Hello Everyone, a quick ?

[tdexxx]

Hi Everybody,
I'm hobbyist with an electronics question that I hope someone here is willing and able to answer for me. I want to rig an ordinary GFCI-equipped electrical outlet to trip in the presence of light. Can I arrange this by simply bridging the outlet's hot and neutral with a resistor and light sensitive device so that light shining on the outlet would result in a flow of current between them and thereby cause a deliberate trip of the mechanism? Would that be safe and reliable? Is there a simpler way to use light to triggered a trip of the GFCI? What kind of light sensitive device would be best? I want the trip to occur within a second or two of light exposure; the device to be small, inexpensive, rugged, and easy to get.

Many Thanks,
Tom

 

[Hero999]

You wouldn't connect the live and neutral via a resistor, you'd connect the live and earth which is a very bad idea, don't do it, it isn't safe. Use a dark activated relay circuit powered by a transofmer connected to a socket and make sure you switch the live/hot wire and not the neutral.

 

[mneary]

You must be able to do mains wiring safely.

Get a wall-wart with an AC output. 5V-15V is pretty good. Attach one side to the neutral before the GFCI, and the other side through the LDR to the neutral after the GFCI. Do not touch or attach to the hot sides at all.

When the LDR lets current through, the neutral current causes an imbalance which trips the GFCI. The GFCI doesn't need to know who provided the current, it trips on an imbalance.

 

[tdexxx]

When the LDR lets current through, the neutral current causes an imbalance which trips the GFCI. The GFCI doesn't need to know who provided the current, it trips on an imbalance.

I understand, thanks. Do you happen to know how much current on the neutral it would take to trip the gfci?

 

[Hero999]

It depends on the GFCI.

Here in the UK we call them RCDs and a typical trip current is around 30mA, I don't know about the US though, I've heard it's something around 5mA.

 

[tdexxx]

It depends on the GFCI.

Here in the UK we call them RCDs and a typical trip current is around 30mA, I don't know about the US though, I've heard it's something around 5mA.

Thank you.

Tom