Ring main measures 600R

[brackers99]

Trying to identify a ring main before extending it to fit new sockets in a bedroom. Found what looks like a ring main as it has two cables going to one socket, however when I measure across the two brown wires that I have disconnected from the socket, I get 600 ohms instead of a short. I removed the tails from the consumer unit and have 600 ohms there too (with the socket reconnected).

Am I right to think something is loose or completly disconnected somewhere on this ring and not completing the return circuit properly?

I have had a new consumer fitted recently and the RCD would trip several times a day even with nothing plugged in. The tails have been moved to the non- RCD side of the CU for now.

Is the 600R reading and the RCD trips a related fault?

 

[martinxxxxxx]

No good

What is the Rn?

Sorry typing with baby on lap

Martin

 

[brackers99]

No good

What is the Rn?

Sorry typing with baby on lap

Martin

Is the Rn something I can check with a Fluke DVM? Sorry, I am not an electrician, but I am guessing you want a measurement of the neutral ring? If so, do I need to unplug everything as it means pulling out a 100kilo washing machine to reach the socket behind!

 

[DCC]

Let me get this straight - you've had a new CU fitted and the existing wiring or the CU installation is not up to scratch.

Question, why haven't you got the electrician back in? Surely the tests done at that point would have indicated what wiring problems existed... you do have the test results dont you?

Your RCDs trip, solution - bypass them. Who did that?

You now want to extend your already faulty and possibly dangerous wiring.

Don't you think maybe fixing whatever problems exist would be the first step?

 

[bongos]

Hi Brackers.

You have tested the end to end resistance of the live conductor (r1). If you test the end to end resistance of the neutral conductors (rn) what reading do you get?

Do the same test on the end to end resistance of the earth (r2). What is this reading. The tests on live and neutral should be very similar. The earth should be slightly less than both as the earth conductor in 2.5mm² ring final circuits is often smaller than the live/neutral so has a higher resistance.

However, 600Ω on r1 is far too high anyway. It suggests that there is a loose termination or damaged cable somewhere on the ring. A good start would be to open all the sockets outlets on the ring and look for damaged/loose cables.

A circuit protected by a B32 MCB has a maximum uncorrected figure for the resistance of the live and cpc (earth) conductors of 1.44Ω.

I have had a new consumer fitted recently and the RCD would trip several times a day even with nothing plugged in. The tails have been moved to the non- RCD side of the CU for now.

Who did this?! The spark who installed the CU should not have just moved the tails across to the non protected side of the CU just because the RCD was tripping. They should have sorted the problem out when they installed it. What results did you get for R1+R2 (not the same as r1+r2) on this faulty circuit on the certificate the spark left you?

 

[Taylortwocities]

Found what looks like a ring main as it has two cables going to one socket, however when I measure across the two brown wires that I have disconnected from the socket, I get 600 ohms instead of a short.

It sounds to me like that socket is not on a ring. Probably it is already a spur with another spur connected to it. The 600Ω is probably a connected load on a socket downstream - the washing machine, maybe.

The electrician should have done tests on the existing installation before teh consumer unit was changed.
He should have identified if there was a spur off a spur. What did his inspection report say?

I'm beginning to wonder why you didn't get him to add those sockets and include them in his certificate for the whole installation.

I am also having problems with this bit

I have had a new consumer fitted recently and the RCD would trip several times a day even with nothing plugged in. The tails have been moved to the non- RCD side of the CU for now.

A recently fitted CU would have two RCDs so there shouldnt be a non-RCD side to the consumer unit. Do post a picture of the board.

 

[bongos]

It sounds to me like that socket is not on a ring. Probably it is already a spur with another spur connected to it. The 600Ω is probably a connected load on a socket downstream - the washing machine, maybe.

I'd not read the OP properly and assumed it was a ring. As stated it may not be.

It's beginning to sound like your spark has done a bodge on the CU install though. How recently was this recent CU install anyway?

 

[nozspark]

Hi Brackers.

You have tested the end to end resistance of the live conductor (r1). If you test the end to end resistance of the neutral conductors (rn) what reading do you get?

Do the same test on the end to end resistance of the earth (r2). What is this reading. The tests on live and neutral should be very similar. The earth should be slightly less than both as the earth conductor in 2.5mm² ring final circuits is often smaller than the live/neutral so has a higher resistance.

