Continuity test after Ring Circuit

[Neptune]

After completing a new RFC or modifying an existing one, I will always test continuity across all 3 conductors at the Consumer unit. I use the continuity function on my Fluke 2 pole tester to do this. This is done whilst the circuit is dead.

Prior to this, I am very diligent with the conductors in each socket terminal and ensuring that I have the correct amount of cable length. I also screw the terminals tight again once the excess cable is bent in the back box and before I screw in the socket plate incase anything had come loose.

This means that when it comes to the continuity test, everything is okay. Else, I will revisit each socket, rectify and test again…

I know “proper” electricians will do R1, etc. tests using a low ohm meter. What am I missing without doing these tests and can any of these be done without buying the very expensive low ohm meters that electricians have?

I appreciate that the very simple response is that these test have to be done.

Thanks in advance.

 

[Neptune]

Would a short circuit not immediately trip when energised? Also, why it it happy with the load of the plug in socket tester and not the drill?
Thanks for your help.

 

[westward10]

You have many 'how do I do this threads' so is this linked to this property or somewhere else.

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[timhoward]

Would a short circuit not immediately trip when energised?

The MCB will trip if enough current flows. If there was a L-N fault it would depend on the resistance. For example if the fault was in the region of 4 ohms it would be pulling 57.5 amps and trip the 32 amp MCB.

The RCD will trip if a very small amount of current 'leaks' to earth.
If there was a N-E fault then the fault is only introduced when a load plugged in.

The plug in tester won't draw enough current to upset either device.
The drill is pulling considerable current.

I'm pleasantly dosed up on wine so I hope that makes some sense.

 

[timhoward]

You have many 'how do I do this threads' so is this linked to this property or somewhere else.

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Has the OP had the DIY badge all along? If so my eyes need testing and I think I was mixing him up with a different trainee.

@Neptune you've got more out of me that you normally would, and as you've perfectly demonstrated adding circuits yourself and not testing them before energising them is not safe. If it had been a metal appliance and not a drill then you or someone could be getting unpleasant shocks. The RCD is saving the day and these can stick.
Time to get some help in.

 

[Neptune]

Also, could I not split the ring into 2 radials and then test my drill to see which radial it trips? I could gradually increase the “good” radial until it reaches the problematic part of the circuit.

 

[Neptune]

Has the OP had the DIY badge all along? If so my eyes need testing and I think I was mixing him up with a different trainee.

@Neptune you've got more out of me that you normally would, and as you've perfectly demonstrated adding circuits yourself and not testing them before energising them is not safe. If it had been a metal appliance and not a drill then you or someone could be getting unpleasant shocks. The RCD is saving the day and these can stick.
Time to get some help in.

I am planning to purchase a tester for these types of situations. That’s the advice I had n an earlier post but wanted to share this particular issue to see what advice there may be.

 

[Baddegg]

Also, could I not split the ring into 2 radials and then test my drill to see which radial it trips? I could gradually increase the “good” radial until it reaches the problematic part of the circuit.

What you are proposing mate is called bang testing, you will eventually damage the circuit protective device to a point where it may not trip and then you’ll be in a world of pain, you need some proper testing equipment and someone to help you…..

 

[Neptune]

Is the MFT 1553 the ultimate choice for me? I can see that Tim’s suggested a few devices in his recent post. I am happy to pay a bit more for something that will serve me well.

With this tester, is it the initial R readings that would identify such an issue? Would I then Plug this tester at each socket to determine which section of the ring the issue is at?

I would appreciate some guidance around this please. Thanks for your help.

 

[timhoward]

The 1553 is definitely a good solid capable all round tester. It will do all dead tests (continuity and IR) and live tests (earth loop and RCD) to confirm something is fit for use.
Electrical testing is a complex subject and even new sparks don’t learn it initially. It’s not something a quick forum post can teach and must be done with great care. John Ward has made some good YouTube videos on the subject.

It’s not as simple as plugging into sockets, you’ll have to break the circuit down, initially into two and then see which leg has the fault and then continue tracking it down. It will be insulation resistance tests that are needed.

 

[timhoward]

You might want to look at this thread

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[IzzyS]

What am I missing without doing these tests and can any of these be done without buying the very expensive low ohm meters that electricians have?

The current range of Fluke 2 pole testers have a continuity range of 0 - 400kOhms. They are worse than useless for continuity checks on domestic wiring. At one end of the scale you could have a perfect connection, at the other you could have 2 (30A, 2.5mm2) radials connected by a 40kOhm resistance and you won't know the difference.

