Every machine should have its own supply disconnecting device, which is outside the scope of BS7671 and covered by BS EN 60204-1. A lot of people have been injured or killed by inability to isolate a machine.
Isolation
- Thread starter wiefil
- Start date
Thanks. To answer the OP's question, is it acceptable for that isolation device to be 'on the machine'? ... and, in relation to what other people have suggested, is 'pulling the plug' an acceptable 'device'?
Kind Regards, John
It is seldom acceptable that the only isolation device is on the machine or in the hazardous area surrounding the machine.
Several things create a hazardous area when a machine goes wrong, such as the space a rogue robotic arm can reach, an area that may be affected by leaking chemicals, or jets of compressed air or hydraulic fluid, and many other possibilities.
It's really 'emergency switching', rather than isolation, which is the issue. Isolation can be achieved 'at leisure', perhaps just by unplugging the machine.
As far as 'emergency switching' is concerned, in terms of common sense (I don't know about regulations/Standards), I suppose a lot depends upon the nature and size of the machine, and on exactly what is meant by 'on the machine' - and also on the location of the postulated 'external' switch/isolator. If that 'external' device were only a few inches away from 'the one on the machine', then it would be virtually as susceptible to the problems you mention as would be the 'one on the machine'.
Kind Regards, John
It is part of the electrical equipment of the machine, not the installation, so it is usually on the machine's control panel.
It can be, as long as the plug-socket pair is suitable for unplugging under load, or interlocked with some means of disconnecting under load, and is accessible.
Thanks - so it is acceptable for that control panel to be "on the machine"?
Kind Regards, John
They're not - but, as I've just written to bernard, I don't think isolation (which can be achieved by pulling the plug, and probably in other ways as well) is the issue in this discussion - it's really 'emergency switching' which everyone is, at least implicitly, talking about.
Kind Regards, John
They usually are. However, many small machines, such as a drill press, have only an on/off device on the machine, and rely on unplugging for isolation. That's acceptable as long as the plug can be kept under the control of anyone working on the machine.
I don't know, is it? The title of the thread is 'Isolation'.
Thanks. That's what I rather thought.
I think it essentially is, despite the title of the thread. The OP's colleague could not really have thought that what had been done (temporarily) was a problem in relation to isolation in the true sense, since it remained possible to unplug the machine, even if there were no other means of isolation. The suggestion that what had been done (temporarily) was 'dangerous' must have related to 'emergency switching' - and I think the OP was correct in believing that the switch on the machine (with 'pulling the plug' as a backup) was adequate to render the situation 'safe'. Do you agree?
Kind Regards, John
You might be right, but it does no harm to publicise the difference between stopping a machine, e-stops, and isolation.
I agree - but I think the OP's situation, and question, was as I described.
Isolation is obviously never an issue in relation to an item of equipment which is supplied via an accessible plug and socket.
Kind Regards, John
It is when people think that hitting an e-stop, for example, achieves isolation.
a socket on/off switch would not be considered a suitable method for emergency switching and as such doing this temporary mod would not matter.
What is a concern is that the post implies that the socket front was removed in order to fit a circuit breaker inside and then closed back up meaning that it would be expected somebody would open up a live three phase socket in order to turn off the mcb.
What is a concern is that the post implies that the socket front was removed in order to fit a circuit breaker inside and then closed back up meaning that it would be expected somebody would open up a live three phase socket in order to turn off the mcb.
Unplugging a machine alone is also not a suitable method of isolation unless a plug lockout is used with the key to the lock being under the control of the owner of the job in hand.
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