Discuss Me again in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

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nicsin02

Regular EF Member
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hi guys a few questions again, was out testing at a biscuit factory today its a massive property with around 60 D/B and we will be doing 20% over the next few months.

1. was at the d/b and tested the Zdb using a meggar, for brown & grey phase it was <0.01 and for grey phase it was 0.01 i know u want your earth to be as low as possible but never had this result before?

2. when doing my pefc and pscc i was getting between 18.4 and >19.9 anybody had this before

3. is it still ok to subtract Zdb from Zs to get (R1+R2) because its not the actuall Ze, think it is just reasurring myself

thanks guys :)
 
G

Guest55

hi guys a few questions again, was out testing at a biscuit factory today its a massive property with around 60 D/B and we will be doing 20% over the next few months.

1. was at the d/b and tested the Zdb using a meggar, for brown & grey phase it was <0.01 and for grey phase it was 0.01 i know u want your earth to be as low as possible but never had this result before? the factory may have its own transformer on site so Ze / Zdb can be super low.

2. when doing my pefc and pscc i was getting between 18.4 and >19.9 anybody had this before
yes , a few times.


3. is it still ok to subtract Zdb from Zs to get (R1+R2) because its not the actuall Ze, think it is just reasurring myself
its preferable to measure r1+r2 as it forms part of your polarity checks but can be calculated instead due to operational limitations in the testing process.
yes you can use Zdb as the origin of the final circuits


thanks guys :)
.......................
 
G

Guest123

You can not and should not transpose the Zs=Ze+(R1+R2) to obtain an R1+R2 value as a measured Zs will include parallel paths which will result in an inaccurate value of R1+R2.

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nicsin02

Regular EF Member
Messages
127
You can not and should not transpose the Zs=Ze+(R1+R2) to obtain an R1+R2 value as a measured Zs will include parallel paths which will result in an inaccurate value of R1+R2.

Sent from my HTC Desire C using Tapatalk 2

ive always been told it was ok to do so, even on thursday the SELECT inspector said that was they way he did it?
 

Brightspark2

Regular EF Member
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1,978
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The loop was probably that low because it was so near the transformer.

Was the main board not in the same building as the transformer?...obviously seperated by a wall etc.

The PSFC will be high because of the low Ze...

As long as its written on the cert but your better calculating your Zs rather than your R1+R2 and so measuring the R1+R2...
 

plugsandsparks

Electrician's Arms
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super low Ze/Zdb is normal in industrial sites where they have an 11KV feed from distributor and local produce 400V, PSC will be off the scale on alot of testers, but you can work it out. Important thing is to make sure that the breakers can handle maximum PSC, so i would expect to see much larger breakers with 25K+ breaking capacity. Its not un-common to find a local board with just regular 10K breakers in and a super low Zdb.
 
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