Ring Mains or Ring Circuits

[tonyi]

Re: Ring Mains or Ring Circuits

Couldn't your wire A/B/C be a single unbroken continuous conductor? (albeit with a lot of installation effort, and bugged taps for the receptical in each box).

Imagine such a ring with only a single receptical near the geographic middle of the cable. mentally remove the breaker, cable, and receptical and stretch it out on the ground.

BREAKER========RECEPTICAL(w/bugged on pigtails)

In this minimalist case, the paralleling becomes more apparent.

 

[don_resqcapt19]

Re: Ring Mains or Ring Circuits

Tony,
In my first post in this thread, I implied that a ring circuit feeding a single outlet would have the conductors in parallel. As far as your comment about an unbroken wire, how is a single unbroken conductor conductors in parallel?
Don

 

[tonyi]

Re: Ring Mains or Ring Circuits

OK, cut the wire in the middle and attach under the receptical screws instead if you'd like as if they were a multi-wire terminal block. The electrical situation is the same. Or wire nut a light bulb in the middle. The conceptual validity of an implementation shouldn't depend on the mechanical details of connections. ex. the NEC doesn't care if a feeder/branch is continuous or spliced a hundred times.

If a notion can't hold up in the most simplistic degenerate case, then its flawed. This has been a basic component of debunking proposed scientific theorys going back to Newton - existence of a counter example.

 

[pierre]

Re: Ring Mains or Ring Circuits

In a technical sense, these ring circuits provide a parallel path. As far as the NEC description of a parrallel set of conductors, there are many reasons they would not fit the description, termination, lengths (if more than one receptacle/outlet), size of conductors (unless you are running 1/0 to the receptacles ).

I would love to see all the players here discuss this in the same room - that would be fun to see

Pierre

 

[c-h]

Re: Ring Mains or Ring Circuits

Nitpicking, I know, but the UK ring circuit requires 20A wire for the 32A circuit breaker. The current flow will almost always be unbalanced, which means that the current can exceed 16A in one leg. In addition there are requirements as to where you put the sockets to prevent the current in either leg to exceed 20A.

 

[roger]

Re: Ring Mains or Ring Circuits

Tony,

Oh, I see now - they really overload the heck out of it

in what way does overloading come in to play?


Draw the circuit in a 360 degree ring, install three loads (attach a value) say at 90, 180, and 270 deg, now look at current travel on the conductors. You can reach overcurrent at the breaker, but any one portion of the ring would not see enough loading to damage insulation in a normal overload. I'm not talking about a shorted fault between conductors.

Now, as Don has pointed out, with more than one load in the circuit and the fact that the current will take two individual paths back to source, I wouldn't say the current is traveling in parallel with each other.

Roger

 

[brian john]

Re: Ring Mains or Ring Circuits

My two cents:

I think of this ring circuit as a parallel circuit, no matter how many outlets are installed. Think of parallel feeders feeding a trough with multiple FSS’s, same as the multiple outlets, that the conductors are not run side by side seem’s irrelevant to me.

I saw a job where the electrician ran 3 sets of 750kcmil in the deck t5hen realized there were suppose to be 4 sets. He ran the fourth set overhead. I made my recommendations and submitted a number for their budget, never heard back from that customer.

In the houses I’ve been in England the utilization outlets were switched and all the plugs had fuses.
But I’ve only been in a few English homes., so I can’t say the switching is a standard.

 

[don_resqcapt19]

Re: Ring Mains or Ring Circuits

Brian,
What is a "FSS"?
Don

 

[karl riley]

Re: Ring Mains or Ring Circuits

Pierre, if you re-read my last post: the 310.4 defines paralleled as connected on both ends. The restrictions on allowed parallel circuits that you cite are not a definition of paralleled, only a description of the only permitted way to parallel (which would not include #14 conductors in any case).

Don, at least we got to the point of disagreement: whether "paralleled" refers only to physically unbroken conductors or includes runs that are pigtailed. I agree with the poster who argues that electrically continuous trumps physically continuous.

But at least we got to the point of disagreement. Will Mr. NEC now please step in and settle it? (Where does Mr. NEC live, anyway?)

Karl

 

[tonyi]

Re: Ring Mains or Ring Circuits

Originally posted by roger:
in what way does overloading come in to play?

The high resistance/break scenario. The way we size OCPD and wire here, the wire will never be in a position to burn no matter what reconfigurations may happen in the future.

