A ring main wiring circuit is the alternative to a radial wiring circuit. In a radial wiring circuit, the wiring starts at the circuit breaker and connects to each device on the circuit (fans, outlets, lamps, etc) in turn. When it reaches the last device, the wiring simply ends.

Ring main wiring goes one step further: instead of ending the wiring at the last device, it pulls more wiring back from the last device to the circuit breaker, completing a loop. Ring main wiring is required in some places, and illegal in others. Modern homes in the United Kingdom tend to have a ring main setup.

The main advantage to a ring main system is smaller wiring. Since each device on the ring has two hot wires connecting it to the circuit breaker (one on each side of the loop), smaller wiring can be used to safely carry the electric current. Smaller wire is both cheaper and easier to work with -- it bends more easily, can be pulled around corners with less effort, and is easier to fit into the screws and connectors you need to attach it to.

One other advantage is wiring distance. Wire has some small amount of resistance, and the longer the wire goes to reach the device it is powering, the more resistance it has. This results in a voltage drop over the length of the wire run (by Ohm's Law), which could affect the operation of your electrical devices if it drops too low. The maximum distance from the circuit breaker around the ring is the midpoint of the ring, while the maximum distance in a radial circuit is the end of the chain. In this manner, the ring setup effectively cuts the distance to the farthest device in half.

The radial system does have one advantage over ring main. If a break were to occur somewhere in the wiring loop of a ring main system, you wouldn't know it. Everything would still function normally because it is still powered from one end. However, this means that if you took advantage of the ability to run smaller wiring (and everyone does), your wire is now undersized for the current it is expected to handle because the system is no longer powered from two wires, only one. This can result in overheating of the wires, which in turn breaks down the insulation and can start a fire.

The concept of ring main also applies to demolitions. Or at least in military demolitions, which is the context in which I learned about it.

The ring main is also known as the 'trunk line', and the attached explosive charges are connected via what are called 'branch lines'. The thing is, most military explosives aren't sensitive. They have to be pretty stable so you can trasnport them without them going off. So they have to be sensitized by being linked somehow to sensitive explosives, mostly blasting caps. Blasting caps have to be taken pretty well care of, isolated from each other, and transported separately from explosives.

Both the trunk lines and branch lines are made out of detonation cord, or det cord. Det cord is just an explosive in cord form, with a layer of insulation. The difference between det cord and time fuse is that the whole cord will detonate pretty much instantaneously.

To set off the blasting cap, you need an ignition assembly. These are either electric or non-electric.

A typical electric ignition assembly connects a clacker, like the ones in movies that kind of look like staplers and they hit three times, often attached to claymore mines, to the blasting cap via some kind of electrical wire. The clacker simply turns the clacking motion into an electrical signal that sets off the blasting cap. Our XO explained to us that clackers suck because they're not that reliable and they make a lot of noise. Really, you can just as easily use pretty much any size battery, as long as the wire is good, because the blasting caps are pretty sensitive, both to concussion and to electrical signal.

A typical non-electric ignition assembly connects the blasting cap to some time fuse. Time fuse works pretty much how you'd imagine. You light it, it burns along its length at a more or less constant rate and when it reaches the end, it sets off the blasting cap. The longer the time fuse, obviously, the more time you have to get the hell away from your explosive.

Once you have an ignition assembly, you attach it somewhere onto the trunk line, and this sensitizes the whole thing, because the blasting cap will set off the det cord, which will set off the explosives.

The reason it's a good idea to use a ring main is for redundancy. If the the det cord somehow gets cut somewhere along the trunk line, the explosion will still traverse the entire trunkline from the opposite direction, and detonate all the explosive charges.

Log in or registerto write something here or to contact authors.