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Neutral Isolation. A Safety Necessity or a Practical Nightmare?

AMK

How should regulation 537.2.1.7 be interpreted and applied? This regulation, which I believe has been deleted but is still being followed by some, requires the neutral to be isolated with a linked switch or removable link when carrying out isolation. However, this can cause a lot of trouble and inconvenience, especially for 24/7 departments that need continuous power. The Lead Engineer argues that both supplies, essential and non-essential, need to be isolated to work on the Essential Line side isolator, where the neutral is linked between the line and load. But is this really necessary? Regulation 531.2.2 allows the neutral to remain connected if it can be reliably assumed to be at earth potential. Can this be verified prior to work commencing by a simple calculation of Un-E = neutral current x Zn (TN-S) or a voltage test between neutral and earth? Some suggest that these methods are sufficient and practical, and that isolating the neutral is unnecessary and impractical. Others assert that these methods are not reliable and safe, and that isolating the neutral is essential for safety reasons, even in a well balanced 3 phase system having minimal neutral current and a low Zn. What is your view?

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  • 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/.../

  • in reply to Sparkingchip

    That NZ article is remarkable, and I take away two things,

    firstly that a system of registered electricians is no guarantee of intelligent thought,

    and secondly  that

    While it makes a song and dance about inaccurate test results, clearly no test at all was done really as even a £5 plug in socket checker  would have made it obvious there was a problem.

    Part of me also wonders if there was no RCD in circuit, or if there was but it failed to operate.

    Mercifully both here and there, such events are rare enough to make the news, which I suppose is something.

    Mike.

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  • in reply to Sparkingchip

    That NZ article is remarkable, and I take away two things,

    firstly that a system of registered electricians is no guarantee of intelligent thought,

    and secondly  that

    While it makes a song and dance about inaccurate test results, clearly no test at all was done really as even a £5 plug in socket checker  would have made it obvious there was a problem.

    Part of me also wonders if there was no RCD in circuit, or if there was but it failed to operate.

    Mercifully both here and there, such events are rare enough to make the news, which I suppose is something.

    Mike.

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