Final Ring Circuit Continuity

[justasparky]

Hi there,

New to the forum so be kind. I have recently been given the task of inspecting and testing a large special needs school. I thought myself confident in my testing abilities until i started to question the readings obtained from final ring continuity testing. The readings at each socket should be approximately equal to 1/4 of the total resistance of both conductors. Now i understand that the readings obtained at each socket will be slighlty higher due to the contacts of the sockets and how tight the terminals are, but how much will the reading rise by which will indicate a connection loose enough to cause concern? I have removed sockets for further inspection and found nothing to be wrong, I have also discovered that with some of these new sockets the contact can have a small amount of dirt or something on them and require turning on and off again so that a good contact is made.

 

[ProDave]

Check the end to end continuity of the ring at the CU for each of the three conductors.

The R1+R2 check at each socket is a means of identifying irregularities, like spurs, cross connected ring etc.  They should all be pretty much the same.  If you get a bad reading, unscrew the socket and test at the terminals to eliminate a poor switch or poor contacts.

 

[justasparky]

Hi Dave,

Thanks for the reply. I have followed the first steps correctly, my concern is how much can the reading change before it becomes a fault. For instance Line and Neutral interconnected giving a reading of 0.48 ohms, is 0.50 a concern. Some circuits have risen slightly to mid point and back again, i know they are rings because they have all been wired in the same way. The loose connections i have found have always been a higher unsteady reading.

 

[m4tty]

As long as they are within 0.05 ohms of each other it's ok

 

[Theorysparky]

not sure what you are testing for with LN interconnected ???

if your L-L is  say 0.50   then your N-N should be within 0.05 of this

Your cpc-cpc should be 1.67 x greater than 0.05

cross connecting L-CPC at cu and checking at the sockets should give you 1/4  L+CPC readings

most guys have a gut feeling when something is not right so a little more tolerance can be given

 

[kme]

Don`t forget that a spur can be taken from the ring; the readings at such a socket will be higher than the ring, due to the presence of the extra cable.

As said, E-E should be in the order of 1.67 times L-L; UNLESS there are elements of structural metalwork, which could give rise to parallel paths.

I must say, and don`t take this wrong - if you`re this unsure about acceptable test results on a ring, are you CERTAIN you`re competent to test a premises such as this?

 

[Steve3948]

As its a School it may be singles and 2.5mm cpc, so maybe not 1.67

 

[steptoe]

or, it may be a 1.0mm cpc and thus x2.5 the L-L reading

parallel paths can be a nightmare, I often find cpc readings lower than L-L readings.

stuff like this really only boils down to one thing, experience and knowing the expected results and what can be considered acceptable or not.

 

[philbas]

Hi Dave,

Thanks for the reply. I have followed the first steps correctly, my concern is how much can the reading change before it becomes a fault. For instance Line and Neutral interconnected giving a reading of 0.48 ohms, is 0.50 a concern. Some circuits have risen slightly to mid point and back again, i know they are rings because they have all been wired in the same way. The loose connections i have found have always been a higher unsteady reading.

This concerns me a bit, you should know they are rings because you tested them , what results did you get?

 

[philbas]

If someone is going to de scoob it would me nice if they left a comment to say why, I stand by my statement, you can't know they are rings just because they have all been wired in the same way,

they only way to prove they are rings is to test them, so I ask again what readings did you get from the tests?

 

[m4tty]

Who de scoobed mate ?

 

[philbas]

Who de scoobed mate ?

I have no idea, you may be able to see on this forum someway but I have not found out how.

I do know someone scoobed the the post, then it went back to zero so someone de- scoobed.

Not that it bothers me, I would just like to know who and why.

My reputation can go to - 100 or more for all I care, but if someone doesn't like my opinion I would like to know who it is so I can talk to them.

I expressed my opinion which I stand by at the moment, someone does not agree with it (fair enough) but it would be nice if they left a post to say why they disagree, otherwise no discussion can take place.

They may be correct but until I know why they object I can't discuss

 

[pickleye]

Some circuits have risen slightly to mid point and back again

have you cross connected your incoming and outgoing legs correctly?

From GN3 (16th edn :Blushing )

Note: Where single-core cables are used, care should be taken to verify that the phase and neutral conductors of opposite ends of the ring circuit are connected together. An error in this respect will be apparent from the readings taken at the socket-outlets, progressively increasing in value as readings are taken towards the midpoint of the ring, then decreasing again towards the other end of the ring.