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

[Simonslimline]

Do these low reading suggest that a ring inside a ring exists?

 

[happysteve]

I had a couple of ideas about this which I pm'ed, but I can't figure a way of getting 0.125 ohms at all sockets. 0.125 ohms at one socket (half way round the ring), yeah, but not at all of them. Or another scenario whereby the resistance varies between 0.1667 and 0.25 ohms as you go from one end to midpoint. But for the answer to the question... guess we'll just have to wait, but I don't mind saying I'm stumped!

 

[SirKit Breaker]

I had a couple of ideas about this which I pm'ed, but I can't figure a way of getting 0.125 ohms at all sockets. 0.125 ohms at one socket (half way round the ring), yeah, but not at all of them. Or another scenario whereby the resistance varies between 0.1667 and 0.25 ohms as you go from one end to midpoint. But for the answer to the question... guess we'll just have to wait, but I don't mind saying I'm stumped!

You are almost there.

When testing for R1+R2, the expected values at all sockets on the ring is r1+r2/4, so in this scenario you were expecting (0.5+0.5)/4 = 0.25 at every socket outlet. You obtained 0.125 because you had the incorrect ends of the circuit joined together, so only measured half of it because instead of having one continuous loop with all 4 conductors, you created 2 loops each with 2 conductors, hence half of the expected value.

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

 

[Silly Sausage]

You might want to re-think this Howard!

 

[happysteve]

If you connect the wrong ends together (ie L1 to E1 and L2 to E2 instead of L1 to E2 and L2 to E1) then the only place you will get 0.125 ohms is half way round the ring. Right next to the join, you will get zero ohms - think about it, you're just shorting L and E. This is explained nicely in GN3. What I couldn't work out is how you get 0.125 ohms at all sockets on the ring. You just can't!

 

[SirKit Breaker]

I will have a proper look and report back. I hope you are correct, it is nice to be put right from time to time if i have explained or got it wrong. It is on my tomorrows to do list.