High integrity earthing

Farmelectrics · Aug 7, 2013

In the office building were we are doing 5 year eicr s I've come across this under the floor are bus bar power tracks supplying various power points under floor and to desk top pcs so the maintenance guy on site tells me the pcs are plugged in to the red sockets because they have 2 earths in fot high integ earthing and the power under floor goes into the white ones but supplying the bus bar tracks is a 3 core 16mm swa so we have one earth back in db so how have they achieved high integrity earthing bit confused

Richard Burns · Aug 7, 2013

?using the armour and third core as twin earths?

Darkwood · Aug 7, 2013

As long as the swa earth tails are into separate earth terminals then it still follows the practices for high integrity earthing.

WilcoxElec · Aug 7, 2013

Desk top PCs often have a small leakage to earth from the internal power supply unit. This can be as much as 5 mA. Here in France we put red sockets in offices &c especially for these to indicate that they are on a circuit which is NOT behind a 30 mA RCD -- since if you have 6 desk tops you may have 30 mA leakage - which will trip out. In industry in the UK - as far as I know, computer equipment supplies are specialized and not put behind a 30 mA RCD for the same reasons. Don't know if this is any help

I found this on this forum .... http://www.electriciansforums.co.uk...-computer-sockets-high-integrity-earthing.pdf

Darkwood · Aug 7, 2013

WilcoxElec said:
Desk top PCs often have a small leakage to earth from the internal power supply unit. This can be as much as 5 mA. Here in France we put red sockets in offices &c especially for these to indicate that they are on a circuit which is NOT behind a 30 mA RCD -- since if you have 6 desk tops you may have 30 mA leakage - which will trip out. In industry in the UK - as far as I know, computer equipment supplies are specialized and not put behind a 30 mA RCD for the same reasons. Don't know if this is any help

I found this on this forum .... http://www.electriciansforums.co.uk...-computer-sockets-high-integrity-earthing.pdf

A standard RCD will trip anyway from 50% to 100% of its rating this we have a 3mA per computer benchmark so usually max 4-5 units, you can fit SI units that recognise the frequencies of the earth leakage created by designed leakage and these SI units ignore this and only trip on fault leakage these allow many more stations per circuit.

WilcoxElec · Aug 7, 2013

The SI (Hi Haute immunité ) RCD would still be used only for the Computer circuits - so the sockets here would still be distinguished by being red..... The 3 mA benchmark is closer to the 3,5mA limit than the 5 mA - but since I would not (cannot) use a ring here and have to limit the number of outlets to 8 Double sockets per MCB protected spur - It is easier to excuse the considerable extra cost of the SI/Hi RCD.:wink5: Er ... I think we are actually agreeing - but I am not sure we are helping with the original question, which I think you had already answered above - now that I understand it. :smile5: Sorry :yes:

Farmelectrics · Aug 7, 2013

Ok in reply to using the armour as part of the earthing the cable gland is glanced into the db but still there is only one eart of the swa in the earth bar so were have they achieved high integrity earthing

Darkwood · Aug 7, 2013

farmelectrics said:
Ok in reply to using the armour as part of the earthing the cable gland is glanced into the db but still there is only one eart of the swa in the earth bar so were have they achieved high integrity earthing

To meet BS7671 the swa at the dist-board is required to be tailed from the Banjo to the earth-bar, as this is high integrity the BS7671 requires separate terminals to be used for each earth, as you have 2 earth conductors now in the board they should enter separate terminals and appropriate label fitted warning of the high integrity earth and what circuit involved. It can be argued that the gland on the enclosure provides separate contact but that may have been the case many years ago but earth tail now required.

Farmelectrics · Aug 7, 2013

Well that Santa happened on these buildings and there only 8 years old

- - - Updated - - -

Hasn't not Santa haha

Darkwood · Aug 7, 2013

Well on the next inspection it needs noting as its a mechanical thing and requires separate termination just in case a lose earth terminal exists it has a functional alternative path to take current away ....if the doubled up earth terminal came loose in the board the high integrity earth is lost and users may be getting shocks off the computers etc ...a dangerous set-up.

tlangdon12 · Aug 7, 2013

The requirements for high integrity earthing can be met by a number of methods, multiple protective conductors are not the only option, a single conductors of sufficient cross-sectional area can also meet the requirement.

The Electrak busbars meet the requirement as they at 13mm sq. A single conductor in a 3core SWA cable with 4mm sq conductors will also meet the requirement. (Requirement is 10mm sq or 4mm sq with mechanical protection). If the SWA cores are 2.5mm you would then need to use the armour as a duplicate protective conductor.

I expect the SWA cores will be 4mm sq.

Engineer54 · Aug 8, 2013

darkwood said:
To meet BS7671 the swa at the dist-board is required to be tailed from the Banjo to the earth-bar, as this is high integrity the BS7671 requires separate terminals to be used for each earth, as you have 2 earth conductors now in the board they should enter separate terminals and appropriate label fitted warning of the high integrity earth and what circuit involved. It can be argued that the gland on the enclosure provides separate contact but that may have been the case many years ago but earth tail now required.

Well we didn't have any problem before they started supplying Banjo's with SWA gland termination kits!! But then that was in a time when SWA cables were all virtually made off correctly and solidly!! Can't really say that today, not with some of the abortions we've seen in posted photo's on here recently!! lol!!

Brightspark2 · Aug 8, 2013

Engineer54 said:
Well we didn't have any problem before they started supplying Banjo's with SWA gland termination kits!! But then that was in a time when SWA cables were all virtually made off correctly and solidly!! Can't really say that today, not with some of the abortions we've seen in posted photo's on here recently!! lol!!

What like this?...