Supplementary bonding

[STI]

This forum is really helpful but unfortunately as I read more questions and answers they raise other questions in my mind or make me go check things to make sure we have whats needed. Our house is very old and was owned by an old lady so if it wasn't broken it didn't get fixed.

So my latest area of concern/interest is...

I have found the earth bonding to our main water pipes and also to/from our oil supply pipe, we do not have gas.. Our bathroom which has a metal roll top bath and a wash basin also has a false wall of T&G behind which the water pipes run. All that comes out of the T&G is about an inch of copper pipe which then joins some flexible metal pipe to join to the taps. What i cant see is any supplementary bonding to the pipes.
I have run a wire from the CU earth bar (about 10 foot) and measured continuity from this to the pipes and there was a continuity reading, But thinking about this i think all i proved was that the main bonding was in place. Am i correct ?

Other than stripping out the T&G is there any way of testing for the supplementary bonding. I want to make sure the bathroom is safe and as i mentioned in a previous post it is protected by a RCD but it is a 100ma. Which leads me to another question. When I asked about this it was suggested that if i had a TNS system this might be why its a 100ma rather than a 30ma. i visually checked my earthing and i believed it was a TNCS set up as the earth was going into the main breaker below the meter. However i understand from reading the WIKI stuff here that a TNS system can also look like this. So how can you check what type you have without breaking the suppliers seal.

One day it will all be sorted and i can sleep easy but then i guess the regs will change

 

[ericmark]

The meters to test ELI are not cheap and although you could hire I would think if you want piece of mind that it is OK it would be far easier to ask some electrician to do it for you.

As to TN-C-S or TN-S this should be found out by enquiry. i.e Phone your supplier and ask they are duty bound to tell you.

Having said that it make very little difference and unless you were supplying a caravan you don't really need to know as once in the premises it is a separated system. There may be a difference to the ELI reading Ze as it is called again you can phone up supplier and ask for that if you really want to as the meter is expensive and not really a DIY task.

The 100ma RCD is really more for fire protection then anything else and does not really stop injury they were used where the ELI was high as with TT systems in the past but since 2008 they have become pointless as most systems now need a 30ma RCD.

However these don't need fitting unless you are doing some changes.

 

[STI]

Thanks for the quick response. I do have access to a megger MFT but i didnt think this would help checking specifically for the supplementary bonding. Is it a different sort of device thats needed.

On the 100ma, i live in devon and not long ago a person was killed in their bath by electrocution. I believe this was put down to no supplementary bonding in place and no RCD in place for the bathroom. Again looking at the stiki (not wikki) it looks like a 50ma leakage can kill.

 

[flameport]

Measuring for continuity won't help to identify supplementary bonding, as there will probably be several other parallel connections between the pipes elsewhere, such as the boiler, kitchen sink with a mixer tap, hot water cylinder and so on.

If you have continuity between the pipes, this is what you want, but the problem is that if pipes or other items are altered elsewhere in the house, the continuity could be lost without anyone realising.
You also need continuity between the pipes and the cpc (earth wire) of any electrical circuits in the bathroom such as the lighting.

You could install your own supplementary bonding if the pipes and electrical cables for the bathroom can be accessed just outside the room such as in the loft, adjacent cupboard etc.

The RCD being 100mA isn't really a problem. New installs would have a 30mA RCD for all bathroom circuits, but probably wouldn't need supplementary bonding.
Older installations would need the supplementary bonding but probably won't have an RCD.

 

[STI]

Flameport thanks again for your help. If i have understood your reply correctly. I have confirmed continuity of the pipes to the CPC of the lights by running the lead fro the earth bar in the CU and measuring there is continuity betwen it and the pipes. ?

The house was put up for sale before the need for a HIPS or electrical safety check was a requiement and does not appear to have had a PIR. If i was to come to sell the house and have an inspection for the hips or a PIR if i wanted to rent the place out would the 100ma RCD proteting the bathroom pass the inspection. The wiring is about 11-12 years years old if this helps.

 

[flameport]

If the supplementary bonding was done properly, it should link the various pipes and CPCs together either in, or just outside of the bathroom. They will already be linked at the CU/main bonding etc., the supplementary bonding is an additional safety feature in case a fault elsewhere caused a lack of continuity.

e.g. someone changes a light fitting in a bedroom, and the cpc is not fitted properly. This causes the bathroom light to have no connection to earth, and later on, a second fault causes the bathroom light to become live. Now someone climbs up on the bath and touches the live light fitting and at the same time has their foot on one of the bath taps and gets a shock.
Supplementary bonding would prevent that as it is likely the MCB would trip (the fault current would flow to earth via the water pipes), and even if not, the bonding would ensure the bath tap and light fitting were at the same potential. In your case the 100mA RCD should trip anyway.

HIPS are worthless junk and contain nothing about electrical installations at all. Unfortunately there is no legal requirement to have electrical installations in homes inspected, even if they are rented out.

If you had a PIR done, the apparent lack of supplementary bonding would probably be listed as something to be improved or investigated further, and so would the 100mA rather than 30mA RCD. That doesn't mean it is dangerous, and there would probably be many other items which don't comply with current regulations.

 

[STI]

Flameport, Thanks again at least i now know nothing reqires urgent attention on this bit. Interesting comment on the need or not for the electrical inspection if i rent out. The potential agent was saying if i rent out then its a commercial property and therefore needs the safety check, which i assume is a PIR. Having said that she did sound a bit hesitant over this part of the agreement.

Thanks again for your help