Low IR reading on ring main

[monkey5]

evening all

similar question MarkieMarque

i did an IR test on an existing ring main today live/neutral to earth and got 3.65Mohms. its the first time ive done live/neutral to earth, i normally make sure everything is disconnected and do live to earth, neutral to earth and live to neutral (test on 250v first). but as advised on here im now going to start live/neutral to earth on existing installations. should i have still disconnected everything? and would you investigate it further?

its a ring main on 32a breaker which is RCD protected.

thanks in advance

wayne

 

[Adrian]

if you have things connected this will bring the ir down

if you can disconnect things I do but like you test 250v first

I have IR a cooker still connected and that gave me a 2meg reading

the reading is a pass and because the way you have test I would not bother to investigate

 

[Robin Spark]

1. Cant see how leaving items connected is going to make much difference unless those items are faulty or/are inherent to leaking current to earth ie appliances with heating elements in them.

2. How old was the ring main? If it looked fairly new then I would probably investigate. Monkey, is this a domestic property?

3. Was it unreasonable to ensure all items were disconnected because I think really the guidance is to do L/N to E where it would not really be practicable to do the normal tests ie lighting ccts with loads of trannies.

4. What work did you carry out or was this a pre-check test before commencent or a PIR maybe.

5. I can see your concern with 3.65Mohms, however your not going to have any prolems with the RCD as leakage is approx 0.00006ohms at that IR test value.

 

[monkey5]

[quote name=How old was the ring main? If it looked fairly new then I would probably investigate. Monkey, is this a domestic property?

the ring main is approx 9 years old, and its a domestic

Was it unreasonable to ensure all items were disconnected because I think really the guidance is to do L/N to E where it would not really be practicable to do the normal tests ie lighting ccts with loads of trannies.

not really, just trying to save a little time, like i said it was the first time ive done it this way and was hoping for a better result, then got worried when it was so low. but might just go back to the way i normally do it

What work did you carry out or was this a pre-check test before commencent or a PIR maybe.

i had added a couple of outside lights from sw/fcu in lounge, all work fine and no rcd tripping

I can see your concern with 3.65Mohms, however your not going to have any prolems with the RCD as leakage is approx 0.00006ohms at that IR test value

circuit was rcd protected before and no trips, i just got abit worried when i got such a low reading, even tho its a pass. .

how do you work out the leakage just out of curiosity?

thanks for reply

 

[Badger]

i was wondering that also

 

[davie garden]

For Monkey5 and Badger, I see you didn't get a reply to your question so here's the amswer.

You divide the 230 volts by the 3.65 megohms and it gives you the value 0.000063 amps. This of course is only when nothing is plugged in and switched on. My advice would have been, do the test with nothing connected to the ring, after all, you are supposed to be testing the 'hard wiring only', not any appliances as well, that's what Portable appliance testing is for. The method you used is really to save you time disconnecting things like dimmers, indicator lamps, transformers etc. So assuming a client is paying you to do the testing, you should suggest that P.A.T. testing is a separate job/contract from installation testing and you then negotiate a separate price for each job.

 

[green-hornet]

I always disconnect everything from a ring main to do the IR test. I also switch off all fused spurs on the circuit. Neon indicators will give or rather interfere with IR tests, as will any appliance left pluged in.

I can see your concern, especially when it is the first time you have tested this way.

Out of interest my tester will not allow a full 500v down the line if anything is detected as using power, this is often my way of finding lost or covered up sockets etc.

 

[Robin Spark]

For Monkey5 and Badger, I see you didn't get a reply to your question so here's the amswer.You divide the 230 volts by the 3.65 megohms and it gives you the value 0.000063 amps. This of course is only when nothing is plugged in and switched on. My advice would have been, do the test with nothing connected to the ring, after all, you are supposed to be testing the 'hard wiring only', not any appliances as well, that's what Portable appliance testing is for. The method you used is really to save you time disconnecting things like dimmers, indicator lamps, transformers etc. So assuming a client is paying you to do the testing, you should suggest that P.A.T. testing is a separate job/contract from installation testing and you then negotiate a separate price for each job.

Cheers Davie for helping out on this, I have had a long day and only just sat down to log on the forum.

