Surprising LED behaviour

[stillp]

I should know better, but...
Today I bought some bargain-priced dimmable LEDs at Elex. We have a four-spot fitting in the kitchen, run via a Clipsal dimmer about 10 years old. No idea if it is a leading or trailing edge.
Fitted the LEDs, turned the dimmer on - a brief flash of light and the MCB tripped. Put the halogens back in, reset the MCB, and all worked fine. At this point the senior moment ended and I realised the dimmer is rated for 40 - 400 W, the LEDs 4 W each. Fitted just one 50 W halogen instead of one of the LEDs, and the same happened. Then I tried 3 halogens and one LED - tripped again!
Now I know I should have checked the dimmer was a trailing edge type, but I'm surprised the LEDs could trip the MCB. I'm also a bit surprised the dimmer survived the abuse. I would have expected flickering or just no output at all, but not a surge of current sufficient to trip a B6.
The supplier checked the LEDs were still working and gave me a refund, but can anyone suggest why the surge of current? It's puzzling me!

 

[JohnW2]

Very odd. I hardly dare ask, but I presume you are sure that they were LV LEDs?

Kind Regards, John

 

[stillp]

I had to laugh at your question John, since I did check - after fitting them! They have a very wide voltage range, but it definitely includes 240 V.[/i]

 

[JohnW2]

I had to laugh at your question John, since I did check - after fitting them! They have a very wide voltage range, but it definitely includes 240 V.

Well, I had to ask - not the least because I could tell a tale about myself which would require quite a few !!

As you said, the story you tell really makes no sense. Regardless of the primary problem (whatever that might be), I just can't see how you could get enough current through the dimmer to trip a B6 (which is a lot of current if it tripped more-or-less immediately) without totally destroying the dimmer.

Accordingly, if it weren't you, I'd probably be asking whether you were sure that it wasn't a 6A RCBO (or even an RCD) that had tripped!

Kind Regards, John

 

[stillp]

I just can't see how you could get enough current through the dimmer to trip a B6 (which is a lot of current if it tripped more-or-less immediately) without totally destroying the dimmer.

Also without totally destroying the LED! I don't think the MCB is unduly sensitive, since it doesn't trip with all the lights on that circuit switched on. Poltergeists?

 

[JohnW2]

I just can't see how you could get enough current through the dimmer to trip a B6 (which is a lot of current if it tripped more-or-less immediately) without totally destroying the dimmer.

Also without totally destroying the LED!

True - although it's just about conceivable that there was something about the combination of the lamps and your sockets which somehow resulted in an 'external' (to the lamp) L-N short, such that the fault current didn't go through the LED. However, it would still have to go through the dimmer.

I don't think the MCB is unduly sensitive, since it doesn't trip with all the lights on that circuit switched on. Poltergeists?

Indeed. Given that you returned the lamps, I presume there is no real prospect of our ever getting a better answer than that! Had it been me, I think I would probably have experimented a little - e.g. to find out whether it still happened if one removed the dimmer from the equation.

Kind Regards, John

 

[stillp]

Before issuing a refund the guy at Elex checked each lamp individually by plugging it into his display. All worked fine, and the exhibition hall didn't go dark.

 

[JohnW2]

Before issuing a refund the guy at Elex checked each lamp individually by plugging it into his display. All worked fine, and the exhibition hall didn't go dark.

I realise that, which is why I wrote "... something about the combination of the lamps and your sockets which somehow resulted in an 'external' (to the lamp) L-N short ...". Seemingly extremely unlikely - but how else could a lamp which caused an MCB to operate in your hands work perfectly when tested somewhere else?

Kind Regards, John