Ring Main test

[john25]

Hi im currently doing the L2 2330 course and of my Practical Tutors asked us to look on the internet about a Ring Main test and also mentioned a *Figure of 8* (which im guessing is some Kind of Test) so if anyone could explain to me how to test the Ring Main circuit and also explain the *Figure of 8* that would be really helpfull
thanks.

 

[m4tty]

Have you got an On-Site-Guide or GN3. They explain it well.

 

[G_FUNK]

the figure of 8 is the r1(phase) of one leg of the ring and r2(c.p.c) of the other leg of the ring connected together via connectors you do this for both legs of the ring and it gives you a figure of 8. This will give you an R1 + r2 reading and each reading in the ring should be around the same, if not may be 0.5 of an ohm out. spurs will be a little higher. you all so do this r1 + rn this is the phase and neutral in a figure of 8 and again test every socket you should get the same reading at every socket again and spurs being higher. this test is to see if there is a ring with in a ring. your also need to do any end to end test. rembering that the cpc will be 1.67 times higher that the phase or neutal if it is 1.5mm.

 

[nickp78]

hello, a ring main should be one complete loop, to test a ring circuit which is two 3 core twin and earth cables ( generally ) you need to disconnect both cables, you will be left with 1 cable of 3 cores brown, blue, green and yellow and a second cable with brown, blue, green and yellow, carry out a continuity test between both brown cables ( call each end P1 for cable 1 brown and P2 for second cable brown ) between them P1 to P2 you should get a continuity reading ( for example say 0.5 ohms ) , carry out same step for neutral cables ( Blue ) calling them N1 to N2 and again you should get a reading of the same say 0.5 Ohms, do the same for the CPC and you should get a higher reading due the CpC being smaller that the neutral or phase conductor, connect P1 with N2 using connector block and P2 with N1 again using connector block. Carry out continuity test at each socket between phase and neutral, the reading from each circuit should be 1/4 of the total of P1 to P2 added with N1 to N2, if P1 to P2 + N1 to N2 = 0.5 + 0.5 = 1.0 ohms so each socket should read 0.25 ohms

 

[john25]

cheers for the info guys il write it down

as for the on site guide i dont have the book but theres copies in the College library so il rent it and look it up as ive been
reading and taking notes from it on my Dinner breaks

 

[ezzzekiel]

asked us to look on the internet about a Ring Main test

isnt he getting paid to teach you?

how about you give me £500 per term and I tell you to google it.

 

[m4tty]

isnt he getting paid to teach you?

how about you give me £500 per term and I tell you to google it.

Whos rattled your cage Meow

 

[john25]

isnt he getting paid to teach you?

how about you give me £500 per term and I tell you to google it.

yer it wasnt a Mandatory Request mate .He just advised us to read/ find info on what is and how to test a Ring main /plus the Figure of 8 test as he said that will be the hardest test we,ll do this year at level 2

 

[NoSparks]

John,

Lets start with the fact that it is a Ring Final Circuit (not a Ring Main which is what the distribution company arranges around the country).

Ring Final Circuit Testing complies with the normal test requirements in order:

Dead Testing
Continuiety
Insulation
Polarity

Live Testing
Earth Fault Loop
Polarity
Functionality


Ccontinuiety testing of a ring final circuit comprises 3 steps.

Step 1
End to end testing of the ring as described by Nick above. May I just add that the resistance of the circuit when open ended (P1 to P2) is known as r1. The resistance of the CPC vv the Line conductor will be in the inverse ratio of their cross sectional area eg for a 2.5mm T&E with 1.5mm cpc, the cpc resistance should be 2.5/1.5 (ie 1.67) times the line resistance. The resistance of the open ended cpc is known as r2.

Now if you think of the ring, when the line conductor is joined togther (P1 to P2) and you measure the resistance of the ring at any two points, the highest resistance is when you measure from one side of the ring to the other. It will be 1/4 of the open ended circuit resistance. (I can give you the maths it you want). This maximum resistance of the Line conductor of any circuit (ring or radial) is known as R1. and similarly for the cpc where the maximum resistance is known as R2.

Step 2
Line and Nutral conductors are cross coupled as described by Nick. P1 - N2 and P2 - N1.


Step 3
Line and CPC conductors cross coupled C1 to P2 and C2 to P1. This is the important configuration because now if you measure the resistance between the Line and the cpc at the opposite side of the ring to the point at which the cables are connected, you are measuring R1 + R2 (as defined in Step 1) the resistance of the line cable plus the resistance of the cpc, which dictates the currents that flow during an earth fault, and as you will learn later, the speed at which the protective devices will switch off.

The mathematics are too complex to comprehend, but if you measure the resistance between line and cpc at other points not too close to the point you have joined them, their resistance will be roughly the same.


Fiinally, checking the resistance in these three steps automatically confirms the polarity of the connections to the sockets, so the third stage of Dead testing has been completed as well.

 

[john25]

cheers for the info NoSparks

 

[cavecellar]

Hi,
I have used a FlukeSM300 socket tester to test the sockets on my ring main and all are o.k. with mcb tripping as required in each case, therefore I assumed the ring main was o.k.
However when a light is plugged to a socket and swicthed on the mcb trips,
Can anyone suggest what the problem might be ?????

 

[acat]

Do you mean MCB or RCD they are different. Have a look and see if your MCB has a Test button on it if it does its an RCD.





Chris

 

[cavecellar]

Yes I'm sorry its a RCB in a wylex split consumer unit

 

[Guest123]

Is it just the one socket that you're plugging into???

Also have you tried plugging anything else in besides the lamp???

 

[acat]

RCD means a leakage to earth so your lamp may be duff does any other appliance trip the RCD. If you have sockets on another RCD try plugging the lamp into that circuit if that RCD trips you need to repair the lamp




Chris