Around fifteen years ago I was working for an orthopaedic surgeon, he said he had heard stories like that on many Saturdays, "I was going to change the landing light, so I turned the light on  the MCB off, the light went off so I started work, got a shock and fell of the steps and down the stairs".

I did a similar thing over twenty years ago, the light fitting had a permanent live and switched live from different circuits. 

I saw an advertisement for the new Wylex "domestic" three phase consumer unit which has a three pole main switch with the neutral wired directly into the neutral bars.

I thought all domestic installations have to have a switched neutral, I checked BS7671 and found I was wrong. 

The risk of the neutral being not connected when the phases are - which requires an offset contact in the 4 way switch block, is considered worse than the risk of leaving it connected.

And to be fair to the DNOs in most cases the neutral really is at or very near earth potential of course.

I have also been shown pictures of an expensive mistake with wring to a 3p and n main switch in  large installation where the neutral was not routed through the offset contact, but one of the phases was. The switch was just fine, but sometimes when it was operated for maintenance  some unrelated random failure would occur. Apparently It took ages to work out what was happening.

Mike.

Chris

No time to re-prove the 2 pole voltage tester as he was on his way to hospital in an ambulance.

The other suggestions were worth considering but not the cause.

MAPJ was the closest for the explanation.

A couple of months earlier a contractor for the meter operator came and swapped out the supply meter.  He connected the meter reverse polarity. So now switching off the MCB switched off the neutral.

There was no continuity on the CPC to the ceiling rose.

The 2 pole tester was of the type that needs to see a potential difference between the probes and did not gibe a warning of the presence of a live conductor with only one probe connected. I have a collection of a range of 2 pole testers. Some do not give a "one handed" probe warning even from the same reputable manufacturer. With no CPC continuity and the neutral isolated the 2 pole tester could not "see" a potential difference.

Make sure your 2 pole tester does a one handed test for live or drop it in the bin and but a new one.

So make sure your 2 pole tester does give a one handed warning. Also as I have said, keep a good quality volt-stick tucked in the top of your shirt and use it before touching anything conductive.  The Kewtech dual voltage non-contact tester in my view is the best there is on the market as it indicate live if it is anywhere near live and then press the button to desensitize it to  to identify individual live conductors.

See the IET Guidance Note 3 and The Electricians  Guide to the Building Regulations for their recommended procedure for safe isolation and the last step for identify lost PEN conductors. 

I wonder whether Colin sued the meter company?

2 faults in the installation!

I suppose that whoever put in the ceiling rose with a 2-core flex to the lampholder did not find it necessary to check the continuity of the CPC.

Isn't the other important point about proving dead that it only proves it there and then? I had wondered about a borrowed neutral and another occupant turned a device on just afterwards, or even a timeswitch operated. Ideally, the main switch should have been opened, but the wife was doing the cooking, the kids were watching the telly, etc., etc.

Is the neutral a source of electrical energy

Yes it is possible.

Years ago in the UK we had the

Live, Neutral and Earth

We now have

Line, Neutral and CPC ( I am talking domestic)

LIVE conductors now refer to Line and Neutral (or L1,L2,L3&N in 3 pahse).  Personally I think that in time CPC will be added to this list of LIVE conductors or should we say Possible LIVE Conductors.  Think about Earth leakage currents and PEN faults.

Is the neutral a source of electrical energy

Yes....Consider

Shared neutral in a lighting circuit with no RCBO in domestic scenario.  (MCB tolorate shared neutral but RCBO will not)

Missing identified or labled conductors from CU to fitting

Missing identified or labled conductors from Main service cut out to CU

Missing identified or labled conductors from Meter to CU

Pen fault in property and down the road

Off peak tarrif or timer circuit kicks in at time of work but after test for dead

Solar PV on roof

Battery storage

Chris

Substantial damages from the meter operator for their negligence, his injuries and time of work and loss of earnings as he was a self employed electrician. He did not tell me how much but I think it was a significant sum.

JP

I have experienced the reversed polarity scenario, but I was not expecting a double fault scenario.

There has been an extremely sad incident in New Zealand, an electrician has been found to be responsible for the death of a builder, from the news report’s I have been reading over the last few weeks it appears that over twenty years ago someone wired a light with two-way switching using the circuit protective conductor as a strapper with some red insulation tape wrapped around the end of the CPC in the switch box. The electrician connected a new cooker hood to the existing cable, unaware of how it was wired.

www.nzherald.co.nz/.../

Well my reading of it is that 4-pole switching is recommended (537.2.6) and since no one seems to know what the hell 461.2 means, it would seem reasonable to drop the reference to it in 537.2.6 and run with the recommendation in the first bit of that regulation.  

Is this conclusion correct? You can use single pole devices to isolate circuits or equipment if the neutral is earthed and does not need to be disconnected, as regulation 537.2.6 says. Regulation 461.2 says that you do not need to disconnect the neutral or PEN conductor if the supply conditions make sure that the neutral conductor is reliably at earth potential. This means that the neutral is connected to the earth at the supply source, and it cannot become live because of a fault or other reason. What conditions are required to decide that there is no possibility of the neutral becoming live ?