Ring circuit testing problems

[brizospark]

Found myself in a bit of a predicament

Carrying out a PIR in a factory

Testing an existing ring circuit in an industrial distribution board which must be nigh on 35 - 40 years old, asbestos flash guards and all!

The problem with that the DB does not have cpc terminals, and all the cpc's are twisted together and then looping around and fixed via the one available earthing nut at the DB

I carried out the ring tests on phase and neutral which returned satisfactory results of around the 0.75 ohm mark each.

Now to test the cpc's I would have to disconnect every cpc to untwist them all from each other and find the correct cpcs and carrying out the test.

Because of this reason I informed the supervisor that the entire DB would have to be isolated as there would be no cpcs connected.

Low and behold the supervisor had a week earlier tested a similar DB about 20 metres away, exactly the same scenario. He carried out the tests live and spent an entire day disconnecting all the cpc, finding the correct ones, testing and then reconnecting them.

The DBs are due to be upgraded anyway by the way, and the ring tests could be confirmed then

So anyway after informing him that the entire DB would have to be isolated he said thats fine just go ahead and do it. I told him that I would require adequate lighting as the lights are fed from this DB and he handed me his torch!

So I thought about this a bit more, I had tested the phase and neutral which were satisfactory, I could see the cpc's from the two ring cables were connected to earth, surely I could just go to the middle socket of the ring, split the cpcs and carry out the tests from here

OK, I know that the standard practice is to do this at the DB, but in this particular circumstance, given the amount of time that would be required I decided that, in my professional opinion, I would be happy with this and if the ring was broken there would be no continuity between the two legs.

So I went to the middle socket, split the cpcs and returned a reading of 0.92, which would add up, slightly higher that the L & N given that it is Twin and earth (2.5/1.5)

My supervisor returned to see how I was getting on, I informed him of the way I had carried out the test to which he said thats no use that aint the way you do it. i tried to explain my reasons for doing this including the theory but he was having none of it and it ended with him saying he was going to report me to the big boss for refusing to carry out his procedure.

What do you guys think?

 

[DurhamSparky]

what you did was dam right......

You confirmed the Ring of both L/N/E , does not really matter where you take ring reading from as it should all be the same any way!
tell your supervisor to sod off...!!

 

[brizospark]

cheers durham spark

 

[tony mc]

Aggree with Durham on this
IMO you did it right whats the point of causing more problems faults etc with the stripping down the CU.
Refer him to the regs 621.2

 

[brizospark]

tony mc can you quote this regulation please I don't have BRB to hand

 

[tony mc]

621.2 Periodic inspection comprising of a detailed examination of the installation shal be carried out without dismantling ,or with partial dismantling as required,supplemented by appropriate tests from chapter 61 to show that the required disconnection times,as set out in chapter 41 for protective devices,are complied with.to provide for
1 safety persons livestock etc
2protection against damage to property
3confirmation that the install is not damaged deteriorated
4 the identification of installation defects and departures etc

Hope this helps

 

[Geordie Spark]

As I was walking out the house at the tender age of 15 to start my very first day in the world of work, my Father said to me: "Do whatever they tell you exactly as they tell you as long as it isn't dangerous, and if you think it is dangerous, then ask them to put their instructions in writing and sign it !!"

Good advice I think, as here I am now at the wrong side of 60 and still with all my fingers & toes intact & both eyeballs still in their sockets.

 

[BlueToBits]

Absolutley right. 100%. except that you don't have to worry about finding the mid-point, any socket will do.
This is a good example of a situation where classroom theory can't cut it without real life experience.
It is why the NVQ level 3 has to be entirely done on a work placement.
The PIR is all about promoting electrical safety. It has to be possible to carry out a PIR with minimal disruption to the client's operation or he just won't have it inspected or tested and safety goes out of the window. It's the inspector's remit to find a way to meet the requirements whilst minimising the inconvenience.
I'm surprised your boss saw it as an issue. Does he (or she) insist that you disconnect all the fluorescent fittings, low bays, high bays, floodlights, daylight sensors, LV transformers, Led drivers, fans, emergency lights, neon indidators etc and remove all the lamps, to do an IR test on the lighting circuits?

 

[High Tower]

As Blue says, the interconnection can be ANYWHERE! you will still get exactly the same results, i know a few sparks who prefer to do it this way!

 

[londonlec]

I generally use the socket method quite often. Delving into an untouched CU should be avoided, if possible, IMO.

 

[Knobhead]

******

 

[Knobhead]

Good on you kid. That’s thinking on your feet, good use of theory in a practical and safe way.
Stick to your guns!

I will add all the boards I worked on of the age your talking about would have nothing but SWA’s coming out of them and NO CPC’s, the armour being the only CPC.
All gland plates would have either a brass plate or banjo’s as you call them now arranged so

View attachment 5698

Just one 7/.064 would be run back to the incoming SWA.

 

[brizospark]

Thanks for all the positive replies - it has given me the confidence to stand my ground on this issue, which I will be doing!

Also now that I think about it any socket will indeed do so thanks for the info.

I can see why the method of testing at a socket is preferred by some sparks as it would not take much to disconnect the wrong neutral at the DB which would then be live if the circuit is energised

 

[truckster]

your supervisor is only further proof to the rule: Everyone gets promoted to their own level of incompetence. As already said, any socket would do as it is a ring, all points should be equal.

 

[ezzzekiel]

usually much easier to remove a socket for cross over testing anyways, much easier to identify which leg is which when the db is a jumble

 

[PC Electrics]

Two observations:

# your method was perfectly sound. A ring is exactly that, a ring. You can break the continuity at any point and measure the end to end resistance and get the same result every time. Personally this is how I do it on domestic PIRs. Since I'm going to be inspecting behind most sockets anyway, I find one on each circuit that is easy to remove completely and carry out my testing there. I'd rather not dismantle the CU if I can help it, though i do check it over thoroughly.

# 0.75 end to end? That ring must be just about on the recommended length limit. Might be worth checking out the loading, load distribution and likely voltage drop. Indeed it might have been over length to previous editions when vd was still 4%!

 

[guest119]

Hey Briz,
Clearly your gaffer has a management problem or he just dont like you but he does have a point.

Removing a socket for inspection purposes prior to testing is all in order as you subsequently (normally) then test the ring from the DB which tests continuity across the socket or sockets you have re fitted.

However, removing a socket to carry out figure 8 tests etc does not provide you with the final result as it does not include your work of fitting (re fitting) a socket.

Worst case scenario being that you have procured healthy results and then walked away and left a fault as you dont know if continuity is good after pushing back your socket, especially with solid core 2.5 as in t&e.

Boyd

 

[brizospark]

Boydy,

i see your point nut surely us sparks can be confident that the connections we make will be ok once the faceplate is pushed back.