Why earth oil pipe at tank?

[stuban]

Hi chaps

Just quoted for a job based on a spec which included earthing a metal oil pipe to a new rod at the plastic tank about 15 yards from the house.

The house is out in the sticks but pme. The pipe is not plastic coated that I could see so is there any reason for this? I would think this is a no-no rather than being of any benefit.

I could maybe understand it if the pipe was insulated and the system TT(or is that rubbish) but assuming we bond where the pipe comes into the house is there any situation where you'd earth this pipe to a rod?

Thanks a lot
Stu..

 

[IQ Electrical]

Comes under 411.3.1.2 only strictly necessary if it's extraneous is my understanding.

You're right if we're only looking at main protective bonding as opposed to some sort of functional or anti static bond at the tank end.

Once that rod is connected (maybe on advice of the tank manufacturer) the pipe automatically meets the definition of an extraneous-conductive part.

 

[stuban]

Netblindpaul point taken. In reality that applies more to dusty industrial atmospheres and petrol stations?

 

[netblindpaul]

^ Yep! Oh and a few others!

 

[stuban]

Jason, yes it is buried and not plastic coated so I would bond it as a normal service

That was what was throwing me. Surely the whole reason for bonding it goes against the reason for an earth stake at the far end - it's either at earth potential or not?

In which case one of these is not necessary(?)

Stu..

 

[netblindpaul]

What about OFTEC "regs"?

 

[IQ Electrical]

Jason, yes it is buried and not plastic coated so I would bond it as a normal service

That was what was throwing me. Surely the whole reason for bonding it goes against the reason for an earth stake at the far end - it's either at earth potential or not?

In which case one of these is not necessary(?)

Stu..

There's a difference between the potential of the distributors PME MET and the true earth that the pipe is buried in, saying that though, it's not a setup that I'd consider necessary on a domestic oil tank.

 

[stuban]

Fair points all of them.

I'll get some details of the tank - see if they spec it. And also have a chat with an oil heating engineer about the oftec regs.

Thanks a lot
Stu..

 

[truckster]

I do not understand this at all. Surely if you have PME then you bond the pipe as per usual but if the tank requires a stake for static this shuld be kept separate frm the PME by an insulated section of pipe. It seems risky sending potential earth faults towards a tank of oil. Just reread OP, its a plastic tank why would it need any sort of stake?

 

[IQ Electrical]

I do not understand this at all. Surely if you have PME then you bond the pipe as per usual but if the tank requires a stake for static this shuld be kept separate frm the PME by an insulated section of pipe. It seems risky sending potential earth faults towards a tank of oil. Just reread OP, its a plastic tank why would it need any sort of stake?

I'm reversing this discussion here, what we are doing in effect is connecting the oil pipework (and possibly the metallic fuel filler) to the neutral conductor of the installation.

The tank is then probably mounted on 'true earth'.

Maybe whoever initially proposed the electrode at the tank position was attempting to 'tie down' any potential difference between the suppliers MET and 'true earth'?

It reminds me of the advice from the Guidance Notes to insert an insulating link in copper pipework feeding an external tap on a PME system!

This is

 

[stuban]

IQ this is pretty much all I could guess at but since the pipe is buried and doesn't appear to be insulated would there be any benefit of the stake?

There were no specific instructions in the tank so in this case I'll bond where the pipe comes in have a chat with an oil engineer next time I see him.

Thanks all for the input
Stu..