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NVR switch failures ... why?

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Eugene:
I seem to be a jinx where NVR safety switches are concerned; one look at me and they die :(.

In the last few years I've had three expire on my table saw, and the latest one to take the hara kiri route lasted two weeks on the Myford lathe. The supplier (Axminster) bless them, have offered an FOC replacement, so that's good, but what causes these things to fail? In all cases the relay gave up the ghost, ie the "On" switch refused to stay in.

The tools are in and around my garage / workshop which was professionally wired for domestic supply some 5 years ago. The feed lines come quite a long way from the house distribution board (also new), say 20 metres underground to the kennels and another 20 metres underground from there. Could there be some sort of problem with the feed that knackers up the relays? Or are they just cheap crap from furrin' parts?

Eug

DavidA:
Have you measured the voltage coming in at your machine ?

Dave.

philf:

--- Quote from: Eugene on December 10, 2014, 08:18:43 AM --- Could there be some sort of problem with the feed that knackers up the relays? Or are they just cheap crap from furrin' parts?

--- End quote ---

Eugene,

You're probably right.

I made my own NVR for my lathe using a normally open start switch, a normally closed stop switch and a relay to latch the supply. It's simple to wire and the plug-in relay is easy to replace if necessary.

I've never had a problem with it unlike the Chinese? NVR on my T&C grinder which packed up after about a month and I replaced it temporarily with a plain on/off switch about 5 years ago.

Phil.

Eugene:

--- Quote ---Have you measured the voltage coming in at your machine ?
--- End quote ---
Nope, nor do I have the means to do so. What would be the implications of low / variable voltages for the life of the relay as opposed to i's function?

Eug

awemawson:
The imported far eastern NVR switches do seem to be very flimsily made in comparison to MEM and other older brands, but I suppose that's the way the world has gone  :(

When I've built my own machines, or re-built industrial stuff without some form of NVR I've done like Phil and used an appropriate Red & Green pair of buttons and a contactor with a latching n/o contact. All a bit more robust.

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