TT system help.

[ChrisElectrical88]

Hi, I have a lad working on a farm at the moment and he phoned me today panicking at a high ZE and PSC. 3.50ohms and 79kA. I asked him what system was in place and he said TN-S. I then told him to go earth rod hunting. Got a phone call back saying he couldn't find anything. I'm on a course this week so I don't have access to my regs etc. Are these good TT reading? (I'm not to familiar with TT so don't have much clue without my books) and should I tell him to open his eyes and go searching again? Or should I tell him to leave our new circuit switched off and go and investigate myself?

Sorry if its a stupid question.
cheers

 

[Octopus]

Could you lad not refer to his regs books?

 

[ChrisElectrical88]

Wouldn't 100% trust his judgement on this one mate

 

[shagbite]

you can trust google.

 

[Taylortwocities]

PSC of 79kA.????? Is he testing the pylon? :nuke:

You aren't going to be able to use MCBs on that, or BS88's........

 

[telectrix]

crazy readings there.

 

[shagbite]

i assumed that he'd missed out the decimal point.

 

[telectrix]

doesn't make sense. if it's TN-S the Ze should be below 0.8. and to give a PSC of 79KA, it would be 0.003

 

[varilite]

Probably 7.9 not 79

 

[ChrisElectrical88]

Sorry just double checked with him and he said 79 amps.

 

[telectrix]

that's better. however, that Ze is not acceptable so get DNO to sort it out. meanwhile leave any of your new work disconnected from supply.

 

[Bobster]

So is this a TT install? Or TN-S

 

[stigwart]

Max permissable ze for TT is 200 ohms so thats okay, bearing in mind it should be r.c.d protected.
Pscc at 79 amps is low so something strange there isn't there?

 

[Richard Burns]

Those results are good and consistent for a TT install but obviously way out for a TNS.
If he thinks it is a TNS ()and has seen the connection on the cable) then I would say that the earth connection at the cable is not good and the eareth is being provided by a service pipe through the bonding.
DNO call out to repair.
However do check again it is not TT because it can be a bit embarrassing if it is!

 

[stigwart]

I thought the 79 amps was okay for pefc Richard, but isn't that low for pscc?