Crossover in ring circuit

[KeenPensioner]

HI, as my profile says I'm not a sparky and know my limitations. I'm trying to learn (for the sake of it only as I'll never do it) what tests for "Ring Final Circuits" are. I understand how the Tests 1, 2 and 3 are done but in one of the videos I watched the presenter (John Ward) mentions a "crossover" see image and says that this "could lead the current being shared in an undesirable fashion. I don't understand that.

 

[HandySparks]

Actually not, in terms of imbalance, the reverse is true ...

Nice one. I'd spotted that, but couldn't be bothered to do a decent explanation.

 

[Ian1981]

Actually not, in terms of imbalance, the reverse is true (although you still need to watch the Ze at the furthest point)
To illustrate I'll start with spinlondon's excellent example:

Suppose we are worried about imbalance, so we shorten the two legs to the CU to 0.5m each.
The other two sockets would have different resistance on each leg at a ratio of 5:1.
A 20A load connected to the middle socket would see 10A on each leg.
A 20A load connected to either of the other two sockets would see 16.6A on the short leg and 3.3A on the long!

If you follow my suggestion and we make a loop of slack and extend the two legs to the CU to 2m each.
The other two sockets would have different resistance on each leg at a ratio of 3:2 i.e. 1.5:1.
A 20A load connected to the middle socket would see 10A on each leg.
A 20A load connected to either of the other two sockets would see 12A on the short leg and 8A on the long. Much better.

Hope this helps.

F#ck me you need to get out more !

 

[EbolaSideRoom]

And this is why I avoid installing RFCs....

 

[willy fixit]

And this is why I avoid installing RFCs....

Only in high load areas - kitchens and utility rooms!