Undersized earth on TN-S, maybe

[Norv]

Just quoting to fit a new CU but the main earth from the incoming supply is the armoured twisted & connected into the MET in the existing CU & there is also a piece of 6mm earth wire twisted in with the armour & also connected to the MET of the CU. Ze reading 0.15.

Somehow I think this needs improvement/upgrading but I'm not going to dabble with it.

Should I get the DNO to do something about it or would it be ok ?

 

[Norv]

I did another search & found this from a previous post, so thats it then

Leave the existing earth in place ( it probably does provide enough safety but probably less than the regulations require in terms of impedance and operating times )

Install new earthing the regulations to an earth block located adajacent to the cut out with enough spare cable for it to be moved to where ever the DNO want it when they up-grade earth they provide from the incomer.

You have then done all that is required and are waiting for the DNO to upgrade. Leaving the existing earth connected maintains safety while waiting for the DNO.

 

[oharaf]

Leave their substandard crap alone, I have had the same issue.

Do your part, ensure your earthing etc meets the regs.

If however you are unhappy about the Impedance, phone DNO, tell them what you have found, they will probably tell you to fit a temp earth rod!!!

 

[GaryMo]

Just quoting to fit a new CU but the main earth from the incoming supply is the armoured twisted & connected into the MET in the existing CU & there is also a piece of 6mm earth wire twisted in with the armour & also connected to the MET of the CU. Ze reading 0.15.

Somehow I think this needs improvement/upgrading but I'm not going to dabble with it.

Should I get the DNO to do something about it or would it be ok ?

You'll probably find that 6mm would be fine anyway (adiabatic).

 

[oharaf]

Norv, don't forget Ze for TNS =< 0.8 ohms, so 0.15 is fine.

Remember, that the purpose for obtaining Ze and Zs and R1+R2 is to ensure that should a earth fault occur the current can flow back through the system to the source of transmission i.e. the substation to earth.

 

[GaryMo]

Remember, that the purpose for obtaining Ze and Zs and R1+R2 is to ensure that should a earth fault occur the current can flow back through the system to the source of transmission i.e. the substation to earth.

....and back through your overcurrent protective device tripping it within the required time.

 

[oharaf]

Sorry Garymo, had to answer the phone there