Electrical question

MQMurphy · Post by **MQMurphy** » Mon Aug 14, 2006 8:37 am

Can two lights (combo mast/deck light) share one ground wire, or should I pull a pair of wires for each up the mast? Thanks.

Figment · Post by **Figment** » Mon Aug 14, 2006 8:56 am

I dunno if they should, but they can. My mast lights (masthead, steaming, foredeck) share a common ground.

JetStream · Post by **JetStream** » Mon Aug 14, 2006 9:24 am

It makes good sense to share wires in a mast where weight aloft is an issue. The only requirement is to make sure the wire is large enough to handle the combined ampacity of all the loads it shares.

Ceasar Choppy · Post by **Ceasar Choppy** » Mon Aug 14, 2006 10:09 am

Absolutely! And like the previous post stated, it saves weight aloft. The only caveats are:

1. avoid mid-mast splices.
2. Upsize the ground wire a bit to handle the extra amps.

When I rewired my deckstepped mast I installed a tri-color with anchor light, and a combo masthead/decklight. All four lights shared a common ground. I used 14 AWG hot with 12 AWG for a ground. My problem was that the connectors on the lights were such that I couldn't get two wires on the negative post of the masthead/deck light to keep ground sharing simple. I was forced to do a mid-mast three way splice. Very bad since there is no way to fix that splice if it fails without unstepping the mast. But I did what I could to protect the splice from coming apart and keep it waterproof.

MQMurphy · Post by **MQMurphy** » Mon Aug 14, 2006 10:18 am

Thanks for the replies -
I like the idea of the heavier ground wire. As for mid-mast splicing, I could solder the splices up at the fixture location and then heat-shrink them.

Post by **Tim** » Mon Aug 14, 2006 12:09 pm

Weight aloft is always an issue, but for most cruisers and non-diehard racers, the extra pound or two (or even 5 or 6) if you run dedicated ground wires for each fixture is pretty insignificant. I wouldn't let the weight be the sole determining factor, but it can definitely factor in to help you lean one way or the other. Obviously, the taller the mast, the more weight the extra wire beings into the equation.

I prefer dedicated grounds for every fixture as it's easier to troubleshoot and avoids other issues found with common grounds, such as mid-mast splicing, additional connectors, and the fact that if the ground goes bad for whatever reason, you lose all your mast lights rather than just one.

There's no one right answer. It's perfectly sound to use a single ground wire. Each method has its pros and cons; choose which method works best for your specific situation. Of course it costs less to use a single ground wire rather than 2 or 3 or 4 as well.

martin · Post by **martin** » Mon Aug 14, 2006 2:15 pm

On my PS25 there is no easy way to get at the steaming light wiring except by running it through the mast. I made my splice with the mast top lights ground at the deck. It was not really my idea but the through deck coupling only has 4 pins and one more for the ground. I don't know who designs some of this stuff but they must not have sailboats. Anchor, tri-colour, steaming, and fore deck light is the usual configureation I'm used to dealing with and I guess there may be speader lights on a lot of boats too but all the sealed disconnectable type connectors seem to only have 4 pts and a ground. Maybe there is a money making idea to be had here hhhhhmmmmmmmm........martin

westsail42 · Post by **westsail42** » Tue Aug 15, 2006 9:17 am

Our sloop has a common ground for the masthead lights. We did it for simplicity when we rebuilt the mast.

We ran a six conductor cable up the mast (marine grade, made by Anchor) to power all the lights. It was much easier to run a single cable through the PVC conduit in the mast. Plus, since we had no more two conductor wire running through there (except for spreader lights), we made space for the radar, and ham-vhf antenna.

As I think of it we have
- anchor light
- steaming light
- masthead tri-radial nav
- strobe

All powered by the six conductor cable with one lead to spare, sharing the same ground.

This made room for
- marine vHF
- ham-vhf
- radar
- two-conductor for spreader lights
- spare RG-8X run (long story)

All running through 1 1/2" PVC conduit. Yeah, it is a tight fit, but without the six conductor we would have never got it all in there.

Works fine. Cable is 14 guage I think. Not very often all lights are on simultaneously, so current is not an issue. Still, I think the cable could handle it.

MQMurphy · Post by **MQMurphy** » Mon Aug 21, 2006 8:00 am

Re: that combo steaming/deck light - there isn't any clear identification of the POS or NEG terminals on the unit I bought - does it matter which I use?

Ceasar Choppy · Post by **Ceasar Choppy** » Mon Aug 21, 2006 12:01 pm

MQMurphy wrote:Re: that combo steaming/deck light - there isn't any clear identification of the POS or NEG terminals on the unit I bought - does it matter which I use?

Yes it does. Let me guess, its in German.

Actually I was able to figure it out from the diagram (but I can't remember if it was because I could read German or if it just took me a long time to figure it out), but if you take some lead testers and put it to your battery, you can figure out which ones are which before you mount it.

MQMurphy · Post by **MQMurphy** » Mon Aug 21, 2006 12:38 pm

Not sure I follow - the steaming light has one of those lozenge-shaped bulbs with the contacts at each end. It has two small brass terminals that have a hole and set screw to attach wires to. The deck light is one of those little self contained halogen floods that faces downwards - two white wires coming out of it. I haven't a clue . . .

Figment · Post by **Figment** » Mon Aug 21, 2006 12:54 pm

I haven't read my 12V Bible in a while, but a light bulb is a simple resistor. It shouldn't matter which is positive and which negative.

Are the wires the same color?

MQMurphy · Post by **MQMurphy** » Mon Aug 21, 2006 8:30 pm

Yes, they are. I could post a photo if needed. I think the fixture is a (<$) version of the Aqua-Signal type combo light.

Post by **Tim** » Tue Aug 22, 2006 6:06 am

I suspect you can attach the wires any which way, based on your description of the fixture.

If you have a picture, though, post it just in case there's some other visual indicator that might factor in.

MQMurphy · Post by **MQMurphy** » Tue Aug 22, 2006 7:38 am

Alright - here they are. Sorry about top photo size - tried resizing it a couple of times, still comes out BIG.

My guess is that they intend the tail coming out of the halogen that then goes through the back up behind the steaming light is the ground.

It would attach to one of the two setscrews at the top. The other setscrew would be for the return ground??? Lower setscrew terminal is for hot to steaming and other white is halogen hot??

Ceasar Choppy · Post by **Ceasar Choppy** » Tue Aug 22, 2006 10:41 am

My earlier comment was in reference to the Aquasignal combo tricolor/anchor unit. For some reason I thought that is what you were installing.

Yes, I think you have it correct.... From the looks of it, the two screws at the top of the festoon bulb socket (masthead/steaming light) are for a common ground. Run the neg. from the halogen deck light to one of these terminals and then use the other terminal to run the neg. back to your panel etc.

As someone mentioned earlier, it doesn't matter which is pos and whcih is neg.... but the two screw terminals on the one side of the festoon socket is there to make a common ground for the unit possible. Again, if you are unsure, run some test leads in a configuration that suits you and test it on your battery.