Increasing Size Of Cable Conductor

[annieigma]

Hi,

We want to install a door intercom. it says the conductor size of the cable should be 0.75, it works on 12v DC and consumes 1000ma. I have some telephone cable for oudoor use, but its 0.5 conductor. the telephone system is 50vdc. so, if we joint two wires together to make one conductor, and another pair to make the second conductor, have we now got a 1.0 cable conductor? Will this work?

thanks,
Annie.

[The Builder]

Annie, 0.5mm has a current carrying capacity of 3 amps with a DC supply.
It should easily handle your 1 amp on its own.

Assuming the higher impedance of the 0.5mm cable doesn't present a problem, then it should be fine.

[bert_h]

Two conductors of diameter 0.5 each are equivalent to one conductor of diameter 0.707, because it goes by area.

[Old_Geezer]

Provided of course the wires are in parallel not series ;-)

[annieigma]

Thank you builder.
the 0.5 cable has a resistance of 13 ohms per mtr, so if the cable run is max 30 mtrs, total resistance is 390 ohms. therefore......... buggered if i remember the rest. ohms law was not my favourite subject. I only remembered the ohms to mtrs because it was a slogan almost, used by us GPO girls to measure faults,
" resistance, in ohms, is inversely proportionate to length in mtrs."
what a lovely phrase.
annie

[BRIGHT SPARK]

annie.....resistance is PROPORTIONAL TO THE LENGTH.If the resistance reduced with length I would be a lot richer :-)

[heathfield]

Are you sure about the resistance of the 0.5mm wire, Annie? 13 Ohms per metre seems very high. According to tables for copper wire, the resistance should be just under a tenth of an Ohm per metre.