High integrity earthing

[Guest 004]

Can anybody here give some examples of this, and in what situations it would be used?

More importantly my understanding is that you would need an extra bar at the DB, which is then maybe insulated?

 

[Guest123]

Most commonly found in IT suites due to the high earth leakage current of the equipment associated with them.

543.7 refers.

Also see attached PDF.

 

[Deleted member 26818]

The extra bar at the DB is not really that necessary, I don't quite know what you mean by insulated.
Obviously it will be insulated from any live conductors or bars.
There are two methods for providing high integrity earthing.
one is to use a substantially larger CPC than is normally used, the other is to use a second CPC.
When using a second CPC, the conductors should be terminated in different terminals from those for the first CPC.
This is where a second earth bar would be used, if ther is only one earth bar, then the usual practice is to terminate the second CPC in the terminal next to the first CPC. This will often entail doubling up conductors with those of a different circuit.

 

[Guest 004]

The extra bar at the DB is not really that necessary, I don't quite know what you mean by insulated.
Obviously it will be insulated from any live conductors or bars.
There are two methods for providing high integrity earthing.
one is to use a substantially larger CPC than is normally used, the other is to use a second CPC.
When using a second CPC, the conductors should be terminated in different terminals from those for the first CPC.
This is where a second earth bar would be used, if ther is only one earth bar, then the usual practice is to terminate the second CPC in the terminal next to the first CPC. This will often entail doubling up conductors with those of a different circuit.

well that differs from the pdf doc

 

[Deleted member 26818]

Does it?
I'm not really suprised, as from glancing at the document I note that it is written by Mark Coles.
I'd suggest that rather than relying on Mark's opinions, you have a look at Section 543.7 in BS7671.

 

[telectrix]

the pic on page 10 is useful. also, you would use socket outlets with 2 earth terminals and connect 1 cpc leg to each, rather than the more usual way of puuting both in 1.

 

[Deleted member 26818]

the pic on page 10 is useful. also, you would use socket outlets with 2 earth terminals and connect 1 cpc leg to each, rather than the more usual way of puuting both in 1.

The two terminals are intended for two separate CPCs, one CPC in one terminal and the other CPC in the other terminal.
If only one CPC is being used, there is no need to use socket-outlets with two terminals.

 

[telectrix]

The two terminals are intended for two separate CPCs, one CPC in one terminal and the other CPC in the other terminal.
If only one CPC is being used, there is no need to use socket-outlets with two terminals.

hmm, i was taught , rightly or wrongly, that if, say, the circuit was a ring final, then you used both terminals in case of a break in 1 cpc, i'll have a read of 543.7, the guy that tol,d me the above, however, was adamant that fly leads must be fitted to back boxes. tbh, it's not something i come across , so have not bothered to research hi integrity earthing fully.

 

[Deleted member 26818]

"543.2.7 Where the protective conductor is formed by conduit, trunking, ducting or the metal sheath and/or armour of a cable, the earthing terminal of each accesory shall be connected by a separate protective conductor to an earthing terminal incorporated in the associated box or other enclosure."
"543.7.1.4 Where two protective conductors are used in accordance with Regulation 543.7.1.3 (iii), the ends of the protective conductors shall be terminated independantly of each other at all connection points throughout the circuit, e.g. the distribution board, junction boxes and socket-outlets. This requires an accessory to be provided with two separate earth terminals."

 

[Guest 004]

I fail to see where you would this type of circuit, other than in IT rooms, or MER's, and SER's

 

[Deleted member 26818]

Offices where there are lots of computers, School computer rooms, internet cafes etc.
You should also consider other items of equipment such as TVs, game consoles, stereos even washing machines and microwaves. Then there's alarm systems and these new controlable lighting systems to consider.
In fact just about any item of equipment that uses a PLC can have earth leakage.
Older desktop PCs can have as much as 3.5 mA, so an office or internet cafe with 3 or more PCs could easily top the 10mA limit.
I believe the NICEIC video even shows earth leakage from something connected to a fish tank?

 

[Guest 004]

Offices where there are lots of computers, School computer rooms, internet cafes etc.
You should also consider other items of equipment such as TVs, game consoles, stereos even washing machines and microwaves. Then there's alarm systems and these new controlable lighting systems to consider.
In fact just about any item of equipment that uses a PLC can have earth leakage.
Older desktop PCs can have as much as 3.5 mA, so an office or internet cafe with 3 or more PCs could easily top the 10mA limit.
I believe the NICEIC video even shows earth leakage from something connected to a fish tank?

so any hi integ circuit would not be protected by an RCD then

 

[telectrix]

well, it would if considered necessary for the safety of users, but you would be limited to the number of, say, pc's you could connect via the rcd. this would be a deserving case for rcbo's .

