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Leesparkykent
I’m not sure why you would need the discussion with your area engineer? What value would you record on the schedule if it was TT....The max Zs value of the OCPD or the max Zs permitted for the RCD that’s providing the earth fault protection? It’s clear to me what you should be doing.
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Nigel
I do not need to speak to my NICEIC Engineer. I understand what is required.
How else would you meet disconnection times if the Zs is too high?
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Dan007
Is there an excerpt from BS7671 that details this (Use of max RCD values) over the Max Zs of the OCPD when considering Zs values that exceed the 80% factor?
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Nigel
To be honest the use of an RCD to cover fault protection on a TN system is not ‘textbook’. But sometimes you need to think outside the box. There are otherways to combat this issue, which is only an issue due yo poor design but it is completly unrealistic to rewire a circuit due to high measured Zs when an RCD will provide protection and still meet 7671.
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Dan007
Absolutely! Couldnt agree more. But is there an excerpt for stating one value over the other? Or is this just an understanding you have with your engineer. I'll definitely raise this with mine tomorrow if thats what you guys/girls are doing and its deemed acceptable.
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Nigel
I don’t run anything by my engineer.
You used the value of whatever the OCPD is that you are using.
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Why the disagree Essex.
My inspector didn't insist upon 100%. Fact!
Unless your not disagreeing with what I said, but with my inspector not insisting on 100%??
My inspector didn't insist upon 100%. Fact!
Unless your not disagreeing with what I said, but with my inspector not insisting on 100%??
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Nigel
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- SparkyChick
What the foot note on the model form says is...
"Where the maximum permitted earth fault loop impedance value stated in column 8 is taken from a source other than the tabulated values given in chapter 41 of this standard, state the source of the data in the appropriate cell for the circuit in the 'Remarks' column (column 25) of the schedule"
So it doesn't state you must record the 100% value, only that if it isn't from BS 7671 that you state where you got it from.
"Where the maximum permitted earth fault loop impedance value stated in column 8 is taken from a source other than the tabulated values given in chapter 41 of this standard, state the source of the data in the appropriate cell for the circuit in the 'Remarks' column (column 25) of the schedule"
So it doesn't state you must record the 100% value, only that if it isn't from BS 7671 that you state where you got it from.
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Nigel
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Yeah, but I've just looked and I can't find anything in the regs that stipulates you record the 100% value. Just that footnote which stipulates if it's not from BS 7671 you state where it is from.
If you multiply a value from the tables by 80%, the source of the value is still the standard.
I said earlier I record 80%... I do because it's the default in NAPIT Desktop which I use for doing EICs and EICRs, you can change it, but the cert then includes markup to show whether it's the 100% value or the 80% value.
It's how I was taught when I did C+G 2932, 2394 and 2395 a couple of years ago.
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Nigel
S
Strima
Get me some more funny post notifications?
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Silly Sausage
- Mar 21, 2011
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Well the little chart I chopped up & used for the 80% figures, now excludes the preamble I previously mentioned, but it does mention App 14. Which I've just read, and haven't the scooby what its on about.
But I guess its you can do some maths, or just use the table.
But I guess its you can do some maths, or just use the table.
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Ian1981
Well if you consider the formula for compliance is zs x Ia < Uo x cmin we must have to use the maximum zs value for that OCPD given in appendix 3 ie for a 32 amp type B 1.37 ohms
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Anyways, just as an aside, been called across to my vacant house up for sale. Neighbour has just had a small fire, FB in attendance. Water everywhere. Laptop in upstairs bedroom appears to be the culprit.
Too high Zs values, or dodgy lithium batteries?
Too high Zs values, or dodgy lithium batteries?
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