Computers flickering

[GG]

Hello, If I have computers that are flickering could this be a grounding problem? The receptacles the computers are plugged into are 3 prong and the EMT is being used as the equipment ground fault path. Would installing an insulated EGC in the conduit get rid of the flickering on the computer screen?

 

[iwire]

Re: Computers flickering

Originally posted by GG:
Would installing an insulated EGC in the conduit get rid of the flickering on the computer screen?

I doubt it, you could try it temp with some extension cords, but do not move the monitors while testing.

It is very likely the problem is EMF in the area the monitors are in.

 

[hurk27]

Re: Computers flickering

GC look for boot legged grounds or grounded neutrals, 3-way/4-ways picking up a neutral from another circuit or not running return path with travelers. Look for transformers close to area also.

It is very common to find on a pipe job where the electrician just grabbed a neutral that was in the box for the circuit or ran travelers through pipes that didn't contain the return path like the switch leg or hot feeding the common on the 3-way/4-way.

 

[karl riley]

Re: Computers flickering

The usual cause of this flickering in my experience is net current on a circuit near the computer. This is usually a lighting circuit but not always.

If you had a gaussmeter you could measure and trace it. Otherwise you can try moving the monitors to see where the flickering starts or ends. If you have a digital clamp on ammeter you can clamp around circuits running nearby (usually in the dropped ceiling) to find the circuit with the net current and its magnetic field. Correct circuits will measure zero.

Sometimes the net current circuit is a feed to a subpanel where the neutral bus has been grounded. There can be many causes, including sheet rock screws.

Karl

 

[karl riley]

Re: Computers flickering

Wayne, you got in there while I was writing my reply. Good answer.

Karl

 

[GG]

Re: Computers flickering

Bob, I noticed in the crawl space above the office that someone tapped off of an ungrounded conductor and ran that to a switch for some lights. I have no idea where they are pulling their neutral from. Could this be a possible source of the EMF? Could I use a gauss meter to check for any EMF, and if I did what are considered high levels? I have never used a gauss meter.

 

[hurk27]

Re: Computers flickering

I noticed in the crawl space above the office that someone tapped off of an ungrounded conductor and ran that to a switch for some lights.

Yep sounds like it.

 

[karl riley]

Re: Computers flickering

GG, that tap would definitely do it. At this point you don't need the gaussmeter, though it would show you what is happening. In a correctly wired office you would read 0.5 mG or less unless you are near an appliance, assuming you measure a couple of feet out from walls. Computers start to jitter at between 5 and 12 mG.

Right now you need a clamp-on ammeter, which is actually a magnetic field meter calibrated to read in amps, since there is a direct relation.

If you can run a neutral from the same source as the hot, and disconnect the present neutral, you will kill that field. Or conversely, find the hot that should run with the present neutral.

I wrote a book on how to do this circuit tracing, so I can't repeat it here, but it involves going from junction box to junction box with your clamp-on until you find where the wrong connection was made.

Karl

 

[GG]

Re: Computers flickering

Karl, I look forward to reading your book. I ordered it last night. "Tracing EMF's in Building Wiring and Grounding". I purchased it from www.lessemf.com for those interested. It looks like a good read.

 

[ryan_618]

Re: Computers flickering

You can also see Karl in action at the end of Mike Holt's 2005 Grounding vs. Bonding DVD/VHS.

Karl: Thanks for the lesson, I enjoyed it and learned quite a lot from it.

 

[karl riley]

Re: Computers flickering

Ryan, I am glad you liked the video. It worked because the crew that produces videos for Southern Cal Edison did the animated graphics and filmed it. Their EMF division donated their services.

One thing they thankfully edited out: the director noticed I have some resemblance to Clint Eastwood, so we conspired and at the end of the video I looked at the camera and rasped, "Make my day, punk, ground that neutral". This broke up the crew, but we decided to leave it out.

By the way, the bow-legged old guy in the video got both knees replaced, and now runs around like mad chasing tennis balls, as well as net currents.

Karl