Circulating network currents?

[RF Lighting]

Today I have been carrying out a PIR at a branch of a well known convenience shop company.

In the switchroom I found an old 100A TP head which had clearly been too small to supply the premisis, so by the looks of things a new supply has been put into the building about 2 - 3 yeary ago.

The new supply is a 250A per phase TP supply with TN-C-S earthing.

The old supply which is still live (The fuses have been pulled but the supply is still there) was a TN-S supply

The two different earthing types have ended up connected together, and when I put my clamp meter on the earth there is a current flow of about 4 amps

This entirely dissapears when the two earth supplies are seperated, and yet no potential exists between the two supplies when seperate.

Is this something to do with parallel earth paths?

Old supply:

New supply:

 

[RF Lighting]

To remove any confusion my clamp meter is definatly reading 4A, It is just the scale is strange with it being on an AC volts setting

 

[EdwardCurrent]

Not my cousin Eddie is it ??

 

[JohnD]

Today I have been carrying out a PIR at a branch of a well known convenience shop company.

I hope Crafty made you a mug of tea.

 

[EdwardCurrent]

"Slice of cake and look through the album Sir ?? "

 

[Steve]

Today I have been carrying out a PIR at a branch of a well known convenience shop company.

I hope Crafty made you a mug of tea.

JohnD, you're alarmingly close! I have spoken to Rob and it is the same company I work for

 

[RF Lighting]

And no tea

 

[Lectrician]

Good old paralll paths...

Ever shorted N to E on a well loaded TN-S near the origin? Try that!!

 

[plugwash]

This entirely dissapears when the two earth supplies are seperated, and yet no potential exists between the two supplies when seperate.

If current flows there must be a potential.

It just doesn't take a very big potential to shove 4A down a short peice of copper wire .