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Nuissance RCD tripping

 
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Ninja_s2k



Joined: 25 Sep 2008
Posts: 2

PostPosted: Thu Sep 25, 2008 6:29 am    Post subject: Nuissance RCD tripping Reply with quote

Hello all,

First of all well done for your forum, I ve been following it for the past months with interest and glad to say that i have learnt a lot.

My difficulty today is a mixture of electrical and power electronics.

http://img88.imageshack.us/my.php?image=sketch1ll9.jpg

The image above is a sketch of the power input to this LED display system. The difficulty is as follows: As this display is located outside, everytime it rains the RCD trips. First thing to do was to seal the unit against all water ingression.

Another suspect i had was that since there is a good quantity of Switch-mode power supplies, these could be creating residual current which trip the RCD, however why only after it rains?

The RCD trips only when the unit is switched on and the cabling is not the issue. The RCD can then be reseted (without any modifications) after 3 or 4 days.
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torbjorn



Joined: 07 Jun 2007
Posts: 370
Location: Sweden

PostPosted: Thu Sep 25, 2008 9:27 am    Post subject: Reply with quote

Probably you get high leakage currents due to high moisture or condensation within the sealed display box. Then, some days after the rain, the internal moisture has gone away

Usually, making a electronics box watertight does not relieve you of moisture and condensation problems unless it is fitted with desiccator cartridges which then are regularly maintained (like in military electronics).

A better method is to make sure that rain cannot enter the box, and that there are proper drainage holes (protection class IP43 or similar). The electronics inside it, or at least the mains powered parts and insulation barriers around them, should be coated with a suitable protective varnish.

A simple thing you can do is to try interchanging line and neutral conductors to see if you get better reliability.
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Ninja_s2k



Joined: 25 Sep 2008
Posts: 2

PostPosted: Fri Sep 26, 2008 6:20 am    Post subject: Reply with quote

torbjorn thank you for your reply. Yes unfortunately where I live - Malta (small island) there are high humidity issues. Was just wondering if a 100W incandescent bulb would actually heat the space inside the enclosure hence eliminating possible high humidity due to rain. Do the filter capacitors on the incomer side of the Switch mode power supplies be effected due to high humidity?
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torbjorn



Joined: 07 Jun 2007
Posts: 370
Location: Sweden

PostPosted: Fri Sep 26, 2008 7:46 am    Post subject: Reply with quote

I don't think the filter capacitors should be affected, it is more likely that the problem is leakage (creepage) currents on the PCB surface.

You could check whether the PCBs are clean or if there is lots of flux residue etc from the wave soldering process. If so, try cleaning off the flux residue by alcohol or isopropanol, then rinse with plenty of water and let the boards dry out well.

Do you know the tripping current of the RCD? Here in Sweden, RCDs normally trip for 30 mA but in some cases more sensitive ones, tripping at 10 mA are used (for instance for medical equipment). Also, sometimes very insensitive ones (300 mA) are used where only fire protection is required and there is no risk of personal injury (for instance, in heavy industry where it is difficult to keep a good insulation standard but all equipment has good ground connections).
In case you have a 10 mA RCD, try replacing it with a 30 mA unit if this is legal in your case.
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