- Reaction score
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I quite often contribute on other's posts about issues with RCD's, thought I'd tell you about what happened to me yesterday as a little bit of a tail and maybe a lesson.....
Huge stadium show lighting rig, fed in three sections, each section being about 300/3 draw, mostly all LED fixtures. Thankfully only on set-up day but one of the feeds tripped - upstream, at the generators. Should never have happened, main ELCB had tripped.
Investigation and much headscratching, mutterings in Frenglish (this is Paris) with the local generator guys..... and this is what was happening: Their lighting rig contains a large number of some fixtures that have come straight from the factory in China. And the electronics in them are so poor that each one dumps about 10-15mA to cpc. Each. So the 30mA RCBO each one is on is happy enough. The control and distribution end of the system has 'divisional' RCM that's not seeing anything at all. Over 7 amps to the cpc cumulatively, non-fault. So why had nothing downstream tripped when the upstream ELCB was set to 3A 500mS?
Because.... wrong type of RCD's. These needed to be A types and they were all standard AC. So much DC going on when I measured it properly that the RCD coils would have just been permanently saturated the same as an MFT does. No option to disable the upstream protection (even if I'd been tempted to do that couldn't anyway due to French regulations) so had to solve the problem another way. With some butchery we split the loads up to spread the dump across more than one device and set the ELCB's to 5A.
The other option I had was the control racks all have bonding points in them (for other occasions), linked directly from the incoming cpc. So I could have also bonded them back to the venue MET and dumped the current that way via parallel path back to the generation PEN, upstream of the outlet monitoring.
And this was a 'perfectly good working system'. The games we play.
Huge stadium show lighting rig, fed in three sections, each section being about 300/3 draw, mostly all LED fixtures. Thankfully only on set-up day but one of the feeds tripped - upstream, at the generators. Should never have happened, main ELCB had tripped.
Investigation and much headscratching, mutterings in Frenglish (this is Paris) with the local generator guys..... and this is what was happening: Their lighting rig contains a large number of some fixtures that have come straight from the factory in China. And the electronics in them are so poor that each one dumps about 10-15mA to cpc. Each. So the 30mA RCBO each one is on is happy enough. The control and distribution end of the system has 'divisional' RCM that's not seeing anything at all. Over 7 amps to the cpc cumulatively, non-fault. So why had nothing downstream tripped when the upstream ELCB was set to 3A 500mS?
Because.... wrong type of RCD's. These needed to be A types and they were all standard AC. So much DC going on when I measured it properly that the RCD coils would have just been permanently saturated the same as an MFT does. No option to disable the upstream protection (even if I'd been tempted to do that couldn't anyway due to French regulations) so had to solve the problem another way. With some butchery we split the loads up to spread the dump across more than one device and set the ELCB's to 5A.
The other option I had was the control racks all have bonding points in them (for other occasions), linked directly from the incoming cpc. So I could have also bonded them back to the venue MET and dumped the current that way via parallel path back to the generation PEN, upstream of the outlet monitoring.
And this was a 'perfectly good working system'. The games we play.