Continuity Assistance - Lighting Circuit with readings!

[dizz]

Just wiring up a lighting circuit (line and neutral connected at board) and everything was going well with my continuity tester - hearing the beeps and moving on ... but I wanted to ask a question, because something looks suspect when I started testing my two way light switch. Here's the set up, and if you can help me, I'd appreciate it.

1. I've done the lights through to the last one, and get 1.15 ohms (Testing L/N, and L/N connected at board).

2. I have JB to spur off from one of the lights closer to the CU in the circuit, then have a normal T&E going to one switch and 3 Core and Earth connecting that switch to a second switch. The switches operate two light in parallel.

3. Now, when I directly connect the T&E switch using a connector block (and not connecting the switches together) just to test that both lights come on, I get 0.62 ohms from Light 1, and 0.73 ohms from Light 2 (running to the CU). This makes sense, as light 2 is a little further away.

4. Now I disconnect the connector block to wire up the 3 core to connect the two switches, and test again. This time I get 2.01 ohms and 2.17 ohms from Light 1, and 2.10 ohms and 2.13 ohms from Light 2 (closing switch one and opening switch two and vice versa). Now given that a lot more cabling down stream to the furthest ceiling rose only gets me just over 1 ohm, this seems far too high, so ...

5 ... I disconnect the two switches to test continuity down the 3 Core. I directly connect the three cores at one switch together, and test between pairs of wires at the other switch, and get 0.22 ohms (for each of the combination of pairs).

6. In summary, the resistance down the 3 cores is 0.22 ohms, the resistance using a standard 2 core switch to operate the lights gets me 0.62 and 0.73 ohms, the furthest ceiling rose gets 1.15 ohms, but when I try to connect the 3 core it jumps up to over 2 ohms. The distance of the 3 core is about 5 metres. The connection of the 3 cores to each switch is the same and matched to COM / L1 / L2. The connection of the 2 core goes to L1 / L2.

7. In my mind, I am happy with the resistance down the three cores by themselves, down the single 2 core switch connected by itself, my connections are tight - I've checked them over and over ... does it just leave the problem down to a dodgy switch, or am I missing something?

 

[PrenticeBoyofDerry]

Is this a two way lighting circuit?
What does your r1+r2 read?

 

[dizz]

1. Yes - (hence the four resistance readings (at point 4 above) - two each at the two lights)

I feed off one of the earlier lights (i.e nearer the CU) and do this.

Feed into JB - Out to : T&E to light 1, T&E to light 2, T&E to switch

At Switch 1 - T&E coming in, and 3 Core going out to 2nd switch

At switch 2 - 3 Core

2. I haven't done a R1+R2, I'm just literally doing the wiring. I have done this by connecting L/N at the CU, and work forward from there, testing for continuity as I move down the circuit. I finished the main run to the furthest light, and I have just come back to an earlier point in the circuit to get the spur to do the two way lighting in the hall (as I mentioned, the feed goes to two lights, and there are two switches (two way switching to operate both these lights (in parrallel, at the same time)

[added - As I move down the circuit, I just test for direct continuity at each ceiling rose I wire, and switched continuity, from the switched live at the ceiling rose - everything was looking good until I came back to spur off and I didn't get the continuity buzz after wiring the two way lighting, hence my check of resistance with the Megger).

3. ALL resistance readings I have given relate to the resistance from the point taken, running to the CU (apaert from my little test to verify the resistance of the length of 3 core).

 

[dizz]

As I see it, if I get 0.62 ohms without the two way switching at Light 1 (i.e. by using a standard switch), and 0.22 ohms down the 3 Core, when I wire up the two way switching I should see about 0.84 ohms but it's over 2 ohms (uuuhhggg).

 

[PrenticeBoyofDerry]

What distances of strapper cable, what the CSA of the cable and how you testing them?
You should be testing for r1+r2 though not r1+rn!

 

[dizz]

What distances of strapper cable, what the CSA of the cable and how you testing them?
You should be testing for r1+r2 though not r1+rn!

The 3 Core is 5 metres (as per point 6 in my original post), and 1mm for the new cabling.

I am not doing testing at the moment that's why I am not quotiong any R1 R2 figures - I only gave the resistance figures because of the glaring problem, which is thus.

1. With a one way switch connected, and going to the ceiling rose, and using a Megger, appropriately zeroed, and with the L/N connected at the CU, I get 0.62 ohms - that's the run from that ceiling rose to a couple of others to CU and back)

2. Now removing the one way switch and using a 2 x two way switches with 1mm 3 Core connecting TWO switches, about 5m apart, I go back to the same ceiling rose. The only extra bit of cabling is the connection between the two two way switches. But now I get just over 2 ohms.

3. That looked odd, so I think somehting might be wrong with the cdable between the two switches, so I go to one of them and connect all three cables, go to the other and check the resistance along this cable ONLY (not back to the CU). I get 0.22 ohms along each pair (3 results the same as expected).

4. 0.62 + 0.22 does not equal, or is anywhere near 2 ohms - I would expect to see 0.84 ohms - i think it must be the switches.

 

[PrenticeBoyofDerry]

the switches will offer some resistance, try linking them out and see what you get.

 

[dizz]

OK - will test each one in the morning to see if they are similar. If it's the switches, would you think that an acceptable level of resistance?

 

[PrenticeBoyofDerry]

Well it's higher than expected, have you got other switches to swap with?
But r1+r2 and Zs is what we need.

 

[riveralt]

OK - will test each one in the morning to see if they are similar. If it's the switches, would you think that an acceptable level of resistance?

