contact surface material

Yes the material is important but also is the contact design.Look at how a relay closes it's contacts. Fast contact and a slide action called wipe.

Why not use a micro switch ??

That would be my first choice too. Duh... Too easy maybe.

Plan "B" add a relay to switch the heavy current

Plan "C" would be to take the contacts from a relay or contactor.

Plan "D" would be to punch two silver slugs and braise them to some steel stock.

A mosfet or a relay would let you run the contacts at low current. You could use a proper interlock switch.

Or maybe just buy an interlock switch rated for 5 amps.

A reed relay on the inside, and a small magnet glued to the lid, gives you a 100% reliable safety switch.

Thanks all. I am trying two problems with one stone, and creating a third. Wire fatig ue has been a problem. Having a live wire grid attached to the lid is OK f or me but the thing is an incubator with metal egg cradles . I would hate h earing of someone dropping a cradles' worth of expen$$ive eggs because of u nexpected spark fun. It may be a good idea to move the contacts from the hinge edge to the oppos ite side. I was leveraging switching speed for firm contact. Tom, I don't recognize the slide action in the relays I have looked at. Lo oks like slam bang to me. Thanks again

If you look at the spring blades that hold the contacts you can see a slight slide as the spring blades push the contact down. It's only a little. If you are looking at a heavy duty contactor you will not see this.

stock about 1 x 1/2 inches. When I close the lid they make contact and 12V DC flows into 2.5 ohms worth of nichrome heating wire. The idea being NOT to have live voltage exposed when the lid is open. Also, wire fatigue was c ausing problems.

Hese carbon scabs are not easy to clean off. Flatness of the contacts is an issue.

ave sheet copper. And tin plated steel from a shielding cage.

entist , after carrying it around in my mouth for years)

malua mada! wrote on 4/3/2017 1:32 PM:

-------o--------v--

-------o--------^--

-------o.

-------o.`-. `-.`-. `-.`L. `^.

This very crude and a bit hard to read, but you can see the contact points move as the contacts are bent. If you contacts move enough there will be some wiping which helps to remove the crud.

I think you will be better off with a sealed commercial switch. It is easy to mount the switch on the box and have the lid press the actuator. Are you familiar with micro-switches? They aren't necessarily small as the name would seem to imply.

Or is this intentionally a home brew project that you want others to be able to build as cheaply as possible? Home made switches aren't always a good idea for the reasons you are finding. Some aspects of switches aren't immediately obvious.

Nope!

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Then, at least 5 millivolts could be.

It's current that kills, not voltage. If you are surrounded by conductive water the current will go around you rather than through you.

In a perfect world perhaps. I flooded the bilge of my boat where the battery compartment is and I could feel the 12 V when trying to save the batteries from salt water. It was damned uncomfortable but only for the cuts and abrasions on my hands.

Current may kill but voltage pushes the current along and overcomes resistance. They told us in school that it takes ~100 milliamps to kill, and that is through the skin and in a path with vital organs (like arm to arm).

One of the linemen on a job I worked on took a jolt of ~5KV through his arm. HT power line on distribution pole; flash of light, sounded like a loud gunshot or cannon, he was slumped over in his harness out cold, and his arm was still smoking... he lost the arm, but lived, and has no memory good or bad of the accident.

Absolutely not correct! People swimming near docks where a power line leaks current into the water have died. You are not supposed to jump in to help such a person because you will also die.

I mentioned this to my neighbor who has 110 volts on his dock and couldn't remember if they had a GFCI on that line. I told him if it didn't and someone died, he would be in a lot of trouble. He ignored me. It is unlikely for a short to develop, but if it does it can and does kill people.