Earth wire on domestic heating oil tank - various questions

[Evans Electric]

Personally I don't think the oil tank rod was necessary TBH  ,just a bond where the oil feed enters the house . 

However if you ARE having a rod at the tank  a nut & bolt through the clamp would be a good addition.

Regarding the RCD test button ... I've found quite a few where the test button doesn't work but the tester knocks them out with no problem .     

No idea what the rod on the oil feed pipe is there for . 

 

[Doc Hudson]

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? 

An RCD test button has no connection or relevance to earth, it creates an imbalance between the live & neutral conductors by cross connecting the input & output legs of the RCD with a load to create sufficient current to cause a trip. One of the fundamental principals of the RCD is to protect against electric shock, irrespective of how good or bad any earth connection is. Unless that bit of exposed pipe and the tap lever are introducing some hazardous potential with respect to earth or other exposed metalwork I am not sure what it is achieving, If you did get a lighting strike on your oil tank I'm not convinced that bit of 10mm is going to do much. And if there was some valid reason for the earth rod then there should have been some suitable mechanical protection over the joint to prevent it getting to the state it currently is in. Sounds more like you have a temperamental RCD button. I would like to know what the actual trip times and trip current is when tested with a proper meter.

Doc H  

 

[Lurch]

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.

I'm sure he's not completely incompetent, but more likely just misunderstands some of the finer points of earthing methods and the purposes of why things are done.

The earth clamp and rod at the tank are completely superfluous and are not adding anything to the safety of the electrical installation, they probably don't adversely affect it either so you can do whatever you like with it - remove it entirely, clamp it up properly, leave it as it is. The choice is yours.

 

[Tony S]

It looks like a plastic oil tank and feed line in which case the earth connection is totally pointless. Therefore I can’t see a correlation with the RCD functioning after connecting the earth pigtail.

 

[Andy™]

It looks like a plastic oil tank and feed line in which case the earth connection is totally pointless. Therefore I can’t see a correlation with the RCD functioning after connecting the earth pigtail.

looks more like plastic coated copper pipe. there is no join between the copper and plastic part

 

[Lurch]

looks more like plastic coated copper pipe. there is no join between the copper and plastic part

Correct.

 

[Tony S]

Ooopps

 

[barkymalarkey]

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. For the sake of curiosity if nothing else! 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.

 

[binky]

Belt and braces and extra work?

think I would concurr with this. He wasn't sure, so put it in anyway. Can't see it's doing any harm, can't see it's doing any good either really. Bond for tank pipe should be internal and connected to earth terminal near/in the board, not that I'm very familiar with oil tanks as I mostly work in the city.

 

[Lurch]

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?

Short answer, no.

Slightly longer answer, it didn't need any bonding to anything anywhere at that point, it only needs bonding at the point at which it enters the house.

 

[Sidewinder]

I have seen this recently also, obviously done by someone who has little real understanding.

It could encourage diverted currents, and encourage electrochemical corrosion due to minute voltage gradients, but, that would depend on the exact details of the composition of the soil surrounding the pipe, the rod, etc. and whether the pipe coating was intact, damaged, where it was damaged, and a whole raft of other things.

IMHO it should not be there, and I would want it removed.

 

[steptoe]

In the distant past I've done loads of new builds where it was an SR (or perhaps BC spec) where the oil tank was rodded, what reason,? I'm unsure, static build up perhaps,? I have no definitive answer, perhaps the spark in question was working to a legacy system that he has always done so. :C

 

[sparkytim]

It used to be a requirement to Rod oil tanks when PME earthing system in use. The reasoning  was that the copper oil pipe could not be segregated so could present danger if supply N came adrift. Staking down minimized risk. Also common for outside taps etc where segregation was not possible.  

 

[Sidewinder]

At supply end though, not remote end, the damage would be done by the time it got to the remote end.

This is harking back to the 15th now though, earth and bond everything including metal window frames 2 storeys up in a timber building with no other extraneous, or exposed conductive parts!

 

[sparkytim]

Think the idea was to protect persons who may happen to be in contact with the tank while outside at the time of the fault by providing a lower impedance route to earth for the fault current then thru the person. 

 

[Sidewinder]

Think the idea was to protect persons who may happen to be in contact with the tank while outside at the time of the fault by providing a lower impedance route to earth for the fault current then thru the person. 

That must have been a longggg time ago!

Tanks have been plastic for many years now.

Also a rod supply end would offer a lower resistance path to true ground than one tank end.

I've posted a section in another thread about the current thoughts from the IET on outside taps supplied from metallic pipework.

 

[sparkytim]

Yes long,long time ago {bin at it 40+ years now, about time I retired!) when PME was very tightly controlled with strict requirements before the Electricity Board Inspector would allow it to be connected. Had one crawl thru a loft once to check I had bonded the Gas!  No one cares now!