Copper resistance question

[PeterPan27]

Doing this question now and the Zs works out as 0.94
And the permissible value is 1.09x0.8= 0.87

Says this is acceptable??
I thought it has to be equal or higher for it to be ok??

 

[mtfpuk2011]

no its has to below the correct value

 

[PeterPan27]

Yeh that's what I ment. Comes out as o.94 and permissible value is 0.87 so I would say this would not be acceptable.
The answer in the book says its ok lol

 

[ruston]

Has the question asked you to use correction factors or the rule of thumb , you only answer the question.

 

[PeterPan27]

Yes it's says "using the rule of thumb for temperature correction the maximum permissible value is 1.09 so 1.09x0.8=0.87
It's strange for book to be wrong

 

[ruston]

Yes it's says "using the rule of thumb for temperature correction the maximum permissible value is 1.09 so 1.09x0.8=0.87
It's strange for book to be wrong

Depend where you got the book lol. .Are they stating they have used the rule of thumb , or for you to use the rule of thumb in the context of the question

 

[mtfpuk2011]

you dobt corrextion facter if your using on site gide as they have all ready be corrected.

 

[PeterPan27]

Practical guide to inspection testing and certificating by Christopher kitcher......
This is there exact answer

"Zs will be 0.34+0.6=0.94 ohms
So Zs=0.94 ohms
The maximum Zs for a 30A Bs 3036 fuse from table 41.2 inBS 7671 is given at 1.09 ohms.
Using the rule of thumb for temperature correction the maximum permissible value is : 1.09 x 0.8 = 0.87 ohms
This value means the gained value is acceptable"

 

[iamelectric]

tip for u mate know your inspection schedule , there are a lot of inspection questions in it

 

[bartkusal]

I don't think there is an average pass mark. I believe the passmark i dependant on how hard C&G think the paper is and on how many people have answered the questions right. I sat 2391 a couple of times and I was told the pass mark was different each time. Having said that I think we need to get at least 70% but don't hold me to that! Good luck to us all!

Correct, it fluctuates between 60% and 80%.they must fail someone, depends from how good the people sitting the exam doing, if good % rises

 

[bartkusal]

Practical guide to inspection testing and certificating by Christopher kitcher......
This is there exact answer

"Zs will be 0.34+0.6=0.94 ohms
So Zs=0.94 ohms
The maximum Zs for a 30A Bs 3036 fuse from table 41.2 inBS 7671 is given at 1.09 ohms.
Using the rule of thumb for temperature correction the maximum permissible value is : 1.09 x 0.8 = 0.87 ohms
This value means the gained value is acceptable"

Ok, mistake in the book it is, then

 

[ruston]

Ok, mistake in the book it is, then

There is also a correction factor for 3036 fuses of 0.725 . need to see the book lol.

 

[bartkusal]

I no the 3 steps off by heart
Steps 1 identify the in going an outgoing
Then measure the line loop , neutral loop and cpc loop an record as r1 rn and r2. The line and N should b within 0.05 ohms of each other. The cpc be 1.67 greater .
Step 2 connect incoming line with outgoing neutral and vice versa. Then calculate the predicted reading I would expect to see at each socket using the formula r1 plus rn divide by 4
Step 3 then do same with line and cpc.. R1 plus r2 divide 4
Any higher reading means loose connections or spur off ring

While doing steps 2 and 3 take reading at every socket making sure within the 0.05 which each other..

Remember that that for other sizes this 1.67 value is different. it comes from L / CPC, in this instance you have 1.67, if you have 4mm / 2.5mm you get 1.6, if 6mm / 2.5mm you get 2.4. It is not like you will see any bigger rings then 2.5/1.5 bet you get my drift

 

[iamelectric]

i am not being funny or think i know it all but there wont be any calculations as hard as this in the test they are straight forward calculation just know your basics and when to apply corection factors they usually tell u its tested at 20oc so theres not temp correction factor

 

[ruston]

Thats the way it was in 2391 all the factors were in the question , you just had to know the equation and read the question twice lol.

 

[PeterPan27]

Yeh I know. To be honest I've only really had few days to revise so not expecting to pass just said I would have a go and never know and surly it will give me more insight I I did fail when doing the exam in August..

 

[PeterPan27]

Did a practice test today and only got 50percent haha

 

[bartkusal]

There is also a correction factor for 3036 fuses of 0.725 . need to see the book lol.

Not sure where you going to use this 0.725 factor at this stage, we all know what it is for and it is for calculating the cable size, but at this moment an from OP the cable size is given, so its too late to use it anywhere.

 

[ruston]

Not sure where you going to use this 0.725 factor at this stage, we all know what it is for and it is for calculating the cable size, but at this moment an from OP the cable size is given, so its too late to use it anywhere.

I wasn't going to , just wondered if it had been considered in the book he had.