Rather Low R1+R2 Query

junksamiad · Feb 24, 2019

Quick query I’m hoping someone can clear up. Im just looking at an example of a schedule of test results in a book I’m studying and I’ve come across an example I don’t understand. A lighting circuit protected by a 6amp 60898 Type C (Ref Method 100) using 1.5/1.0 T&E is measuring out R1+R2 at 0.12. The circuit is approx 38 metres in length.

Working off the calculation that the R1+R2 should be around 30.20 ohms x 38 / 1000 = 1.14. I can’t understand how they have reached this figure. There may be a shaver socket on the circuit as it mentions one of the circuits does have a shaver socket (but it doesn’t specify which), but I don’t know if that would impact anything? It could just be the test reading has been mis-typed but it would be great to get to the bottom of it by learning something new. Just wondering if it’s anything obvious to the vast sea of experienced helpful heads out there.

Thanks again.

Pete999 · Feb 24, 2019

Not Ohms micro Ohms

telectrix · Feb 24, 2019

i'd say it was a missprint- dec. place 1 to the left. should read 1.2 ohms.

SparkyChick · Feb 24, 2019

What is the book and in what context are you studying it?

I believe R1+R2 for a 1.5/1.0 cable is 0.03 ohms per metre which would make it 1.14. This suggests it is a typo in the book.

telectrix · Feb 24, 2019

SparkyChick said:
What is the book and in what context are you studying it?

I believe R1+R2 for a 1.5/1.0 cable is 0.03 ohms per metre which would make it 1.14. This suggests it is a typo in the book.

1.14 @ 20 deg. C, so probably 1.2 @operating temperature. typo.

Pete999 · Feb 24, 2019

telectrix said:
i'd say it was a missprint- dec. place 1 to the left. should read 1.2 ohms.

just done a quick calc and get 1.14 approx, so you coyld well be right.

telectrix · Feb 24, 2019

Pete999 said:
Not Ohms ~~micro~~ milli Ohms

corrected that 4 u. red wine glasses???

.

Pete999 · Feb 24, 2019

telectrix said:
corrected that 4 u. red wine glasses???.

Yeah OK cheers mili, micro, Mega

Pete999 · Feb 24, 2019

telectrix said:
corrected that 4 u. red wine glasses???.

Not at this time of the day TEL, could be the after effects of last night though, but yeah you are correct should have checked my answer.

junksamiad · Feb 24, 2019

Geez, thanks guys, good to get your advice. The book is Practical Guide to Inspection, Testing & Certification of Electrical Installations (18th ed.) by Christopher Kitcher.

These books can cause more questions than give answers when they contain errors like that. It's a bit annoying sometimes for someone trying to learn. Thank god for forums like this.

[ElectriciansForums.net] Rather Low R1+R2 Query

Deleted member 26818 · Feb 24, 2019

Not sure I like that picture of the IR test on that TP&N board.
That RCBO is still energised and Neutral has not been linked to the phases.

TJ Anderson · Feb 24, 2019

Also goes onto show that the Zs is incorrect too. He has just added the 0.63 Zdb reading to the R1 + R2 therefore extending the error across too lol. Look at the relationship between Zdb, R1+R2 and Zs's. They never work quite like that when measured. Goes to show why you should always really take a Zs!! Maybe Chris Kitchener threw that in there to see if you'd notice......NOT haha. Anyway, we'll done OP, you are a sharper student than many that you noticed it. Good on you mate!!

Rather Low R1+R2 Query

junksamiad

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Pete999

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telectrix

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SparkyChick

telectrix

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Pete999

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telectrix

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Pete999

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Pete999

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junksamiad

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Deleted member 26818

TJ Anderson

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