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Topic Title: Ze testing on a sub-main db
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Created On: 13 May 2016 04:30 PM
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 13 May 2016 04:30 PM
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jphughes

Posts: 6
Joined: 11 May 2016

Hi, hopefully someone on here can clear this up for me:
When carrying out a PIR on a sub-main board, do you regard the Ze value as external to that board and carry out the test there with main switch off and main earth disconnected, then simply add this figure to your R1+R2 values to get Zs? Or, must you obtain the Ze value at the main board, then carry out a Zs test at the sub-main (Zdb) and add this to your R1+R2 values?
Assuming it's the latter, would you record the Zdb value on the schedule of test results and the Ze 'at the origin' on the 'supply characteristics and earthing arrangements' form?

JP
 13 May 2016 06:19 PM
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RB1981

Posts: 484
Joined: 16 September 2007

The Ze is external to the installation, so the installation will only have one Ze figure. (This is tested with the Earthing Conductor disconnected (or all Main Protective Bonding Conductors disconnected).)

At the distribution board it will be a Zs, and should not be tested with the cpc of the distribution circuit disconnected. Likewise all bonding conductors must be connected.

-------------------------
Walsh Electrical Services
http://www.walshelectrical.ie/
RECI REC & NICEIC Approved Contractor
 13 May 2016 06:23 PM
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mantutu

Posts: 123
Joined: 16 June 2013

The Ze will always be the external measurement and will be tested at origin with the bonding removed.
The distribution board will be tested as Zs (Zdb) with bonding in place. The best way to complete a certificate is to use column 1 as the distribution cable in preference to final distribution circuit.
The certificate software that I use allows me to add details for each board in turn. I am not sure why you would want to add together R1+R2 and Zs or Ze? Unless you are checking for a ball park figure for measurement.
 13 May 2016 08:19 PM
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jphughes

Posts: 6
Joined: 11 May 2016

Thanks for the advice. Like the sound of that- supply to sub-main on first line of schedule.
I am workin on a site where we have to keep the live testing to an absolute minimum, hence R1+R2 testing to calculate Zs.
Cheers??
 13 May 2016 08:21 PM
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jphughes

Posts: 6
Joined: 11 May 2016

That was a thumbs up btw!
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