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

 

[bigspark17]

Hi max at a glance i dont think its possible or suitable to comment on your questions, i would suggest get a local electrical contractor in or post your location on here as you need someone with knowledge to test out these isuues with the correct test equipment.

 

[westward10]

Absolutely no idea why anyone would earth that oil pipe to an electrode which itself has no fixing bolt. It should not have affected the rcd whether connected or not, the earth is pointless. Rcds can stick sometimes it may well be one of those things.

 

[Max Rasa]

Many thanks for the replies.

Well, I feel like a bit of a ---- now! I've just gone out and disconnected the oil tank earth again, hit the test button, and it tripped fine. That's just weird. It was a few days ago that I first discovered that the RCD wasn't tripping when tested. I've tried it a few times since and never got it to work. The only time it worked (up until now) was when I reconnected the oil tank earth. And - just for the record - minutes before reconnecting I had tested and it still wasn't working. Hence why it seemed an almost certainty that it must have something to do with it (not from a theoretical point of view as I don't know much about such things, but just from straight logic). Very confused now.... Someone has suggested that if not used for a long time, these buttons sometimes have to be pressed a few times before they start working. I guess that is a possibility, although the coincidence is odd (how it worked when I connected the earth).

So yeah, it could be that it was sticking a bit...

Like I said in the OP, the consumer unit was fitted 3 - 4 years ago, and at the same time we had various other electrical jobs done around the house, including an Electrical Safety Certificate which as we had not long moved in and the house hadn't had one for quite some time (although it was only built in 1993). it was then that the earth was added to the tank (there was nothing there before that). I seem to remember he said it needed it before he could sign the house off and give the certificate. The missing fixing bolt may be down to me and perhaps was lost when it first got disconnected (bloody dogs!). But I'm left wondering why the electrician said this was necessary now that you're saying it wasn't...

Maybe I need to get in touch with him!

Thanks for the help.

 

[westward10]

Might be an idea to get an electrician out to test the rcd for peace of mind, as for the earth to the oil tank I see no purpose for it.

 

[Pete999]

Try pressing button on each RCD

 

[HandySparks]

I'd agree. 'Earthing' the oil pipe by connecting it to a rod in the ground is totally pointless. It may need 'bonding' from the point that it enters the house to the Main Earth Terminal, but that is quite different.

RCDs should be tested quarterly (as the label in your photo shows), but householders rarely do this. Since one may be faulty, they should be tested with the correct test equipment by an electrician who knows how to use it.

 

[Max Rasa]

@westward10 Yep, I think that might be a good idea. But in the meantime I can’t help but prod the situation. Like a sore tooth!

@Pete999. That’s what I have been doing over the last few days. The one on the left always worked, the one on the right didn’t. Until today. Now both are working fine. As above, I thought it was something to do with me connecting the earth at the oil tank, but it clearly ain’t that because after I’ve re-disconnected it (!) the test button still works fine.

@HandySparks. Yes, lesson learnt. Will put it in my diary to test quarterly.

One other thing….

I've been trying to think back, and I can't be 100% sure, but I think the electrician might have said it was something to do with the possibility of lightning striking. I've just rung the other half and asked her if she remembers why he said it was needed. And she said the same thing. So I can't imagine we've both imagined it!

So would that make any sense at all?

 

[westward10]

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

 

[Max Rasa]

I'll call him. He comes highly recommended by a electrical store, which I've always found to be very hlpful and has been around since I can remember. Likewise he has apparently been in the business for over 20 years. It will be interesting to hear what he says, and I will of course report back.

 

[westward10]

Yes it would be interesting to know.

 

[Octopus]

Is it possible to merge threads across 2 different forums?

 

[westward10]

What do you mean?

 

[Octopus]

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

 

[Max Rasa]

Oh dear, I feel unfaithful now... Is this akin to sleeping with the neighbour's wife?!

 

[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.

 

[Barry White]

Thanks for updating us please update again when the electrician returns.

 

[bigspark17]

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 !

So you wouldnt bond that buried oil pipe because it has a plastic covering? What happens when the plastic gets damaged or breaks down and the pipe is then extraneous?! Rediculous.. bond it!

 

[davesparks]

So you wouldnt bond that buried oil pipe because it has a plastic covering? What happens when the plastic gets damaged or breaks down and the pipe is then extraneous?! Rediculous.. bond it!

Or the joints in it which are normally exposed compression joints.

 

[DPG]

So you wouldnt bond that buried oil pipe because it has a plastic covering? What happens when the plastic gets damaged or breaks down and the pipe is then extraneous?! Rediculous.. bond it!

But he hasn't bonded it. He's earthed it with a rod. Daz.

 

[Marvo]

If it's not bonded at the other end and connected to the MET then earthing it via its own rod could cause issues in the equipotential zone of the main installation. Also, connecting it via bonding to the MET could be an issue if the installation earthing arrangement isn't PME'd by the DNO.

 

[Barry White]

More info on other forum including the cutout its TNCS and a photo of the oil pipe at the boiler it looks bonded too.

 

[bigspark17]

If the oil pipe is bonded in the house then the earth rod connected @ tank end is not creating a danger nor has it any use, classic example of somebody doing something without knowing why or what there trying to achieve.

 

[Midwest]

Perhaps they just wanted to earth the earth rod

 

[westward10]

That's funny because on TT systems I often say the conductor to the rod is doing just that, earthing the rod. Take it away it will probably make no difference.

 

[madmaz]

So you wouldnt bond that buried oil pipe because it has a plastic covering? What happens when the plastic gets damaged or breaks down and the pipe is then extraneous?! Rediculous.. bond it!

I would bond at the point of entry to the property I would not Earth it with an earthrod. My suggestion is that the addition of the earth rod has more than likely made the installation less safe

 

[Midwest]

I would not Earth it with an earthrod.

You crazy guy

 

[DPG]

I would use a bonding rod. Daz

 

[westward10]

I would use a bonding rod. Daz

Would you bond the rod.

 

[DPG]

I would connect the bonding rod to an adjacent earthing rod. Belt and braces. In fact I'd earth my braces to be sure.

 

[madmaz]

I would connect the bonding rod to an adjacent earthing rod. Belt and braces. In fact I'd earth my braces to be sure.