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Old 06-06-2014, 05:18 PM   #1
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Wiring question

I am trying to install a convenience light near my stern light on the roof of the cockpit. I have a primary wire from the panel to the location but do not have a second wire. I am wondering - can I use the primary wire for the positive lead to the light and connect the negative lead to the negative of the stern light?
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Old 06-06-2014, 05:47 PM   #2
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Yes
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Old 06-06-2014, 05:48 PM   #3
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Yes you should be able to do that.
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Old 06-06-2014, 06:16 PM   #4
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It will physically work but no one (that I've ever seen anyway other than PO's) wires a boat to share the negative with maybe the exception of a two bulb fixture like a masthead light. Use the single primary wire to pull a pair of #16 ga tinned marine wire into place.
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Old 06-06-2014, 07:32 PM   #5
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The only way I know to safely answer the question would be...

1. What is the combined wattage of the lights?
2. What are the individual wire gauges and lengths back to either heavier wire junctions or the source panel?
3. Whether the light sockets could possibly take much higher wattage light bulbs that someone could accidently do without knowing of the shared negative...if so the sockets need warning labels if you proceed and the negative wire gauge could be over taxed.
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Old 06-06-2014, 09:00 PM   #6
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Why not use a pair of LED lights then you will have the lights as bright as needed and you will reduce the overall current from both fixtures to less than a single filament bulb would draw.
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Old 06-06-2014, 11:33 PM   #7
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Quote:
Originally Posted by Billylll View Post
Why not use a pair of LED lights then you will have the lights as bright as needed and you will reduce the overall current from both fixtures to less than a single filament bulb would draw.
Bill

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Old 06-06-2014, 11:37 PM   #8
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Both lights are LED.
The stern light was originally a 10w socket / bulb. I replaced that light with a LED fiture
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Old 06-06-2014, 11:55 PM   #9
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Both lights are LED.
The stern light was originally a 10w socket / bulb. I replaced that light with a LED fiture
Then you should have no problem using the same ground for both lights.
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Old 06-07-2014, 01:16 AM   #10
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I agree more than likely the original light wasn't LED either way you will have no issues using a pair of LED fixtures.
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Old 06-07-2014, 06:28 AM   #11
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>The stern light was originally a 10w socket / bulb. I replaced that light with a LED fiture.<

>Then you should have no problem using the same ground for both lights. <

However in an accident the use of a LED in a lamp that was certified for a filament bulb could come to bite.

The Fresnel housing is built for a pinpoint 360 deg source , not for a bunch of LED glued to a stalk.

There is a difference between what works , and what works till the liars for hire get involved.

The risk is all yours.
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Old 06-07-2014, 08:22 AM   #12
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However in an accident the use of a LED in a lamp that was certified for a filament bulb could come to bite.

The Fresnel housing is built for a pinpoint 360 deg source , not for a bunch of LED glued to a stalk.

There is a difference between what works , and what works till the liars for hire get involved.

The risk is all yours.
I don't believe there is any legal risk involved if the light can been seen from two miles or more and the intensity is the same whether the lens has a LED bulb behind it or not.
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Old 06-07-2014, 10:58 AM   #13
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I don't believe there is any legal risk involved if the light can been seen from two miles or more and the intensity is the same whether the lens has a LED bulb behind it or not.
From the regulations I have seen and read, the standards are performance based. Any light source that meets the performance standards should be acceptable.

A fixture that is marked with a USCG approval pretty much guarantees that it will meet the performance standard if installed correctly. Otherwise, it's up to you to make sure the standards are met.

It wasn't long ago when sailboaters used kerosene lanterns for anchor lights.
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Old 06-07-2014, 12:42 PM   #14
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It will physically work but no one (that I've ever seen anyway other than PO's) wires a boat to share the negative with maybe the exception of a two bulb fixture like a masthead light. .
This is correct. It will work but it's not standard procedure for boat wiring. It would be confusing to another person working on your boat or even you if you forgot how you wired it.
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Old 06-07-2014, 12:58 PM   #15
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different bulbs can change the sector angles...which is what I believe FF is referring to...that's why vessels 20 meters or more shall have screens fitted usually...

5. Screens for sidelights
The sidelights of vessels of 20 meters or more in length shall be fitted with inboard screens painted matt black, and meeting the requirements of Section 9 of this Annex....

ANNEX I: INTERNATIONAL POSITIONING & TECHNICAL DETAILS OF LIGHTS & SHAPES
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Old 06-07-2014, 02:31 PM   #16
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different bulbs can change the sector angles...which is what I believe FF is referring to...that's why vessels 20 meters or more shall have screens fitted usually...

5. Screens for sidelights
The sidelights of vessels of 20 meters or more in length shall be fitted with inboard screens painted matt black, and meeting the requirements of Section 9 of this Annex....

ANNEX I: INTERNATIONAL POSITIONING & TECHNICAL DETAILS OF LIGHTS & SHAPES
Well based on what he posted: "The Fresnel housing is built for a pinpoint 360 deg source , not for a bunch of LED glued to a stalk."

He seemed to be talking about the way a Fresnel lens focuses light. Not shading the light source.

But, I could be mistaken I guess.
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Old 06-07-2014, 02:44 PM   #17
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he also used the word filament...

I let him say what he meant then....
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Old 06-07-2014, 03:29 PM   #18
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Some folks would have you believe that if you have a "Perko" brand navigation or anchor light that it would only be approved if you relamp it with a "Perko" brand lamp, not a Sylvania or GE lamp with the same number. This is absurd.

The people who inspect my boat each year just look to see if the lights work.
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Old 06-07-2014, 03:58 PM   #19
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The people who inspect my boat each year just look to see if the lights work.
What, you mean they don't stand the correct distance away required for each light to be visible from and measure the exact output and angle of visibility of each light!? Slackers! :-)
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Old 06-07-2014, 04:22 PM   #20
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