Earth wire on domestic heating oil tank - various questions

[Max Rasa]

Hi all

I had a new consumer unit fitted 3 - 4 years ago. I was never told that I had to periodically test the RCDs by pressing the T buttons. Still, you live and learn!

Anyhow, it is a split unit. The left side tripped when I hit the button. But the right side didn't. Did a bit of reading but could figure it out. Until today. I remembered that when the unit was fitted the electrician also added an earth to our domestic heating oil tank, but this had become detached. I've re-attached it and hey presto, the RCD now works when tested.

So I thought I'd better check in with you guys....

1. Does it sound right that having the earth disconnected would have stopped the RCD tripping on being tested, and re-attaching would fix it?

2. What kind of connector is it (see picture below)? When I put the earth cable into the holes, the RCD wouldn't trip. When I out it into the gap and made sure it was touching the rod, it DID work and the RCD tripped when tested. So how should the cable be connected properly to that piece?

3. Just for my curiosity, why is the oil tank earthed?

4. Do I need to somehow cover that earth point/rod so that the dogs can't get to it, people don't trip on it etc?

Here are the pics:

Cheers

Max

 

[westward10]

The exact same OP is on a forum we mustn't talk about!

Oh right didn't realise, did we have the same conclusion.

 

[Had8Lives]

Just a thought, but has the oil pipe been used as an earth wire to the earth rod? And the earth rod is infact part of a TT earthing system? I would never do it that way but the OP did mention about lightning strikes?!

 

[westward10]

Just a thought, but has the oil pipe been used as an earth wire to the earth rod? And the earth rod is infact part of a TT earthing system? I would never do it that way but the OP did mention about lightning strikes?!

This crossed my mind too. Op any chance of a pic for the service head.

 

[Pat H]

Can't see that earth wire doing much in a lightning strike except explode like a fuse wire.

 

[Had8Lives]

Can't see that earth wire doing much in a lightning strike except explode like a fuse wire.

I wasn't meaning that the earth wire would earth a lightning strike, I meant that whoever put the earth rod in possibly mentioned to the OP that they needed to put an earth rod in as a method of earthing as TT systems tend to be used in areas where there is a high chance of lightning striking.

 

[Barry White]

Copied and pasted a reply from the other forum contains a lot of info! Deffo same OP as same pictures etc this is from the cert.

Quote

"OK, let's see.... It's pretty much Greek to me, but I'll give you what I think might be relevant!

TN-C-S.

1-phase (2 wire)

Means of earth - Distributor's facility

Installation earth electrode - either says MA or NA.

Conductor material - copper

Condutcor CSA - 10.00mm2

Water service box = ticked

Oil service box = ticked



Do you need anything else?


Cheers"

 

[DPG]

So it looks like he's 'bonded' the oil pipe by earthing it? Daz.

 

[madmaz]

So it looks like he's 'bonded' the oil pipe by earthing it? Daz.

Sounds like it ... total lack of understanding oil pipes are generally sheathed so its highly likely he's made the installation less safe than it was

 

[DPG]

Sounds like it ... total lack of understanding oil pipes are generally sheathed so its highly likely he's made the installation less safe than it was

Sheathed or not, he's earthed rather than bond back to the MET. Total misunderstanding! Daz

 

[westward10]

Would love to know why he did it.

 

[madmaz]

Sheathed or not, he's earthed rather than bond back to the MET. Total misunderstanding! Daz

That's why I said total lack of understanding..... chances are the pipework wasn't extraeneous to start with due to sheathing and a plastic bund. that is until the sparky made it so !

 

[Marvo]

None at all, I suspect the person who did it has no idea as to the theory behind it.

Me too. The tank looks like it's plastic from the photo so the rod would only be serving the buried pipe. The way it's connected to the pipe doesn't look like it was intended as an earth point for a bulk supply truck to attach a trailing earth clamp for safety during the filling process so I'm stumped....

The missing bolt is also making me skittish. I've seen enough from the photos to second the advice of getting an experienced sparky to check it out and ramp test the RCD whilst he's there.

 

[Marvo]

If the supply to the premises is TN C S I hope it's already PME'd otherwise that pipe might get warm if there's every a DNO joint fault

 

[Barry White]

Only thing I can think of is as the oil pipe was bonded to the met inside the building and TNCS perhaps there was a touch voltage on the oil pipe at the tank between it and true earth ?

 

[Max Rasa]

Hi all

I thought I was up to date on the thread on here. Just come back and there's a page worth of posts I didn't realise were there! I guess that's the potential when you post on several forums

Anyhow, many thanks for all the posts and help. I emailed the electrician (being xmas and all) and haven't heard back. I think in the New year I'll give him a call and see what he says as to why he fitted the rod and earthed the tank. No one seems to understand why he done it. We recently had an electrician over to fit a new cooker. They had a quick look and couldn't see why he had bothered either. Not that it was entirely pointless, more just an extreme case of belt and braces!

One thought.... Our mains water comes into the house via a blue plastic pipe rather than metal. Could that be anything to do with it? Could it be that he could not earth it to the house's pipework and so had to use the rod? Please bear in mind that this is a totally uneducated stab in the dark!

Cheers for all the help.

PS - the electrician who came also ran a test on the RCD that wasn't working initially. He said it is absolutely fine.