 

[SPECIAL LOCATION]

For Monkey5 and Badger, I see you didn't get a reply to your question so here's the amswer.You divide the 230 volts by the 3.65 megohms and it gives you the value 0.000063 amps. This of course is only when nothing is plugged in and switched on. My advice would have been, do the test with nothing connected to the ring, after all, you are supposed to be testing the 'hard wiring only', not any appliances as well, that's what Portable appliance testing is for. The method you used is really to save you time disconnecting things like dimmers, indicator lamps, transformers etc. So assuming a client is paying you to do the testing, you should suggest that P.A.T. testing is a separate job/contract from installation testing and you then negotiate a separate price for each job.

3. Was it unreasonable to ensure all items were disconnected because I think really the guidance is to do L/N to E where it would not really be practicable to do the normal tests ie lighting ccts with loads of trannies.

In a perfect world yes... Disconnect everything,

take all the time in the world,

the customer doesn't mind they will pay the extra 3 hours hide & seek disconnecting & reconnecting everything

just to verify what you already know is safe and compliant with regs is Actually still safe and complaint with regs!

:|

You are both missing the point that OFTEN is is very impractical to FULLY disconnect everything from a ring main as well, not just lights ...

consider...

1/ An security alarm panel connected via a NON switched fused spur (to prevent anyone accidentally turning it off) taking ye ole fuse out don't disconnect the neutral from the appliance!

2/ That 4way multiblock with integral neon that has been plugged into the socket which is now behind the wardrobe / Bunk-bed / Chest of draws that don't move easily or NOT at all.

3/ That 6way multiblock with integral surge filters with all the computer stuff plugged in, that has been plugged into the socket which is now behind back of the draws on the computer desk wot you cannot get enough room to get the plug out!

4/ The multiple group of sockets right at the back of the TV & video or hi-fi equipment that is now built into the back of a cabinet or is not physically possible to reach without dismantling entertainment system or moving the large TV unit.. that needs two or three people so that the legs don't break off the unit!

5/ That socket in the kitchen with the extractor hood plugged into it, wot the builders hid behind the decorative chimney bit... but you need to take the extractor hood down to get to!!!

6/ And that socket underneath the kitchen units wot the plinth heater has been plugged into..... And you need to dismantle the plinth to get to it!

7/ The socket that the built in dishwasher is plugged into, that the git kitchen fitters didn't an isolation switch for, and you cant dismantle and remove the dishwasher.

8/ The socket behind the big American fridge freezer that cant be moved unless it is emptied!

9/ The socket everyone forget to tell you about and you cant find hid down the corner of a bedroom with a room fragrance thingy still connected.

10/ That doorbell transformer that may have been wired onto the ring via a non switched fused spur (cuz they didn't want to accidentally turn the doorbell off!)

11/ The bit of power in the conservatory that had been extended off the ring, supplying sockets and the lights also put off a Non Switched fused spur so no-one accidentally kills the supply for the light!

12/ The outside security PIR sensor light that DIY bob connected to a non switched fused spur in the bedroom.

13/ An RCD fused spur hard wired in supplying the garden pond pump? reading across the back of the RCD?

14/ An RCD socket outlet reading across the back of the RCD? open up & disconnect?

etc...

etc... :_|

There are many instances where you find something connected electrically safe... but a sod to disconnect for testing!

Ideally it is nice if you can disconnect everything....

But quite often it is simply just NOT practical, even on socket circuits not just light!



OR

you could just read the Notes on Reg 612.3.2

AND ESPECIALLY

reg 612.3.3 page 158 BRB

wot says quite clearly test between the LIVE conductors together to Earthting arrangement.

Guinness

 

[SPECIAL LOCATION]

For Monkey5 and Badger, I see you didn't get a reply to your question so here's the amswer.You divide the 230 volts by the 3.65 megohms and it gives you the value 0.000063 amps.

Not withstanding the point that the IR test is actually being done with an instrument that generates either...

250v DC

500v DC

or

1000v DC

in accordance with the appropriate nominal circuit voltages, as per table 61 on page 158 of Big red!

you is either going to be looking at

250v DC / 3.65Mohm = 0.0000684 amps

or

500v DC / 3.65Mohm = 0.000137 amps

BUT more often than not the actual IR value will be different at the different test voltages.

so @ 230v Ac you may NOT actually get a 3.65megohm ????

 

[monkey5]

i know its been a while since this post but just thought id update (as i got round to retesting yesterday) and let you know what was causing me the low reading - the outside RCD socket outlet spurred off the ring..

SL did mention it could be this but unfortunatly i missed it!!

cheers wayne