Do I need to convert to TT?

[Leader]

Hi,

I'm a trainee and have had two conflicting opinions from my tutors about this question so I'm hoping to elicit the benefit of your combined experience.

I've bought an old house with very old electrics. The earthing arrangement is TN-S with the main earth clamped onto the sheath of the incoming supply cable. One tutor tells me that I have to convert it to a TT system and the other tells me there are special spring loaded clamps that conform. So my question is a) do I really have to change it (I think the answer is yes) and b) which tutor is right?

Thanks

 

[hightower]

Clamped as in with a BS951? Surely the clamp is the issue of the DNO, so I would suggest you don't touch it and phone your DNO to come and sort it?

 

[Paul.M]

You can ask for the DNO to install a PME earthing arrangement, wont cost that much.

 

[Bobster]

A ring to the DNO is the first point of call. If TN-S is available why someone would convert it to TT is beyond me. However if TN-S or TNC-S is unavailable TT may be needed although unlikely.

And yes there are proper clamps, BS951 clamps can crush the cable.

 

[Leader]

Fabulous, thank you! The "TT" tutor gave me the impression the DNO would charge an arm and a leg. I would much prefer that option. Thanks for your help.

 

[Octopus]

Sounds like you need more informed tutors!

 

[Simonslimline]

Got a picture of the cable and clamp? It is either a proper DNO clamp or a bodged up TN-S with a BS951.

 

[Andy78]

Fabulous, thank you! The "TT" tutor gave me the impression the DNO would charge an arm and a leg. I would much prefer that option. Thanks for your help.

Round our way Northern powergrid charge around £165 for a PME/TN-S connection onto existing service cable where they do not have to make the cable dead at the breach joint in the road.

This is the route I direct all my customers to as for me to provide a TT with similar values would cost them more. A TT with poorer values would be cheaper, but I never like to use RCDs as primary fault protection where there is a reasonable alternative.

 

[Leader]

Got a picture of the cable and clamp? It is either a proper DNO clamp or a bodged up TN-S with a BS951.

I've managed to attach them but you may need to lie down to view!!

 

[Paul.M]

I've sorted out the pictures for you luv

 

[Leader]

Thanks honey :winkiss:

 

[Bobster]

Could do with a close up of the clamp itself. It doesn't look like a BS951

 

[Andy78]

Could do with a close up of the clamp itself. It doesn't look like a BS951

I was thinking that too. It certainly doesn't look like any of the DNO sheath clamps I'm familiar with, but that doesn't mean it's not safe and legit.

I would be looking at the value of Ze and whether or not it was a secure and undamaged connection. It may be fine for continued use. The DNO might even come and have a free look at it to verify it.

 

[Leader]

Could do with a close up of the clamp itself. It doesn't look like a BS951

How's this one?

 

[telectrix]

needs a a bit more light. as in separate from your phone's piddling torch.