When is a dual path to earth required?

[sirocosm]

I am new to UK wiring, having done quite a bit of DIY in Canada, and was looking over the rules here.

I am looking at BS7671:2018 543.7.1.203 and it looks like circuits with sockets where the earth leakage can exceed 10mA require two paths to earth. This comes naturally with a ring circuit, but what about radial circuits? Since radials can be branched, do you need a separate earth path back to the CU from every leaf of the tree?

It also says in 543.2.6 that you can bond to other metal items as a path to earth. Does this mean that you can you just bond to the heating system piping if in copper? (assuming it is bonded to the earth in the CU).

We have a lot of computers and other devices with switched power supplies, so it could be possible to go over 10mA, I think.

 

[EFLImpudence]

I am looking at BS7671:2018 543.7.1.203 and it looks like circuits with sockets where the earth leakage can exceed 10mA require two paths to earth. This comes naturally with a ring circuit,

Yes, but the two should be in separate terminals so if one comes loose, one remains.

but what about radial circuits? Since radials can be branched, do you need a separate earth path back to the CU from every leaf of the tree?

Same requirements to ensure an earth path remains.
A separate conductor back from the end of the circuit would suffice so also from the end of each branch.

It also says in 543.2.6 that you can bond to other metal items as a path to earth. Does this mean that you can you just bond to the heating system piping if in copper? (assuming it is bonded to the earth in the CU).

Yes, with the conditions met.

We have a lot of computers and other devices with switched power supplies, so it could be possible to go over 10mA, I think.

It does not say though shalt not exceed 10mA; just what you must do if it does.

 

[333rocky333]

https://professional-electrician.com/technical/high-protective-conductor-currents/

I think the idea is to get 2 Earth connections within each socket AND the Db, in case one comes adrift, so I take it you could achieve that as above and by also running an extra earth cable from the spurs Donar socket to the spurred socket.

As for the other question, I think you may need to read it in conjunction with the other regs it mentions and the definitions of the items mentioned, I think its more to do with Protective conductors for Bonding Extraneous conductive parts, rather than providing an Earth to sub circuits, usually earthed by the Circuit Protective Conductor .

Thus if your mentioned heating pipes were also Extraneous conductors and hence required Earth bonding, then once that is done they would then become and be classed as Protective conductors, from the bonding point to there point of entry into the Ground, hence why they need to conform to the other regs and requirements mentioned.

 

[sirocosm]

In my case the radial would not be just a long chain, but more of a tree with separate branches. So if I can bond the ends to the radiator pipes, that would be great, otherwise it looks like I would have to run an additional earth wire alongside everything. They probably don't make 2.5mm cable with 2 earths, or if they do it is probably very expensive.

543.2.6 says: Except as prohibited by Regulation 543.2.3, an extraneous-conductive-part may be used as a protective conductor ....

543.2.3 says it can't be a gas pipe, flexible metal pipes and conduits, and other unsuitable items.

So it looks like bonding to the heating pipes is allowed, although somewhere else I read that it must be possible to expect all bonding connections, so I don't know if it would be in violation there.

 

[EFLImpudence]

So if I can bond the ends to the radiator pipes, that would be great, otherwise it looks like I would have to run an additional earth wire alongside everything.

Is that so bad?

They probably don't make 2.5mm cable with 2 earths, or if they do it is probably very expensive.

They make 4 core flex, but how would it remain continuous? Joint at every box?

543.2.6 says: Except as prohibited by Regulation 543.2.3, an extraneous-conductive-part may be used as a protective conductor ....

Yes, as long as they comply with the other requirements for prevention of loss.

543.2.3 says it can't be a gas pipe, flexible metal pipes and conduits, and other unsuitable items.

Yes.

So it looks like bonding to the heating pipes is allowed, although somewhere else I read that it must be possible to expect all bonding connections, so I don't know if it would be in violation there.

Inspect ? Yes, of course.

 

[flameport]

I am looking at BS7671:2018 543.7.1.203 and it looks like circuits with sockets where the earth leakage can exceed 10mA require two paths to earth

That's what BS7671 says, however in reality that situation can never occur.

All socket outlets require protection with a 30mA RCD. (411.3.3)
The maximum leakage current for a 30mA RCD in normal use is 9mA. (531.3.2)

 

[sirocosm]

Inspect ? Yes, of course.

Yeah I meant inspect. Which means practically you cannot bond to the radiator pipes as it would be hidden under the floor.

For the dual earth wire I suppose you could do it by having each earth in/out connected to the same terminal in each socket, with the two earth feeds using the two different terminals. That way they would both be continuous, and independently connected back to the CU.

I guess 4 core is for 3 phase, so that would be common. Are you allowed to use the black for ground, and the grey for neutral? Do you have to mark them at the all the connections somehow?

 

[sirocosm]

That's what BS7671 says, however in reality that situation can never occur.

All socket outlets require protection with a 30mA RCD. (411.3.3)
The maximum leakage current for a 30mA RCD in normal use is 9mA. (531.3.2)

My problem is electronic stuff. I have read that a switching power supply can leak up 3.5mA. I am looking at 8 of them in my livingroom alone. We have too many computers.

 

[JohnW2]

That's what BS7671 says, however in reality that situation can never occur. .... All socket outlets require protection with a 30mA RCD. (411.3.3) ... The maximum leakage current for a 30mA RCD in normal use is 9mA. (531.3.2)

It is probably sometimes necessary to note the potential difference between "can" (particularly "can never") and "could" or "must" .

As implied in subsequent post, the "9mA limit" is probably unrealistic in this day and age. Whatever the "should" and/or "must" may say, unless a designer restricts a sockets circuit to a very small number of socket outlets, there is no way that he/she can ever be confident that there will never be more than 9mA total earth leakage due to whatever might be plugged in.

Kind Regards, John

 

[Taylortwocities]

I guess 4 core is for 3 phase, so that would be common. Are you allowed to use the black for ground, and the grey for neutral? Do you have to mark them at the all the connections somehow?

When the new colours were introduced, there was a drive to stop people using black as the neutral in the new cables. Black was always neutral in the old red and black days. So the recommendation was that, in a3-core + cable the grey is used for neutral. The black for other purposes, perhaps a switched live.
What is required is that the conductors must be sleeved to indicate their function. So a grey used as neutral must be sleeved blue. A black used as a switched live must be sleeved in brown.

 

[333rocky333]

What is required is that the conductors must be sleeved to indicate their function. So a grey used as neutral must be sleeved blue. A black used as a switched live must be sleeved in brown.

I thought Black was a designated Live/Line colour and did not always need sleeving Brown, in multicore cable, even on single phase for certain applications.
Similar to where used in Rock and Klik roses and emergency lights
That said I still like to sleeve it Brown