How to test if I've got a ring main or radial Ask questions and find answers to many subjects relating to electrics and electrical work

[Reynardine]

With my floorboards up I'm finding it difficult to tell if I have a radial arrangement or a ring main in my flat.

At the CU, the whole arrangement is off a 30AMP MCB. Under the floorboards two 3 terminal junction boxes are visible so far. The two junction boxes are connected by 25mm cable. These junction boxes feed what appears to be six spurs to flying to double sockets in each side of the living room. Inspection of the sockets shows that each is fed by only a single 2.5mm cable.

With the mains isolated, I'm planning to test if I've got a ring main.

Suppose I disconnect what looks like the first cable entering the first junction box. If all the sockets still work after the disconnection, does this prove I've got a ring main ?

Thank you for your help.

[BLAKEY1963]

[quote="Reynardine"]With my floorboards up I'm finding it difficult to tell if I have a radial arrangement or a ring main in my flat.

At the CU, the whole arrangement is off a 30AMP MCB. Under the floorboards two 3 terminal junction boxes are visible so far. The two junction boxes are connected by 25mm cable. These junction boxes feed what appears to be six spurs to flying to double sockets in each side of the living room. Inspection of the sockets shows that each is fed by only a single 2.5mm cable.

With the mains isolated, I'm planning to test if I've got a ring main.

Suppose I disconnect what looks like the first cable entering the first junction box. If all the sockets still work after the disconnection, does this prove I've got a ring main ?

Thank you for your help.[/quote]

REYNARDINE
NOT ALWAYS, BECAUSE U COULD HAVE TWO FEEDS
AND THE RING COULD B INCOMPLETE.
A LOW RESISTANCE OMHMETER IS REQUIRED , AND AFTER
ISOLATION IS CARRIED OUT, AND CIRCUIT PROVED DEAD,
THE RANGE OF THE TESTER WOULD B SET TO THE 20
OMH RANGE.
THEN AT EACH SOCKET CONTINUITY OF LIVE - LIVE
AND NEUTRAL - NEUTRAL IS CARRIED OUT. THESE READINGS
DEPENDING ON LENGTH OF RING MAIN SHOULD BE

UNDER 1 OMH. FOR 2.5 MM2 CONDUCTORS
THE CONTINUITY OF THE EARTH S R ALSO CHECKED
AND BEING 1.5 MM2 THE READINGS WILL 1.67 TIMES
MORE THAN THE VALUE OF THE 2.5 MM2 CONDUCTORS.
NO CONTINUITY MEANS A SPUR AND ONLY A MAX OF ONE DOUBLE OFF THE RING.
BLAKEY1963

[Reynardine]

Thank you for that Ohm figure Blakey.

I just browsed the IET website. The "Domestic Installer" guide has a table that seems to say that if your multimeter gives a reading of around 1 Ohm you have a ring main, if your multimeter gives a reading of around 2 Ohms you have a radial circuit.

[sparx]

Hi. not too sure of validity of ohms readings but the only way to know if you have any sort of ring is to disconnect ends @ con. unit and see if you get live to live & Neutral to Neutral readings which are low and very similar to each other, also do earth to earth readings which should be about 60% hihger, regards SPARX