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Topic Title: Emergency switching for motors
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Created On: 03 November 2017 01:23 PM
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 03 November 2017 01:23 PM
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jonel

Posts: 9
Joined: 19 October 2017

Hi All,
I have come across the following multi-choice question from a C&G 2382 paper.

25. Which one of the following may be used to provide emergency switching for an electric motor?
a. A key switch latched in the on position.
b. A plug and socket.
c. A switch fuse with a removable handle.
d. A device which latches in the off position



a - ruled out by 537.4.2.6 and perhaps obvious
b - ruled out by 537.4.2.8 and obvious
c - I'm not sure. I would say yes unless the handled can be removed in the on position
d - according to BS 7671 Regulation 537.4.2.7 is correct.

Anyone with a definite answer please?

Jonel
 03 November 2017 01:36 PM
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mapj1

Posts: 9553
Joined: 22 July 2004

The removable handle like the key, is bad, if you can switch it on, and walk off with the key / handle.

'd' would get my vote, and I'm thinking of the latching E-stop.

Wait for other responses though.

-------------------------
regards Mike
 03 November 2017 09:50 PM
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paulskyrme

Posts: 1291
Joined: 12 February 2003

Have a look at section 537, & table 53.4 for some guidance.
 04 November 2017 07:30 AM
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davezawadi

Posts: 3895
Joined: 26 June 2002

My answer would be d, although it not a particularly good question because the descriptions are not very complete. It is important not to "overthink" these questions, the correct answer can usually be decided by simply choosing the closest answer to the ideal situation. However I am sure that you have come across this kind of switch, usually a red button which twists as one pulls it out to switch on then holds until pressed, where it latches unless twisted to unlock again. They are common on machine tools and similar items, although it seems that sometimes they are fitted with too much accessibility, and some yobs love to push them as a "laugh", particularly on generators which can be very dangerous itself!

-------------------------
David
BSc CEng MIET
david@ZawadiSoundAndLighting.co.uk
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