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  1. #51
    Quote Originally Posted by EddyCurrent View Post
    It's about meeting certain standards;

    "PNOZ safety relays comply with international standards and are approved by BG and international certification bodies. They provide maximum safety up to and including Category 4 in accordance with EN 954-1, Performance Level "e" in accordance with prEN ISO 13849-1 and SIL 3 in accordance with IEC 62061. "

    Manufacturers have to demonstrate their product meets these standards and this can be a costly and lengthy process.

    These things matter under scenarios like, legislation, reliability, safety, compensation, prosecution, etc. So if these is an accident for example, you may need to demonstrate that you or your company have exercised 'Due Care' by using components that comply with the required safety category.

    These devices are also called 'Safety Monitoring Relays' there are basically 4 safety categories, it's up to the owner to work out which category is applicable to their particular application, this information is used;

    You then select a safety relay that meets the required category and also has the required electrical characteristics for the application.

    Further reading would also be this,
    Thanks for the references Eddy, I had a look at them, but I gave up trying to understand those sort of documents when I retired in 1999.
    They may be relevant for a corporate engineer, but I am just a hobby player.
    That's all well and good, but how do they get to be 25 on eBay (if they haven't fallen off the back of a stores shelf ).
    I'm not an employee and I don't need to have duty of care over some moron who is bound for self destruction by his own stupidity. All I need is that if I have to bang E-stop the damn machine stops PDQ, and if it can't account for all the electricity going in through the live and coming out through the neutral, I also need it to isolate itself until the leak is fixed (within 30 milliseconds, preferably a lot less, if it is more than 30 milliamps going through me). There may be other requirements yet to be determined.
    As a silly aside ;- Pilz is German for Mushroom.
    Thanks anyway for the input, but it is far too heavy for my butterfly brain.

  2. #52
    Maybe the mushroom reference is to do with the red botton on an E/Stop, typically referred to as a mushroom.
    The one I bought was from a place that had closed and they were clearing out the stores.
    You are correct about these not being applicable to hobby use but when you consider what's inside it can work out cheaper than standard relays, timers, etc.
    Also I value my health so I'm prepared to go the extra mile to preserve it.
    Last edited by EddyCurrent; 26-07-2014 at 10:53 AM.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  3. #53
    Mine was cheap because it's an obsolete model and therefore probably no longer certified for new build commercial equipment. Box was damaged as well but relay looks in perfect condition. What I haven't seen cheap on eBay are the double-pole e-stop switches although I'm not too worried as I reckon that a n/c contact is more likely to work when it gets thumped in a hurry than n/o. While safety is important, I'm not building a machine that will be used by a numpty on piecework. But we all draw lines in different places...

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