Reply
 
Thread Tools Search this Thread Display Modes
 
Old 11-20-2017, 07:18 PM   #1
Veteran Member
 
aenlic's Avatar
 
City: San Leandro
Country: USA
Join Date: Mar 2017
Posts: 58
Powering two DC devices from a single pair of wires?

OK, despite scouring my reference books on DC wiring, I can't answer a small-but-important question:

The recommendation as I understand it is that every 'endpoint' should be powered with an independent pair of wires from the buss.

In my case, I'm installing a TINY fan for my Airhead vent hose (sub-sub-1-amp), and I can either (a) create a "Y" off the wires which are powering a little-used DC outlet, (b) try to disassemble a teak 'airway' used by the current (large and powerful) head vent fan, and use that set of leads, or (c) decommission the power outlet and just steal its leads.

The most likely use of said power outlet would be for a larger fan, still only 1 amp, so I would think that choice (a) is reasonable.

That said, I find that honest ignorance is the only sound path to enlightenment... and I got plenty of the former, lol.

What say ye, mateys?

aenlic
__________________
Advertisement

aenlic is offline   Reply With Quote
Old 11-20-2017, 07:39 PM   #2
Guru
 
Lou_tribal's Avatar
 
City: Quebec
Country: Canada
Vessel Name: Bleuvet
Vessel Model: Custom Built
Join Date: Jan 2016
Posts: 3,216
Quote:
Originally Posted by aenlic View Post
OK, despite scouring my reference books on DC wiring, I can't answer a small-but-important question:



The recommendation as I understand it is that every 'endpoint' should be powered with an independent pair of wires from the buss.



In my case, I'm installing a TINY fan for my Airhead vent hose (sub-sub-1-amp), and I can either (a) create a "Y" off the wires which are powering a little-used DC outlet, (b) try to disassemble a teak 'airway' used by the current (large and powerful) head vent fan, and use that set of leads, or (c) decommission the power outlet and just steal its leads.



The most likely use of said power outlet would be for a larger fan, still only 1 amp, so I would think that choice (a) is reasonable.



That said, I find that honest ignorance is the only sound path to enlightenment... and I got plenty of the former, lol.



What say ye, mateys?



aenlic


Just be sure the source wires and fuse/breaker will support the new fan load and document your new connected device for future reference.

L
__________________

Lou_tribal is offline   Reply With Quote
Old 11-20-2017, 07:57 PM   #3
Guru
 
djmarchand's Avatar
 
City: Litchfield, Ct/Punta Gorda, Fl
Country: USA
Vessel Model: Atlas Pompano 23- outboard
Join Date: Aug 2012
Posts: 4,335
While AC wiring has some specific requirements such as never "double lugging", ie putting two conductors on one screw terminal, DC wiring is much more forgiving.

Connect it any way you can to the existing DC outlet. Make sure that the wire size you use to connect up your little fan is ok for the breaker that protects that circuit, ie 14 gauge for a 15 amp breaker.

You will be fine as that fan draws milliamps and it hard to screw up a connection that draws so little current.

David
djmarchand is offline   Reply With Quote
Old 11-20-2017, 08:03 PM   #4
Guru
 
tiltrider1's Avatar
 
City: Seattle
Country: USA
Vessel Name: AZZURRA
Vessel Model: Ocean Alexander 54
Join Date: Aug 2017
Posts: 1,145
First assuming the existing wire matches the existing circuit breaker then tapping into it is fine. I would recommend running the existing wire to a terminal strip and then branching from the terminal strip to each appliance. Sine circuit breakers and fuses are to protect wiring make sure you continue with the same gauge wiring.
tiltrider1 is offline   Reply With Quote
Old 11-20-2017, 08:22 PM   #5
Guru
 
O C Diver's Avatar
 
City: Fort Myers, FL... Summers in Crisfield, MD
Country: USA
Vessel Name: Slow Hand
Vessel Model: Cherubini Independence 45
Join Date: Dec 2010
Posts: 6,706
Most likely you will want to install a fuse for the fan where you connect it to the power outlet. It's likely that the fuse that protects that power outlet is too large for the fan wiring and the 1 amp fan load. Remember, the fuse is to protect the circuit wire.

Ted
__________________
Blog: mvslowhand.com
I'm tired of fast moves, I've got a slow groove, on my mind.....
I want to spend some time, Not come and go in a heated rush.....
"Slow Hand" by The Pointer Sisters
O C Diver is offline   Reply With Quote
Old 11-21-2017, 05:50 AM   #6
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 18,779
I think a CB with the rating for the wire , and then a fuse matched to each load works just fine.

