Ring Final Circuit testing, What is wrong. Trainees only to answer please.

[SirKit Breaker]

You have been asked to carry out a full test on a ring final circuit. It is wired in 2.5mm single core cables. (I have made the test result values up to make things easier to work out).

You have confirmed that the ring is continuous, and your r1 value is 0.5 ohm, your rn is 0.5 ohm and your r2 is 0.5 ohm, and these readings were the expected readings for the length of the circuit. So you have established that the ring is continuous, there are no interconnections, and there are no spurs.

You are expecting your R1+R2 value to be a quarter of the r1+r2 value, so 1ohm/4 = 0.25 ohm, however when you test at all the socket outlets, you get a reading of 0.125 ohm, what have you done wrong?

Answer over the weekend.

GN3 will help you, and if you are reasonable at maths, then it should also be easy "ish" to work out.

Cheers...............Howard

 

[telectrix]

howard, i think you missed a zero or added a couple.

 

[SirKit Breaker]

howard, i think you missed a zero or added a couple.

Cheers Mate, I've edited it....

 

[Paul.M]

I'm guessing the CPC is the same CSA as the Line conductors

 

[telectrix]

usually is with singles, paul.

 

[Paul.M]

usually is with singles, paul.

Do the trainees know that off the top of their head???? Just thought I would mention it Tel.

Also, if this was a RFC for computers it would have a 4mm cpc.

 

[telectrix]

Do the trainees know that off the top of their head???? Just thought I would mention it Tel.

Also, if this was a RFC for computers it would have a 4mm cpc.

OK paul, give you that. why 4mm? as it'sa RFC , 2.5mm with hi integrity earthing is adequate, IMO.

 

[Paul.M]

The "powers that be" now demand a 4mm earth for all socket circuits designated for computers in schools etc, even if you run a RFC in 2.5mm T&E you still have to run a single 4mm for "earth leakage"!!!! Two lots of dead tests to carry out due to parallel return paths lol. The council Clerk of Electrical Works is a right :censored:

 

[dazza1981]

The "powers that be" now demand a 4mm earth for all socket circuits designated for computers in schools etc, even if you run a RFC in 2.5mm T&E you still have to run a single 4mm for "earth leakage"!!!! Two lots of dead tests to carry out due to parallel return paths lol. The council Clerk of Electrical Works is a right :censored:

I did not know this.......every day is a learning day Paul

 

[telectrix]

if t's not in BS7671, then the "powers that be" can shove their 4mm where it hurts.

 

[Paul.M]

It is in the regs, the Clerk hit us with it a couple of years ago but I cant remember the number or section it is in. I'll have a look later for it.

 

[northstar]

The "powers that be" now demand a 4mm earth for all socket circuits designated for computers in schools etc, even if you run a RFC in 2.5mm T&E you still have to run a single 4mm for "earth leakage"!!!! Two lots of dead tests to carry out due to parallel return paths lol. The council Clerk of Electrical Works is a right :censored:

Hi Paul.M where is the 4mm earth info from ? thanks

 

[Paul.M]

Hi Paul.M where is the 4mm earth info from ? thanks

I'll have a look for it later today when I get back from doing an EICR, just leaving home atm. (yes I know it is Saturday, only time I have to it. Been working 60-70 hours a week for the past 3 weeks and on the bank holiday, thats the reason why I hae not been posting up questions). Thanks Howard for this one, better then what I ask lol.

 

[Sintra]

Sorry but nowhere in the BGB does it does it state a 4mm cpc for high integrity socket outlets.

View attachment Reg_543.7.pdf

 

[telectrix]

think your man is confused with the reg. about a cpc being min. 4mm if not mechanically protected. nothing to do with PCs.