Masts and Earthing

[chas]

As I was measuring up to see how much wire I would need to rewire my mast, it occured to me that I could use the mast as an earth for the various items of electrical mundungus hanging off it. Is this practical? I would be very grateful for any advice from the electrically initiated.

 

[HaraldS]

The way I read your question you seem to suggest using the mast to substitue the negative return wires- automotive style.

I would (strongly) recommend against that for two reasons:

(1) In general, the mast is (should be) solidly connected to ground for lightning protection, and in a good installation also your chainplates would be tied to ground. Also tied to this at some other spot is your battery bank minus pole, the engine, prop shaft and so on.

Any return current from your appliances up on the mast would go partially through the mast, partiaclly through the standing rigging and then spread out over your grounding system towards your battery minus.

Since some of these elements are connected outside and below the waterline, some small part of the return current will also make its way through the water.

In the end you could be provoking serious electrolytic corrosion.

For that reason, ships are almost religiously wired with all separate return wires. Anything else you will never get under control.

(2) I think you would also have problems making good conducting and lasting connections of your appliances with the aluminum of the mast. Connecting a copper wire to the mast will corrode it until, in sort of a self defence, the oxide will isolate it.

P.S. A common problem of accidentially getting return currents through the mast, is via active masthead antennas. They get their DC power through the coax cable with its shield connected to the chassis. Here you either need an isolated mounting bracket, or like I do it, use an galvanically isolating DC-DC converter to feed it.

 

[chas]

Thank you for this excellent reply - I will just have to bite the bullet and buy some more wire!