Ring main problem ... two circuits but joined!

[sdelasal]

In my fusebox I have two 30A fuses- unmarked but I assume ring main circuits. The house is a 1970 3 bedroom ground & top floor. I assume that the power sockets in the house are split 1st floor & ground floor or left of house & right of house - you get the picture ...either way there are two ring mains.

Here's the problem...When I remove one fuse ...all the power sockets in the house are still live. If I reinsert that fuse & remove the other ...they are all still alive. The only way I can disconnect all power sockets is to remove both fuses.

So it appears that some comedian has linked the two ring main cicuits together... does anyone have any idea why this would be done deliberately..? I can't think of any..

Apart from removing every 13A socket and buzzing through the circuits ..anyone got any tips on how I figure out what has gone wrong & where?

Steve

 

[Steve]

Most homes are wired upstairs, and downstairs seperately. You need to find a link. This shouldn't be too hard. Look for later additions / alterations.

Before you go looking, open up your fuse box and check that there are two 2.5mm² cables into each 30A fuseway. And no link here.

 

[nozspark]

Or 1 leg from each ring into seperate fuses

 

[Taylortwocities]

It could be either, more likely as nozspark says, have seen this before - usually shows that the installation wasnt tested properly on installation or after some work has been done.

Get a qualified spark in if yr not sure.

 

[sdelasal]

Okay - more info. Each of the two fuses has two red cores into it - as expected. I unclipped those wires. Lets call them A & B for fuse #1 and C&D for fuse #2.

Now i'd expect minimal resistance 'short' between A&B and between C&D and I'd expect open circuit between all other combination i.e. these shoudl be two seperate circuits.

What I measure is ..
A-B = 160 Ohms,
C-D = OpenCircuit (OC)

A-C = 160 Ohms
B-D = OC

A-D = OC
B-C = 0.5Ohms


A mess really ..

What would give 160 Ohms? that's 1.5A, 360W!

Steve

 

[Adam_151]

I reckon B and C are a ring final circuit, find the neutral and earths that go with them, check they measure about 0.5 of the neutral and a little more for the earths, if they do, put them in one fuse (make sure neutrals and earths go in the right terminals - this is so they can be identified at a glance - modern CUs might have the terminals numbered, yours may not, but still get them in the right terminal).

Put the phase wires of A and D in connector blocks separatly and investigate what doesn't work

(160ohms is probably a combination of resistive loads connected to the circuits in question, first circuit has a few parallel resistances connected phase to a common neutral terminal, the other has a few from the neutral to the phase - drop the neutral out and it should go O/C)

 

[sdelasal]

The fuse box is an original MK item from 1970. It looks like all the neutrals are connected together onto one bus-bar.

I don't understand you explanation of the 160 ohm - could you try again please!?

Steve

 

[Adam_151]

Yes, one busbar unless its a split board, but neutrals have to be in correct terminals for indentification, depending on your cu, it may or not be numbered

160 is from various loads connected between phase and neutral on the two circuits you tested between. As the neutrals are in a common block you saw the resistance of them in series, drop the neutral and it'll be oc[/code]

 

[Taylortwocities]

In those old boards there were no cct idents on the neutral busbar. It was common practise to twist em together and stuff as many in one terminal as you could.

 

[ColJack]

it's not rocket science though.. there should be as many neutral ways as there are fuse ways.. so you just count left to right and stick the neutrals in the hole that coresponds with the fuse..



your 160 ohm reading is down one live, through a load to the neutral, back up another neutral and through another load to the other live..

if you take the neutrals out then it should dissapear..

which then leave you with a problem..



B - C should be one ring.. but then that leaves A and D as the other.. but your readings don't support that...

 

[sdelasal]

Okay - thanks for the help. I switched off all loads & got o/c everywhere except the 0.5 Ohm. So I made that pair a circuit. Now I have one good ring on the right hand side of the house and a bloody mess on the left hand side of the house. The kitchen wiring is ...interesting ... and i'll spend some time getting to the bottom of it. Thanks again. steve

 

[ColJack]

since you have no connection from A to D then that indicates 2 radials..

isolate D in a terminal block, connect A back up and then see if D is live, and find what sockets etc now work...

repeat for D...