New Office Computer Circuits - High Integrity Earth?

Stevoon · 13 Apr 2018

I'm in the process of working with an Office Fit out company to build a new office. I have specified that each desk cluster should be its own circuit giving either 4 or 6 PC's per circuit. I'm interested to know based on this information if the Electricians on here would of designed the circuits using a High Integrity Earth or not?

Thanks

Stevoon

EFLImpudence · 13 Apr 2018

There are a few regulations - 543.7.~ - for equipment with protective conductor current of between 3.5 and 10 mA and over 10mA.

Do you have access to the regulations?

Stevoon · 13 Apr 2018

Hi, no sorry I'm the IT guy so don't have access to the regulations. I had been on site however and spotted they had been ran as a radial in 2.5mm Twin and Earth with no sign of a seperate earth wire. The Electricians I would normally use would of ran this and as the fit out company hadn't I thought I would ask a further opinion before I "go into battle."

Thanks

Stephen

EFLImpudence · 13 Apr 2018

Is this just a normal circuit with 13A sockets?

Does any item of equipment have a protective conductor current >3.5mA or would there be more than that on the circuit?

bernardgreen · 13 Apr 2018

There is often confusion between a "high integrity earth" and a "clean earth".

High integrity earthing involves one or more alternative earth cables from sockets to the main Earth terninal at the consumer unit. The earths in sockets connect to this earthing system,

Clean earthing involves two separate earthing systems. The cable and metallic fittings ( back boxes etc ) are protected by the standard earthing system of a conductor in the cables. The earths in the sockets connect to a separate earth system which is grounded to a clean ( free of electrical noise ) earth. Often a ground rod or rods.

The link is cut if a clean earth to sockets is required with a separate CPC earthing to the fixing screws and ( in this socket ) the metallic front plate

The terminals with the half circle are for a clean earth that protects the equipment plugged into the socket. A clean earth is NOT the CPC and should NOT be connected to it. A clean earth uses a separate wire which connects to a local Ground and as such is not affected by electrical noise that is present on the CPC

Where there is no provision or need for a clean earth then the two earth terminals must be linked so that the CPC is connected to both the Clean Earth terminal and the CPC earth terminal in the socket.

Clean earths are used for sensitive equipment and for communication equipment where the case / frame of a machine must be at true ground potential to avoid potential differences along communication cables that connect the frame of one system to the frame of another system at a remote location.

Adam_151 · 13 Apr 2018

Stevoon said:
I had been on site however and spotted they had been ran as a radial in 2.5mm Twin and Earth with no sign of a seperate earth wire. The Electricians I would normally use would of ran this and as the fit out company hadn't I thought I would ask a further opinion before I "go into battle."

If the socket circuits have already been wired as radials, then HIE can be implimented on radials by pairing the circuits and linking the earths of the two 'end of line' sockets with a bit of single earth, each socket then has the earths terminated in separate earth terminals as normal for HIE. The result is the earths are effectivly a ring for two circuits, but the live and neutrals remain separate

Stevoon · 16 Apr 2018

Thanks for the replies

I have tested today to find out the current on the Earth for a PC when plugged in. I have measured 3mA, so on that basis a radial with 6 PC's will have 18mA on it. Am I right that this does need High Integrity Earthing as the total is over 3.5mA or it doesn't as no one item is over 3.5mA?

ban-all-sheds · 16 Apr 2018

Doesn't the qualified electrician/electrical design engineer know?

Stevoon · 16 Apr 2018

That is kind of my problem, the installers say it's not needed, the project manager is complaining I didn't specify it and the QS we are using is saying it's needed. As I will be the one who is asked "is this ok?" shortly I'm just canvasing opinion.

Thanks
Stevoon

ban-all-sheds · 16 Apr 2018

Who will be signing the EIC to say that they did the design?

Stevoon · 16 Apr 2018

The installers will be signing the EIC.

ban-all-sheds · 16 Apr 2018

I'm not trying to score points or anything.

Stevoon said:
That is kind of my problem,

It really shouldn't be.

the installers say it's not needed,

They are responsible for the design. They are responsible for ensuring that the design of the circuits, and the provision (or not) of a high integrity earth complies with the relevant requirements of BS 7671. It is what they are being paid to do. It is their area of professional expertise.

the project manager is complaining I didn't specify it

It is not your job to specify it - it is the job of the person doing the design. It may very well be your job to tell them about the characteristics of the loads, and what sockets you want where, and what granularity of isolation is needed, etc, so that they can do the design properly, but that's not the same thing. You should no more be telling them whether a HI earth is needed that you should be telling them what size cables to use, or what types of breakers are needed for server racks etc.

If the project manager or the QS has issues with the design of the electrical installation then they must raise them with the designers.

If the designers don't know if it is needed then they should be sacked.

As I will be the one who is asked "is this ok?" shortly I'm just canvasing opinion.

That you are having to canvass opinion shows that this is outwith your area of professional expertise, and therefore in a commercial professional context it is outwith your competence to answer.

Absolutely nothing wrong with that, nobody can possibly know everything. You wouldn't expect the electricians to be able to comment on a SAN zoning design, for example.

Diver Fred · 16 Apr 2018

Does the info on the following link help?

http://tisltd.com/wp-content/uploads/2012/04/HIE-Earthing.pdf

SimonH2 · 28 Apr 2018

I came across this some years ago when the outfit I worked for at the time was having a new warehouse built. The contractors said that they could only install single sockets because of the need for such earthing - and as it was the first time I'd heard of it I had to go away and find out about it.
One thing I did was to actually test a representative sample of our equipment and found absolutely nothing with a significant earth leakage current - nothing at all. So we concluded that there was no issue and "normal" double sockets were installed. I do have to wonder though whether this issue is a bit exaggerated at times - especially when it's common to find an extension lead (even if only short) being used to allow the multitude of devices on a typical desk these days to share one socket.
I've also seen contractors (at a customer site) do rings with HIE at all the sockets (ie using two separate terminals on each device) and explicitly state that it's needed - but then put both ends into the same screw at the DB

ericmark · 29 Apr 2018

Stevoon said:
Thanks for the replies

I have tested today to find out the current on the Earth for a PC when plugged in. I have measured 3mA, so on that basis a radial with 6 PC's will have 18mA on it. Am I right that this does need High Integrity Earthing as the total is over 3.5mA or it doesn't as no one item is over 3.5mA?

A standard RCD is designed to trip at between 15 and 30 mA there are some specials I have read about RCD's which trip between 90 and 100% of rating, they were the X-pole range and google seems to only find pole dancers. But 18 mA is over 15 mA so either special RCD or RCBO for each circuit, or the circuits are too big.

I have measured computers and some old units did have a high leakage, in the main due to the filters on the supply, but newer units don't seem to leak that much, so no longer do the supplies need splitting into so many circuits.

As an installer I would say if items to be used have a high earth leakage then they should be informed before the circuit is designed. Since new PC's don't have a high earth leakage simply saying to supply 6 PC's is not enough, the person ordering the work would need to specify PC's with high earth leakage.

The problem arises when it comes to the bill, having a charge for "Altering to cater for high earth leakage PC's not specified in original design" which could double the price if not more, I would assume you would not want to have to explain to your bosses.

I would be very careful what you say, 10 years ago yes most PC's did have a high earth leakage, today many laptops only have two core cable supplying them.

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

New Office Computer Circuits - High Integrity Earth?

Similar threads