A small enough fuse for a miliamp fan can be had , just not from NAPA.
FF is offline   Reply With Quote
Old 11-23-2017, 09:44 AM   #7
Senior Member
 
City: Washington
Country: US
Join Date: Nov 2017
Posts: 467
Quote:
Originally Posted by aenlic View Post
................ The recommendation as I understand it is that every 'endpoint' should be powered with an independent pair of wires from the buss..................
Not really. If you have lights in your cabin, V berth, cockpit, etc. it's unlikely that each fixture is wired directly back to the main electrical panel. Most likely the pair of wires goes to the first fixture and then on to each additional fixture.

What is important is that you never have any conductors without overcurrent protection. Your DC outlet is probably wired with#12 wire and ha a 20 amp circuit breaker on the panel. To tap off the outlet or the wiring, you would need #12 wire to your new fan. If the fan wiring is smaller than #12, you could install an inline fuse holder at the outlet and use the appropriate fuse for your new wiring.

Possibly the easiest way to add the wiring is to use "piggy back" connectors.
aboatman is offline   Reply With Quote
Old 11-23-2017, 11:00 AM   #8
Guru
 
koliver's Avatar
 
City: Saltspring Island
Country: BC, canada
Vessel Name: Retreat
Vessel Model: C&L 44
Join Date: Nov 2007
Posts: 2,813
aenlic "In my case, I'm installing a TINY fan for my Airhead vent hose (sub-sub-1-amp), and I can either (a) create a "Y" off the wires which are powering a little-used DC outlet, (b) try to disassemble a teak 'airway' used by the current (large and powerful) head vent fan, and use that set of leads, or (c) decommission the power outlet and just steal its leads."

That sounds similar to my fridge, where there is a single source of DC and at the bottom of the fridge Norcold provided a spade connector from which DC goes to the fan.
__________________
Keith
koliver is offline   Reply With Quote
Old 11-23-2017, 11:11 AM   #9
Guru
 
High Wire's Avatar
 
City: Cape May, NJ and Englewood, FL
Country: USA
Vessel Name: Irish Lady
Join Date: Dec 2007
Posts: 2,557
The small gauge positive wire fed from the receptacle needs to be protected by an appropriate fuse. If the fan itself shorts, the 15 amp breaker feeding the receptacle will not trip before the fan leads are glowing. Easy to do with a simple inline fuse holder and 1 amp fuse. Make sure it is accessible.
__________________
Archie
1984 Monk 36 Hull #46
Enroute to Cape May, NJ
Currently Charleston, SC
High Wire is offline   Reply With Quote
Old 11-23-2017, 11:50 AM   #10
Guru
 
LarryM's Avatar
 
City: League City, TX
Country: USA
Vessel Name: Pelago
Vessel Model: Wellcraft 3300 Coastal
Join Date: Aug 2011
Posts: 898
Quote:
Originally Posted by High Wire View Post
The small gauge positive wire fed from the receptacle needs to be protected by an appropriate fuse. If the fan itself shorts, the 15 amp breaker feeding the receptacle will not trip before the fan leads are glowing. Easy to do with a simple inline fuse holder and 1 amp fuse. Make sure it is accessible.
+1
__________________
Larry
M/V Pelago
LarryM is offline   Reply With Quote
Old 11-23-2017, 03:34 PM   #11
Guru
 
C lectric's Avatar
 
City: B.C.
Country: Canada
Vessel Name: Island Pride
Vessel Model: Palmer sedan 32'
Join Date: Oct 2007
Posts: 2,364
I will add that between where you take off the tap to the fuse for the small fan that the wire between the tap and the fuse should be the same size as the wire to the plug. After the fuse you can use a smaller wire.
C lectric is offline   Reply With Quote
Old 11-23-2017, 03:37 PM   #12
Veteran Member
 
aenlic's Avatar
 
City: San Leandro
Country: USA
Join Date: Mar 2017
Posts: 58
Thanks all, the fusing makes sense. It would/will be tricky, though, as I'm in essence performing 'arthroscopic surgery' within a teak-enclosed airway.

I'll examine the mini-fan that's going in to see if there's any feasible way to replace the wires to the unit completely, as they are WAY smaller than those going to the plug.

Thanks again-

aenlic
aenlic is offline   Reply With Quote
Old 11-23-2017, 04:05 PM   #13
Guru
 
C lectric's Avatar
 
City: B.C.
Country: Canada
Vessel Name: Island Pride
Vessel Model: Palmer sedan 32'
Join Date: Oct 2007
Posts: 2,364
I assume you have thought about it but this might be a good instance for an inline fuse holder. It will have the heavier wire with which you can produce the tap itself, the fuse, and then the smaller fan wire can be attached. Even the infeed side of the fuse holder could be lengthened so it can be brought close to where easy/easier access would be possible.
__________________

C lectric is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

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





All times are GMT -5. The time now is 05:11 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012