 

[Deleted member 26818]

RCD protection would still be required, it may mean however that the installation is divided up into more circuits.
I don't know what equipment a typical household would have.
My Sister's house has a 30 odd inch LCD TV in the front room, along with a desktop PC and a Wii. In the back room there's a 40 odd inch LCD TV with a surrond sound system and a tumble dryer, there may be a stereo as well.
In the kitchen is a small LCD TV, washing machine, a dishwasher, microwave, fridge freezer and quite a large cooker.
Upstairs there's another 40 odd inch LCD TV and a Playstation 3.
All of the items will have varying levels of earth leakage, if there were just one RFC downstairs, the combined earth leakage could well be above 10mA.
Both my Nephew and my Sister have laptops.

 

[Guest 004]

I am going to stick with what I read in the PDF article,

 

[Deleted member 26818]

Just out of interest, what is it that differs in the article to the information I have provided?

 

[IQ Electrical]

It's a big deal in schools and offices now but I'll say categorically that I've yet to see this mythical 3.5mA or anything approaching 3.5mA on the IT room equipment that we test.

The move to laptops in many schools and offices seems to have helped too, probably because the more modern switch-mode power supplies seem to have far less earth leakage.

I think when the op mentioned an 'insulated earth bar', he was confusing clean earthing with high integrity earthing.

 

[Guest 004]

Just out of interest, what is it that differs in the article to the information I have provided?

The fact that you can put the hi integ earths in the same terminal at the DB as long as they are labelled

 

[Deleted member 26818]

The fact that you can put the hi integ earths in the same terminal at the DB as long as they are labelled

I'd suggest you look again, at the diagram in the article.
I think you'll find that it shows the conductor ends for the high integrity earth circuits in separate terminals.
Tthe reason they are labelled, is so as they can be identified because they are not in the same terminals.
The only problem I have with the diagram, is that it does not show how the connections are made for a RFC when two CPCs are used.

 

[Guest 004]

I suggest you read the document again from start to finish, then look at circuit 2 which is a radial, but has the hi integ earth terminated on the same terminal as the cpc of the said radial

 

[Deleted member 26818]

I suggest you read the document again from start to finish, then look at circuit 2 which is a radial, but has the hi integ earth terminated on the same terminal as the cpc of the said radial

Looking at the diagram, terminal 1 has a conductor labled circuit 1 and one labled circuit 2. Terminal 2 also has a conductor labled circuit 1 and another labeled circuit 2.
I don't see how you can confuse maters and believe that both conductors from the radial (circuit 2) are in the same terminal?

 

[Guest 004]

A radial circuit will only have one earth in normal circumstances, as a diagram it is poor, but clearly shows the hi integ earth with the cpc of the circuit. On the previous page it is stated how to overcome the earth connections on a DB which does not have additional earth bars, and at full capacity

 

[Deleted member 26818]

Yes the diagram is not very good, but are you seriously stating that you cannot see that the conductors with arrows pointing at them marked 'circuit No 2' are in separate terminals?

 

[Guest 004]

Yes the diagram is not very good, but are you seriously stating that you cannot see that the conductors with arrows pointing at them marked 'circuit No 2' are in separate terminals?

Good heavens old chap, indeed I stand corrected. Thanks for pointing that out.

I think the diagram should show 3 earths in the first terminal.

Kind of brings the point home though.

Thanks again

 

[Deleted member 26818]

Yes if using two CPCs for the RFC, I would also expect there to be three earths.

 

[Guest 004]

Couple of questions to add

1. Are there any new values for Zs for this type of install?
2. If the combined earth does not equal 10mm is it still considered an HI circuit? even though the earths have been terminated into there own terminals?

Just having a little debate with the resident tester that's all, would like some concrete ammo

 

[Deleted member 26818]

No the Zs values for the circuit remain the same, however each of the CPCs must be sufficient to satisfy the mazimum Zs values for the CPD on their own.
The 10mm² value refers to non-copper conductors such as the armour of SWA or metal conduit. It also refers to the total CSA of all conductors when a multi-core cable is used for instance 1.5mm² 3 core & earth would not be allowed, as the total CSA of all the conductors is only 5.5mm². Even 2.5mm² 3 core & earth would not be acceptable, as the combined CSA would only be 9mm², although 2.5mm² T&E with an additional 2.5mm² (if mechanically protected) would be.

 

[Guest 004]

The circuits in question are twin and earth 2.5mm RFC's and installed on basket, with no other mechanical path, so IMO this fails miserably

 

[Guest 004]

The circuits in question are twin and earth 2.5mm RFC's and installed on basket, with no other mechanical path, so IMO this fails miserably

I stated this to the resident tester, and his response was "no no no, there is another reg, " , but indeed he could not quote it.

 

[Guest 004]

I stated this to the resident tester, and his response was "no no no, there is another reg, " , but indeed he could not quote it.

I read again, the regs has an 'or' included, so the circuit can have 2 separate earths of 1.5mm 'or' a combined value of 10mm. A bit ambiguous it would seem.

 

[Deleted member 26818]

Yes the circuits do fail, they require a sheathed 2.5mm², or non-sheathed 4mm² conductor to be installed as a second CPC.
The combined value of 10mm², relates to the combined CSA of all the conductors (including live) of a multicore cable.
Yes you could have two separate 1.5mm² CPCs, if both are in conduit or trunking.

 

[Guest 004]

Thanks spin