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telecom cable OK with 12 volts?

 
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mistafeesh



Joined: 07 Oct 2006
Posts: 2

PostPosted: Mon Jun 14, 2010 11:40 am    Post subject: telecom cable OK with 12 volts? Reply with quote

Hi, I have a nice big reel of telecom cabling that I rescued from a friends hotel when he was selling up. It's got 10 cores of solid brass wire 05.mm wide. It says on the reel "5pr 0.5mm PET", and it looks like this:

It's Belden cable, with the product code 055730, but I couldn't find any info on it googling or looking on the belden website.

I want to use it for wiring in a campervan conversion that I'm working on, and it'd be utterly awesome if it could carry 12v for lighting and other stuff. Then I could use some cores for supplying power, and other for speakers etc.

Any advice on how to tell if it's safe?
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torbjorn



Joined: 07 Jun 2007
Posts: 370
Location: Sweden

PostPosted: Fri Jun 25, 2010 9:14 pm    Post subject: Reply with quote

The voltage should not be any problem for that cable, but due to the small cross-section area of the conductors, such cables are not of much use for 12 V lighting and power distribution installations.

0,5 mm conductor diameter gives an area of approximately 0,2 mm². Although a such conductor can carry a current of up to 2 or 3 ampere, the voltage drop will be very annoying.

For speaker installations, you can use that cable without restrictions. As a rule, keep the wiring resistance below 10 % of the speaker impedance. I.e. for 4 ohm speakers, the wiring resistance should be below 0,4 ohms. For this cable, this limits the length to 2,3 m. For larger lengths, you should connect two or more conductors in parallel.

I recommend that you use at least 0,75 mm² wires for all lighting and power installations. Calculate the voltage drop in each case to check whether this is sufficient or if you need a heavier wire. Make sure that you use fuses of correct rating for the wire area in order to avoid a fire in case of a short circuit. As a rule, maximum 6 A fuse for 0,75 mm² wire, 10 A for 1,5 mm² and 16 A for 2,5 mm² (this is for fuses rated according to european standards, for fuses according to US or Canada standards you can multiply the rated current by 1,2 or 1,3). Also, you should calculate the short circuit currents and check the breaking time graphs for the fuses to make sure that the short circuit current surely will cause the fuse to blow within 5 seconds, preferrably within 2 seconds.
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