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Topic Title: Flawed safe insolation procedure
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Created On: 12 July 2013 10:01 PM
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 12 July 2013 10:01 PM
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DR2366

Posts: 705
Joined: 09 April 2006

Had my niceic assessment. Part of our discussions was when proving safe isolation on a single phase installation you test live to neutral, live to earth and neutral to earth for voltage. Another test to perform is to test across the incoming phase to the load side neutral as the other tests don't check that the neutral conductor has been isolated by the main switch.

The last check seems to make sence but its not in the standard safe isolation procedure prompts.

Edited: 12 July 2013 at 10:21 PM by DR2366
 12 July 2013 10:14 PM
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leckie

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This is the way to test for any electricity being present.

http://s1361.photobucket.com/u..._zps8abdb732.jpg.html

It is just so simple!
 13 July 2013 10:22 AM
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perspicacious

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"Another test to perform is to test across the incoming phase to the load side neutral"

What happens when there is an existing load side fault between neutral and earth?

Regards

BOD
 13 July 2013 05:34 PM
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slittle

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Or an installation with a earth that has been pulled up.....

We've been here before with our own ways of doing it, but I don't see a lot of benefit in incoming L, outgoing N for the reasons BOD has already covered.

Out of interest what did Mr NICEIC want you to use to test with ?


Stu
 14 July 2013 09:11 AM
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DR2366

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I was using a drumond tester this time.

The case used to justify is that neutral is a live conductor and therefore needs to be isolated. Testing for the absence of voltage dosen't prove its isolation by the main switch.

He had come across a single phase installation were the DP main switch had been operated but failed to disconnect the neutral.

It all sounded very plausable at the time but I did point out that in a three phase installation the neutral isn't normally isolated via the main switch but does have a removeable link to facilitate testing. Why not 4 pole isolation if it's important. Answer was the type of users in a domestic house and a single phase board would be unskilled hence DP isolation.

I struggled to think of a down side of this additional check at the time.
 14 July 2013 10:14 AM
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sparkingchip

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Picking up on Stu's comment, if you use a combined voltage and continuity tester it will not show voltage it will show continuity if both the live and neutral have the same voltage on them, whilst your test lamp won't light up at all.

Cue, the man with a long screwdriver!

Andy
 14 July 2013 02:33 PM
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DR2366

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You could just use one of those to check continuity across the main switch N - N and L - L but thats not in the standard safe isolation procedure either.
 14 July 2013 09:56 PM
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leckie

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Go to my link and use that procedure. It works every time. It's called "Old School Testing".
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