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What size cable please

Discussion in 'Automotive Electronics' started by Tony K, Mar 31, 2017.

  1. Tony K

    Tony K Member

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    Hi,

    For those of you who don't know I am about to fit a replacement engine in my boat of 6m.

    I am using relays for starter, engine stop solenoid and I have discovered the engine has a coil heater in the air intake. (Diesel Engine system 12v).

    The heater draws 33 amps, I am fitting a timer relay (because it needs to run for 60 seconds) of 10amps connected to another ordinary relay of 40 amps for this.
    The engine stop solenoid draws 30 amps and so I am using a 40 amp relay.
    The starter motor solenoid I am using another 40 amp relay.

    1. Looking at all the charts it appears that I should be using a 10mm cable to supply the power to each from the relays, but this seems a bit big to me? Maximum cable length in each case will be 2 metres.

    2. Also will 1.5mm cable be OK to carry the operating current to the relays from the switches ( max 2 meteres) and what fuses should I use?

    3. Same goes for the ignition circuit, what is a normal fuse for a supply to this please?

    4. I am using a 5 core cable ( 5 x 1.5mm) to run power up through my hollow mast to the roof where it will power 3 x LED navigation lights (say 0.5 amps each), 2 x LED interior lights (say 0.5 amps each), 1 x horn (5amps) and 1 x LED search light (1.5 amps). One cable for each item plus a common for earth. My question is, with a possible total at one time of 9 amps is the common earth at 1.5mm big enough or should I run a separate 2.5mm earth cable?

    Thanks
     
  2. Old dog

    Old dog New Member

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    Hi tony, I,m no engineer but hope this helps.
    most cable makers quote (cross sectional area) so at 10mm squared, you actually have a cable that's about 3.5mm in diameter.
    also hope this helps. http://www.rpc.com.au/pdf/Wire_Chart.pdf
     
  3. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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  4. dave

    Dave New Member

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  5. Tony K

    Tony K Member

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    Thanks Guys
     

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