Does 3" aluminum dryer venting around electrical cables eliminate interference caused by flourescent lighting?

[brxndxn]

I work at Home Depot in the plumbing department. I decided to get a job at Home Depot because I figured I could learn a lot more than if I got a job flipping burgers. The job is basically a way to spend my free time after I switched from Computer Engineering (hardware) to Finance.

I thought this question was funny because I am a huge computer nerd: (it also left me curious)

Anyway, I had some guys come in today (one with a Newegg.com cap) with a 'plumbing' question. They wanted to place 3" dryer duct around their electrical wires for shielding because their 'electrical precise instrument' was being affected by interference. I began by telling them to try a line conditioner first because they are made to eliminate AC interference. They told me their instrument was plugged into a 1000VA APC UPS along with a computer and a modem. So, I told them to call APC because their unit was probably failing to condition the line properly. Then, they said that wasn't it because they had 5 other setups that all worked fine using the same type of APC unit. So, I told them to call APC because their unit was probably failing to condition the line properly. They decided to go with some length of 3" dryer duct to put over their internal building wiring. I guess this is because it is much easier and cheaper to put 3" dryer duct over the internal building wiring than it is to call APC.

So anyway, am I right? Shouldn't a 1000VA APC UPS be able to condition the interference caused by flourescent lighting out of a power line? Or, is the line conditioning in a UPS crappy? Is 3" aluminum dryer duct going to fix the interference?

Either way, they were definitely surprised to see a young dude in plumbing talk about computers.

 

[HappyPuppy]

Sell them a gigantic roll of aluminum foil and tell them to make hats out of it.

 

[43st]

The APC won't stop line interference like that.

Shielding the source and grounding the shield would probably work though. I'm not sure dryer duct will allow that, guess it's worth a shot. Why don't they just change the light fixture?

 

[brxndxn]

I want more opinions.. APC certainly advertises that their 'power conditioning' UPS's do fix interference..

 

[Joony]

I think only some specific models do power conditioning (Smart UPS?)

 

[Analog]

UPS's convert line voltage to DC, (to charge the internal battery) and then invert back to AC. I've installed many UPS systems throughout the years, some that are in the range of 30 - 100 KVA, able to power entire computer rooms. UPS's generally are the *cause* of many types of interference! This is because the internal switching semiconductors (IGBTs, or other thyristors) reflect noise back into the power grid. Many incorporate harmonic balancing networks or power factor correction circuitry to prevent this, but these units are generally noisey, especially the cheaper ones.

As far as your dryer duct, it could be effective, as long as it is grounded, but what about the ends? A 1:1 isolation transformer between the UPS and the line power may also help reduce noise, because it acts as an impedance between the lower impedance line network and the UPS. I would also recommend checking the grounding system all the way back to the system (house) ground at the power entry point (usually a ground rod and copper braided cable).

HTH

 

[AlienCraft]

The aluminum dryer duct would have ZERO shielding capacity, regardless of how it's grounded, as the ends would still be open, not closed tightly around the conductors.
The interferance is most likely being conducted on the neutral line and as long as they are using a single ended AC supply, the noise will always be there.
Sensitive electronic installations are now (and have been for some time) using a Differential Supply system. Also called "Balanced" AC in that there are two conductors with a 60v AC / 180* out of phase thus rendering 120v referenced to GROUND. This set up is discussed in the NEC and is very effective in eliminating RFI / EMI effects on AC supplies.

Using a Balancing Transformer after a U.P.S. allows for uninterrupted power with superior noise rejection.
Balancing transformers are available from Furman and Equi-Tech.