Proper Wiring

[Liquid Asset]

I need some help. I went to replace my spreader lights because one had broken off. They are 500 Watt halogen floodlights that are of standardard household 120Volt AC power. The old lights were wired with only two wire boat cable without a ground. I assume this was because you would not to ground you 120v AC system to the tower. The lights are mounted into a threaded pipe that is welded to the tower by the tower builder. If I were to hook up a ground wire, this would esentially ground the tower because the light casing would be touching the tower.

Is this the correct way to hook up the system? do you not want to use the ground wire so that the tower does not get grounded? I want to make sure that I do this correctly because I do not want to have someone get shocked or cause a problem. Hopefully I explained this clearly.

 

[Genesis]

If there is any possibility of the wiring or lamp shorting to the tower you need to connect the safety ground.

The tower is PROBABLY grounded (for lightning protection if no other reason!) and as such it may already be protected, but I'd check!

 

[SKYCHENEY]

2 wire boat cable should only be used for battery voltages. Any line voltage lights, plug, appliances, etc should have a separate ground. The spreader lights may have been hooked up wrong in the first place or they may have been switched by someone from 12v to 120v without adding a ground wire.

 

[Liquid Asset]

Ok, for lack of my understanding, if the light shorted to the tower, and it was grounded, would that not cause the tower to become electrified with 120v??

If that were to happen, this could shock or even worse, seriously injure somone. or woudl this cause the system to blow the breaker because it shorted..

 

[SKYCHENEY]

If it shorted to the tower and the tower is grounded, then you should blow a breaker but you could still have a shock hazard as the power flows through the tower as it goes to ground. If it is shorted to the tower and the tower is not grounded at all, then the tower becomes electrified without tripping the breaker. It's always best to have a good known separate safety ground terminated as close to the load as is possible. This helps to assure that the short travels down the ground wire and not through the tower to the ground.

 

[Brian Degulis]

The tower MUST be grounded if it isn't get that done. More than likely who ever wired the lights was depending on the towers ground to ground the housing of the light. The problem with that is should the light mounting threaded or bolted etc. become coroded and no longer makes a good conection to ground the light becomes a shock hazard. So when you re wire use 3 conductor cable and give the lights there own ground. Again make sure the tower is grounded also if not give that it's own seperate ground also. This is one of those situations were everything can be working perfectly yet be very dangerous especialy in a salt water enviroment.

Brian

 

[Liquid Asset]

The tower is grounded. I do know that. I will wire up the lights with 3 wire cable so that they have their own ground. I have no problem hooking this up, but wanted to make sure I did it safetly.

 

[REBrueckner]

As I read the above posts, they are all correct. The tower ground should be a heavy battery size cable primarily for lightning protection; I think #4 is now the minimum specified. The separate ground for your new light fixtures would be attached to the light fixture itself and would be the third wire for each lamp, as someone noted above.

Given all the above, I'd be inclined to try and find a lamp fixture that was non conductive, say some kind of plastic, or if metal, is disintinctly insulated from your tower. That means even mounting screws or bolts must not be connected to both a conducting portion of the light fixture and your conducting tower.

There are likely ABYC specs for such fixtures and perhaps someone can post them.

 

[krush]

I'd run GFCI on it too (if it isn't already present).

 

[Brian Degulis]

As I read the above posts, they are all correct. The tower ground should be a heavy battery size cable primarily for lightning protection; I think #4 is now the minimum specified. The separate ground for your new light fixtures would be attached to the light fixture itself and would be the third wire for each lamp, as someone noted above.

Given all the above, I'd be inclined to try and find a lamp fixture that was non conductive, say some kind of plastic, or if metal, is disintinctly insulated from your tower. That means even mounting screws or bolts must not be connected to both a conducting portion of the light fixture and your conducting tower.

There are likely ABYC specs for such fixtures and perhaps someone can post
them.

Why would you want to isolate a grounded metal light fixture from a grounded metal tower?

