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.

 

[timhoward]

I’m not going to comment line by line on your exposition, but will simply say that the continuity tests need doing, but are less likely to help you fault find.
Insulation Resistance tests will more than likely be where you can see evidence of the fault and track it down.

 

[Petej999]

The purpose of a low hom meter is to test a ring or other to see what values you have got.

Mr HOM is a bloke in Star Trek isn't he? big tall geezer always carrying suit cases

 

[telectrix]

morning pete. not seen youmuch. how's life?

 

[buzzlightyear]

Me too, how's life Pete. Still gambling on
tools tart. Just bought a nice new Stanley
Tool box too throw my crap in.
There is nothing like good tool to drool
On like a kid in a candy shop.

 

[Petej999]

morning pete. not seen youmuch. how's life?

Fine thanks Tel, you?

 

[Neptune]

I’m not going to comment line by line on your exposition, but will simply say that the continuity tests need doing, but are less likely to help you fault find.
Insulation Resistance tests will more than likely be where you can see evidence of the fault and track it down.

Am I right in thinking that the continuity tests are a prerequisite for the IR tests? Also, if we have a screw or something of that ilk smashed into one of the conductors, would you not expect the continuity test to provide a lower (perhaps a 0?) reading? In any event the live conductors would have different readings and hence indicate an issue. That's what I was anticipating.

On IR testing, if we have a short, I am expecting a reading of less that 1 (probably 0?) and that's when I move in to the halving method to locate the issue. Is that the general approach?

Thanks for your help.

 

[timhoward]

Am I right in thinking that the continuity tests are a prerequisite for the IR tests?

Doing things in the right order has long gone out of the window for your install!
You are right that it would be normal to do continuity tests first. Whether or not any IR testing is also done at first fix, IR testing must be done when the installation is 'assembled' to pick up any damaged / trapped / snagged wires.

Also, if we have a screw or something of that ilk smashed into one of the conductors, would you not expect the continuity test to provide a lower (perhaps a 0?) reading?

Maybe but this will vary according to the nature of the fault. Hence why I'd personally dive straight to the test that will definitely show it up.

On IR testing, if we have a short, I am expecting a reading of less that 1 (probably 0?) and that's when I move in to the halving method to locate the issue. Is that the general approach?

Yes. A healthy new cable should be hundreds or even thousands of Mohms.

 

[Neptune]

Insulation Resistance tests will more than likely be where you can see evidence of the fault and track it down.

A few more questions on this please Tim:

• Can I remove USB sockets with 32amp junction boxes for the purposes of the IR test?
• Do FCU's that are on the ring and not a spur need to be removed? The neon is on load and can be switched off
• If we have continuity as part of earlier tests, when doing the IR test for L and E (or the other conductors), does it matter which leg of the ring you use the L and E from? I assume not but was mindful of the other end of the leg hanging mid air at this point:

- If there are failures, we can use the halving method and I can gradually increase the working leg of the ring to see where the failure appears. At this point, I could either replace the cable or convert the ring into two radials powered by a 20amp breaker. Is that a valid approach?

 

[westward10]

This is not a step by step guide to testing. Testing should be carried out by competent persons or by persons under supervision of a competent person. I have no idea if this is linked to your other threads which follow the same theme of step by step guidance.

 

[Neptune]

This is not a step by step guide to testing. Testing should be carried out by competent persons or by persons under supervision of a competent person. I have no idea if this is linked to your other threads which follow the same theme of step by step guidance.

Wasn’t asking for a step by step guide to be honest. Just the above questions in addition to the detail and understanding I’ve already set out. I’m not an expert but comfortable with my understanding and the fact that this is a dead test.

 

[westward10]

When undertaking any test whether electrical or not you must understand how the test equipment operates and how to interpret the results it gives you, you do not understand either of these from the questions you are asking.

 

[Neptune]

A few more questions on this please Tim:

• Can I remove USB sockets with 32amp junction boxes for the purposes of the IR test?
• Do FCU's that are on the ring and not a spur need to be removed? The neon is on load and can be switched off
• If we have continuity as part of earlier tests, when doing the IR test for L and E (or the other conductors), does it matter which leg of the ring you use the L and E from? I assume not but was mindful of the other end of the leg hanging mid air at this point:

View attachment 98571
- If there are failures, we can use the halving method and I can gradually increase the working leg of the ring to see where the failure appears. At this point, I could either replace the cable or convert the ring into two radials powered by a 20amp breaker. Is that a valid approach?

I would really appreciate any direction that could be provided on the above please.
Thanks in advance

 

[westward10]

Is this related to your other threads.

 

[Neptune]

As to your fault, my best guess is a nail used for capping has missed and has damaged a cable. Or a screw at a socket has caught the Neutral.
Breaking down the ring, with an IR tester is the only way to proceed I'm afraid.

This is precisely what happened! I wanted to share my experiences.
I used my newly purchased Megger MFT to run the continuity, crossover tests and then the insulation tests. The IR test failed.
I halved the ring and identified the good and bad legs. I then kept adding sockets to the good leg until it turned bad. Hope that's making sense...

That's when I noticed that a neutral wire was nicked behind an electrical screw of the face plate. The Megger MFT and halving method made this light work and I enjoyed the experience of troubleshooting it.

• I didn't remove USB sockets and they are fine. I started with a 240v IR test and then increased it to 500v. Although, the latter probably wasn't required as fault showed on the 240v test.
• The FCU on ring remained in placed with switch in off position
• I was able to use either L or N as there was continuity all the way around the Ring before I started the IR test.

My only question is why this fault only caused the RCD to trip under load and a certain amount of load i.e. phone charger plugged in seemed okay but the hammer drill would immediately trip it?

Thanks for your support with this.

 

[timhoward]

I'm glad you found the issue.

My only question is why this fault only caused the RCD to trip under load and a certain amount of load i.e. phone charger plugged in seemed okay but the hammer drill would immediately trip it?

An RCD works essentially on the principle that what goes out must come back, and if more than a certain amount is 'missing' it trips.
So no load at all, nothing, goes out, nothing goes back.
A phone charger is a very low load, and the "missing" amount wouldn't be high enough.
A drill pulls enough current that enough goes the 'wrong way back' (via the cpc/earth ) that the RCD would have an aha moment.