earth leakage of a computer

[beaver74]

Hi all

does any ony know what earth leakage a computer gives.
as i have a site which will have only a few computers all cable are flush and customer wants a few additional sockets.
543.7.1.3 is for circuit with 10mA of leakage,

also if so can you clarify

543.7.1.3(i) a 10mm earth conductor i asume this is intended for sub mains
543.7.1.3(ii) run 4.0mm additional ring terminated in seperate terminal in each accessory
543.7.1.3(iii) use of and 4.0mm earth inside metal conduit or if swa L+N+E to equal 10mm

if this is correct i would go with the 4.0mm ring but i is going to be a pig as the place if flush and has no additional earth installed

 

[beaver74]

sorry
should of been looking at 543.7.2.1

a ring final circuit with ring protectice conductor but is this an additional 4.00mm earth as in 543.7.1.3

can any one comfirm please

 

[Deleted member 26818]

I think the average computer has an earth leakage of about 3.5mA. This would appear to indicate that you can have up to 8 computers on a circuit without tripping the RCD, however many 30mA RCDs actually trip well below 30mA, some as low as 10mA.
(i)The requirement for the 10mm² protective conductor applies both to final circuits (i.e. ring mains) and distribution circuits (i.e. sub mains), this is for when the conductor is not copper.
(ii)Where there is a single copper conductor (i.e. just the one), it must be not less than 4mm².
(iii)You can use 2 protective conductors that when added together are less than 4mm², as long as each conductor meets the requirements of Section 543 (i.e. each CPC either satisfies the adiabatic equation or is selected in accordance with Table 54.7). The conductors do not both have to be copper, one could be metal conduit and the other the CPC of T&E.
I'm not certain what you mean by flush?
Anyway, you have a number of options, you can wire the circuit in 2.5mm² singles using a 4mm² CPC, or two 2.5mm² CPCs, you can use 2.5mm² singles with an extra 2.5mm² CPC, you can use 6mm² T&E as long as the CPC is 4mm², you can use metal conduit with 2.5mm² T&E and the condit as the extra CPC or even just 2.5mm² Line and Neutral conductors and the Conduit as the only CPC.
Remember that any CPC less than 4mm² has to be mechanically protected, and if two CPCs are used then the socket-outlets have to have two connection terminals one for each conductor.

 

[IQ Electrical]

Have a read of the guide below, interesting bit on the splitting of cpc's at the distribution board!

http://www.powerfaraday.org.uk/publishing/wiring-regulations/mag/2008/26-5437earthing.cfm?type=pdf

 

[beaver74]

thank you all

so in my situation the existing is T+E
so if i run a 4.00 around to each socket installing these in to a seprate terminal in each accessory as a radial this is as stated it does'nt need the 4.00 run in a seperate ring and terminated in the seperate terminal

 

[Deleted member 26818]

If it's a RFC then the extra 4mm² CPC would also have to be in a ring. Both CPCs have to comply with Section 543 including Reguation 543.2.9.

 

[beaver74]

thanks
543.7.1 states 60309-2 socket but i find no menchon of bs1353 which 543.7.2.1(i) states must comply to 543.7.1

I have all way done it with 4.00 ring twin termeinal ect but i have to put down compliants to which regs but cant see how 13A sockets will comply now why cant the regs be more clear
this is turning in to a time consuming job

 

[Deleted member 26818]

BS EN 60309-2 refers to industrial plugs and sockets, to be used on equipment where the earth leakage is between 3.5mA and 10mA.
BS1363 plugs and sockets are acceptable where the earth leakage is anything up to 3.5mA.

 

[IQ Electrical]

Beaver, the file I posted covered this topic well, including ways of terminating the cpc's to comply with the requirements of installations with high protective conductor currents:

It's one to keep in your technical folder as this subject is so misunderstood!

 

[beaver74]

with the risk of starting a long thread of aposing views i have found a lot of threads where the way of wiring is not agreed on .
i have alway been told that with twin and earth the 1.5 earth is done away with and the 4.00 earth is installed connected in seperate terminals through out in a ring.
but there are also views of the 1.5 ring should be terninated in 1 terminal 4.00 in a seperate 1 giving 4 earth conductors in each accessory .so having 2 rings .what is the correct way

 

[Deleted member 26818]

It's not really 4 conductors at each accessory, 4 cables for 2 conductors.
But yes that is how it should be wired the cables of one conductor in one terminal, the cables of the other conductor in the other terminal.
The reason why some people do away with the 1.5mm² CPC, is because a single 4mm² conductor is all that is required, and normal socket-outlets can then be used.

 

[High Tower]

3.5mA per unit

Any more than 9 on a rcd then split circuits up, rcbo's and high integrity earthing

 

[kmcgold]

if wired in a ring with separate cpc terminals for each cpc at the sockets
also at the board then ok
don't forget the warning label
a 30ma rcd can trip from about 22ma

 

[cptspaulding]

Does anyone have any documented data on typical earth leakage from a PC?

 

[daveelectrician]

According to the on site guide (Red book page 67) 7.6.3 reg 543.7.2.1. A ring final circuit wired in T+E with 1.5mm
earths is adequate, as long as dual earth sockets are used and earths are split at the db

 

[Marvo]

Does anyone have any documented data on typical earth leakage from a PC?

The earth leakage from a PC would come from the switch mode power supply which is different in every PC. There's no 'one size fits all' answer. The EMI and RF filters also cause earth leakage currents. I would suggest you refer to the datasheet from the PSU manufacturer.

Some networked installations, especially longer distanced ones with fieldbus transceivers, utilise an earth referenced communications system which can also result in small earth currents.

As IQ points out above, high integrity earthing is designed to accommodate predictable leakage in IT systems.