Earth Bonding

[autolycus]

Hi,

I've just discovered a card from Transco on top of my gas meter which points out that the gas pipework has no equipotential earth bonding. This was obviously issued prior to my buying this house a month ago and was left there by the previous owner.

I've already mentioned the slightly unusual setup that we have got in this post:
//www.diynot.com/forums/viewtopic.php?p=767848

Basically, in summary, we have got a supply cable that rises up from the floor of the integral garage (but which is presumably fed from an overhead supply because every house in the street apart from mine and the next door neighbour's have an overhead supply cabel to the property).

This goes to the meter and from there to (a) a consumer unit (with MCBs and an RCD) that feeds some of the house and (b) an isolator switch and 60A cartridge fuse that feeds a spur to a second consumer unit (old style with cartridge fuses) in the utility room. This, in turn, has a spur to a modern RCD/MCB protected consumer unit in the external garage/outbuilding.

Outside the integral garage (the one where the supply comes in) we have an earth rod. There is an earth cable which, as far as I can tell, runs from this back to the consumer unit.

There is no obvious sign of any earth wiring connecting to either the gas supply pipe or the incoming water supply pipe.

So, the first question is do I need to earth the incoming water and gas supplies and, if so, can I do it simply by running two earth cables: one from the gas pipe to the earth rod and one from the water pipe to the earth rod?

The next thing is that as far as I can see, there is no separate bonding in the bathrooms. Is this needed? The electrician who did a load of work in a flat I lived in back in the late 90s made a big deal of bonding everything in the bathroom, but a few years later in a different house when I had wiring installed for some bathroom lights and a power shower, the spark who did that said that bonding was not a requirement any more (this was in 2003).

I said in my post about shower pumps that I the shower pipework appeared to be earthed. However, closer inspection reveals I was not necessarily correct.

In terms of the two shower pumps in the loft, one has copper feed pipes from the tanks and then plastic output pipes going to the bathroom. No sign of any earth wiring here.

The other pump has copper pipes for the two inputs and two outputs. There is a short length of earth wire bonding all four of these copper pipes together, above where they go into the flexible inlet/outlet pipes of the pump. Not sure how worthwhile that is, given that the hot and cold pipes from the pump to the shower have several plastic joints in them.

Does any of this sound worrying?

David.

 

[Adam_151]

Ah, there would seem to be a serious aspect thats only just become apparent

It would seem you have a TT supply, and not enough RCD protection

Is it possible to get a photo of the setup in the garage?

 

[securespark]

Need photos. If you have a TT supply WITHOUT RCD protection, you are AT RISK of electric shock.

You may have a PME supply or TT > PME conversion.

Either way, you NEED MAIN EQUIPOTENTIAL BONDING.

EDIT: Sorry, Adamski!

 

[autolycus]

Sorry, guys - you;re losing me a bit now.

TT?
TT -> PME??

Photos to follow shortly......

 

[securespark]

TT is either an overhead or underground supply cable with no earth connection.

TT>PME is where they alter the supply cable to make provision for an earth connection to be made from it, like PME.

 

[Adam_151]

Three ways of providing an earth connection:

//www.diynot.com/wiki/electrics:earthing_supply_types_and_bonding:earthing_arrangements

PME is (basically) another name for TN-CS

As TT uses the physical mass of the planet as an earth path, impedances are high, earth fault currents low, and RCDs needed


We'll explain more when we can see the pics and make it relevant

 

[securespark]

Both the above pictures show a supply with no earth connection to the supply cable.

The following picture shows how with PME (TN-C-S), the earth connection is made to the neutral (or PEN) conductor:

 

[autolycus]

Right, here are some photos. I can make them bigger/higher res if more detail is needed.

This one
http://www.photobox.co.uk/shared/photo.html?c_photo=1643229803
gives an overview of everything in the integral garage.

The big metal box top left is the one that feeds the secondary consumer unit in the utility room.

The small white box underneath the trunking below that is just a junction box - looks like one of the cables was too short to reach when the new consumer unit was installed.

The switch immediately to the left of the gas meter is just a switch for an outside light.

This photo is a close up of the consumer unit:
http://www.photobox.co.uk/shared/photo.html?c_photo=1643229946
I can tell you what each of the circuits does if you want.
All the circuits (except, I think, the cooker circuit) are protected by the RCD that you can see in the photo.

