What are those safety switches?

Forums › Gadgets, robotics, home automation, electronics (including wearables) › What are those safety switches?

kenkeniff

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#191629 10-Feb-2016 23:25

I'm looking for a type of appliance safety switch that automatically flicks to the off position when power is cut so that when power is restored the appliance doesn't automatically start up.

There is a name for such a switch??

I'm looking for a 250V panel mountable e-stop with this functionality.

Stu

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#1490038 10-Feb-2016 23:39

Would you be going of an RCD? Residual Current Device. I guess the panel mounted are the same as in-line.

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kenkeniff

628 posts

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#1490039 10-Feb-2016 23:45

Stu: Would you be going of an RCD? Residual Current Device. I guess the panel mounted are the same as in-line.

No, not RCD;

Imagine you have an appliance with moving parts, there is a power-cut so device stops working, you stick your hand in said device then power comes back on...

The sort of switch I'm looking for protects against such by "tripping" when power is cut requiring a manual reset.

gzt

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#1490046 10-Feb-2016 23:52

No idea. I have an inline plugin RCD behaves the same way. If the input power is dropped then the device must be reset. I think it is PDL brand can look tomorrow if you need to know.

But one call to JD Russell or Ideal Electrical will get the info you really need...

kenkeniff

628 posts

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#1490048 11-Feb-2016 00:00

gzt: No idea. I have an inline plugin RCD behaves the same way. If the input power is dropped then the device must be reset. I think it is PDL brand can look tomorrow if you need to know.

But one call to JD Russell or Ideal Electrical will get the info you really need...

Yeah there are devices like this: http://www.mitchellinstrument.com/electrical-test-and-measurement/general-electrical-testing/sensing-saf-start-plugs/sensing-saf-start-plug-1996.html

Seems like the terms I'm looking for are "anti-restart" or "drop-out" protection.

As mentioned I'm looking for something I can panel mount otherwise may have to build my own with a push button + relay.

sidefx

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#1490049 11-Feb-2016 00:01

http://www.mitchellinstrument.com/electrical-test-and-measurement/general-electrical-testing/sensing-saf-start-plugs.html

EDIT: Doh, seems my google-fu was too slow :p

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DarthKermit

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#1490052 11-Feb-2016 02:50

PDL plug in RCDs are designed to trip when the power is cut. The PDL hard wired RCDs are designed to reset themselves when power is restored. An important difference between the two types.

elpenguino

3419 posts

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#1491372 12-Feb-2016 20:46

You can do what you describe with a relay/contactor.

Get one with a mains powered primary. Wire up the primary to the supply via a momentary switch. Connect load to secondary.

See a sparkie / engineer for help.

I am not sure how much one would cost but my guess is 'not much'.

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nickb800

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#1491373 12-Feb-2016 20:53

Sounds like a 'magnetic starter' and normally has a green/red start/stop switch combo. But might be cheaper as above to implement your own solution with a contactor

Aredwood

3885 posts

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#1491452 12-Feb-2016 23:27

Easiest just to do with a contactor as said above. You can also add a "push to break" switch if you want to as well so you can make the contactor turn off without having to manually cut the power. So you can have both a start and a stop button.

Also if the machine runs on 3 phase power. Consider adding a device that detect lost phases and check that phase rotation is correct. (can't remember proper name of it) Would your machine be unsafe if the motors unexpectedly started rotating the opposite way to normal?

Guessing this is a workplace - AFAIK you can't use a control circuit as isolation for safety. So you will still need a manual isolation switch in the power feed to the machine. And then require your employees to turn that switch off and fit a "danger do not use" lockout tag to the switch. Before they reach into the machine. And add that process to your training and policies and procedures manual. (Dont know if your machine example is the actual situation or just hypothetical).

kenkeniff

628 posts

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#1491521 13-Feb-2016 10:16

elpenguino:

You can do what you describe with a relay/contactor.

Get one with a mains powered primary. Wire up the primary to the supply via a momentary switch. Connect load to secondary.

See a sparkie / engineer for help.

I am not sure how much one would cost but my guess is 'not much'.

Yeah this looks like the way to go; however I'm wondering if there is a way to implement the breaking action also with a single push/mom button so I can toggle it on/off (with the same button).

andrewNZ

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#1491523 13-Feb-2016 10:35

Not without some pretty tricky wiring or some smarts behind it. A self holding relay/contactor is the way to go, and wiring is simple.

elpenguino

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#1492327 14-Feb-2016 23:15

kenkeniff:

Yeah this looks like the way to go; however I'm wondering if there is a way to implement the breaking action also with a single push/mom button so I can toggle it on/off (with the same button).

It will be cheaper & easier to build and possibly safer to operate with 2 buttons. You would need a momentary green that's normally open and a momentary red that's normally closed.

Buy a green that's somewhat concave so it needs a deliberate pressing action. Buy a mushroom shaped sticky-outy red so you can easily bump it off with one hand while the other is holding your hair/tie/shirt/whatever got stuck in the machine :-)

Imagine if had a system with a single button as you mentioned and you needed to turn it off quickly but you pushed the button twice by mistake.....is that something you want to avoid?

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richms

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#1492343 15-Feb-2016 00:13

I got a cheap red/green button switch thing off aliexpress to replace a bust one on a bench grinder that has that type of operation built into it. when the AC input is turned off with it running, it clicks out and will not start again till you press the green one. I dont have access to that aliexpress account anymore since it was aaages ago back when I had on an old work email address so cant link to the exact one, but I think I just searched for start stop button 220v latching or similar.

Richard rich.ms