Volts x Amps = Watts

[Mike53]

Whenever I look for electrical cable I am immediately confused. I remember V x A = W from school 60 years ago.

Situation is I need new wires for the navigation lights which are up my yacht mast. The boats electrical system is 12v and the light bulbs are 25w. Therefore according to the formula I only need 2 amp wire. The cable run will be +/- 15 metres.

I am looking at some cable on ebay. Oceanflex marine grade 2 and 3 core tinned 12v/24v 1.5mm 21A overall diameter 6.1mm.

Although this wire seems massively over the top considering it is 21A and I only need 2A please could anyone advise if this would be a good choice?

Thanks

Mike

 

[robinbanks]

It fulfils the electrical demands as long as there is only one bulb per run of wire.

Ability to resist the harsh environment is probably far more important for your application

 

[morqthana]

It fulfils the electrical demands as long as there is only one bulb per run of wire.

At 2A/bulb, why only one?

Ability to resist the harsh environment is probably far more important for your application

Indeed.

 

[SFK]

For 12V wiring there is some useful and interesting reading here.

Cable Size Calculator - Cable sizing and selection | 12 Volt Planet

Cable Size Calculator - Read our guide to selecting cable of the correct type and size for your automotive, marine or leisure wiring application. Auto and Marine Electrical Components from 12 Volt Planet

www.12voltplanet.co.uk

 

[ericmark]

Yes, Volts x Amps x PFC = watts with AC, and no PFC with DC, but with modern bulbs they have a built-in switch mode power supply, so typically 10–30 volts, so 25 watt at 10 volts = 2.5 amps, and at 30 volts = 0.83 amps, not that this really changes the cable required, as to be strong enough not to be damaged unlikely to find cable under a 5 amp rating.

 

[SUNRAY]

At 2A/bulb, why only one?

Only one mast?

 

[Mike53]

Thanks for replies.

Only 1 mast but 3 bulbs.

At masthead there is a combined unit tricolour and anchor light. The tricolour has only 1 bulb but a triple colour lens. The anchor light has 1 bulb. The anchor light and the tricolour lights will never be used simultaneously.

There is also a steaming light half way up the mast on a separate circuit which requires 2 core.

The next wire size is 2.5mm/29amp

Mike

 

[FrodoOne]

The next wire size is 2.5mm/29amp

??????

 

[Mike53]

The wire size referred to in my original post is 1.5mm 21A.

As far as I am aware the next size up in the Oceanflex marine grade (tinned) range is 2.5mm 29A

Perhaps there is a 2mm?

As I said in my original post this always confuses me.

Mike

 

[Munroast]

Whenever I look for electrical cable I am immediately confused. I remember V x A = W from school 60 years ago.

Situation is I need new wires for the navigation lights which are up my yacht mast. The boats electrical system is 12v and the light bulbs are 25w. Therefore according to the formula I only need 2 amp wire. The cable run will be +/- 15 metres.

I am looking at some cable on ebay. Oceanflex marine grade 2 and 3 core tinned 12v/24v 1.5mm 21A overall diameter 6.1mm.

Although this wire seems massively over the top considering it is 21A and I only need 2A please could anyone advise if this would be a good choice?

Thanks

Mike

from 60 years ago teacher said Womens Voluntary Institute & Very Important Rat