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hi have been doing some testing on a existing light circuit usual methos line /cpc linked at board leads and link lead nulled. come accross a very strange problem regurding a R1 R2 reading

Now measuring between sw live and cpc. rose 1/ 0.47 rose 2/1.15 (2WAY SWITCHING) 3 rose 3/0.51 rose 4/ 0.54 rose 5/1.07 rose6/1.97 (2 WAY SWITCHING)

all connections at rose 2 have been checked, switch connections on 2way switching checked, resistance of the actual switches has been measured and switches replaced as i just just thought it was a bad connection giving a false reading,or a high resistance switch but im still getting a high reading which is impossible as the R1 R2 reading at the next rose in the line is only 0.51. Its very strange as the measurment from loop in at the rose to CPC is fine and is as expectected which scuppered my other theory that this rose had been wired out of sequence.

any ideas any one. Just to add when ZS tested readings as expected which again just makes iot stranger.
 
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O

Octopus

Had some similar this week (R1 + R2 of 2.4ish) whereas the "previous" fitting was 0.95, so I disconnected the pendent, fitted a new one and all the readings returned to what I was anticipating to see.

I was doing a CU change so couldn't see what the Zs would have been

Have fun.
 

widdler

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Mentor
Arms
I would double check that it is not just resistance of the contacts in the switches.
 

spark 68

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Arms
Esteemed
hi have been doing some testing on a existing light circuit usual methos line /cpc linked at board leads and link lead nulled. come accross a very strange problem regurding a R1 R2 reading

Now measuring between sw live and cpc. rose 1/ 0.47 rose 2/1.15 (2WAY SWITCHING) 3 rose 3/0.51 rose 4/ 0.54 rose 5/1.07 rose6/1.97 (2 WAY SWITCHING)

all connections at rose 2 have been checked, switch connections on 2way switching checked, resistance of the actual switches has been measured and switches replaced as i just just thought it was a bad connection giving a false reading,or a high resistance switch but im still getting a high reading which is impossible as the R1 R2 reading at the next rose in the line is only 0.51. Its very strange as the measurment from loop in at the rose to CPC is fine and is as expectected which scuppered my other theory that this rose had been wired out of sequence.

any ideas any one. Just to add when ZS tested readings as expected which again just makes iot stranger.
This could also be down to the different lengths of the switch drops, what are your readings like on the P Lives to CPC ?
 
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  • #5
thats a thought one thing i didnt measure maybe its pendant giving a high reading at that point, what is baffling me is the next pendant is showing a lower reading surely this pendant would also be giving a high reading
 
Could it not just be a long 2 way cable route? 1.15 isn't that high anyways
 
  • Thread Starter Thread Starter
  • #7
readings on lopp lives to cpc are fine all away round the radial and as expected even at rose 2 (problem rose)

whats baffeling me is the high reading at rose 2 (R1 R2 ) between sl and cpc dissapears at the next rose. which seems impossible as all switches closed on circuit. if the reading is on rose 2 it should carry forward to rose 3 reading and so on
 
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  • #8
the reading of 1.15 is not really a major problem its the fact the next rose is 0.51 which is impossible as the reading of the next rose has to be higher
 
Not on 3 plate wiring though mate, the lives are looped at each fitting so you need to take a measurement at evry fitting really, regardless of which rose it is in the circuit, the landing light normally gives the highest reading due to its lengthy 2 way switch wires
 

spark 68

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Arms
Esteemed
the reading of 1.15 is not really a major problem its the fact the next rose is 0.51 which is impossible as the reading of the next rose has to be higher

Why would it ?, as surely the next rose has it's own S/L, unless both on the same switch.

As I said it could be the longer switch drops, and as Widdler said it has to go through two switches on the 2-way circuit.
 
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  • #12
the resistance measured at the rose (3) surely cant be lower than rose 2 no matter how long the switch wires are as the resistance measured at rose 3 should include this. if all switches on circuit are switched on
 

spark 68

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Arms
Esteemed
the resistance measured at the rose (3) surely cant be lower than rose 2 no matter how long the switch wires are as the resistance measured at rose 3 should include this. if all switches on circuit are switched on
Yes it can,
think about it,
you have your PL to the rose which you said is fine, then it has to go through the length of the switch cable to the switch, and then through the switch and return back along the switch cable to the lamp connection, so depending on how long the switch cable is will alter your readings.
 
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  • #14
yes totallly agree spark that the longer the switch run the higher the reading but wouldnt the previous switch run resistance still show if all the switches are in closed postion at the next rose or am i missing something simple here its been along day
 

Strima

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Arms
Esteemed
yes totallly agree spark that the longer the switch run the higher the reading but wouldnt the previous switch run resistance still show if all the switches are in closed postion at the next rose or am i missing something simple here its been along day
No it wouldn't as your measuring the resistance on the loop and the specific switch run for that pendant. By your way of thinking non of the lights would work if the previous switch in the run was in the off position.
 

spark 68

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Arms
Esteemed
yes totallly agree spark that the longer the switch run the higher the reading but wouldnt the previous switch run resistance still show if all the switches are in closed postion at the next rose or am i missing something simple here its been along day
I think you are confusing your switch lives with your permanent lives.

The switch cable may be quite abit longer (bearing in mind the S/L has twice the distance of the run) than the next roses P/L which is only one length of the run (no return).

Each rose normally has it's own S/L unless both roses are switched from the same switch.
 
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spark 68

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Arms
Esteemed
Ian,
your S/L's are all only connected to the P/L via the switch cable at one side of each switch, you are effectively measuring your R1 at the other side of each switch at each rose, these are seperated from each other, or else all of your lights would come on together
 
  • Thread Starter Thread Starter
  • #18
thanks alot guys for all your help much appreciated
 
P

PC Electrics

Draw it out on a piece of paper and it will become obvious to you what is being said above.

thanks alot guys for all your help much appreciated
Does this mean you're fed up thinking about it, or is the "light" on now?
 
  • Thread Starter Thread Starter
  • #21
yes thanks guys the light has come on as has been said when you draw it out its obvious thanks again
 
M

Moses

thats a thought one thing i didnt measure maybe its pendant giving a high reading at that point, what is baffling me is the next pendant is showing a lower reading surely this pendant would also be giving a high reading

there could be a connector/ J/B on the switched wire, with loose connections giving rise to Hi R1+R2
 
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