Earth wire on domestic heating oil tank - various questions

[DIYNotIan]

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

 

[bernardgreen]

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?

No it is not right. The test button creates an inbalance inside the RCD to simulate an earth leakage on the house woring / appliances. If the RCD did not trip when its test button was pressed with the nains switch ON then the RCD is defective and needs replacing

The left side tripped when I hit the button. But the right side didn't.

The test button on one RCD should not affect the other RCD

 

[DIYNotIan]

No it is not right. The test button creates an inbalance inside the RCD to simulate an earth leakage on the house woring / appliances. If the RCD did not trip when its test button was pressed with the nains switch ON then the RCD is defective and needs replacing

Hmm, that's not what i expected to hear! Not that I'm disputing it... It's just that with the oil tank earth disconnected, I pressed the test button and nothing happened. With it connected, I pressed the test button and it tripped. Nothing else changed as far as I'm aware. So there must be some kind of connection mustn't there??? I'll try doing it again and see if I get the same result...

Many thanks for the reply.

 

[RF Lighting]

Can you post a photo of your main incoming supply, the black or grey box it terminates into, and any earth wires near to this.

The photo you have supplied doesn't make sense!

An earth rod is used to earth an installation when an earth isn't provided as part of your incoming supply.
The cable attached to the earth rod should run from the rod to your main earthing terminal (MET) which will be near or in your consumer unit.


Any metallic object likely to introduce a potential into your property must be bonded.
As the oil supply pipe to your property is metallic, and as it comes from outside to inside and it appears to run in the ground, this pipe must be bonded.

The bond should be attached to the pipe within 600mm of the point of entry to your property if possible, and the bond should run back to your MET.

Your current set up does not achieve either of those things, and can only have been installed by someone who has very little understanding of what they are doing, presumably thinking they have earthed the pipe and made the installation compliant. They haven't. Pipes need to be bonded - NOT earthed.

As for why this affects your RCD tripping I have no idea, as the RCD test button does not reference earth to allow it to function.

I would advise you get your installation checked over by a competent electrician asap as it could but in quite an unsafe condition as things stand at the moment.

 

[DIYNotIan]

Well, don't I fell like 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 reconnected 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....

RF Lighting - here's a photo. Does it show what you need to see:



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.

Maybe I need to get in touch with him!

Thanks for the help.

 

[EFLImpudence]

The bond should be attached to the pipe within 600mm of the point of entry to your property if possible, and the bond should run back to your MET.

Naughty. Have you been reading the OSG?

The 600mm. only applies (wrongly) to internal meters.

As near as practicable to the point of entry.

 

[RF Lighting]

Well, don't I fell like 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 reconnected 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....

RF Lighting - here's a photo. Does it show what you need to see:

View attachment 110501

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.

Maybe I need to get in touch with him!

Thanks for the help.

Yes that shows that you have an earth supplied with your electricity supply, so you shouldn't have an earth stake outside at all.

It would be interesting to hear why your 'electrician' thought it necessary to install it.

 

[DIYNotIan]

Yes that shows that you have an earth supplied with your electricity supply, so you shouldn't have an earth stake outside at all.

It would be interesting to hear why your 'electrician' thought it necessary to install it.

I've been trying to think back, and I can't be 100% sure but I think he 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?

 

[flameport]

something to do with the possibility of lightning striking

So would that make any sense at all?

None whatsoever.

 

[DIYNotIan]

I think in the New year I'll give the electrician who did the work 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.

 

[EFLImpudence]

Nope. It's not earthing; it is bonding (joining together electrically).

I appear to be confusing what you are talking about. The wire in the picture IS earthing although it seems unnecessary and is not really connected.

However, we bond things because they are already earthed by some means - this includes in the ground.

If they are not earthed - by any means - they do not need bonding and
definitely should not be earthed so that they do need bonding.

 

[bernardgreen]

Petrol stations must use a Ground Rod to provide the Earth for the electrical supply. They cannot use the "earth" supplied from a PME electrical supply. This is due to the risk of the PME "earth" becoming a different voltage to true Ground at the station. This would result in high Earth currents from the PME earth to ground through the pipework and the underground storage tanks. This would be a possible source of ignition of petrol fumes.

Home heating fuel is far less volatile than petrol but is still classed as a fuel. This may be why the electrician used a Ground Rod and did not export the PME earth from the house to earth the tank

 

[JohnW2]

The cable attached to the earth rod should run from the rod to your main earthing terminal (MET) which will be near or in your consumer unit. ... Any metallic object likely to introduce a potential into your property must be bonded. ... As the oil supply pipe to your property is metallic, and as it comes from outside to inside and it appears to run in the ground, this pipe must be bonded. ... The bond should be attached to the pipe within 600mm of the point of entry to your property if possible, and the bond should run back to your MET. ... Your current set up does not achieve either of those things, and can only have been installed by someone who has very little understanding of what they are doing, presumably thinking they have earthed the pipe and made the installation compliant. They haven't. Pipes need to be bonded - NOT earthed.

Unless I'm missing it, I don't think we have been told/shown enough to be sure that the oil pipe is not properly bonded to MET after entering the building, have we??

If such bonding did exist, then is it possible that the earth rod and cable being discussed were deliberately installed (as bonding, not earthing) to minimise any pd between the metal pipe/tank connectors (at PME 'earth' potential, if bonded within the property) and the surrounding ground? I seem to recall that we've heard of oil supply companies requiring this, as a result of their employees having experienced 'tingles' whilst touching oil tank fittings/pipes whilst standing on adjacent ground.

Kind Regards, John