Specifications here

Fluke Two-pole Voltage and Continuity Testers | Fluke

Fluke Two-pole Voltage and Continuity Testers give you more ways to get results, a redesigned cable assembly, and Fluke’s longest two-pole warranty ever.

www.fluke.com

 

[Eddy Currents]

In the meantime, I have a ring main issue that you may be able to help me troubleshoot please. Here is some background:

This isn't surprising to me I'm sorry to say just by your previous questions. It seems you are dong a lot of electrical work which in my opinion is well beyond the limits of DIY and installing as you have and hoping for the best without doing the correct safety tests is a recipe for disaster. You are lucky that you only have some faults and not caused a fire or worse

I really wouldn't recommend buying an MFT because without the correct training which will give you the knowledge to understand the results and if they are acceptable and what to do about it if they aren't, then you are just wasting your money

Trying to install electrical systems step by step through a forum isn't a safe way to work with electricity and by your many questions it is obvious you don't have the knowledge to do it safely

Do you realise that installing new RFCs is notifiable work? How are you or who is notifying?

 

[Petej999]

What you are proposing mate is called bang testing, you will eventually damage the circuit protective device to a point where it may not trip and then you’ll be in a world of pain, you need some proper testing equipment and someone to help you…..

Don't sink that low Mate, test properly, too many Cisco Kids pretending to be Electricians don't become one please

 

[timhoward]

For less than the price of an MFT he could have skills, knowledge and experience on site for at least a morning. I'd bet most would find and fix his issue within 2 hours.
(Thinking about how long it takes to become comfortable testing, I agree it isn't logical to buy an MFT. I also can't imagine him not forging ahead though, and after an internal argument I thought it best he at least had access to some information about testing)

 

[Neptune]

Thanks for the many helpful responses. I really appreciate it.

I’ve had to halve a ring previously to locate a break in continuity. I am famously with the concept.

I also have a plan for my testing and would welcome your constructive feedback please.

After purchasing an appropriate tester, I am ready to commence the testing. Properly! The MFT is my likely choice from what I’ve been reading above. Again, happy to pay a bit more if it provides some future proofing. Please let me know if you have any further recommendations.

1. Continuity / end-to-end tests
Whilst I thought that my earlier Fluke 2 pole tests were conclusive, @IzzyS post shows that it’s far from it!
This will be a dead test and I am familiar with the safe isolation process.
I will locate the 6 wires for my ring. I will initially do this with the ‘good’ ring and then the ‘bad’ one. I will also ensure that everything is unplugged and the FCU is bypassed.
Here I plan to do the r1, rn and r2 tests. On the “good” ring I expect the r1 and r2 to be the same (Within 0.05) and the r2 will be 1.7 times higher due to the higher resistance of the smaller CSA. The readings for r1 and rn should be less than 1 ohm and determined by the length of cable in the ring. I don’t anticipate any issues with the “good” ring but when I do this with the “bad” ring, I think I will get a different reading for r1 and rn/r2. Even after taking into account the expected uplift for r2. The problematic reading shouldn’t be an open circuit/infinity as the fluke tester detected a closed circuit but it’s probably going to be a high reading. I think this indicates a short circuit or a loose connection?
I should now be in fault finding mode…
My plan is to split the ring into 2 radials by breaking the ring (cables disconnected and hanging mid air for the mid socket in ring) and on the CU end will have the first leg of the (now) radial in terminal block. I can then test at the break point of the ring and see if I get a high/low reading. If this leg is fine, I move on to the other and repeat the process. This should have a fault (unless I am unlucky to have multiple faults!). This is where I will need to continue halving until I’ve narrowed down where the problem is. I can then inspect the back of the socket or even try bypassing this section to see what the overall r readings look like.
I would appreciate your comments on the above as I’ve got my head wrapped around this approach if it’s the most suitable way to proceed.

2. Once the above is fixed, I am ready for the cross connection tests: R1+Rn and R1+R2
The expected results can be calculated from the above r readings.
This is where we create the figure of 8 across different wires of each leg. L from one side connected to N of the other side and the same for the other legs of the ring. This creates an infinite loop. I can then measure resistance at all and any point and it should be the same. Unless it’s a spur.

3. Repeat the above for L and CPC

I am not anticipating issues with 2 and 3 as I’ve checked the route of the ring using a wonder lead and my fluke continuity function.

My main issue is likely to be the first tests. I think…

Thanks in advance.