johnb2713
Well-known member
Whilst I am retired, we still have a family run I.T. business. A year ago we purchased some retail shop premises for the business to move into and residential flats developed upstairs. The shop is essentially long and thin, 8 metres wide x 22 metres deep with warehousing going a further 35 metres back, the incoming supply (3 phase) is at the back in the warehouse.
We replaced the 45 fluorescent lights in the shop with LED panels in the suspended ceiling, the LED panels had separate drivers, double insulated etc. The circuits were wired into groups of 3 rows with around 15 panels on each row.
In the workshop which is to the rear of the shop, trackpads on computers sometimes played up, the mouse pointer was quite jittery nut only when the laptop was plugged into the mains, not necessarily switched on but plugged in. I took my ocilloscope down to see what was going on to find the mains voltage was fine 238v, the AC waveform looked fine even though we have inverter driven heat pumps running.
I connected the probe to a biscuit tin lid on the bench and found 2KHz @ 20v noise superimposed on a 50Hz sinewave. I was surprised to see this level of airborne noise. Switching the middle row of shop lighting off reduced the noise dramatically and trackpads worked fine, much to the amazement of all observers.
I earthed the ceiling (the ceiling is continuous throughout the shop and workshop area) grid to the mains earth, this reduced the noise allowing the trackpads to work.
So my question (there at last), what is the normal good practice with regard to suspended ceilings and earthing of the metal rails?
We replaced the 45 fluorescent lights in the shop with LED panels in the suspended ceiling, the LED panels had separate drivers, double insulated etc. The circuits were wired into groups of 3 rows with around 15 panels on each row.
In the workshop which is to the rear of the shop, trackpads on computers sometimes played up, the mouse pointer was quite jittery nut only when the laptop was plugged into the mains, not necessarily switched on but plugged in. I took my ocilloscope down to see what was going on to find the mains voltage was fine 238v, the AC waveform looked fine even though we have inverter driven heat pumps running.
I connected the probe to a biscuit tin lid on the bench and found 2KHz @ 20v noise superimposed on a 50Hz sinewave. I was surprised to see this level of airborne noise. Switching the middle row of shop lighting off reduced the noise dramatically and trackpads worked fine, much to the amazement of all observers.
I earthed the ceiling (the ceiling is continuous throughout the shop and workshop area) grid to the mains earth, this reduced the noise allowing the trackpads to work.
So my question (there at last), what is the normal good practice with regard to suspended ceilings and earthing of the metal rails?
