Syetem Repeatedly Cooking Equipment

[username]

Background is that we completed an installation around 3 months ago. Around 6 weeks ago we had a call from the client - no lights working, all LEDs in system cycling upwards (no comms on QS Link). On the same day, the client says that there were people working on the air conditioning system in the house, so this might be related.

We tracked the problem down to several pieces of equipment (LQSE-4M, QSE-DMX, couple of keypads) that had failed and were bringing down the QS link that they were on. I should also note that the different pieces of damaged equipment were all on different cable loops.

So we replaced the equipment and all was well again. Sent the faulty equipment back to Lutron for testing and found that various components had been fried by an over-voltage to the QS Link. I must say that Lutron have been excellent and replaced everything under warranty.

But I've no idea whatsoever how this might have happened - all of the QS cables in the system are terminated and labelled like a work of art, Hellerman sleeves and everything. I just don't see how someone could have accidentally applied 230v (the local voltage) to the 24v QS Link.

Anyway, a few weeks later and the electricians are back in the house trying to fix a wiring problem with the boiler. Next thing I get a call and the same thing has happened, this time taking out two components - a QSE-DMX which is now totally dead and a LQSE-4M that brings down it's QS Link when connected. I have not yet returned these items to Lutron but I think it's probably safe to say it's the same issue again.

I have absolutely no idea why this is happening and perhaps more importantly, how I can prevent it happening again. And again...

Lutron tech assure me that any mis-wires on the mains voltage side of the components wouldnt be able to damage the components on the QS/low voltage side, so the only possible explanation seems that a mains voltage is somehow being intermittently applied to the QS Link, but given that we're using proper QS cable that's all really nicely terminated, I just don't see how... unless maybe there's a mains cable intermittenly touching a damaged QS cable somewhere in a ceiling void/wall/whatever.

So we've disconnected the latest faulty pieces while we await replacments and we're back up and running... for now.

Any thoughts you have are absolutely welcome, sometimes when you've been looking at a problem for too long you miss the obvious so I'm hoping one of you guys will be able to chime in with some useful perspectice!

[David C.]

There does not have to be a direct connection of 230 volts to the QS link. It could possibly be a surge caused by something the electrician or HVAC techs are doing. Surge protection is a good idea anyway especially if you're in a lightning-prone region. There are several manufactures of high-quality surge protection devices which are designed for the voltage and communications protocol of the QS link. Lutron has information and a white paper about this.

[abutchart]

Just a note for everyone. I have seen and experenced the same problem using 4A modules. With the Earth terminal next to the two Live inputs of the module. If someone does not know the Earth is the left terminal and puts a mains signal down it the module goes bang and so did the QS link.
I lost 5 keypads and a few other modules including the processor and it's power supply !!! in the process.
BE CAREFULL