 

[tonyi]

Re: Ring Mains or Ring Circuits

Here's my take on multiple recepticals - with nothing plugged in, they're electrically just another splicing technique (essentially invisible electrically in a branch/feeder as far as the NEC is concerned), like a bug, wire nut, etc. The fact that something could be plugged into them doesn't alter this aspect of their nature. Once something is plugged in they take on another aspect - that of a tap.

So saying multiple recepticals somehow alters this scheme DEPENDS on loads being plugged in to cause imbalances so some receptical somewhere near the gegraphic center doesn't see equal paralleled currents. A dicy proposition at best to depend on loads being plugged in.

 

[roger]

Re: Ring Mains or Ring Circuits

Tony, I never used the word receptacle, where did that come from?


Now, the other part

The high resistance/break scenario. The way we size OCPD and wire here, the wire will never be in a position to burn no matter what reconfigurations may happen in the future.

if you go back and read my earlier posts, we would protect the ring at the conductors
listed ampacity.

Doing this would allow the conductor to operate cooler at any point in the circuit, even if loaded heavier at one end of the ring.

What is "electrically" connected and how is it different than mechanically or physically connected? We aren't talking about magnetic coupling.

(edited for punctuation.)


Roger

[ November 28, 2003, 03:49 AM: Message edited by: roger ]

 

[pagano21]

Re: Ring Mains or Ring Circuits

I do not really see a purpose for this circut. It reminds me of a class A fire alarm circut. If the circut is broken it will still operate but will give a trouble and it is for life saftey. I would not want this in my house. If there is a break in the circut I want to know about it. I will keep the good old 120v! It also seems this would be a parralel circut but by code the wire would be to small.

 

[hurk27]

Re: Ring Mains or Ring Circuits

Pagano21

I do not really see a purpose for this circut.

Power company's use it all the time. The primary lines that run down your street are wired like this and have been for a long time. They use it for two resones.
1. for redundancy
2. for stableization of voltage drop

 

[brian john]

Re: Ring Mains or Ring Circuits

Fused Safety Switch

 

[Guest]

Re: Ring Mains or Ring Circuits

Stabilization of voltage drop is what I was getting at when I compared the ring circuit to a forced air heating plenum. Ohm's law (and Kirchoff's Laws) won't let the amperage of one "leg" get too far from the other leg. Yes, there will be slight variations, but it will only depend on the delta of the voltage drop of each "leg".

One implementation I can think of is putting low-voltage lighting in the landscaping around the perimeter of an odd shaped swimming pool with various sizes of low-voltage lighting.

Let's assume you want to put all the low-voltage lighting on one circuit (one 12-volt transformer). Since it's 12-volts there's more voltage drop. The drop is also dependent on amps. The distance to the furthest fixture is significant. You could make a T at the transformer and go clockwise around the pool with one conductor until you get to the middle at which point you would dead end it. The fixtures on the clockwise conductor would tap off of that dead-ended conductor. You could run another conductor in a counter-clock-wise direction around the pool, and dead-end this conductor about where the other conductor ends. Then you start tapping various lights off this conductor. Because of the length of the wire, and the unequal load the voltage drop would vary on each conductor. This would impact the brightness of the lights to a degree.

You could balance things a bit by making it a ring circuit instead of dead-ending the conductors. That way the voltage drop would stabilize on the ring. You wouldn't have to apportion the conductor, nor would you have to balance the loads. It would be self-balancing.

That's the only advantage I see to a ring circuit. I don't believe a ring circuit should be used to increase (double) the amperage of the circuit. That's a recipe for failure.

 

[tonyi]

Re: Ring Mains or Ring Circuits

Originally posted by roger:
if you go back and read my earlier posts, we would protect the ring at the conductors
listed ampacity.

This is apparently not how the Brits do it though.

If the conductors are fully protected then I think this would be as "safe" as anything else even though I believe it to be paralleling. In this case, the paralleling would be essentially harmless since each conductor is capable of handling full load independently.

 

[c-h]

Re: Ring Mains or Ring Circuits

Yup, there is just a single 32A breaker. Harmless parallelling would require fusing of the grounded conductors, i.e. a four pole breaker. (Hint: What happens if you loose the grounded conductor on one side only?)

Several posters have pointed out the usefulness when it comes to limit voltage drop. If you run cables outdoors, like the utilities, distances are much longer than indoors and voltage drop becomes the big problem. 300' is a very long hallway, but it's a very short street If you need to pick up a lot of loads along the way, a ring sized for voltage drop is a good thing. And it reduces the risk of a loose neutral.