You know there is a very good reason to dead test in the proper order
Continuity
Insulation Resistance
Polarity
rather the haphazard way you seem to be approaching this.
First thing is to draw out your circuits so that you can see where potential problems could occur.
Then do the R1+R2 test - do you know how to do that?
You should expect the continuity value to increase the further you are away from the consumer unit.
What value have you got for Ze by the way?

If you think you are having problems with the two way switch then disconect the strappers first at the switch which controls the power and test that you have continuity up to that point.

The Zs =(R1+R2+Ze) reading should always be read from the last ceiling rose (point) on the circuit.

 

[dizz]

OK - will test each one in the morning to see if they are similar. If it's the switches, would you think that an acceptable level of resistance?

You know there is a very good reason to dead test in the proper order
Continuity
Insulation Resistance
Polarity
rather the haphazard way you seem to be approaching this.
First thing is to draw out your circuits so that you can see where potential problems could occur.
Then do the R1+R2 test - do you know how to do that?
You should expect the continuity value to increase the further you are away from the consumer unit.
What value have you got for Ze by the way?

If you think you are having problems with the two way switch then disconect the strappers first at the switch which controls the power and test that you have continuity up to that point.

The Zs =(R1+R2+Ze) reading should always be read from the last ceiling rose (point) on the circuit.

I don't think it's haphazard at all. As I have said I am not "testing" anything yet - I am just connecting the switches, ceiling roses, and junction boxes - I have connected the L and N at the CU so that I can ensure the L/N runs to the next light and that the switch switches L. It doesn't preclude me from connecting E and L at the CU to then test whether I am actually switching L at the switches (an not neutral for example) as the next step, nor taking R1+R2 readings later. I was using a basic continuity tester as I go along to check continuity. Its all dead, so what's haphazard about it? Do you take R1+R2 at each connection, check with R1+R2 tables before moving on? I only got the Megger out when I saw a potential problem, and as I was near to completing the wiring, I thought I'd check resistance levels because it was blindingly obvious something was wrong. Can I Please Leave now?

 

[riveralt]

I don't think it's haphazard at all. As I have said I am not "testing" anything yet - I am just connecting the switches, ceiling roses, and junction boxes - I have connected the L and N at the CU so that I can ensure the L/N runs to the next light and that the switch switches L. It doesn't preclude me from connecting E and L at the CU to then test whether I am actually switching L at the switches (an not neutral for example) as the next step, nor taking R1+R2 readings later.

The purpose of conducting R1+R2 test is to test for continuity and polarity.

I was using a basic continuity tester as I go along to check continuity. Its all dead, so what's haphazard about it?

Well as I said, but you seem to have missed, the order of testing is important, your haphazardness is not necessarily from a danger perspective but rather your illogical approach to testing leading to your current confusion.

Do you take R1+R2 at each connection, check with R1+R2 tables before moving on?

Yes you should (though you should already know the Ze so you can quickly see if the Zs exceeds the maximum allowed for that cable and MCB size) - and you would see the resistance values gradually increase as you got to the end of the circuit.

I only got the Megger out when I saw a potential problem, and as I was near to completing the wiring, I thought I'd check resistance levels because it was blindingly obvious something was wrong. Can I Please Leave now?

You can leave anytime since you don't appear to want to hear the advice being given - in part I suppose by the frustration of not being able to understand whether the readings you have are actually a problem or not.
If this blindingly obvious problem is so blindingly obvious you should be able to physically see what the problem is - which is why I suggested you sketch out the circuit you have created and work through the problem logically.
If the problem is the way you have wired this part of the circuit rather than a loose terminal connection creating a higher than normal resistance value, then the drawing will help you diagnose it quickly.
Double check when using a two way switch that the line drops to L1 and the switch line moves to L2. The three strappers colour conductors must be in the same terminal numbers C, L1 and L2 in both switches.

 

[dizz]

Tested the resistance across the Com-L1, and Com-L2 on both switches today. First switch has negligible resistance (0.02 ohms) when closed, while the other switch has 0.78 ohms. It didn't even occur to me that I would be in possession of a brand new dodgy switch fresh out of its wrapper!!! Time to return it.

Riveralt "Can I Please Leave" was just a bit of fun, my way of remembering which order to do the tests ... but I'll be back on here when I run into trouble during my testing, which will be next week sometime ...

 

[riveralt]

Riveralt "Can I Please Leave" was just a bit of fun, my way of remembering which order to do the tests ... but I'll be back on here when I run into trouble during my testing, which will be next week sometime ...

No problem, always willing to help - though the reading you have so far would suggest you will be well within the B6 Zs limit..
Just remember when stuck testing or problem solving its sometimes worthwhile stopping what you are doing and having a cup of tea - then get back into it. If that doesn't help there always whiskey and failing that come back here.

BTW new switches are sometimes sticky and a few seconds flicking them on and off sometimes clears the cobwebs - might be worth trying that before you take it back.

 

[dizz]

Now I'm getting a bit hacked off - Continuity on the circuits, and finnaly started to attck the ring. Cross connect CPC and neutral at the CU and took a reading of 0.85 ohms. Checking for bridges, so cross connect both phase and neutral at CU, and go round the sockets, 0.21, 0.24, 1.74, 0.22, 1.55, ... and on one double socket I get a reading of 0.22, and on the same socket, over 1 ohm. Click the switches and the reading changes a bit, sometimes I can get it down to just over 0.2 ... it's all looking a bit problematic.

Take the face off and I get a solid reading within 0.05. So what is it with these sockets? I have bought the contractor pack from Toolstation - OK not the best, but surely you should expect a little bit more?

I have eliminated the socket tester I am using and I have opened up live and neutral by pushing a screwdriver in the earth and pushing the tester staright in. And it's not the Megger cos I get accurate readings from behind the socket???

Does anyone else get this problem with the Toolstation packs or is it me buying one off faulty batches, and should I be worried if I left them in situ?