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Topic Title: Using Unswitched Plugs and Sockets as Isolators?
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Created On: 08 November 2017 01:01 PM
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 08 November 2017 01:01 PM
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jonel

Posts: 9
Joined: 19 October 2017

Table 53.4 shows that plugs and unswitched socket outlets can be used as devices for isolation while carrying load current!. Functional switching can also be carried out in this way as well. Is this really a safe procedure?
Am I interpreting this table incorrectly.

Thanks
 08 November 2017 01:35 PM
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Legh

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Joined: 17 December 2004

Yes, now that from 1981 the standards changed to comply with insulated sleeving along the first part of the connector pins. Although the only time I ever use this type of socket is to connect under work surface appliances where isolation is provided by a above work top 20A switch, sometimes i'll use a SFCU if I haven't got the former in my stock.

Legh

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 08 November 2017 01:53 PM
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AJJewsbury

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Generally plugs & sockets up to 32A can be used for functional switching as well as isolation. Above that they're only suitable for isolation - suggesting that they're not intended to make/break load current - just provide isolation after the load has been switched off elsewhere.
- Andy.
 08 November 2017 01:55 PM
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Legh

Posts: 4044
Joined: 17 December 2004

Oh yes............
1. I once put an unswitched BS1361 socket half way up a wall behind a LED flat screen TV
2. Another time I installed an unswitched socket on a garage ceiling for automated doors

Legh

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 08 November 2017 02:05 PM
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broadgage

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I would observe that unswitched sockets are permitted, and installed domestically for use by unskilled persons, so must be considered safe for load breaking/functional/switching, and for isolation.
AFAIK, the regs only require domestic socket outlets to be switched if the supply is DC, and just how many DC mains supplies exist these days.

This however has got me thinking, do ALL DC sockets have to be switched, or only those over a certain voltage ?
 08 November 2017 02:20 PM
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AJJewsbury

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This however has got me thinking, do ALL DC sockets have to be switched, or only those over a certain voltage ?

I suspect it might be more to do with the current rather than (or as well as) the voltage - I think the problem is that if you draw an arc on d.c. it can just persist and can then be drawn out for a worrying distance - on a.c. it will automatically extinguish every half cycle so unless the contacts are still very close together the arc doesn't persist.

Note that almost everywhere else in the world uses unswitched sockets as standard for domestic and similar situations.

- Andy.
 08 November 2017 03:17 PM
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ArduinoXR

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Every half cycle is a +peak OR a -peak. I know, pedantic as anything, but it's a slow wintry day
 08 November 2017 03:50 PM
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AJJewsbury

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Every half cycle is a +peak OR a -peak.

Not necessarily - it all depends on where you start from. If you think of it as a conventional sine curve, starting at 0V at 0 degrees, it's at a +ve peak 90 degrees later (quarter of a cycle or pi/2 radians), back to zero at 180 degrees (half a cycle or pi radians), negative peak at 270 degrees (three-quarter cycle) and back to zero again at 360 (or 0) degrees.
- Andy.
 08 November 2017 05:01 PM
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mapj1

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Or you may prefer to consider it as a cosine wave, so each half cycle is a little 'sea horse' shapes, starting on one side of zero and finishing on the other.
When performing Fourier analysis of distorted waveforms to estimate the harmonic content, it is sometimes easier to calculate with the cosines than the sines. (symmetry and all that) Though nowadays the computer sorts it out, and it had better be equivalent over more than one cycle anyway.

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regards Mike
 08 November 2017 09:48 PM
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MHRestorations

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broadgage, your comment also has me thinking. If the regs do indeed state that ALL dc sockets must be switched, the manufacturers of USB outlets are going to be in for a nasty surprise!

(can't check now, my copy's in the van, and it's 20 miles away lol)
 09 November 2017 12:31 PM
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broadgage

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Originally posted by: MHRestorations

broadgage, your comment also has me thinking. If the regs do indeed state that ALL dc sockets must be switched, the manufacturers of USB outlets are going to be in for a nasty surprise!



(can't check now, my copy's in the van, and it's 20 miles away lol)


Indeed, and what about all the unswitched 12 volt or 24 volt DC socket outlets in off grid homes ?
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