Limit Swithces NO or NC????

[Al_The_Man]

Originally Posted by acondit I was simply pointing out that the choice of NC rather than NO doesn't guarantee safety in all circumstances. One should look at the other possible points of failure and weigh the risks against the cost of protecting against them. Alan

For many years, north american practice has been to use 'simple' forms of e-stop or overtravel protection using limit switch and/or common relay latching circuits.
If anyone is concerned about the frailties of these common usages, then maybe the recourse is to look at devices that have been in prominent use in Europe for a couple of decades at least, and are slowly being seen in N.America, This is the use of Safety Relays, These devices come in all kinds of configurations and attempt to cover many probable eventualities such as welded relay contacts etc.
They may become mandatory here in Commercial equipment, as they have in Europe, if not already.
Now its a case of to what extent or how far you want to go in search of protection.
Al.

[gar]

071104-2128 EST USA

alan:

With a NC contact connected from +5 V to the gate input you need a pull down resistor at the gate input.

.

[acondit]

Originally Posted by gar 071104-2128 EST USA alan: With a NC contact connected from +5 V to the gate input you need a pull down resistor at the gate input. .

Yes