That means everything is RCD protected apart from the circuits which are fed off the secondary consumer unit, namely:
- utility room lights and sockets
- 2 of the living room sockets
- 2 of the dining room sockets
- 1 of the kitchen sockets
- immersion heater
- socket in loft for shower pump

This photo is a close up of the incoming supply cable:
http://www.photobox.co.uk/shared/photo.html?c_photo=1643229942

Probably also worth noting that:
1. There is one socket in the kitchen which is running off one of the downstairs lighting circuits (circuit 2 on the board pictured above). Bit of a problem if you try to use the microwave when the living room lights are on

2. It seems from what I have spotted so far that at least some of the lighting circuits (all of which run off the consumer unit pictured above) are using twin cable with no earth whilst others are using twin & earth.

David.

 

[Adam_151]

It looks like it could have been TNS at one stage, but there seems to be no sign of a connection to the sheath (don't play about with it mind)

That CU, looks like it could be a split board with just one MCB on the non-rcd side, between the main switch and the RCD? cooker?

If we are going to have to treat this as TT, then you've overlooked a few things that need to be RCD'd, starting with that 60A switchfuse itself

That gas meter looks a tad too close to the leccy stuff!... but at least the gas bond is easy

I'd give the DNO a call about them providing an earthing point, where abouts in the country are you? might be best you have a MET and earthing and bonding conductors installed prior to them calling at your door?

Socket outlet on lighting circuit is a bodge and wants fixing

Lighting circuit in twin with no cpc needs re-wiring sooner or later, it doens't comply (though safe if you have only class 2 fixtures), lighting circuits have been installed with cpc since the 14th edition which came out in 1966, and early PVC wasn't too great, so probably time to be replaced from that POV as well"

You need to sort out you main earthing arrangements ASAP!, its a risk as it is!

 

[JohnD]

edited: my mistake

agree with adam, ask your supplier if they can provide an earthing point.
(you can approach the DNO if you know who, but you haven't got to, just write to the address on your electricity bill, it's their job to know)

Might be free, might cost £50 to £100, might (rarely) be impossible

 

[autolycus]

Thanks for the ongoing help. Much appreciated.

It looks like it could have been TNS at one stage, but there seems to be no sign of a connection to the sheath (don't play about with it mind)

Indeed, there isn't.

That CU, looks like it could be a split board with just one MCB on the non-rcd side, between the main switch and the RCD? cooker?

Correct on both counts.

If we are going to have to treat this as TT, then you've overlooked a few things that need to be RCD'd, starting with that 60A switchfuse itself

Yes. Or could I just replace the old consumer unit in the utility room (which that switchfuse feeds) with a modern RCD protected one?

I'd give the DNO a call about them providing an earthing point,

Do you mean one that would be used instead of the earth rod that I have at present? Are they obliged to do that if I ask them to (with or without payment)?

where abouts in the country are you?

Essex. What would have been Eastern Electricity Board when I were a lad.

might be best you have a MET and earthing and bonding conductors installed prior to them calling at your door?

How come? And is that something I can do myself? Is it just a case of installing the connection block and running earth bonding wire to the gas pipe and the incoming water main?

Lighting circuit in twin with no cpc needs re-wiring sooner or later, it doens't comply (though safe if you have only class 2 fixtures),

Yes, all class 2 apart from the metal light fittings and the metal wall swicthes.

lighting circuits have been installed with cpc since the 14th edition which came out in 1966, and early PVC wasn't too great, so probably time to be replaced from that POV as well

Original part of house was built in 1964 so must have just missed 14th edition.

You need to sort out you main earthing arrangements ASAP!, its a risk as it is!

Presumably only a risk for those circuits that are not running off the consumer unit with an RCD?

If I could get the utility room consumer unit swapped out for one with an RCD then is TT in itself really a bad thing?

Whilst getting this sorted, would it be advisable to fit that RCD faceplate to the soket that supplies the shower pumps?

 

[Adam_151]

Yes. Or could I just replace the old consumer unit in the utility room (which that switchfuse feeds) with a modern RCD protected one?

If we were leaving it as TT, then just having an RCD in the utility room DB would not be sufficent... it is downstream of that switchfuse and the submain cabling, if for example a earth fault between phase and the casing of that switchfuse was to occur, which RCD would disconnect it? (with TT the impedance of the earth path is too high for any great currents to flow, so fuses wouldn't blow, as they would in a TN system)

What you could so, is replace that board with a 30ma RCD one, and place a 100ma time delay one in the main tails comming from the meter, this is a common set up on TT systems, anything protected by 30ma will trip that first, but if a fault occurs in the switchfuse the time delay device will catch it, but see what the DNO can offer you first

Side point? how is that switchfuse supplied? does the supply from the meter loop into the DB main switch and then onto the switchfuse?

Do you mean one that would be used instead of the earth rod that I have at present? Are they obliged to do that if I ask them to (with or without payment)?

