TT Amendment 3 and 100mA S-type RCD

[Paulgwat]

Hi all,

99.9% of my work is TNS or TNCS but I am currently working out of my normal area at a property that is presumed to be TT (I say presumed because some helpful soul has encased the service head where the Live and Neutral emanate in expandy foam along with about 4 feet of wall, from the top of the head the two cables go to a henley block in the case of the Neutral and the cutout for the Live.)

The earth also comes out of the foam but slightly further along the wall.

Below the meter location is a basement but this has been boarded out and no service cables are visible at all

Externally I can't find an earth rod - but there is a lot of concrete that has been put down in recent years to make paths etc, most recent changes to install were probably 35 years ago -Concern is that it may be a water main bond and not an earth rod.

Contacted WPD the local DNO and they were no help, although they may be able to upgrade supply to PME (waiting on quote) according to them they aren't obliged to keep records relating to earthing or even supply an earth.

I have been asked to upgrade the existing install to 17th Amd3 boards from the collection of about 10 fuse boards and switch fuses, currently there is a 500mA ELCB at the output of the meter.

Ze is somewhere in the 30ohm range.

I have bonded the gas but water main is proving difficult to find as property owner is not aware of where it comes into house and doesn't appear there is an internal stop tap anywhere, there is however supplementary bonding in each of the 3 kitchens (its one single owner occupier house not an hmo, kitchens are a hangover from previous use)

Apologies for the long winded preamble but here are my questions

1. Assuming WPD aren't stupidly expensive my recommendation is going PME - Does anyone think this is a bad idea?

2. If it stays TT I am confused as to whether 100mA RCD is required when all CU ways will be RCD/RCBO covered and consumer units are within 12 inches of service head - I understand historically higher current rating RCD's were used to protect against fire but is this necessary now?

3. If i need the 100mA RCD i understand it can't be in a metal CU and under amd3 cant be plastic -what do i do? is it metal cu and wiska plastic insulated gland like i am using for the consumer units or.....?

4. If it stays TT I would feel a whole lot happier sinking a new earth rod - Is there a reg stating that the earth rod needs to be visible and available for inspection that i can use to explain the new rod to client?

5. Haven't done a wander lead test yet but if water does need bonding do I just pick an available pipe or?

Any questions please let me know

Paul

 

[davesparks]

Have the DNO seen this expanding foam encased in comer yet? I suspect they may be less than impressed and decide they wish to gain access to their property via sledgehammer, possibly even charging for the replacement of the old head etc.

Is it an overhead supply or underground?
If underground then it's most likely to be TNS at the apparent age of it.
If it's overhead then you should be able to tell quite easily if it is the original TT overheads or if it has been replaced with modern ABC overheads and made into PME.

 

[Welchyboy1]

Well i would say the issue with access to the main head needs sorting out for inspection and maintenance for a start

you could keep it TT, but i would install an accessible rod, hopefully you should get a better ra than 30ohms

if all circuits are 30ma protected you dont need a 100mA device, you would use this in a case of any submains before the board usually

i would get the LEB involved as least as possible if it were me as they are usually a pita to deal with