r1 and r2 Stranded cable

[stilllearning]

Hi Folks

Is the difference in the r1 and r2 readings of stranded 2.5mm T&E the same as for solid T&E; i.e the resistance of r2 is about 1.67 greater?

Just done a test on a ring circuit cabled with stranded and get 0.12ohms for phase and neutral and 0.3ohms for earth (this was after I checked and tightened all accessories - it was originally 0.36). The 1.67 rule says it should be nearer 0.2ohms.

Is it true that you should now recommend a rewire if stranded cable is found??

Thanks

 

[plugwash]

IIRC older 2.5mm T&E often has a 1mm rather than a 1.5mm earth, this shouldn't be a problem though in a normal domestic sitation provided Ze meets. If you are really paranoid you could calculate the adibatic to check.

I don't belive there is any need to rewire a property with stranded T&E in good confition.

 

[stilllearning]

Brilliant, thanks Plugwash.

 

[Adam_151]

If its stranded T+E , its quite likely to be 7/.029 (2.9mm²) with 3/0.029 cpc (1.3mm²) You really ought to do the adiabatic to check, but any installation wired with imperial cable will be quite a few years old and may not be suitable for todays loads (eg one rfc for whole house, not enough outlets, etc), so perhaps its time to rewire anyway!

When metric cable first came out (which is when T+E went to solid for smaller sizes), 2.5mm² T+E had a 1mm² cpc, this became 1.5mm² when someone realised it failed the adiabatic for a BS3036 fuse, it can be used on a 1361 provided the Zs is below 0.8, breakers you'd probably need the design data from the breaker manufactorer to check, but you should be ok as long as the Ze is not below 0.2 ish (with breakers, its the highest fault currents that presents worst case, with fuses its low currents and drawn out disconnection times)

stranded 2.5mm² T+E does exist, but is quite rare