Electromagetic problem

[Evans Electric]

Had an interesting problem last year which I invite comments on.

The main supply upgraded at one of my regular customers,Printers, to 200amps.

I installed 4 x 70mm meter tails from main switch to the networks metering. Thinking I'd be clever I seperated them on the tray by their own diameter as recommended.

Problem: The other side of the wall (10" solid block) to the meter cupboard is an office using computers, the monitors having interference lines on the screens until we moved them two metres away. Same to the right of the cupboard on another screen.

I screened the screen with an earthed piece of sheet steel to no avail.

In the end we got an elect. consultant on site who recommended the 70mm tails were reclipped in trefoil , result, bringing them together caused each phase to cancel out the eddy currents of the next and no interference to screens . An electromagnetic field extending about 5 ft from the cables and through a solid block wall. Mmmmm !

 

[Evans Electric]

Sorry this one is rambling on a bit but the affect on the computers was startling

 

[DonkeyDong]

tell them to change to flat screens!

 

[steptoe]

ooohhhhh, never seen that quite so far away TBH.

but, Ive always been taught(and always have) to keep 3PH grouped.

kinda goes against what is recommended tho, as you say DEKE, but obviously there was a reason for grouping 3ph.

 

[Evans Electric]

Yes you are right Steps, I think they should always be grouped too.

I forgot to say that it nearly caused a strike in their office, the person on that particular screen saying they would be sitting within an electrical field and up with it they were not going to put !!

 

[springcrocus]

Had a problem in my factory once. The radio hung on the wall near to the trunking carrying the wires to a couple of lathes. Bloody thing wouldn't stop buzzing. Took the wires (3-phase) out of the trunking, twisted them like an old-fashioned light flex. Problem gone instantly!

 

[Apache]

Had a problem in my factory once. The radio hung on the wall near to the trunking carrying the wires to a couple of lathes. Bloody thing wouldn't stop buzzing. Took the wires (3-phase) out of the trunking, twisted them like an old-fashioned light flex. Problem gone instantly!

I'd have moved the radio

 

[Evans Electric]

I'd have moved the radio

Thats too easy Apache, :^O but it does show how powerfull the eddy currents can be. I for one have never had occassion to measure them .