check this pls

[NWDS]

Test on a 300m lenght of single core MIC produced the following results: conductor resistance 2.4 ohms, insulation resistance 40 Mohm. What will the anticipated conductor and insulation resistance values of a 120m lenght of cable.

I worked it out as follows,

300/2.4 = 125 ( 1/125 = 0.008 ) so 120*0.008 = 0.96

300/40 = 7.5 ( 1/7.5 = 0.1333 ) so 120*0.1333 = 15.996

the answers given are 0.96ohm & 16Mohm.

I have the right answer but have I used the right formula ??????

 

[Apache]

You've worked it out the long way around!

I'd have done 2.4 / (300/120) = 0.96 ohms

and 40 / (300/120) = 16M ohm

Just using the ratio! (you could simplify it by working out 300/120 = 2.5 if you want!)

 

[Andy™]

You've worked it out the long way around!I'd have done 2.4 / (300/120) = 0.96 ohms

and 40 / (300/120) = 16M ohm

Just using the ratio! (you could simplify it by working out 300/120 = 2.5 if you want!)

but IR increases when length decreases! so expected value would be

(300/120) X 40 = 100Mohms

 

[NWDS]

Iam going to burn this bloody book. headbangheadbang

NWDS

 

[Andy™]

Iam going to burn this bloody book. headbangheadbangNWDS

i think you need a better book!

which book do you have?

 

[NWDS]

Electrical Installation Calculations vol 1 7ed by A J Watkins & C Kitcher.

headbangheadbangheadbangheadbang

now Iam going to Guiness DrinkGuiness DrinkGuiness Drink

NWDS

 

[The Godfather]

Electrical Installation Calculations vol 1 7ed by A J Watkins & C Kitcher.NWDS

Looks like my boys need to pay a visit.

The Godfather

 

[Apache]

but IR increases when length decreases! so expected value would be (300/120) X 40 = 100Mohms

I did that first, saw the OP's answers so changed it! headbang

 

[Andy™]

I did that first, saw the OP's answers so changed it! headbang

One very important thing you learn from college....

...Dont expect the answer book to be correct!

 

[madeinengland]

the books i've got are BASIC ELECTRICAL INSTALLATION WORK by Trevor Linsley. and ADVANCED ELECTRICAL INSTALLATION WORK. amazon usually do a deal on buying both.but to be honest you'd only need the advanced one. i found during L3 a lot of the overheads that my numptee tutor would use were straight out of the advanced book.