Equipotential Bond Current showing on Clamp meter earthing

[Emco Elec]

Hi has anybody come across current up to 3 amps showing on water bond? 0 volts, no amps on main earth just water bond?
I put a clamp Meyer to check...

 

[pc1966]

It is not uncommon here in the UK on TN-C-S supplies to see a portion of the neutral current flowing via bonding to service pipes that are bonded elsewhere on the system to another TN-C-S supply (or even directly in to the Earth).

Basically the pipes end up in parallel with the PEN (CNE, MEN, etc) conductor so share some current depending on the relative impedances.

This is also the reason why the UK wiring regs state a minimum of 10mm^2 copper equivalent for such extraneous conductive part bonding, as under open PEN fault conditions they could carry a lot of current for prolonged periods.

 

[Emco Elec]

It is not uncommon here in the UK on TN-C-S supplies to see a portion of the neutral current flowing via bonding to service pipes that are bonded elsewhere on the system to another TN-C-S supply (or even directly in to the Earth).

Basically the pipes end up in parallel with the PEN (CNE, MEN, etc) conductor so share some current depending on the relative impedances.

I found it sort of weird as main earth has no current but bond does as they are all joined via men system..
I even turned off the main switch to cut power to residence and there was still current but less than 3 amps..

 

[pc1966]

Is there a gas supply as well? Could be current is flowing "water - main earth terminal - gas"

Also do the Aus regs have the N-E link before or after the supply point? Do you have DP isolation when the supply is switched off?

Even with the supply off in the UK, there is still a live connection from the power network via the supply side N-E link to the installation's earth and thus on to any bonded pipes. Other uses of the supply network will be pushing current around the PEN system.

 

[Emco Elec]

Is there a gas supply as well? Could be current is flowing "water - main earth terminal - gas"

Also do the Aus regs have the N-E link before or after the supply point? Do you have DP isolation when the supply is switched off?

Even with the supply off in the UK, there is still a live connection from the power network via the supply side N-E link to the installation's earth and thus on to any bonded pipes. Other uses of the supply network will be pushing current around the PEN system.

I have checked on 2 separate properties, one has a gas supply the other doesn't MEN link done at main switchboard after supply ( Main neutral goes in Service neutral link for metering etc then onto customer neutral link.MEN link onto customer link) but what you are saying Is making sense to me.. just abit scary having some current going thru the water bond

 

[LastManOnline]

I found it sort of weird as main earth has no current but bond does as they are all joined via men system..

By "main earth" you are probably referring to the earth going to the rod?? Australia has a TNC-S system. That means you can end up with current flowing in any bonded metalwork because its connected directly to the neutral. You won't get any current (nothing measurable anyway) flowing to earth via the rod because the resistance is too high.

 

[Emco Elec]

By "main earth" you are probably referring to the earth going to the rod?? Australia has a TNC-S system. That means you can end up with current flowing in any bonded metalwork because its connected directly to the neutral. You won't get any current (nothing measurable anyway) flowing to earth via the rod because the resistance is too high.

Main earth is what's going to the earth rod

 

[LastManOnline]

Main earth is what's going to the earth rod

That all makes sense then. Your rod could have a resistance of several hundred ohms while your water pipe will have very low resistance.Could be 0.5 ohms or less. Your waterpipe is simply offering an alternative path back to the transformer. In TNC-S systems this is perfectly normal (though a bit disconcerting)