Ze on a light circuit

[too old to learn]

Just a quick easy one for clarification

when measuring the Zs value on a light circuit they normally say measure at the extremity as this is where it will be highest.

However, I have a situation where my highest reading is on the second loop in loop out ceiling rose (out of 5). This is becauase of two way switching and the length of run to one of the switches.

Am i correct in thinking that this is acceptable?

Or the main poitn im tryign to get at, do you only do the Ze reading on the loop in loop out and therefore disregard the switchign live?

Thanks

 

[holmslaw]

..

 

[ColJack]

it's always awkward doing Zs on lighting..
with T+E, the earth continues from the last light to the switch, but the live returns to the light..
so which is the furthest point?
the switch, where you are then missing out the length of the switched live, or the light, where you are missing out the length of the earth to the switch...?

 

[cleverspark]

I cant remember the exact difference to be honest.

I think the value i was getting for the R1+R2 taking in with the switch wires was something like 3.5 ohms.

just taking on the last link of the loop in out was 1.9 or something.

im going back tonight where all em test sheets are so could confirm if need be / or interested.

 

[Taylortwocities]

Test Zs at the point where R1+R2 is highest.
It should only be a formality for a lighting circuit. You would need a very long lighting run indeed to exceed the max EFLI even on a 6A breaker using 1mm.

 

[holmslaw]

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[mikhailfaradayski]

"cleverspark" has stolen the identity of "too old to learn", I wonder if he's bumped him off.

Strange things happen on these forums. Its a bit like a Russian Sparky, with knowledge of UK wiring regs, currently residing in Switzerland!

 

[holmslaw]

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[Taylortwocities]

You, Tobleroneski!

 

[holmslaw]

..

 

[mikhailfaradayski]

I think you've lost yerself

No Flag for Zaire?

 

[Taylortwocities]

He's a real nowhere man,
Doesn't have a point of view,
Knows not where he's going to

 

[holmslaw]

..

 

[GaryMo]

Here's another idea - measure R1+R2 at every point, record the highest and then add this figure to the figure you obtained when measuring Ze there's your calculated Zs.

 

[GaryMo]

it's always awkward doing Zs on lighting..
with T+E, the earth continues from the last light to the switch, but the live returns to the light..
so which is the furthest point?
the switch, where you are then missing out the length of the switched live, or the light, where you are missing out the length of the earth to the switch...?

Normally the switch (not exactly the furthest but the highest R1+R2 reading) as generally the switched live would be 1.5mm2 whereas the cpc would be 1.0mm2 (assuming 1.5 t&e).

A 1.0mm2 conductor has a higher resistance per meter than a 1.5mm2 conductor.