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Topic Title: 537.1.4
Topic Summary: meaning of 'linked'
Created On: 05 September 2012 09:56 PM
Status: Post and Reply
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 05 September 2012 09:56 PM
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andrew331

Posts: 110
Joined: 21 December 2008

Hi

537.1.4 says:

'A main linked switch or linked circuit-breaker shall be provided......'

then in the next paragraph:

'A main switch for operation by ordinary persons......shall interrupt both live conductors of a single- phase supply.'

So, is a linked switch a switch that interrupts both live conductors or does 'linked' have some other meaning?

The model EICR form also has 'main linked switch' (item 4.6) and just plain 'main switch' (item 4.7)
 05 September 2012 10:12 PM
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spinlondon

Posts: 4523
Joined: 10 December 2004

A linked switch, is one that isolates more than one conductor in a single operation.
With 3 phase it would isolate all 3 phases, or all 3 phases and neutral (if required).
With single phase it would isolate both line and neutral.
 05 September 2012 10:13 PM
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AJJewsbury

Posts: 11699
Joined: 13 August 2003

I'd always taken it to mean a multipole switch (or circuit breaker) that has the switching of the various poles physically linked together, so you can't open (or close) one pole without doing the same to all the others at the same time. Could be DP (for single phase), 3-pole (for 3-phase TN) or 4-pole (for 3-phase TT) for example.

I guess in a non-domestic single-phase installation you could in theory have a single-pole main switch (i.e. not linked) and I've a feeling that single pole devices next to each other but not physically connected can be used for isolation etc in some contexts.

- Andy.
 05 September 2012 10:46 PM
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spinlondon

Posts: 4523
Joined: 10 December 2004

There are some switches which will disconnect the phases first, followed by the neutral.
 05 September 2012 11:06 PM
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AJJewsbury

Posts: 11699
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OK, substantially the same time
- Andy.
 06 September 2012 09:22 AM
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daveparry1

Posts: 6333
Joined: 04 July 2007

I suppose it really means that reliance shouldn't be put on a single pole device, eg an mcb for isolation, (although a double pole mcb would be ok)

Dave.
 10 September 2012 02:58 PM
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AJJewsbury

Posts: 11699
Joined: 13 August 2003

I suppose it really means that reliance shouldn't be put on a single pole device, eg an mcb for isolation, (although a double pole mcb would be ok)

Although the regs do explicitly allow single pole isolation for TN (but not TT) systems ... other than for the main switch of household and similar.
- Andy.
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