A friend of mine is moving to a new office and it is being rewired by a
local company whilst I am fitting in the computer network and alarm, the
thing is the contractor is now running 4mm earths to all the sockets. now I
have looked into section 607 as I was going to do the rewire originally (pre
part p) and the way I read it the min earth size is 1.5mm, now there will
only be eight computers in the office so surely 4mm is a bit over the top or
have I read the regs wrong so I am hoping the one of you more learned sparks
out there could put me right.
Laptops are the only PC's I've seen that don't have an earth conductor from
their separate power supplies. Anything in a metal casing, without double
insulated skins over the hot spots, needs an earth wire. It's da rools, man.
It is a misinterpretation of the rules for high integrity earthing systems
for circuits supplying IT equipemnt. What should be being done is each
connection of the cpc should be mechanically seperate from the other, i.e.
one cable one terminal. The theory is that should one cpc become
disconnected in an accessory then the other is still good. This is to remove
the potential leakage current associated with switch mode psu's.
Fox Electrical Servcices Ltd
Oh Good !!! Because it happened on one of our sites and luckily the T&E earth
centre was still there. I still can't get the culprit to own up on it, but
someone must have loosened the main 4 mm earth from the terminal, because, even
you said it, it is less likely to fall out than the single conductors in the
That's only one of the permitted options for meeting Section 607.
Briefly, all the options allowed by Reg. 607-02-04 are:
(i) Single CPC of at least 10mm^2;
(ii) Single mechanically protected copper CPC of at least 4mm^2;
(iii) Two separate CPCs, each complying with the normal requirements
(Section 543), with independent connections throughout.
(iv) Use of an earth monitoring system to BS 4444, with automatic
disconnection of supply if the CPC is detected to go o/c;
(v) use of an isolating transformer (etc.) in conjunction with one of
Option (iii), used with a ring circuit, is the most common (with (i) or
(ii) used for any spurs). In this case it sounds as if method (ii) was
And the associated filters. And it doesn't remove the leakage current
of course, just reduces the likelihood of it causing danger.
Yes I was aware of using sockets with two earth points and separating the
earths from the ring into two separate terminals on the earth bar in the
C/U, it's the fact they are using a ring of 4mm earth cable as well as the
earth that's in the twin & earth cable.
Which makes? Repaired an NAD recently, and they'd gone to fair old lengths
to make it safe with the top cover removed.
Lots of older Jap gear did have an earth for the UK - and suffered from
earth loops because of them.
*We are born naked, wet, and hungry. Then things get worse.
Dave Plowman email@example.com London SW
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