Brian

 

[REBrueckner]

Why isolate a fixture from the tower....To help keep lightning from touching the electrical system....it's no guarantee, of course, just a precaution.

Commonly lightning ground, ac ground, dc ground, and bonding are all separate systems which may be connected at a single common connection; but BEST practice is to keep the lightning ground isolated from all the others via a dedicated and separate external hull ground plate.

What's even better is to keep a tower or mast lightning ground OUTSIDE the boat...that's why you'll see knolwedgeable ragmen with cables attached to stays with a weight hanging overboard...On my radar arch, I have a stud and wing nut so I can attach a heavy battery cable with a big zinc and hang it overboard in bad lightning storms....Otherwise I use it as a "guppy" to supplement my underwater zincs...

 

[Brian Degulis]

Why isolate a fixture from the tower....To help keep lightning from touching the electrical system....it's no guarantee, of course, just a precaution.

Commonly lightning ground, ac ground, dc ground, and bonding are all separate systems which may be connected at a single common connection; but BEST practice is to keep the lightning ground isolated from all the others via a dedicated and separate external hull ground plate.

What's even better is to keep a tower or mast lightning ground OUTSIDE the boat...that's why you'll see knolwedgeable ragmen with cables attached to stays with a weight hanging overboard...On my radar arch, I have a stud and wing nut so I can attach a heavy battery cable with a big zinc and hang it overboard in bad lightning storms....Otherwise I use it as a "guppy" to supplement my underwater zincs...

I think you might have that backwards. Typicaly anything with a metal housing that's mounted to a metal structure would call for a bonding strap from the housing to the structure that holds true even if they are bolted together it's to insure a good ground. Take a look at the instalation manel for a radar when mounted to a metal mast they call for a bonding strap to that mast along with a seprate ground wire and they want that mast grounded also.

If the light were not electricaly connected to the tower and the light were to be struck by lightning you would be relying on a very small ground cable to carry the load from the strike. If the light and tower are electricly connected the tower ground (which should be a heavier cable) would have a much better chance of staying in tack. I think that's how it works but I'm not sure?

Brian

 

[REBrueckner]

Brian,
While I said what I meant and will stick with it as a recommendation, but offer no guarantees, you make a reasonable alternative argument. While there are no guarantees with lightning no matter what is done, I am assuming with the spreader lights under the conducting mast arm lightning is pretty unlikely there...however, the best solution, I believe, unless there have been actual tests done, is to follow the suggestion I already posted...use a non conductive fixture...All this is a bit academic unless the mast is the high point on the boat, not so common on power vessels.


With RADAR, which often sits at the highest point, or at least is open to the sky above, grounding from RADAR to a conductive mast is good as recommended by the manufacturer...sticking a lightning rod above the RADAR and grounding that to a conductive mast or via cable overboard is better yet, but only if the strapping ground cable can be kept fairly straight...That's what I did with my RADAR arch.

What I have learned from studying as much lightning literature as I could find is to keep lightning grounds outside the boat...and keep the grounding cables as straight as possible or at least with gradual large diameter turns.

The University of Flordia used to have test results and recommendations online, althought I have not looked in about five years. Maybe FP&L would have something as well. I don't remember what Caulder has in his book.

 

[Brian Degulis]

I hear you no one knows what lightening will do but I think it's always best to follow the ABYC ABS USCG guidlines and I checked they all recomend bonding metal fixtures to metal structures with a conductive mounting and bonding straps.

Brian

 

[REBrueckner]

I have limited faith in ABYC bonding (distinct from lightning ground) rules because many arguments over the years have been unable to recommend consensus updates. Perhaps their lightning grounding recommendations are up to date, perhaps not. In any case, if them's the rules there is one advantage to following them: in the event of an insurance claim, you are on the "right" side of any argument.

Does ABYC currently recommend isolating lightning ground from all other grounds... AC,DC and bonding?

 

[Brian Degulis]

The rules I'm reading are not specified as lightning ground they are simply general practice for wiring and grounding under these circumstances.

Brian