High R1+R2 / R1+RN

[Jefferson steelflex]

Hi guys,

Went to do some garden lights, was going to use the existing cable already feeding the old lights in the garden.
Did R1+R2 and R1+Rn on the feed, figures were roughly 1.2 ohms. The feed was tapped of the downstairs lighting circuit.
I further inspected the accessories, and i noticed the switch feeding the old garden light only had one cable with neutral sleeved as live and live going into common.
I then assumed, that there's obviously a junction box feeding all the downstairs lights, and switched in a similar fashion.

I checked all accessories and they were wired like this.

However, before commencing work, i wanted to just do another test on the feed to the outside garden, i was now getting R1+RN R1+R2 of around 33ohms!

I checked all accessories and they were securely fitted, i checked the db as well.
The homeowner told me there was a massive water leak as well, situated near the lights feeding the outside cable, which i presumed would cause high resistance due to the rust.
But I still can't understand why i got a low reading, then suddenly a high reading.

The downstairs lighting did have a dimmer and i didn't take out the bulbs to eliminate the resistance, but i didn't do that when I got a low reading either.

Does anyone have any ideas?

 

[Julie.]

What's R2 +Rn?

If that's still 1.2 ohm, then there is something in circuit R1 - has a switch been operated which previously shorted out a lamp or something

 

[radiohead]

I think you have got a little confused with you testing. You mentioned a dimmer, did you test through that switch to get the high reading? Remember as well there is no neutral sleeved red, it's a black, it's only neutral if it is connected to the supply neutral.
The test you need to carry out correctly is R1+R2. With the circuit disconnected connect line and cpc together either at the DB or at the furthest point on the circuit, then carry out a continuity test between line and cpc at the opposite end. If you are on a feed the position of switches will make no difference, if you are at a switched light then that switch will need to be closed or dimmer bypassed. There is no requirement to test R1 or R2 to the N conductor, but if you do so you will need to short out cpc to N at one end and test at the furthest end in the same way.
If any of those readings are high then you will need to break down the circuits to find the fault.

 

[Jefferson steelflex]

What's R2 +Rn?

If that's still 1.2 ohm, then there is something in circuit R1 - has a switch been operated which previously shorted out a lamp or something

I tested both neutral to live and live to earth to check if something is wrong with r1.
R1rn was just a quicker way of typing it.

I'll check your suggestion. Thanks
[automerge]1592590583[/automerge]

I think you have got a little confused with you testing. You mentioned a dimmer, did you test through that switch to get the high reading? Remember as well there is no neutral sleeved red, it's a black, it's only neutral if it is connected to the supply neutral.
The test you need to carry out correctly is R1+R2. With the circuit disconnected connect line and cpc together either at the DB or at the furthest point on the circuit, then carry out a continuity test between line and cpc at the opposite end. If you are on a feed the position of switches will make no difference, if you are at a switched light then that switch will need to be closed or dimmer bypassed. There is no requirement to test R1 or R2 to the N conductor, but if you do so you will need to short out cpc to N at one end and test at the furthest end in the same way.
If any of those readings are high then you will need to break down the circuits to find the fault.

Hi I didn't test at the dimmer, i only mentioned the dimmer because the whole lighting circuit is powered through junction boxes. The switch in question, was wired with one twin-e, the live (red) going into common, and the neutral (black but sleeved in brown) going to L1, and this switched on the old outside lights.

I have tested cpc and live at furthest point and at DB. Still same figures.

When i return, im going to remove the lamps and test it then.

 

[Julie.]

I tested both neutral to live and live to earth to check if something is wrong with r1.
R1rn was just a quicker way of typing it.

I'll check your suggestion. Thanks
[automerge]1592590583[/automerge]



Hi I didn't test at the dimmer, i only mentioned the dimmer because the whole lighting circuit is powered through junction boxes. The switch in question, was wired with one twin-e, the live (red) going into common, and the neutral (black but sleeved in brown) going to L1, and this switched on the old outside lights.

I have tested cpc and live at furthest point and at DB. Still same figures.

When i return, im going to remove the lamps and test it then.

R2+Rn is neutral - earth it's the only one which doesn't include line (R1)

Both your previous tests include the line conductor, if this is high resistance it would appear in both your previous tests, but shouldn't appear in the R2+Rn test.