help with EMI/RFI

[georgi]

Hi everyone.
I'm trying to figure out an issue with electromagnetic interference caused by equipment at a store above which I live. No formal qualifications here though I've studied some of this in the past. The store's cooling shelves are switched on and off by a timer. When the equipment is on (6am-11pm every day) I can pick up really strong RF emissions which make for a fine buzz all over the long wave and medium wave radio spectra, jamming every weak station. Apparently the "noise" is strong enough to disrupt broadband (adsl) services on the phone line (150khz-1mhz), I guess the unshielded phone wires make for a fine antenna. Strong harmonics at 100, 200, 300, 400, etc. Hz of any signal my radio picks up.

I suspected the store's main lights (ballast or dimmer issue), but it looks like it's the cooling units (been investigating what I can all of last week). In addition to cooling the shelves have fluorescent lights behind their transparent sliding doors. I would state the model if I knew it. Anyway, store people aren't keen on fault-finding at all and are not cooperating.

I'm curious as to the standards these things must adhere to, regarding EM emissions? I tried browsing for a suitable BS (standard) but the list is a maze to a layman like me. Surely RF emissions must be kept under control even on commercial high-powered units?

I'd really appreciate if someone could point out the regulation involved, and maybe advise on standard solutions to kill EM emissions at source? Grateful for any info!

 

[guest119]

Maybe the environment agency could help?

bOYDY

 

[UKMeterman]

Yes,
They have to keep below certain limits, have a chat with Cherry Clough Consultants or try the local radio amateur club for assistance.

 

[georgi]

Yes,
They have to keep below certain limits.

The "should" vs "must" is severely abused in my case. If these are refrigerators that also have fluorescent lights, which of the two systems (cooling v light) is more likely to emit? (I'd say lights as motors start and stop but RFI is continuous all day). Also literally a sanity check - am I right in thinking this can be fixed by their electricians?

 

[amlu]

london? no one cares till you have money for an engineer to measure it and big money for lawyer to do the talking :-(
try plugging your router to master phone socket you have on the property (avoiding telephone extensions).
tune in to internet radio.
experiment with some emi shielding laid on the floor?

 

[georgi]

@amlu, London indeed. I've done all the workarounds before posting here. BT's wires have no shielding so my efforts are in vain, the cause is outside of my flat. I'm at a loss as to what specialised piece of kit one would use for measurements, otherwise I'd have acquired one and trained myself to work it!

 

[georgi]

Thought I'd add some more info since there's been developments and the info might be of use to someone..

I think I've tracked this down to the ballasts of the fluorescent lights on some of the store's equipment. The frequencies affected seem to be the even harmonics of base 69khz or 70khz (triangular wave). Sorry this isn't more exact. The frequency could be so high so as not to interfere with the anti-theft system at the store, also makes sense with T5 HE tubes, which they use. Some of the lights have NVC labels and others have Lightex ones. I could not find any indication of conforming to EMC regulation, only ENEC and the CE mark (which I've seen abused). Some of the lights take plastic two-prong leads, so it's beyond me how they are grounded at all.

Since this kills my ADSL service, BT's engineer today scratched his head, then replaced part of the wiring, which made very little change. I'm talking to the store maintenance staff, now that the managers have stopped ignoring me.. I'll post again if this progresses.

edit: re grounding, NVC's recent fittings of the kind say "This is a Class II luminaire so do not earth". that's that..

 

[georgi]

Here's a follow up: Managers were getting in the way of basic fault-finding, but mentioning Ofcom and standards seemed to get their attention. Maintenance staff found a number of faulty lights of various makes/models, replaced them with spares, and those started buzzing within a half hour. The electricians then noticed a pattern with those lights (always on one particular position in each cabinet, in one particular type of cabinet), and switched them off entirely pending an investigation.

For months while I was emailing management, not one of the electricians had heard a problem existed. Nor had any manager mentioned that maintenance staff visit routinely, not reactively.

A bit early to say, only a week in, but my internet seems to be going back to normal. Just need to wait for BT's line management logic to figure things out for itself now that interference no longer throws it off every 12 hours.