Masthead light wiring

[Piddy]

Having just looked at the recommended size of wire for a tricolour on a Moody 376, I'm curious to know if it will fit up the conduit in the mast provided for it.
The light was fitted a few years ago when we got the boat but has only worked twice when it was new. The horrible domestic mains cable that was fitted is now a dull brown/black colour and is useless.
So, apart from changing to outrageously expensive new wire, the question is - what size?
Index marine and Merlin both have tinned copper wire at around £4.00, but I don't want to buy without being sure it will fit.

-has anyone got experience with this size of wire?

Cheers

Andy

 

[Piddy]

Oops! I should say I am considering 2.5 sq.mm conductors giving about 11mm overall diameter.
Remind me to read what I type!

 

[simonfraser]

how long did the domestic cable last? how long will you keep the boat for?

 

[Piddy]

It stopped during the second season. I hope to have the boat for many more years.

 

[Becky]

HWMBO says:-
I've made one or two assumptions about the boat, based on our Moody 37 which to all intents and purposes is the same. Mast height 45 ft, cable run inside the boat above the head lining to the rear cabin door and then back to the switch panel 20 ft. Total cable run 65 ft. Total conductor run 130 ft. Assume a 25W bulb, current will be 2 Amps.

2.5sq mm conductors in conduit will carry 21 Amps, so no problem there. IR drop (loss of voltage due to current flow) will be 15 mV / m in this size of conductor. ie 600 mV loss. With this size of cable this can be ignored provided your battery voltage is good. If you go down to the next size of conductor, which is 1.5sq mm the loss will be almost 1 Volt. So, if possible stick to the larger size.

It is far more important to insist on tinned copper conductors. This will almost stop the deterioration of the conductors in a (salt water) marine environment. You may not be able to get cable made up of tinned copper conductors, so you might have to use single conductors (multi strand of course) twisted into a cable.