MICRO SWITCH ON A MACHINE DOOR

[ricicle]

Standard micro switches can be over-ridden with tape or cable ties by operators. It can and does happen. Some of the idiots I used to see in our rubber factory with switches out of circuit in large hydraulic guillotines etc beggars belief. These machines do not stop for the human body.
Watch a few of the videos on Youtube and then decide if you want to be so flippant about it.

 

[bhm1712]

i watched the one thats linked to this topic and thats bad enough, but unfortunately it still happens in this day and age. I have worked with people who were quite happy to turn off an isolator and 'just nip in and out quickly, nobody will try to turn it on in 2 minutes'

Some of the other videos are even worse. Im squeamish and there is a video about work accidents that makes my stomach churn. They maybe fictional re-enactments, but all based on stuff thats really happened!

23 years ago at my old place a man was killed and another seriously burned all over his body because they has been working on a section of steam pipe. The older engineer had decided to ignore the safety procedure which had been written after a risk assessment had been done. He was supposed to isolate the steam supply in 2 places and monitor the pressure gauge. Once the pressure was zero he was to open a drain off point between the 2 isolations. In the event of one of the isolation valves passing steam, he would have seen the steam exiting from the drain off point and be able to stop working and get out of the area. However he didnt do this, he isolated only the first valve and didnt check the pressure, and didnt open the drain off. He and the other engineer began to cut out a section of pipe. Once they cut through they had 12 bar of super heated steam right onto them. The younger guy who was operating the cutting disc died within minutes and never got away from the steam leak. The older guy managed to crawl out of the sub floor, naked and burned from head to toe and went into shock. Luckily the exit to the sub floor was opposite the company fire station and they saw him and called the emergency services. The works supervisor,the surviving engineer (once he had come out of hosptial months later) and a company representative where charged with several H&S offences. The company was fined around £12000 (1989) and the supervisor ( who should have signed off the isolation) and engineer were sacked from their jobs and spent time in prison.

 

[ban-all-sheds]

The thing is I'm sure that if Wellsiana was faced with a numpty DIYer who thought he could rewire a house even though he had no idea about the current carrying capacity of cables, no idea how installation method affects that, no idea about matching breaker rating to cable rating, no idea about earthing and bonding, no idea about safe zones, no idea about disconnection times, no idea about voltage drop, no idea about RCD protection, no idea about testing he'd be one of the first to try to make the guy realise that there's a lot more to it than he thought.

And if the guy said "thanks for your interesting views, but I'll just bung the cables in, it'll be fine, I'll check for smoke when I turn it on", he'd be pretty disparaging.

 

[SimonH2]

i dont know if we are looking at this too deep , i only asked as i was given a switch to try to fit and it was a simple 1 amp 230v door contact switch.

Thus proving, as if it needed any more proof, that you lack sufficient knowledge to do this job safely.

It is most likely a 415V control circuit - one phase is picked off, goes around the stop button(s) and the hold in contact on the starter to the coil. The other side of the coil goes to either of the other phases. The start button(s) are wired (in parallel if more than one) across the hold in contact - and you cannot start the machine with the green button if any red button is pressed (or latched down) and thus removing the supply for the coil.

The controls may be 240V (ie between one phase and neutral), but IME it's more common to use 415V as that avoids the need for a neutral to the machine at all in many cases.
If there are light etc, then they are often 110V and run from a transformer. As an aside, on some motors (such as old industrial sewing machine motors I've seen with integral clutches), there are tappings on a winding to get a supply for the bench light.

Hopefully, I hope you can see that a 230V rated switch really, really isn't suitable for use on 415V. Also, as others have pointed out, there are specific types of switch designed for what is a safety critical component. In an industrial setting, you really need to have done a proper risk assessment - if the brown stuff hits the fan, it would not be a defence when stood in the dock that "it was better then before".

 

[bernardgreen]

if the brown stuff hits the fan, it would not be a defence when stood in the dock that "it was better then before".

In fact fitting an "" emergency stop switch "" to a machine door can make operation of the machine less safe.

How ? After the switch has been fitted operators discover that opening the door stops the machine quicker than the stop button. Instead of pressing the stop button, waiting for the machine to stop and then opening the door to clear a jam they simply open the door.

If that is possible then as well as the key lock the door requires an electrical lock that prevents the door opening until the machine has stopped.