Cruisers Forum
 


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 16-04-2009, 20:00   #1
Registered User

Join Date: Dec 2008
Location: New Orleans, LA
Boat: 1993 Lagoon 37 TPI
Posts: 124
DC Circuitry Question

I notice that several switched circuits on my boat (some lights, macerator, etc.) have the switch on the negative side of the load. On the surface, this would appear to increase the possibility of a short. Is there any advantage to having a switch on the negative side of the load?
Mike Sibley is offline   Reply With Quote
Old 16-04-2009, 20:23   #2
Registered User
 
Reefmagnet's Avatar

Join Date: May 2008
Location: puɐןsuǝǝnb 'ʎɐʞɔɐɯ
Boat: Nantucket Island 33
Posts: 4,864
I think it is 6 one way half a dozen the other. If the boat is negative ground it would be more open to shorts as in bypassing the off position of the switch but less exposed to the boat incinerating kind of short. I would suspect the switch has been put on the negative side most probably because either the positive side for the load(s) comes off a common bus supply or it was simply more convenient for the installer. Regardless of the side of the circuit the switch is installed on, it will always have -ve on one pole and +ve on the other when the switch is in the off position - only the polarity side the load is on will change.

More importantly, the fuses / breakers should all be located on the same side of the circuit (polarity) throughout the boat otherwise bad things could indeed happen if one circuit were to short to another.
Reefmagnet is offline   Reply With Quote
Old 17-04-2009, 02:55   #3
Registered User

Join Date: Mar 2009
Location: Australia, Hervey Bay QLD
Boat: Boden 36 Triple chine long keel steel, named Nekeyah
Posts: 909
Your circuits should all be above ground, ie nothing earthed to the boat. What often happens in reality is that the engine and hence prop shaft and prop are connected to the negative. That means that if any of your devices are leaking to earth you may get a current path causing electrolysis. To be on the safe isde, I would switch everything in the positive lead ( Its better to have a coherent system, anyway). We also isolate the engine when it is not running, and switch off both sides of the circuit when we are not on the boat.(Important for a metal boat) Regards, Richard.
boden36 is offline   Reply With Quote
Old 17-04-2009, 03:28   #4
Registered User

Join Date: Apr 2006
Posts: 4,413
My boat came with a key type switch to disconnect the neg buss and all returns not connected directly to the battery.

I haven't seen this on other boats nor heard mention of this, what is the main use etc.

Any thoughts?
Sandero is offline   Reply With Quote
Old 17-04-2009, 04:50   #5
Senior Cruiser
 
GordMay's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 49,128
Images: 241
If single pole switches are used in DC branch circuits, they shall be installed only in the positive conductor of the circuit.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is online now   Reply With Quote
Old 17-04-2009, 08:47   #6
Commercial Member
 
CharlieJ's Avatar

Cruisers Forum Supporter

Join Date: Dec 2008
Location: St. Petersburg, FL
Boat: Gulfstar Long Range Trawler; 53'; BearBoat
Posts: 1,525
I concur with Gord. Having the switch in the negative leg means that the equipment is always powered; i.e., is kept at B+ potential. Any breakdown in insulation in the equipment could cause unwanted current flow.
__________________
Charlie Johnson
ABYC Master Technician
JTB Marine Corporation
"The Devil is in the details and so is salvation."
CharlieJ is offline   Reply With Quote
Old 17-04-2009, 09:36   #7
Registered User
 
Randy's Avatar

Join Date: Oct 2008
Location: San Diego
Boat: Farrier f27
Posts: 704
I agree with Gord & CharlieJ. I think there's good reasons to maintaining standards for all the various systems on boats, Safety is a big one. Simplification as changes are made in the boat its easier to know that not only are the positive sides are switched but the color of wire on the positive side always the same.
Randy is offline   Reply With Quote
Old 17-04-2009, 09:43   #8
Registered User

Join Date: Jan 2005
Location: Seattle area (Bremerton)
Boat: C&C Landfall 39 center cockpit "Anahita"
Posts: 1,077
Images: 6
Another Reason

Another reason to never switch the negative (open) on vessel wiring is that it is more difficult to troubleshoot a problem when something does not work. One takes a DVM with one lead on negative and begins tracing the source of power back towards the load looking for an open. With the negative switched off power seems to appear everywhere.
__________________
"I don't think there'll be a return journey Mr. Frodo". Samwise Gamgee
Rick is offline   Reply With Quote
Reply

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
KEEL/BALLAST QUESTION?? PLUS EXTRA CREDIT QUESTION ;) stephenronning Monohull Sailboats 3 21-03-2009 03:19
Question CptnLBS General Sailing Forum 4 21-01-2008 13:32
New here, have a question ducaticole Atlantic & the Caribbean 3 17-01-2008 09:14
Question hatteras Meets & Greets 8 01-09-2007 01:34
a question haloman Meets & Greets 18 01-12-2006 08:41

Advertise Here


All times are GMT -7. The time now is 02:12.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.