Calculation

[martynb01132]

How do I work out the following question; When measuring the insulation resistance between live conductors of five existing circuits in the installation the following results were obtained.
185Mohms, 150Mohms, 20Mohms, 200Mohms, 2.5Mohms
State
a)the value of the installation resistance if these circuits were measured as a whole show calculations.
b)whether the value obtained in a)is acceptable
c)which further test would be required to complete the insulation resistance testing
d)the minimum acceptable value from BS 7671:2008
e)any observations to be made to the client following the test

 

[Risteard]

185Mohms, 150Mohms, 20Mohms, 200Mohms, 2.5Mohms

1/Rt = 1/R1 + 1/R2 + 1/R3 + 1/R4
1/Rt = 1/185 + 1/150 + 1/20 +1/200 + 1/2.5
1/Rt = 0.005 + 0.007 + 0.05 + 0.005 + 0.4
1/Rt = 0.467
Rt = 1/0.467
Rt = 2.14 Megohms

Value is acceptable.

 

[pushrod]

How do I work out the following question; When measuring the insulation resistance between live conductors of five existing circuits in the installation the following results were obtained.
185Mohms, 150Mohms, 20Mohms, 200Mohms, 2.5Mohms
State
a)the value of the installation resistance if these circuits were measured as a whole show calculations.
b)whether the value obtained in a)is acceptable
c)which further test would be required to complete the insulation resistance testing
d)the minimum acceptable value from BS 7671:2008
e)any observations to be made to the client following the test

c) IR test between live conductors and earth (cpc)
d) 1Mohm
e) the 2.5 value while acceptable is very low and would require further investigation if it is a new installation ; if it is an old installation it could be a sign that it is soon going to need rewiring.