Mains Insulation 'Resistance', Multiple PCs and Load Problems Question

[David Longley]

I had an 'exchange' with a well educated friend the other day - he had been told by a contractor who was putting in some cabling that they could not put a room full of PCs on or several room full of PCs on simultaneously, because there was a problem with computers' wires being too close together and because of imperfect insulation between live and neutral (I think this was the reference to the 'wires being too close together', the cumulative effect would result in overload. (This was not just an odd way of talking about the combined current exceeding the fuse on the circuit, or something about surges).

I nearly choked on what I was eating and made some impulsively regrettable remarks (he is a well educated friend after all). I'm not sure I have put what he believed he was told accurately, but if anyone has heard of anything *like* this, I would be grateful for an elaboration. At the time I put it all down to too much wine and 'folk physics'.

I've put hundreds of PCs into organisations, worked with electricians etc and couldn't make any sense of what I heard at all.

[tony sayer]

In article , David Longley writes

There are new reg's out that limit the number of things using switch mode power units, PC's and IT equipment for example, that have capacitors in them that "connect" the live and earth together so that there is some current flow. This can, if there are enough units on the same line, cause RCD's to trip due to the current unbalance exceeding the rating of the RCD.

There is also a shock risk in that if the earth came undone then the "earth" wiring could have a potential that could pose a shock risk due to the leakage in these machines.

I know of a radio station that had a lot of PC's connected to the same ring main that had a 30 ma trip thereon which tripped quite often until the system was upgraded.

What you heard was, I suppose, an "interpretation" of these regs!......

[Dave Liquorice]

As in switch on simultaneously? The inrush is pretty phenonminal especially if the monitors are CRTs, all those degauss circuits...

Any RCDs? You shouldn't put more than 10 Class 1 devices on a single

30mA RCD because the combined leakage from the suppression components is likely to trip the RCD.

Oh, well knocks the first one out then... B-)

[Jerry G.]

With the proper electrical installation, you should be able to put on as many PC machines as you want. Do not use ground fault type outlets with PC's and monitors, because the switching power supplies can cause the ground fault outlet to trip to off.

The switching supplies can radiate back down the neutral of the AC line, thus causing some over stressing of the electrical feed. The voltage difference between the true ground and the neutral can go out of specifications from this.

There were problems in many older buildings where many devices with switching power supplies were installed. This ended up over heating the power company's wiring, and feed transformers. The location where I am, had this problem. This can all be corrected, but for a cost.

With a proper electrical installation, there should be no problems.

I have worked contracts where we put many servers and PC machines in one room. I have some clients with as many as 20 machine in one large single area. On a 15 amp breaker we would put 2 complete machines with monitors, via a 1000 Watt UPS. Even the UPS has an internal switching power supply.

There are many companies with large offices that have many PC machines in one area. I have seen large opened office areas in large centres, with a few hundred machines. There are banks of routers, and sub systems, with a number of management PC machines in smaller rooms off to the side of the main areas. This is all workable. If not, there are many companies that would not be working at large scales of operation today!

I think that this person who has this problem should get a new electrician who knows about large scale installations.

[tony sayer]

In article , Jerry G. writes

So lets see then. Here we have an office with quite a number of PC's and other IT stuff and then someone plugs in some portable appliance that has a fault where that person contacts the live of the mains so no RCD protection then. Is this what you are suggesting?...

[OldScrawn]

That's why 240 volt tools are banned on our sites; the labs have 110 V sockets and in the offices you have to use a tranny...

[BillR]

The large installations I've worked at recent years had individual RCDs for each desk ...

[Andrew Gabriel]

Original poster is asking a question about the UK I presume but failed to say so and cross posted to international newsgroup, so they got an answer for the US, which is completely wrong for the UK.

[tony sayer]

Real world anyone;-()

[mike ring]

tony sayer wrote in news: [e-mail]:

I don't know what the current thinking is, but in my working life I went through more changes than I can remember with clean mains with walsall outlets, dirty mains, RcD protected mains, backed up mains, ups mains, that all I really know is the problem is not as simple as that.

I don't know if there is now peace at last, but considering how many outages of important services there are, I doubt it.

Whenever I raised the problem for a new installation with the sparks and users depts, as a humble project engineer, I always invoked codeword PYTHON

(put your tin hat on now)

Doing so.....

mike r

[mike ring]

mike ring wrote in news:Xns946DCA6957C2mikeringbtinternetco@217.32.252.50:

PS. if you've ever sat in a busy office full of pcs, copiers, plugged in a bit of kit that's just been deliverd to see if the little lights come on, and heard all the fans spiralling down to a ghastly silence, you'll know how to sneak out unobserved with the device under your coat while they're all still wondering what occurred

m r

[ANt]

I once worked for Manweb (the electricity board as was) and we put a new digital scanning facility (for digitising the network and planning) into a building in Wrexham.....when someone had a No 49 from the Coffee machine all the computers in the room tripped.

Ant.

[BigWallop]

The number 49 must have been the extra strong coffee then ?

[Steve]

A piece of equipment which passed a PAT ? There should be no possibility of contact with the mains live, so why need an RCD ? If it didn't pass PAT of course it wouldn't be allowed on the premises.

Steve

[BigWallop]

And when the 110volt Tranny isn't available they use a standard drag queen. :-))

[tony sayer]

Not so. I once had a bad shock because I trusted someone else do carry out some work correctly, which they didn't.

Come outside and call me stooopid, if U like;-))

Wonder how many grieving parents there are around the time of Christmas whose little ones have been frazzled by faulty Xmas tree lights, where an RCD would have made all the difference?....

[Steve]

I think this sudden reliance on RCDs is stupid and causes more problems with service reliability than shocks it saves stupid people.....

Steve

[Peter Parry]

According to HMG statistics in the last 10 years - none.

Quite a few children, and their parents, have perished in the same time because of RCD's of course.

[Peter Parry]

Probably not, however

, and might explain it all to you.

[tony sayer]

In article , Peter Parry writes

Someone we used to live close to was electrocuted like this about 8 years or so ago?..

In what way Peter?....