Yes, and not sure about on an existing supply, on a new supply they have to supply a TNCS earth unless there is a good reason not to, best speak to them

where abouts in the country are you?

Essex. What would have been Eastern Electricity Board when I were a lad.

EDF then I presume? //www.diynot.com/wiki/electrics:other:dnomap

They're French, make of that what you will

might be best you have a MET and earthing and bonding conductors installed prior to them calling at your door?

How come? And is that something I can do myself? Is it just a case of installing the connection block and running earth bonding wire to the gas pipe and the incoming water main?

Some DNOs will install an earth connection point and leave it there for sparky to install MET, and earthing and bonding conductors, some (EDF), will show up on your doorstep and find you have no equipotential bonding and disappear!

And yes, Main earth terminal, 16mm² to CU, 16mm² to Switchfuse, 10mm² to water to BS951 clamp on outgoing side, within 600mm and before any branches, ditto for water, and then a loop of 16mm² for the DNO guy left hanging (oh and connect your earth electrode to new MET for now)

Lighting circuit in twin with no cpc needs re-wiring sooner or later, it doens't comply (though safe if you have only class 2 fixtures),

Yes, all class 2 apart from the metal light fittings and the metal wall swicthes.

Plan to have it replaced soonish, in meantime replace class one fixtures with class two, use nylon screws in switches

You need to sort out you main earthing arrangements ASAP!, its a risk as it is!

Presumably only a risk for those circuits that are not running off the consumer unit with an RCD?

Lack of main bonding causes a risk should a fault develop on any circuit, but with no RCD on parts of a TT install, they are even more risky in their own right, and the lack of bonding makes these even worse

If I could get the utility room consumer unit swapped out for one with an RCD then is TT in itself really a bad thing?

TT in itself is not a bad system, but as stated above, adding an RCD there is not all thats required unfortunatly

Whilst getting this sorted, would it be advisable to fit that RCD faceplate to the soket that supplies the shower pumps?

I'm afraid that is probably like trying to plug a hole in a dyke with your finger (I'm sure it didn't used to sound as vulgar in the age the expression is from ), if it was mine, I'd probably put a 30ma RCD in the main tails for now, but acheiving the isolation required to do so is illegal and potentially dangerous , so you'd be ill advised to try and do this...

I'd advise you install the MET and bonding, express to the DNO 'nice day girl' the urgency, and possibly switch off the non RCDed? parts for now?

 

[autolycus]

Update time....

Spoke to EDF about getting the earth sorted. They referred me to Scottish Power (my supplier) who in turn arranged for EDF to send round a guy from Siemens yesterday to check the earth loop impedance.

Upshot of it is that yes they can switch us over to PME.

Meanwhile, I have had two electricians round to look at what I've got, make some recommendations and give me a quote. Their advice (based on the assumption I'd be switching over to PME) was as follows:

Sparky A:
- Get the bonding done on the incoming gas and water
- Replace the old style board with a modern MCB board because he reckoned having it partially hidden by the wall cupboard in the utility room is dangerous/fire risk.
- Consider upgrading the cables running from the switchfuse to the utility room consumer unit as they may not be thick enough and/or the voltage drop may be too great
- Install supplementary bonding in the two bathrooms.
- Plan to sort out the unearthed lighting circuits at some point
- Let him spend half a day doing a thorough investigation to see what else might need attention

Sparky B:
- Get the bonding done (for less than half the price quoted by Sparky A)
- Don't worry too much about the secondary consumer unit because it is simple enough to isolate it from the switchfuse if it ever has a problem. Consider replacing cartridge fuses with plug-in MCBs.
- Don't worry about bonding in bathrooms because regs are changing soon and cross-bonding will no longer be required where all circuits to the bathroom are RCD protected.

Re this last point, Sparky A said that the new regs will still require the supplementary bonding in situations where the lights in the bathroom are on a shared lighting circuit. He said the only way to avoid having to cross-bond would be to have the bathroom lights on their own separate RCD protected circuit.

Sparky B says that as long as the circuit for the lights is RCD protected (which it already is) then it doesn't matter what other rooms' lights run off the same circuit. So, according to him, all I need to do from March onwards to avoid having to do extra bonding in the bathrooms is to fit an RCD faceplate to the socket in the loft that powers the shower pumps.

If it makes any odds, the pipework to the shower in one of the bathrooms is plastic and in the other it is copper but with plastic joins and elbows visible where the pipework runs through the loft from the pump tot he bathroom.

Anyone care to offer any thoughts please on the recommendations of each electrician and/or the situation re supplementary bonding?

Cheers,
David.