Insulation Resistance Calculation

[Ben Murray]

Hi, I have an engineer who is completing his 2391-52 exam tonight and he has been told one of his mock questions was wrong, I have completed the working out myself and came up with the same answer as him, so either the paper is wrong or something has literally left my mind!!

"Determine the overall insulation resistance where the individual readings for four circuits are: 200M ohms, 100M ohms, 50M ohms & 20M ohms"

1/RT = 1/R1 +..... you get the picture.

1/200 = 0.005
1/100 = 0.01
1/50 = 0.02
1/20 = 0.05
Total = 0.085
1/0.085 = 11.76470588235294 (11.76 rounded)

The 4 multiple choice options are:
a) 1.68M ohms
b) 16.8M ohms
c) 16.8 ohms
d) 168 ohms

Please re-educate me and tell me where I am going wrong!

 

[Andy78]

I just checked on the C&G website, there is only one mock test for 2391-52, and question 12 is not this (anyone can access these)

Are you sure it's not a centre's version, or from spxxxxfaxxxts website, these are generally wrong, - questions from earlier editions which are no longer applicable to downright wrong!

totally agree. Been on that website and their mocks are full of errors. I did an 18th mock that had a 16th edition relevant question in it.

 

[Sparky jim]

Hi, I have an engineer who is completing his 2391-52 exam tonight and he has been told one of his mock questions was wrong, I have completed the working out myself and came up with the same answer as him, so either the paper is wrong or something has literally left my mind!!

"Determine the overall insulation resistance where the individual readings for four circuits are: 200M ohms, 100M ohms, 50M ohms & 20M ohms"

1/RT = 1/R1 +..... you get the picture.

1/200 = 0.005
1/100 = 0.01
1/50 = 0.02
1/20 = 0.05
Total = 0.085
1/0.085 = 11.76470588235294 (11.76 rounded)

The 4 multiple choice options are:
a) 1.68M ohms
b) 16.8M ohms
c) 16.8 ohms
d) 168 ohms

Please re-educate me and tell me where I am going wrong!

 

[Sparky jim]

Hi, I have an engineer who is completing his 2391-52 exam tonight and he has been told one of his mock questions was wrong, I have completed the working out myself and came up with the same answer as him, so either the paper is wrong or something has literally left my mind!!

"Determine the overall insulation resistance where the individual readings for four circuits are: 200M ohms, 100M ohms, 50M ohms & 20M ohms"

1/RT = 1/R1 +..... you get the picture.

1/200 = 0.005
1/100 = 0.01
1/50 = 0.02
1/20 = 0.05
Total = 0.085
1/0.085 = 11.76470588235294 (11.76 rounded)

The 4 multiple choice options are:
a) 1.68M ohms
b) 16.8M ohms
c) 16.8 ohms
d) 168 ohms

Please re-educate me and tell me where I am going wrong!

 

[Sparky jim]

hi ben you said earlier you had someone completing his 2391-52 .
can please ask how he got on and did he discuss the course and how it was laid out.
i ask because i to will be doing this course of inspection and testing .
ben i would be so grateful if you had any information oh and yes i feel this question is wrong too
yours sparky jim

 

[Ben Murray]

hi ben you said earlier you had someone completing his 2391-52 .
can please ask how he got on and did he discuss the course and how it was laid out.
i ask because i to will be doing this course of inspection and testing .
ben i would be so grateful if you had any information oh and yes i feel this question is wrong too
yours sparky jim

Hi Sparky Jim,

This thread was 4 years ago unfortunately, I would only muddying the waters if I were to offer the course lay out, I did mine in 2017 and the engineer in question on this thread no longer works for us.

Sorry about that, but I do wish you all the luck, hopefully you will smash it