Earth Bonding

[dlyn]

Wonder if anyone can help with my query - I've done search and can find lots of stuff on earth bonding but not this question.
Relative of mine (a qualified electrician) has recently installed a new Consumer Unit ( the thingy by the meter) for us and he has at same time improved/renewed the earth bonding through bungalow loft to water and LPG gas pipes. All tested and seems great, except now we have two lengths of white plastic conduit decorating our external brick walls - we think it looks a bit naff but can live with it if necessary, so I am a bit embarrassed to ask him to do it again.
Can I disconnect the earth cables and re-route them internally alongside water mains and boiler pipework and re-connect on to the same clamps on pipes as before? Its a bit difficult to get into the eaves in the loft but I think I'd be ok. Would this be ok for me to do or does it infringe anything/codes? The fact that at least one of the pipes to the boiler is hot would this present any danger to the earth cable alongside? Would I need to turn off elec. supply when I did this and could I do anything wrong?
Thanks in anticipation and sorry for the long post.

 

[riveralt]

Don't be embarrassed your first port of call should be to get the electrician who fitted the new consumer unit back and ask him/her to re-run the main protective bonding cables as you would like them.

The only criteria is that where possible each must be fitted to the incoming water and gas supply within 600mm of their entry into your property.

It is not a good idea to run cable next to hot water pipes - and there is a minimum distance that cable should be separated from gas pipes of up to 50mm depending on the size of the pipe.

 

[sparkticus]

This is a classic communication failure which happens often. Your electrician appears to have done the job in a technically correct manner. Yet it appears he/she has failed to discuss the esthetics with you before the work commenced.

This also happens regularly with Periodic Inspection Reports (PIRs) in the domestic, commercial and industrial worlds. An inspection of this nature is rarely 100% comprehensive but the electrician-client don't discuss the limitations and if they do then not comprehensively enough. It leads to all sorts of aftermath!

In this case, given the visual impact to your outside wall, I am astounded that this was not fully discussed before work commenced or at least during. Most of the blame I would assign to the electrician (should know better) but clearly a communications issue.

Did you agree with your electrician that all was fine when the work was completed?

 

[bernardgreen]

and there is a minimum distance that cable should be separated from gas pipes of up to 50mm depending on the size of the pipe.

Which poses a problem for the clamp where the cable HAS to meet the pipe in intimate contact.

Turning the electricity OFF will not disconnect the earth at the CU location from the ( assumed ) PME supply. So removing the bond wire to relocate it will not be made any safer by turning off the power.

In theory the end by the meter will be at earth potential as will be the pipe work. But in practice there may be a voltage diffence and this could cause a bit of spark when you disconnect the bonding.

Faced with this task I would leave the present bond in place while you install the new bond wire. After the new one is installed then remove the old one.

 

[dlyn]

Thanks v much for the responses.
I can't really blame b/inlaw cos he thinks its ok and I didn't know if there was another way. As I was helping in loft on the day I think he took easiest way through the loft for me. We're v happy with the job and feel much more secure with the new C/U - just think the conduit looks unsightly.
For the LPG gas pipe, I was proposing not to move the clamp he has fitted but only to disconnect the cable from clamp and bring the cable back into loft and route it inside loft back through to the garage where the boiler is located and re-attach to the clamp on the gas pipe. The earth cable would not run alongside the gas pipe - just attach back at same point as before.
For the water mains - something similar - where the clamp is fitted to the water main, disconnect earth from the newly fitted clamp and bring it back into loft and then run it down the boxed in pipework back to the clamp and reconnect at same point as before.
Bernard has me slightly worried - I didn't expect sparks!!! As I'm not keen on messing with the wiring at the meter end is this getting beyond my competence. I'm happy to give things a go generally but don't want do aynthing unsafe.
Thanks to all again

 

[sparkticus]

For the LPG gas pipe, I was proposing not to move the clamp he has fitted but only to disconnect the cable from clamp and bring the cable back into loft and route it inside loft back through to the garage where the boiler is located and re-attach to the clamp on the gas pipe. The earth cable would not run alongside the gas pipe - just attach back at same point as before.

That part is OK because the LPG bottles (I am assuming bottles) and limited amount of pipework is very unlikely to be introducing any voltage or current of any consequence. If you have an LPG tank then a temporary wire is the best option.

Bernard has me slightly worried - I didn't expect sparks!!! As I'm not keen on messing with the wiring at the meter end is this getting beyond my competence. I'm happy to give things a go generally but don't want do aynthing unsafe.

Bernard is right. I have seen sparks myself from disconnected water and gas supplies. The thing to remember is that pipes can carry hazardous voltages and or currents into a property and out of a property.

Having said that a temporary connection while you re-rout the main earth cable would make it completely safe. Switch off your electrical power at the consumer unit as well.

 

[sparkticus]

edit

 

[bernardgreen]

The thing to remember is that pipes can carry hazardous voltages and or currents into a property and out of a property.

They can bring a true ground potential into the property. If the "earth" supplied by the incoming electrical supply is also at true ground potential then no problem. The bonding is needed as the "earth" supplied by the incoming electrical supply is not always at true ground potential but for safety inside the property the pipes must be at the same potential as the "earth" from the supply.

