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Wiring Matters Article and GN3

Steve Briggs

Good article by Graham Kenyon in the latest Wiring Matters.

Interestingly (to me) I wrote this same thing about four years ago to try and explain to our instructors why they do not see the promised variation at the sockets in Step 3, a supposition which has been around since the early days of the [proper] 2391.

The article suggests changes afoot to GN3 and I just wondered if anybody had yet proposed that Step 3 really ought to be the same as for a radial circuit, Method 1. The current method returns artificially high values of (R1 + R2) for any spurs not at the midpoint and misleads students into expecting near identical values of Zs at each point.

And while I'm on it, is there any chance that the numerous recurring oddities/errors/inconsistencies in GN3 might be addressed in the next edition, or will we just have to continue explaining them to trainees as we go along? Wink

Parents

  • Indeed, a nice clear article - though I suspect in a lot of cases in the field grotty old sockets and slightly tarnished leads also introduce similar random errors when trying to check if changes have been done correctly to an existing circuit, especially measuring a plug in test lead. The cross-over test will always find gross errors like an open CPC but may not find more subtle problems, like a short length of a different cable size or a short fig 8 loop - equally things that cannot be detected are also unlikely to be dangerous.

    Mike.

  • in reply to mapj1
    mapj1 said:
    though I suspect in a lot of cases in the field grotty old sockets and slightly tarnished leads also introduce similar random errors when trying to check if changes have been done correctly to an existing circuit, especially measuring a plug in test lead.

    Agreed ... but not something we'd expect too much of on initial verification, and on many installations, a measurement at the rear of the socket-outlet (if you are fault-finding), unless there's a lot of detritus and corrosion, gets over the issue of dirty switches and socket-outlet contacts.

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  • in reply to mapj1
    mapj1 said:
    though I suspect in a lot of cases in the field grotty old sockets and slightly tarnished leads also introduce similar random errors when trying to check if changes have been done correctly to an existing circuit, especially measuring a plug in test lead.

    Agreed ... but not something we'd expect too much of on initial verification, and on many installations, a measurement at the rear of the socket-outlet (if you are fault-finding), unless there's a lot of detritus and corrosion, gets over the issue of dirty switches and socket-outlet contacts.

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