Unbalanced final ring

[Steve-S]

I have seen a final ring that had the heavy appliances on one leg (L1). Drawing 19.5 amps in total, one leg (L1) was drawing 82% of the 19.5 amps of current. If the ring went up to 32 amps the 2.5mm cable would in theory be just safe enough under the 27 amp maximum.

My question is, if 32 amps worth of appliances were drawing current on L1 would the 82% be reduced as there would be more resistance on L1, so more current would be sent around L2, reducing the 82%?

I have not seen any tests on this. It would be interesting to see some.

 

[littlespark]

Is this a practical situation?

The general norm for 2.5mm rfc is a 32A OCPD, what is on the circuit just now?

If it’s 20A, I’d be worried it wasn’t an ring at all




For your question though….. if you’re pulling the full load of 32A, is the ratio of what percentage of the load goes back on which leg different?

That would be down to how far each leg is from the board, not the load or cable size.

A high load (say 32A) midpoint on a ring, you would expect it to be 50/50 (16 on each leg)
The closer to the board on one leg the further from the other…. But even if your load was only 1m from the board, some of that load would still return on the longer side of the ring. It would never be 100% one way.

The 82% you measured is relative to your particular installation, with its particular lengths of cable.
That percentage will increase as the load moves away from the board, and increase as it gets nearer.

 

[PS Electrics]

I have seen a final ring that had the heavy appliances on one leg (L1). Drawing 19.5 amps in total, one leg (L1) was drawing 82% of the 19.5 amps of current. If the ring went up to 32 amps the 2.5mm cable would in theory be just safe enough under the 27 amp maximum.

My question is, if 32 amps worth of appliances were drawing current on L1 would the 82% be reduced as there would be more resistance on L1, so more current would be sent around L2, reducing the 82%?

In theory yes because resistance is dependant on cable temperature and cable temperature is effected by load current.

I have not seen any tests on this. It would be interesting to see some.

There are calculations for this that would be interesting I guess to play around with.

I would imagine the effect would be very tiny though to be of no practical use.