 

[matt1e]

The thing to remember is that pipes can carry hazardous voltages and or currents into a property and out of a property.

They can bring a true ground potential into the property. If the "earth" supplied by the incoming electrical supply is also at true ground potential then no problem. The bonding is needed as the "earth" supplied by the incoming electrical supply is not always at true ground potential but for safety inside the property the pipes must be at the same potential as the "earth" from the supply.

They can carry hazardous voltages/currents into a property, under certain fault conditions

 

[sparkticus]

The thing to remember is that pipes can carry hazardous voltages and or currents into a property and out of a property.

They can bring a true ground potential into the property. If the "earth" supplied by the incoming electrical supply is also at true ground potential then no problem. The bonding is needed as the "earth" supplied by the incoming electrical supply is not always at true ground potential but for safety inside the property the pipes must be at the same potential as the "earth" from the supply.

They can carry hazardous voltages/currents into a property, under certain fault conditions

Just one possible example: (I think)

Two houses next to one another House A - House B - TT earthing system.


1) House A: TT spike is fine with a nice low Ra.
2) House B: TT spike is missing/disconnected
3) Lead water main serves house A & B
4) Plastic main run to lead at the pavement position.
5) House B has a "leaky" immersion heater and no RCD in circuit (or RCD threshold not reached)
6) House A receives the current from house B on its lead water pipe.
7) In house A Mr Smith cuts into the pipe and now there is (or could be) a significant PD across the two ends of the pipe with the higher end originating from house B

 

[matt1e]

Just one possible example: (I think)

Two houses next to one another House A - House B - TT earthing system.


1) House A: TT spike is fine with a nice low Ra.
2) House B: TT spike is missing/disconnected
3) Lead water main serves house A & B
4) Plastic main run to lead at the pavement position.
5) House B has a "leaky" immersion heater and no RCD in circuit.
6) House A receives the current from house A on its lead water pipe.
7) In house A Mr Smith cuts into the pipe and now there is (or could be) a significant PD across the two ends of the pipe with the higher end originating from house B

how about
Two houses next to one another House A - House B - PME earthing system.
1 house B loses its neutral connection
2 house B's neutral return then diverts to house A's neutral via the E/N link in the cutout > house b's main bonding > metal water pipe that serves both houses > house A's main bonding > houses A's intact neutral via the cutouts E/N link
3 In house A Mr Smith cuts into the pipe ............ etc
or
4 Mr Smith decides to have his consumer unit changed
5 Bonding is done at the consumer unit as appossed to MET
6 sparky turns off power, pulls mains fuse,disconects circuits,
7 disconnects bonding or main earth and is contact with both
8 insert the word "sparky" into paragraph 2 above

It's precisely what is happening Here

 

[JohnW2]

how about
Two houses next to one another House A - House B - PME earthing system.
1 house B loses its neutral connection
2 house B's neutral return then diverts to house A's neutral via the E/N link in the cutout > house b's main bonding > metal water pipe that serves both houses > house A's main bonding > houses A's intact neutral via the cutouts E/N link
3 In house A Mr Smith cuts into the pipe ............ etc
or ...

Indeed, provided that there is no continuity through metal water pipes to a property which has not lost its neutral (and has bonding in place!). If such continuity does exist, the voltage on all the affected pipework ought to remain fairly low.

Kind Regards, John.

 

[OwainDIYer]

All tested and seems great, except now we have two lengths of white plastic conduit decorating our external brick walls - we think it looks a bit naff but can live with it if necessary, so I am a bit embarrassed to ask him to do it again.

Plastic conduit can be painted.

 

[matt1e]

Indeed, provided that there is no continuity through metal water pipes to a property which has not lost its neutral (and has bonding in place!). If such continuity does exist, the voltage on all the affected pipework ought to remain fairly low.

Kind Regards, John.

Hi john, the problem arises when there is continuity through metal pipes to a property that has not lost it's neutral and has bonding in place
refer to the arrows denoting current flow in the diagram

Matt

View media item 35587
note its a quickly amended exisitng drawing ,I know there is a meter missing!!!

 

[JohnW2]

Indeed, provided that there is no continuity through metal water pipes to a property which has not lost its neutral (and has bonding in place!). If such continuity does exist, the voltage on all the affected pipework ought to remain fairly low.

Hi john, the problem arises when there is continuity through metal pipes to a property that has not lost it's neutral and has bonding in place refer to the arrows denoting current flow in the diagram

Thanks, but it looks as if I was not clear/precise enough. I should perhaps have written:

... provided that there is no continuity through metal water pipes to another property which has not lost its neutral (and has bonding in place!).

('another' meaning a property {third or subsequent} other than the one with a lost neutral and the one without a lost neutral in which the pipe was cut.) In terms of your diagram, if point C was connected to supply neutral via metal pipework and the bonding of a third property which had not lost it's neutral, then the PD between A and B ought to be pretty low (just the voltage drop along the length of pipework + bonding) ... isn't that the case?

Kind Regards, John.