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Had a quick question. I am using a Crouzet GA8-6D05 SSR to relay xmas lights for the holidays. I basically hacked an extension cord (120VAC US <1Amp) to do this. I am currently using a spliced extension cord to perform on and off operations via a micro controller.

During the summer, we commonly use this same outlet for a water fountain on our patio (also 120VAC US <1Amp). I was thinking to use the SSR mentioned above to switch the water fountain on and off also. I am thinking that the best way to make this work would be to hack the actual outlet. I already know that you can separate a two plug receptacle by cutting the metal plate which connects positive on one side and negative on the other.

My question is: What will happen to the SSR if the load exceeds more than the max 5 amps it is rated for? Will it blow up, start a fire, or just reject the call for the extra amps? I am concerned about fire hazards, not really concerned about the thing dieing necessarily. I worry about leaving this in the wall if I sell the house as I do not plan to use the outlet for anything more than what is stated above, but the next home owners may not follow directions.

Thanks in advance for your help!

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Might as well drive an even bigger, mechanical relay that can handle the current, with your SSR. – tyblu Dec 23 '10 at 20:11
you can always monitor the current level and turn it off should it exceed rating. If you've already got a microcontroller sitting next to the SSR for control this is fairly easy without too many additional components as long as the uC has an ADC or can measure pulse widths in some manor. Or just use a X10 or Zigbee outlet, thats likely the only option if you actually care about complying with electrical codes. – Mark Dec 23 '10 at 21:02

1 Answer

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With the concerns you state, and especially with having the relay installed in a wall, I guess the answer is:

Don't.

You might add a fuse, but then, you'd have to find a rating in the relay's data sheet telling you if it is approved for usage with a fuse, and if so, what the fuse's rating would have to be. All in all, you would have to do the same qualification for the entire system (relay, fuse, type of outlet socket, possible loads) that the original vendor did for the combinaiton of the relay and fountain.

The relay will not limit the current (amps) to a level that is safe to itself. When overloaded, it will likely act like a short circuit for moderate overload conditions and will fail open (or explode, or burn) for severe or ongoing overload conditions.

The thing to remember is this: Once you exceed any of the ratings, the manufacturer won't guarantee anything they tell you in the data sheet any more and you are on your own.

Also, with having the relay installed in a wall where it can't really get rid of any heat it produces, I recommend using the derating curve for 60...70 °C, which tells you to rather not exceed 2...3 A.

A hacker's answer, however, is:

Yes, your setup might work, ...

... but you would have to make sure all is well and within the specified limits and characteristics.

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