Powering two DC devices from a single pair of wires?

[aenlic]

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

 

[Lou_tribal]

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

 

[DavidM]

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

 

[tiltrider1]

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.

 

[O C Diver]

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

 

[FF]

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.

 

[aboatman]

................ 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.

 

[koliver]

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.

 

[High Wire]

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.

 

[LarryM]

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

 

[C lectric]

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.

 

[aenlic]

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

 

[C lectric]

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.