Cruisers Forum
 


Join CruisersForum Today

Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 19-05-2018, 14:24   #1
er9
Registered User

Join Date: Sep 2014
Boat: 1980 Mariner36
Posts: 393
Wire length/size question

im preparing to upgrade my LED lights and am starting with starboard side. going to have 13 fixtures that will draw approximately 35 watts (3ish AMPS) total if all were on at the same time.

my wire run from distribution panel to last light in v-berth will be somewhere around 40-50' one way if you factor in all the twists and turns.

when im considering wire size do i need to double that wire length number for round trip estimation? if so that would put me at 14 gauge wire for the run behind a 15 amp circuit breaker.

seems like heavy wire for an LED circuit so just want to double check my math.
__________________

er9 is offline   Reply With Quote
Old 19-05-2018, 14:32   #2
Don't ask if you can't handle it
 
sailorboy1's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: On the boat somewhere
Boat: Hunter 410
Posts: 13,617
Re: Wire length/size question

you need to use the round trip length

You don't have to use a 15amp circuit breaker just because the wire can handle that current. Nothing says that you can't use a 5amp breaker on a 15amp rated wire. But you might want to tap into the run someday and use the 15amp breaker
__________________

__________________
jobless, houseless, clueless, living on a boat and cruising around somewhere
sailorboy1 is online now   Reply With Quote
Old 19-05-2018, 14:37   #3
Senior Cruiser
 
TreblePlink's Avatar

Cruisers Forum Supporter

Join Date: Aug 2017
Location: Kentucky
Boat: 1969 Rhodes 28'
Posts: 300
Re: Wire length/size question

Yes, if you're designing for a certain voltage drop (wire resistance) you should include up and back wire length.

#14 should be safe with a 15 amp breaker.

Another thing to consider is that a small % of your load will be fed through the entire wire length.

Folks get into trouble when although the feeder wire gauge is fine, LED small-gauge wires or the internal circuits short, and they can't handle 14 amps without emitting smoke ...
TreblePlink is offline   Reply With Quote
Old 19-05-2018, 14:45   #4
er9
Registered User

Join Date: Sep 2014
Boat: 1980 Mariner36
Posts: 393
Re: Wire length/size question

Quote:
Originally Posted by TreblePlink View Post
Yes, if you're designing for a certain voltage drop (wire resistance) you should include up and back wire length.

#14 should be safe with a 15 amp breaker.

Another thing to consider is that a small % of your load will be fed through the entire wire length.

Folks get into trouble when although the feeder wire gauge is fine, LED small-gauge wires or the internal circuits short, and they can't handle 14 amps without emitting smoke ...

it sounds like your recomending a smaller size circuit breaker? im considering a 5amp breaker since the max load will be so light.
er9 is offline   Reply With Quote
Old 19-05-2018, 14:51   #5
Senior Cruiser
 
TreblePlink's Avatar

Cruisers Forum Supporter

Join Date: Aug 2017
Location: Kentucky
Boat: 1969 Rhodes 28'
Posts: 300
Re: Wire length/size question

Quote:
Originally Posted by er9 View Post
it sounds like your recomending a smaller size circuit breaker? im considering a 5amp breaker since the max load will be so light.
From what you describe, a 5 amp would provide a better margin of safety. If you get random trips without any reason, increment up to the next size.
TreblePlink is offline   Reply With Quote
Old 19-05-2018, 14:51   #6
Registered User
 
Suijin's Avatar

Join Date: Feb 2013
Location: Annapolis MD; currently in New England
Boat: Valiant 40
Posts: 4,146
Re: Wire length/size question

Breakers are relatively inexpensive but on some panels you have to remove the whole connecting bar to change a breaker which can be a bit of a pain. You could probably get away with putting a 5 amp fuse in which might be easier.
Suijin is offline   Reply With Quote
Old 19-05-2018, 15:17   #7
er9
Registered User

Join Date: Sep 2014
Boat: 1980 Mariner36
Posts: 393
Re: Wire length/size question

Quote:
Originally Posted by Suijin View Post
Breakers are relatively inexpensive but on some panels you have to remove the whole connecting bar to change a breaker which can be a bit of a pain. You could probably get away with putting a 5 amp fuse in which might be easier.

ok good to know i will check tonight.
er9 is offline   Reply With Quote
Old 20-05-2018, 11:44   #8
Registered User

Join Date: Jun 2013
Location: canada
Posts: 2,154
Re: Wire length/size question

The last light is that far away. But must current is not going that far. Only the last light. Would be tricky to actually calculate. You probably woukdn't always have all lights on at once.

That said I never use smaller then 14awg. That is certainly not big wire. That is normal wire. 16 is the smallest you're allowed to use on a boat. Which is only one size smaller.


And FYI. 3a at 95' comes up as 16awg on blue sea app.
smac999 is offline   Reply With Quote
Old 21-05-2018, 20:47   #9
er9
Registered User

Join Date: Sep 2014
Boat: 1980 Mariner36
Posts: 393
Re: Wire length/size question

Quote:
Originally Posted by smac999 View Post
The last light is that far away. But must current is not going that far. Only the last light. Would be tricky to actually calculate. You probably woukdn't always have all lights on at once.

That said I never use smaller then 14awg. That is certainly not big wire. That is normal wire. 16 is the smallest you're allowed to use on a boat. Which is only one size smaller.


And FYI. 3a at 95' comes up as 16awg on blue sea app.
thanks...i decided to go with the 14. i erred on the side of caution and estimated 5amp max draw. west marine had a 50% off sale this week so i ordered 200' of red and 200' of black for $80.
__________________

er9 is offline   Reply With Quote
Reply

Tags
size

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Country? Berth cost, Boat Length or Berth Length? sailabroad Dollars & Cents 33 16-04-2018 08:12
Furling line length/size tommyh Deck hardware: Rigging, Sails & Hoisting 6 19-07-2015 23:05
Long wire HF Antenna Length 40 South Marine Electronics 32 28-07-2014 22:26
How to Wire a Battery Isolator with a Three Wire Alternator ? bazzer Electrical: Batteries, Generators & Solar 7 05-12-2010 13:47



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 10:37.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.