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Wierd one....

tonydon
Hi everyone. 


So,  today we installed 6 new led panels in a new ceiling grid

The panels ar Ansell panels.  They are class 2. Low volt.


Then , our plumber says he has had a shock when touching the ceiling grid and a boiler at the same time.


So, we tested the ceiling grid to a local earth.   120V AC  or   -2.9V DC......   The grid  even lights a volt stick....


After trying several ideas I eventually swapped the live and neutral connections on the primary of the led drivers.......


The result..... no measurable voltage  between the grid and earth.......


The driver and the led panel are both marked class 2 ......


How is this possible??


Is it safe?


Do I need to bond the ceiling grid?
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  • 0
    One of the CE marking EMC related tests for double insulated down lights now requires you to look at both the 50Hz and HF currents that flow when an earth tail is added (usually with a  jumbo "jubilee" clip around the perimeter of the show face of the fitting.) I presume the test has been added to try to spot this sort of problem.


    These (highly simplified) schematics show how the HF interference currents can end up circulating and putting significant unwanted voltages outside the LED driver, in earth paths that may or not be actual wiring or may be you and the lighting grid.. the middle one shows why double wound mains xformers are sometimes recommended to clean up EMC noisy loads (sometimes suggested for VFDs, note that as the whole point of the SMPS approach is to not need a mains transformer this is not done very often ) and in the last one, how inter-winding screening can help by splitting the capacitance between the winding layers into two capacitors with the centre point able to divert much of the problem current.

    43bd03026609e0eed63e24b889916f03-huge-smps_emc.png



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  • 0
    One of the CE marking EMC related tests for double insulated down lights now requires you to look at both the 50Hz and HF currents that flow when an earth tail is added (usually with a  jumbo "jubilee" clip around the perimeter of the show face of the fitting.) I presume the test has been added to try to spot this sort of problem.


    These (highly simplified) schematics show how the HF interference currents can end up circulating and putting significant unwanted voltages outside the LED driver, in earth paths that may or not be actual wiring or may be you and the lighting grid.. the middle one shows why double wound mains xformers are sometimes recommended to clean up EMC noisy loads (sometimes suggested for VFDs, note that as the whole point of the SMPS approach is to not need a mains transformer this is not done very often ) and in the last one, how inter-winding screening can help by splitting the capacitance between the winding layers into two capacitors with the centre point able to divert much of the problem current.

    43bd03026609e0eed63e24b889916f03-huge-smps_emc.png



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