However, 600Ω on r1 is far too high anyway. It suggests that there is a loose termination or damaged cable somewhere on the ring. A good start would be to open all the sockets outlets on the ring and look for damaged/loose cables.

A circuit protected by a B32 MCB has a maximum uncorrected figure for the resistance of the live and cpc (earth) conductors of 1.44Ω.

I have had a new consumer fitted recently and the RCD would trip several times a day even with nothing plugged in. The tails have been moved to the non- RCD side of the CU for now.

Who did this?! The spark who installed the CU should not have just moved the tails across to the non protected side of the CU just because the RCD was tripping. They should have sorted the problem out when they installed it. What results did you get for R1+R2 (not the same as r1+r2) on this faulty circuit on the certificate the spark left you?

In fact your r2 reading should be 1.66 x r1 or rn for 2.5/1.5 T&E

or 2.5 x r1 or rn for the older 2.5/1.0 T&E

However as you say this should have been picked up and rectified during the CU replacement[/b]

 

[TicklyT]

There is a possible high resistance path betweem the two live conductors of a spur from a spur, or a radial circuit, via two connected appliances if one appliance is connected each side of the break in the live conductor).

Breaking the neutral conductor whilst testing should eliminate the path (multimeter - live a - appliance a -neutral a - neutral b - appliance b - live b - multimeter).

 

[brackers99]

Thanks for all the replys, which have been really useful. I have done some further checks and my initial check at the tails from the CU showed r1=600R, rn=596R, r2=1R. I then unplugged the washing machine and just checked r1 to find it read about 15MR.

The electrician's test shows very low resistance of below 1R for all the above.

Now, I am guessing something is not connected somewhere. I have removed all sockets on the ring and found nothing conclusive. Before I bought the house, someone fitted a kitchen as an extension about 30 years ago. It is a real bodge and the ring in question, feeds the upstairs of a 4 bedroom house, it also supplies the kitchen and garage!

Something else to note, if the extraction fan is running in the kithen and I turn the kettle on, the extraction fan slows down. The light in the microwave also dims if the kettle or washing machine is on.

 

[brackers99]

Here is a photo of the CU

 

[flameport]

The picture:

Untitled

• brackers99
• 23 Jan 2010
• 1

Any tests must be done with all appliances unplugged, as they are likely to affect the readings.
Clearly the ring is not continuous, so there are one or more breaks/loose connections somewhere.

As for the CU - what are the 3 circuits to the right, which have no RCD protection?
Where are the rest of the CPCs (earth wires)?
Is there a separate earth block with the main protective bonding connected to it? It's certainly not connected in the consumer unit.

 

[brackers99]

The picture:

Untitled

• brackers99
• 23 Jan 2010
• 1

Any tests must be done with all appliances unplugged, as they are likely to affect the readings.
Clearly the ring is not continuous, so there are one or more breaks/loose connections somewhere.

As for the CU - what are the 3 circuits to the right, which have no RCD protection?
Where are the rest of the CPCs (earth wires)?
Is there a separate earth block with the main protective bonding connected to it? It's certainly not connected in the consumer unit.

Thanks. It became obvious after I had spent some time testing, that things needed to be unplugged.

The two circuits to the right are lighting and followed by the ring I have the problem with. The electrician moved it from the far left RCD due to the nuisance trips.

The electrician fitted a new earth rod and upgraded the earthing wire to a thicker gauge. My supply is via overhead cable. Hope this helps.

 

[flameport]

The electrician fitted a new earth rod and upgraded the earthing wire to a thicker gauge. My supply is via overhead cable. Hope this helps.

That makes things much worse. It is likely that the 3 circuits with no RCD are completely unprotected against earth faults.

Are there any other devices between the consumer unit and the meter?
Does that large green/yellow wire connected to the top left of the CU go directly to the earth rod?
Are there other green/yellow wires going to the gas and water pipes?

 

[brackers99]

The electrician fitted a new earth rod and upgraded the earthing wire to a thicker gauge. My supply is via overhead cable. Hope this helps.

That makes things much worse. It is likely that the 3 circuits with no RCD are completely unprotected against earth faults.

Are there any other devices between the consumer unit and the meter?
Does that large green/yellow wire connected to the top left of the CU go directly to the earth rod?
Are there other green/yellow wires going to the gas and water pipes?

There are no other devices between the CU and meter. Mains in followed by 100A fuse then meter, then CU. The wire from the earth rod connects to the earth bar at the top and I was made aware that there is a need for earth wires to be fitted to gas and water pipes.