Discuss Periodic--R2 method-- Ring Main i.d. problems in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

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Silk6911

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Hey guys,

Carrying out a periodic on an office/factory premises with several medium to large 3ph DB's. (36 way etc)
I'm finding one of the biggest pains is trying to find the relevant ring loops (L-L ,N-N, Cpc-Cpc if any!!)..A lot of the circuits have not been connected sequencially (or marked) on the nuetral and earth bars and it's becoming a time and cost issue now to try and find them. Some of the DB's are a nightmare!

What i'm looking at doing is just using the R2 method with the wander lead to at least prove an earth path back. Been told as a rough guide under 1.00ohm is good. There was an R2 table to refer to in the old regs but this seems to have been removed from new 17th edition.

Is it ok to use R2 method for ring mains?

Obviously can note as a code 2 or 3 " poor id of ccts requires further investigation" ...but seems a bit of a get out.

Any advice/tips would be great.

Ta
 
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Spudnik

  • Thread Starter Thread Starter
  • #2
PIR's are only an assessment of an installation, and any defects should be recorded and coded as appropriate.

Sorting out an un identified ring shouldnt be a prob as r1, r2, and rn's should sort them out from each other.

You may find this difficult to do tho, if its done during working hours and power is needed.
 
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Guest123

  • Thread Starter Thread Starter
  • #3
Hey.

IMO end to end measurements are one of the most important tests on any type of form as they confirm the presence/absence of ring circuit continuity. Which in turn shows you if you have the correct overcurrent protection for the cableing.

I'm guessing you have DB's that look like a 3 year old put them together and this does make it very difficult but personally I would soldier on and made sure I found all my rings and that there was continuity between all.

You never know you may find something that if left uncheked could have caused serious problems.

At the very least you could ensure that all conductors connected as a ring actually are and then note that circuit numbers do not correspond on your departures sheet.

Sorry to have gone on a bit, hope this makes sense.
 
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acadennis

  • Thread Starter Thread Starter
  • #4
Hi,
Considerable care and judgement should be applied when deciding upon the extentof the installation subjected to testing, is special if you do not have previous reports or maintenance and modification sheets, as you know if the ring circuit has been extended this should be tested to confirm its continuity, no interconnections or spurs added, as well polarity.

However, alternative test may be carried out.
A plug in earth fault test instrument:
- incorect ring interconnections or spurs can be indicated, by comparing measured value of Zs at socket-outlets on different parts of the ring,
-the maxim value of Zs can be measured,
-a continuity of protective conductors at points or accesories can be confirmed, by measureing R2,(reading 0.05Ohms or less),
-a plug in polarity indicator, polarity of socket-outlets can be confirmed.

Hope this help.:)
 

old dog

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Arms
hi the test can be done from the sockets in the same way you woulde from the db
it wont id conductors at the db but all other rests are possible
 
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Silk6911

  • Thread Starter Thread Starter
  • #6
Thanks for help guys.

test at sockets instead...of course!...ta

yeah i'm checking polarity and loop impedance with the meter at the sockets too.

"-a continuity of protective conductors at points or accesories can be confirmed, by measureing R2,(reading 0.05Ohms or less),"--acadennis can i ask how you know that figure of 0.05 ohms or less??

I understand the principle of the R2 method (subtract the resistance of the wander lead your using) then your left with the R2 value,but cant find a regulation/regs table to refer the R2 value with. How do you know if R2 value might be too high?...or is it not that necessary as i'm measuring loop impedance values at the sockets anyway and reffering to Table 41.3 (etc) in the regs.

Thanks again guys
 
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