Earth wire on domestic heating oil tank - various questions

[barkymalarkey]

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? 

Pics below.

Cheers

Max

 

[Murdoch]

If I were you I would get a local spark to come and look and do some tests for your piece of mind

RCD's sometimes need their trip button pushed a couple of times for them to trip.... If they are not tested regularly. 

 

[barkymalarkey]

Hi Murdoch

Thanks for the reply.  There's a bit of an update...

I have posted this on some other forums and someone there said that the oil tank earth should make no difference.  So 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.... Unless it is as you said and the button needed a few presses to get it to work.  But I had pressed it a fair few times leading up to this with no joy.  Could be coincidence. Who knows!  

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.
 

 

[Lurch]

I have posted this on some other forums and someone there said that the oil tank earth should make no difference.

Correct.

 Could be coincidence.

100% fact (most probably). It would take such an extraordinary amount of odd edge case rare weird faults and errors to be aligned in such a specific way so as to only make the test button on one RCD not work that I am confident in saying that the margin for it not to be coincidence is so small that it is almost unmeasurable.

I seem to remember he said it needed it before he could sign the house off and give the certificate.

Probably best you didn't call him back then.

Find yourself a new electrician.

 

[Andy™]

er... that earth rod just for the heating pipe is seriously wrong. both should be connected to MET

probably best get someone else in to check everything

 

[Murdoch]

It may not be tripping due to a fault!

 

[kerching]

Me Merlot arrived early today....so,this may be complete Chegwin but

how about it being TT

plastic water service

no accessible Earth Rod for board

knock a rod in next to tank

cabe 'pipe to rod'

in house...' run another cable from pipe to MET. ( using oil pipe as an earth conductor )

installation now earthed

it sounds far fetched BUT i have seen much weirder setups.   :C

just clutching wildly at straws

 

[Murdoch]

Me Merlot arrived early today....so,this may be complete Chegwin but

how about it being TT

plastic water service

no accessible Earth Rod for board

knock a rod in next to tank

cabe 'pipe to rod'

in house...' run another cable from pipe to MET. ( using oil pipe as an earth conductor )

installation now earthed

it sounds far fetched BUT i have seen much weirder setups.   :C

just clutching wildly at straws

Are those the ones in your Merlot?

 

[kerching]

Flow  :Y is severely restricted through a straw

anyway....wine glasses are designed to be filled! None of this leaving an air space for the bouquet   

 

[barkymalarkey]

Many thanks for all the replies.

@Murdoch.  Yeah, I can see that and I think I will get someone in to check everything.  But it is tripping now as it should.

@Kerching.  Enjoy the merlot J  I can’t pretend to understand the straws you’re clutching at, but I’m happy to answer any questions and take a look at our Certificate to help see which of those presumptions might be right.  Just let me know what to do if so.

Also…

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?

 

[kerching]

What does it say on your cert regarding 

supply type

earthing arrangements

earth conductor size etc

 

[Andy™]

So would that make any sense at all?

not really. lightning protection wouldnt really apply to you anyway...

 

[barkymalarkey]

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

 

[Andy™]

wow... so its TNCS... with an earth rod at the oil... that is also filled in as not being there...

is the oil at the other side of the house to the electrics? wonder if he stuck in a rod for the water too?

it looks like youve had a muppet there doing the work...

 

[barkymalarkey]

It's strange because he comes highly recommended by an electrical store, which I've always found to be very helpful and which 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.

Both are at the back of the house.  The tank is roughly 10-15 feet away from where the electricity supply enters the house.  Speaking of which, here's a pic of that in case it helps any:

 

[Andy™]

is there any earth connection on the oil where is enters the house or just that bit outside

 

[barkymalarkey]

There's this down by the side of the boiler:

 

[Andy™]

then WTGrape has he put that rod outside for?!

 

[Murdoch]

then WTGrape has he put that rod outside for?!

Belt and braces and extra work?

 

[Andy™]

not sure about 1st part, but definitely 2nd