Andy Burns snipped-for-privacy@andyburns.uk wrote in news:i8ar27Fr30pU1 @mid.individual.net:
3 times.All the phases are carring 32A so that power has to go somewhere, it doesn't matter if the currents cancel in middle.
If in doubt consider 3 x 32A loads to neutral > 3 x power.
Triple and earth for two way switch circuits had two reds and a black. Shows you how old my drum of it is.
Never seen that. I have seen triple red and earth.
And a black core would suggest the intention was to use a neutral?
Could it be intended for looping in a succession light fittings with switched live from a smaller number of switches being connected between them?
No idea.
I found some old red white and blue (with no earth) stranded 3 core a few months ago.
The white changed to yellow in 1966 when I believe that the compulsory earth was added.
From the thread I started a couple of years ago with the subject "Old wiring":
"The old metal-cased picture light came off easily enough, to reveal a connection to red and blue wiring (it was not earthed)! The cable was plastered in, but digging some of the plaster out revealed white PVC cable. A bit more digging, and a cut-off third conductor with very light yellow (maybe off-white?) insulation appeared. Then a cut-off bare earth wire. So it looks like someone used some spare 3-phase cable for this lighting circuit. Sigh."
This place was built from 1965 to 1966, and /some/ of the lighting wiring is earthed.
I'm not sure either. To follow the convention of the day, if using for switching two lights, it would be one red and two blacks. I bought it from a local place that was big on Exchange and Mart. Makes perhaps some sense for a room thermostat. But only some.
I suppose all three cores in a triple and earth should have been all red in the past and all brown currently since at some point in two way lighting they are all live/line with the common always live.
Richard
Nuisance to wire if you have to use some kind of circuit tracing device to know which is the common wire at the other end, though.
Now it's a while since I last stripped out a conduit install using the old cotton insulated cables. But yes they did use blacks and reds for two way switching - presumably to identify the perm live and switched live. But this was in singles and not 3 core and earth.
With 3 red/brown core and earth you can identify the cores by the layout with respect to the earth (and no I am not going to call it a cpc). ie red1 earth red2 red3 is the same at both ends.
Just to note that when using singles the wiring for 2 way switching was different to todays standard setup.
Hadn't thought of that. But did they have earth wires in the old days?
I guess you could have live on one switch common and switched live on the other. Is there any other way than that?
In my factories, most machines were hard wired into the supply, using single core conduit wiring cable, running through trunking, rigid conduit or flexible conduit. Using that, 32A would need 4mm2.
I agree. As far as I am aware there are no set standards for which colour should be used where, although with modern three core wire I suppose brown should be COM as it is the permanent live leaving black and grey as the two switched lives.
Even the term Common in DC circuits is usually the negative (-) connection yet in two way lighting it is the live/line.
Richard
For singles that is pretty standard.
When using a 3 core as the strapper then would normally you would have perm live at L1 and switched live at L2 at the same switch and just match up the second switch terminals using the 3 core.
Don't you tend to end up in an ordinary house with the live supplied from the opposite floor to the light fitting?
Ok, that latter is the popular thing nowadays, but I can't think of any third way to do it?
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