Continuity test after Ring Circuit

[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.

 

[Electro-tech]

As timhoward mentions, it is load related with an imbalance, which might be telling you your drill is on the way out. There is a lot of information regarding how RCD's Work online with pictures too.

 

[Neptune]

might be telling you your drill is on the way out.

I don’t follow this part. I can understand that the drill is drawing current which is then not returning via N, hence the trip.

 

[timhoward]

I don’t follow this part. I can understand that the drill is drawing current which is then not returning via N, hence the trip.

I'm not sure he realised there was a N-E fault at a socket.

 

[Electro-tech]

i.e. phone charger plugged in seemed okay but the hammer drill would immediately trip it?

Apologies having a senior moment should have read the whole senario again.