2391 question multiple choice IR help to break down

[sid521]

During the construction of an installation, insulation resistance tests have been carried out between live conductors and earth on the individual circuits and the L to E results are shown below. What is the expected value of insulation resistance L to E when the whole installation is tested?




can someone explain how to break down this question?

thanks

 

[Risteard]

so with the 0.053 you then move that 2 decimal places?

No. Your answer is 1 over 0.053, so you need to calculate that.

 

[Avo Mk8]

so with the 0.053 you then move that 2 decimal places?

No. Sorry - missed the post above!

0.025 + 0.028 = 1/R
Or 0.053 = 1/R
Some basic maths here!
If 1/R = 0.053, how do you work out R? Use a calculator?
One way of explaining it - Multiply both sides of the equation by R gives 1 = 0.053R
So R = 1/0.053. That you can do on your calculator.
Or by long division, as if if anyone can remember how to do that!

 

[sid521]

No. Sorry - missed the post above!

0.025 + 0.028 = 1/R
Or 0.053 = 1/R
Some basic maths here!
If 1/R = 0.053, how do you work out R? Use a calculator?
One way of explaining it - Multiply both sides of the equation by R gives 1 = 0.053R
So R = 1/0.053. That you can do on your calculator.
Or by long division, as if if anyone can remember how to do that!

thanks

also do you know where i would find the maximum permissible residual operating current for rcd on a TT system . in the bs7671 or gn3 and where about ? thanks