electromagnitic fields interference

[jamesgregory]

basicaly at work we've got this problem where people sitting at there desks close to and on top of where the main cables come into the bilding is interfering with computor screens and making the flicker. anybody know how to sort it?

[cupra]

Do you know what the supply is feeding (ie: just office buildings or factory as well)? There may be some offending equipment being fed by this line that can be filtered - these days EMC regulations are very strict and this sort of situation shouldn't occur! A solution (of sorts) is to shield the offending mains supply somehow (difficult to make a suggestion without knowing the physical arrangement) - perhaps an earthed metal plate to separate the mains from the computers? If you can give some more details, post away!

[jamesgregory]

it only feds the office but this inculdes heating air conditioning etc. and the cables come in to the building through the concrete in ducts there is a metal earthed computor floor each leg has a bar joining one to other, with metal tiles sitting on top. recently we have put do an earthed metal mesh in the area effected which has halved the values. but still the flicker

[trmatthe]

You can replace all the CRT monitors with LCD displays. This will stop them flickering, but obviously won't cancel the possibly harmful levels of EMI. A real solution is to build a faraday cage and put the users inside it. This is going to be expensive. It may be cheaper just to reroute the AC feed. Finally, you may be able to get away with floor tiles that contain a grounded metal mesh. Again, this will cost. You do have a definite health and safety issue here though.

[jamesgregory]

is there any site that could give us some more info?

[jamesgregory]

shorly there are thousands of builds with ac cables going into them, but they don't seem to have any problems! so why should there be here?

[Eddiecurrent]

Sounds like unbalanced three phase to me call the engineers in and try to redistribute the loading across the three phases more equally. Also consider shielding the mains cables, most incomers should be steel wire armoured or MICC both of which sould have earthed sheathing which in most cases would decrease this effect.I have a similar effect in my works and I believe that there is something amiss but my boss won't listen.