Hello all. I was in my electrical class last night and we were covering a section on inspecting and testing.

When we got to ring circuits, it was explained to us that multiple loops, within a ring can be dangerous, in case of a fault.

What l do not understand is why. The tutor was a little unsure himself, though he was completely honest, which l respect him more for, than to give us a duff answer, which some tutors do.

This started a debate where several students who agreed that it was dangerous, with others saying that it wasn't.

My questions:

Let's assume for arguments sake that we are dealing with a single ring circuit, protected by a 32amp breaker, operating under normal conditions. Along comes joe bloggs the DIY enthusiast and adds a double socket, but instead of spurring it, he splits the ring into two.

What effect would making an existing ring into two rings have on the circuit?

Would this in effect allow the 32A breaker to operate faster?

Is it actually dangerous to do this? Or merely not recommended?

Are there any other factors that l may have missed?

I would appreciate any help with as much detail as possible, from people who are in the trade, and know their stuff. Thanks, JabbaJaws...

Thanks for your reply Zambezi. I have just read my post and it does seem a little bit confusing.

I didn't mean to say "split" the ring.

What l mean to say was 'create a parallel path across the centre of the existing ring, so that two loops would occur on the same circuit.'

I hope that makes it a little clearer for you to understand...

Quote:




He means a figure of 8, and thats why you cross connect the line & neutrals and line & cpc's when testing a ring, when you take a resistance at each socket, this helps you find spurs and figure of 8 connections within a ring, as the readings should be the same at every socket, I think there is a +/- 0.05 tolerance between the readings (actually, I think thats with the open ended tests). Cross connections and spurs are significantly higher. A figure of 8 is dangerous because it will look as if you have a ring when testing (open ends), even though there is a break somewhere, which means certain parts of the cable will be overloaded, causing fires etc...  This is why you cross connect. When you have an installation wired in singles it can appear to be impossible to do as you dont know which leg is which, what you do is cross connect as normal, if the reading at the socket rises as you go towards the middle, then you know you have connected them wrong, so cross connect again but with the other earth or neutral, depending on what cross connect test your doing at the time, the readings should almost be the same at each socket.

I have just spent the last 10 minutes drawing circuit diagrams trying to figure out how you would tell if a ring has been bridged (if the 2 sections of the ring that are in parallel are of a similar length). I have drawn a blank...it has been a while since college so that probably does not help!
As TT says you would need to separate all the tails at each socket outlet, by which time you probably would have spotted the bridge.

As far as it being dangerous: you could have 3 live tails at a socket outlet, when you only expect 2. You could disconnect what you think is a spur only to find that it is still live. Both situations are easily overcome by using your tester correctly before carrying out any work. Or do as I do, treat every circuit as live even if you know it is not.

Stick to your guns mate - I admire you for that. If it works for you then that's good.

Have a go at an old installation, where the socket outlets have been correctly wired, but where the mechanical fit between your tester plug and the existing old, worn, and in some cases corroded socket terminals comes into play.

In many cases you'll get a much higher resistance than 1 ohm between any 2 skts.

Don't take the result as gospel - just check the terminal connections for tightness, and plug/unplug your test plug, and switch the socket rocker switch on and off a few times, and you'll see an immediate change in test values.

And yes, the cct has been correctly wired in most cases.

Sometimes, dismantling is the only way to test conclusively one way or the other.

Even a slight squeeze on the croc clips, or even a good poke with the test prod can change the result significantly.

TT

One caveat - be careful what you wish for.

Would you expect for example, a 5 day wonder Part P'eed kitchen fitter to have the requisite knowledge and experience to diagnose something such as a bridged Ring Final?

Remember, under the eyes of the law, and his scheme provider, he is classed as 'competent'.

TT

LSpark wrote on Feb 13^th, 2009, 12:49am:


I understand everybody's comments and have taken them on board, tis true, what you say TT, there are factors involved that affect the readings in the real world and not on a board in college.

Whats a 25a bond test?

LSpark wrote on Feb 14^th, 2009, 12:37am:



Take a look at Reg 507(b) page 72 of the 13th Edition 1962 Amendments.

The tests are preferably made by a.c. of mains frequency,at currents of the order of 1.5 times the rated current of the circuit, although currents of 25 amperes need not be exceeded.

I dont own the 13th edition, way before i was even thought about! Somebody i worked with had it though and that was when we were working to the 16th, he would consult his 13th