>Connecting the new wiring so that it becomes part of the existing ring will increase the overall resistance of that ring. The extra load on the new wiring will then be farther along the ring than if it were joined figure-8.
In the U.S.A. we wouldn't see that as a good thing.
>At this loading the short leg of the ring would be carrying 22.5A
My question was whether a figure-8 was allowed for an extension. If the ring is overloaded at any point, it is overloaded regardless of how the loads are attached.
What I see from this is that a ring really doesn't buy you double the ampacity except for a load at a point that is equidistant from both ends of the ring.
> it's considered far more likely that two heavy loads (e.g. 3kW each) could be connected simultaneously.
What is considered does not alter reality.
>As far as the old ring is concerned, this is equivalent to two 3kW loads at the same outlet at that 12-ft. point, which we've already seen is borderline at best.
The fact continues to be that heavier wire should be used or there should be complete separation.
>I'll admit that a similar situation could arise with a "legal" system.
My point exactly. There is really no new hazard with a figure-8 that wouldn't exist in a larger single ring.
>Do you agree that the proportions are correct when starting with cold cables?
Sure. I'd even agree that they might be worse than you state.
>Does anyone have a temperature coefficient formula for Cu conductors to calculate this?
Sure. But that is a side issue. Nothing will eliminate the overload except sifficiently sized conductors.
>what I meant was that if one heavy (3kW) load has to be connected close to one end, a second similar load would be better on the opposite side of the ring rather than very close to the first.
My point being that the ring is assumed to withstand this. So it should also withstand the load at one end being on while the load at the other end is off. As far as current goes, that's the same as adding a sub-ring close to one end.
>I hope I've shown that an overload is theoretically possible with a "legal" system.
Yes.
[*] What you've shown me is that a ring topology has no safety advantage over a linear topology or the American star topology.
[*] U.K. ring systems may be operating way over conductor ampacity just because of incorrect assumptions about the load distribution; whereas the NEC protects ungrounded conductors based on their so-called actual ampacity.
[*] The system is premised on the idea that more resistance is better. I have never thought of balancing electrical loads by increasing the length of the path back to the source (RF loads are a different story).
Even if I had learned nothing else, your discussion with me got me thinking outside the old box.
Thank you!
[This message has been edited by Dspark (edited 09-29-2001).]
