Isolating electrics at switch/spur

[Jupiter01]

Let me start with, I own a lock-out kit and 2 probe tester. I use these for safe isolation.

Curious - if a fitting has a FCU or there is a light fitting with a single switch cable, can you isolate here whilst someone keeps a look out? Is there inherently something in a light switch or a FCU which mean that they could somehow leak current through them? I appreciate that there is still a small risk that someone could flick the switch.

 

[pete01]

You also need to be careful of borrowed neutrals....

Where a neutral is taken from a different circuit, these can still be live when separated, they surprise many people.

Stairs and landing lights used to be common for this.

 

[Murdochcat]

If there is a minute chance somebody could operate a switch then you have not exercised safe isolation

 

[333rocky333]

Theres a table in the regs that states what accessories are suitable for isioation purposes

 

[plugwash]

I'm fairly sure BS7671 has a list of what standards devices used for isolation should meet and the standards for plate switches (even DP ones) are not on the list.

FCUs *are* on the list, but BS7671 doesn't make it clear which part of the FCU should be used for isolation. Personaly if using a FCU for isolation I'm turning it off *and* removing the fuse.

 

[ericmark]

FCU one hopes will have a double pole switch, but the line can be locked off by putting a lock through the fuse carrier. Lights switches not so easy, my light switches I would never trust,

I could remove the batteries, but I would always switch off at the RCBO, and to be frank, not sure if they are single or two pole switching, I would lock off

but as to if this isolates not so sure. Easy enough to test, neutral to earth should be open circuit if isolated, but just as likely to get a shock from the earth as neutral with a TN-C-S system, so if line switched off, I would not be two worried about true isolation and the neutral (which is technically a live) being switched off as well.

The RCBO locking device can easily be ripped off, but being in place, one would hope shows anyone it is being worked on, although not approved, simple insulation tape over the RCBO/MCB also shows anyone it has not simply tripped, but has been internally turned off. Even if it will not satisfy HSE.

I know my colleague got sacked for throwing a hammer at a guy removing his do not switch on plaque, unfortunately he missed. So no amount of locks makes it totally safe, I have a mauled hand do to someone removing my lock and turning on the concrete recycling machine I was working on, I am an integral part of Heathrow Terminal 5, and dead against recycling.

 

[Jupiter01]

How do I use my 2 pole tester to check if a given switch or FCU is double pole?

 

[EFLImpudence]

How would you use it to check if a conductor is continuous or not?

 

[ericmark]

Neutral to earth either zero, or very low voltage, if zero then ohms test if neutral switched off then infinity, if not then zero ohms, and if a voltage neutral to earth clearly neutral not switched, so don't test ohms as can damage the tester.

 

[plugwash]

Some "two-pole testers" automatically test for continuity if no voltage is detected.