Help Me With This Voltage Conundrum, Please!

11 Jan 2004
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United Kingdom
Hi guys n gals

Called to a no power today.

LE= 246V

LN= 208V


The LN reading was taken with all earthing conductors in situ.

When UU came along, he disconnected the earthing conductors from the cutout (TN-S) and promptly got 400V.

I read it with my Alphatek at 417V.

The problem is an open neutral, that I'd worked out, and the live appearing at the neutral terminal was feeding back through another phase, so effectively at this property, the live was on the blue phase and the neutral was on the white.

What I fail to see (maybe I'm just dog-tired!) is why the NL reading was 208V with the earthing conductors attached to the cutout and 417V with them disconnected?
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Second readig taken with main switch opened whereas the first wasn't?
No surge arrester in sight.

Nice idea Adam, I did think of that, but when I took my readings, the CU lids were off, with all (plug-in) MCB's removed and the iso's off... :cry:
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The Neutral was not connected by metal conductor to the supply star point so was floating and pulled to a phase ( foreign phase )in another house whose neutral was connected to "your" neutral. But there was also a high resistance connection from your neutral via earth cabling and various earthing routes to the star point which would reduce the effect of the foreign phase on the neutral. As soon as the earth cables were disconnected then the neutral was completely disconnected from star point and would have gone to the same voltage as the foriegn phase.
How refreshing to see some genuine trade talk on the DIY Electrics forum.
I'm glad it is trade talk, as I had no idea what you were on about!

I like to read about other trades, which is why I am here.

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