Rather Low R1+R2 Query

[junksamiad]

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]

Not Ohms micro Ohms

 

[telectrix]

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

 

[SparkyChick]

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]

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]

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]

Not Ohms micro milli Ohms

corrected that 4 u. red wine glasses???.

 

[Pete999]

corrected that 4 u. red wine glasses???.

Yeah OK cheers mili, micro, Mega

 

[Pete999]

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]

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.

 

[Deleted member 26818]

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]

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!!