Bonding Advice Needed

[Mikeluker]

Assuming pme of course

 

[Simonslimline]

Assuming pme of course

What about the RCD of the Distribution CCT!

Design of an electrical installation is not based upon assumptions.

 

[Mikeluker]

What about the RCD of the Distribution CCT!

Design of an electrical installation is not based upon assumptions.

Yes you are right, this is all we have to go on in the post. If the distribution circuit is from a pme source and the cabling is not buried within a wall less than 50mm then an rcd would not Ben required or am I missing something

 

[Des 56]

a 16mm twin and earth goes to each flat where the sparky will fit new boards to serve each flat.

Here is a couple of comments I would like to make regards the last few posts


The opening post does not say the cables are buried
Or if they are buried and mechanically protected
Or if it is the intention to have them in surface trunking


It may be the case that the regs can be interpreted to require main bonding only at the point of entry,however,each flat then relies on that main bond remaining intact to ensure the particular service remains bonded for their individual service
It would seem to be an improvement to ensure that each flat has its own means of ensuring main bonding is reliably bonded by doing so locally to each flat

Bonding at the Gas meter in the garden would extend the zone outside of the building,I think it needs fitting where the pipe enters the building

 

[davesparks]

a 16mm twin and earth goes to each flat where the sparky will fit new boards to serve each flat.

Here is a couple of comments I would like to make regards the last few posts


The opening post does not say the cables are buried
Or if they are buried and mechanically protected
Or if it is the intention to have them in surface trunking


It may be the case that the regs can be interpreted to require main bonding only at the point of entry,however,each flat then relies on that main bond remaining intact to ensure the particular service remains bonded for their individual service
It would seem to be an improvement to ensure that each flat has its own means of ensuring main bonding is reliably bonded by doing so locally to each flat

Bonding at the Gas meter in the garden would extend the zone outside of the building,I think it needs fitting where the pipe enters the building

If you consider the information in the guidance note on earthing and bonding then it makes it pretty hard to interpret the regs as only requiring bonding at the incoming.

 

[davesparks]

The main bonding would only need to installed within the gas floor boxes outside on the consumer side of the stop cock. The main water assuming this would be in the riser position would require a main bond only in the incomer position both sized in accordance to the main neutral. They won't require any additional bonding within the flat themselves as there are no other earth potentials being introduced. The submains to the flats will require a disconnection time of 5 seconds so no rcd will be required. Each flat would need rcds / rcbos internally split across lighting circuits etc as not to cause full failure if a fault occurs.
Normally if an underground extraneous pipe goes from one building to another both bonds would be required as to equalise both potential differences between them, I hope this helps.

Main bonding is required at the point of entry to an installation, gas meters are not necessarily the point of entry, especially if the meter is at ground level and the pipes enter the building at the first floor and above.

Each flat has its own electrical installation and therefore requires main bonding to each extraneous part. The fact that some service pipes are bonded at the incomes makes them extraneous to the flat's installation.
Each flat may also have additional extraneous parts of hot water, heating, air handling etc are centrally supplied rather than in each individual flat.

 

[Des 56]

If you consider the information in the guidance note on earthing and bonding then it makes it pretty hard to interpret the regs as only requiring bonding at the incoming.

I can't disagree with you and don't want to do so,my own comment on the bonding was made with the "definitive" advice given by Mikelukers post in mind

I said (it may be the case that the regs can be interpreted to require main bonding only at the point of entry)it was to make the point that even if it was to be bonded at the entry to the building,bonding at the flats would improve that decision

 

[Mikeluker]

if the main bond is in place though outside, and the submain carried its own earth connected to the main terminal this would also common up all of the bonding, nowadays assuming plastic incomers it would only be supplementary bonding and may not even be extraneous, the electrician on site would have to make this decision.

 

[davesparks]

if the main bond is in place though outside, and the submain carried its own earth connected to the main terminal this would also common up all of the bonding, nowadays assuming plastic incomers it would only be supplementary bonding and may not even be extraneous, the electrician on site would have to make this decision.

It's sim not just a case of communing up all of the bonding, each installation needs bonding installed to create an equipotential zone for the installation.
In this respect a block of flats is no different to a row of houses in a street, the physical distribution of the installations is vertical rather than horizontal but electrically they are same each with their own installation

 

[Mikeluker]

The position of the main protective bonding conductor to the services where they are considered an extraneous conductive part should be in accordance with BS7671 regulation 544.1.2.
The size of the main protective bonding conductor should be in accordance with BS7671 regulation 544.1.1 and where PME conditions apply Table 54.8.
The main protective bonding conductor should be connected to the main earth terminal in accordance with BS7671 regulation 411.3.1.2. This would normally be the earth facility provided by the supply/meter operator.
In a block of flats this position may vary depending on the position of the main earth terminal and the supply arrangements to each flat.
It is permissible to provide a "continuous" main protective bonding conductor to multiple services.