp, reduce to 20amp to be safe).

also, don't forget to scratch your head quite a bit, and bare in mind I may well have missed something here, but we have made similar situations work before (and we've also had to entirely redo the wiring from scratch at other times - be sure to double check the length of the cable with the inverter installation manual to ensure the cable losses are acceptable as well).

hope this helps.

 

[Ben Butcher]

Hello BruceB, Just trying to cover all bases, If I were to put a new CU in the house it would surely bring into question the integrity of the existing submain, and as it is too small already me adding to it's load would surely be foolhardy? The supply in the garage is TT with a connection to an invisible rod at no more than 4.0mm. As I will have to record this data on an EIC I would surely be opening myself to serious scrutiny at a later date. I feel I need to leave it in a state where it can disconnect reliably if need be. Would love to hear what you think, Thanks, Ben.

 

[MarkieSparkie]

sound good,sorry cant help

sorry cant help

In technical threads, if you can't help then please don't post as this not Chit-Chat, it's common courtesy to the OP.

 

[Worcester]

There is no earth in the house at all

It's not just the bonding that's missing ...

@GavinA generally great simple advice, however I wouldn't recommend use of the water pipe as the earth, unless you can really ensure it won't be interferred with or removed. Simple enough to install new earth electrode.

​

 

[cbw]

Thing is its really not a big deal to do this properly.......

As long as your not signing anything or putting your name to it, let your company carry on.....

We all need to feed our children.

I for one would sack any employee of mine who didnt properly earth and bond an installation, perhaps thats why I keep getting undercut???

 

[BruceB]

Hello BruceB, Just trying to cover all bases, If I were to put a new CU in the house it would surely bring into question the integrity of the existing submain, and as it is too small already me adding to it's load would surely be foolhardy? The supply in the garage is TT with a connection to an invisible rod at no more than 4.0mm. As I will have to record this data on an EIC I would surely be opening myself to serious scrutiny at a later date. I feel I need to leave it in a state where it can disconnect reliably if need be. Would love to hear what you think, Thanks, Ben.

You are the one on the ground and it is always risky in this situation to give advice when I have not seen it, however:
- yes, if you put a new mini-cu for the solar in the house then you do need to test the sub-main as Gavin has explained.
- 6mm might be just OK for a correctly fused low demand old house - any evidence of overload?
- remember the PV is not increasing the load on the existing sub-main it is reducing it.
- a 4mm earthing conductor is more than adequate for TT electrically. Just check protection, if any, required if the cable is say buried unprotected.
- you can test the existing TT earth resistance to see whether it is adequate. Of course all connections ought to be accessible but not necessarily the end of the world if they are not and Zs is reliably constant.
- sounds like a prime case for declaring your assumptions/limitations/caveats on any EIC you produce.

 

[sedgy34]

just to add my 2 penny

its a requirement you upgrade the earthing arrangment then test the circuit your going to use for the generation circuit
if ok carry on with it.

 

[Gavin A]

It's not just the bonding that's missing ...

@GavinA generally great simple advice, however I wouldn't recommend use of the water pipe as the earth, unless you can really ensure it won't be interferred with or removed. Simple enough to install new earth electrode.

​

I wasn't really recommending it, more pointing out that it is an option (being as I'd just been corrected on that elsewhere, and double checked the regs on it today).

In some situations banging an earth spike in really isn't sensible, eg if you've no idea where the drains, gas pipe, water main, mains electric have been run, or practical eg if the entire house is surrounded by a patio, or has a french drain surrounding it / was badly backfilled so you can't get a decent Ze. I know we had some right nightmares when we were still following the old DTI guide on earth spikes for TL inverters, and sometimes it's just best to be sensible about things and take another option if it's available and safe.

eta - in a lot of case you'll get a much better Ze reading from the pipes than from a spike anyway, as you'd expect from several meters of inch piping in contact with the ground instead of 1m or so TT spike.

 

[Worcester]

@GavinA, I know it's in the guide as (almost) a last resort, though I'd still prefer to put in multiple earth rods or a grid of earth rods like is done on filling stations, to get the Ze down. There again I am paranoid about safety!

 

[Gavin A]

We had a couple of close calls with drains and gas mains, so I'm now seriously paranoid about hitting them (we didn't, but were a bit close for comfort).

I did have it a couple of times on festivals where a tent crew managed to hit a water main with their pegs, and it's a complete nightmare, total stop job scenario even in a field, never mind if you ended up flooding a customers house and having to have their prize roses dug up. Not to mention the **** taking from the water board crew, and then the size of the bill afterwards.

Having lived in a house that's been earthed this way for decades, I'm possibly a bit more open to it than some, and there's a hell of a lot of houses around here that have been earthed this way as well.

We generally advise getting a supplers earth fitted TBH, and usually ring the DNO to arrange it while we're on site, but I'm certainly happy enough leaving it connected to the water pipes in the meantime as long as there's no obvious reason not to.