wiring 12V socket/USB charging port

[freedomrider]

Hi all,

I'm planning to add this 12V socket/USB charging port to my pop-up camper.



Each socket needs to be wired independently as seen in this backside view.



I'm not sure what would be the best approach for wiring it up. I assume the two ports should be fused independently since their amp draws will be considerably different but do I need to run two independent circuits from the power source (the camper's house battery in this case) or is it okay practice to run a single run and then branch it close to installation point. FWIW, I don't anticipate ever pulling more than 10A combined.

Thanks in advance.

Mike

 

[Cyberman]

I think it would be fine to make a single run, with the correct guage wire to handle the 10A.

BTW, where did you get this?

 

[dwh]

The fuse is to protect the supply wire and has nothing whatsoever to do with the sockets - so whatever wire you run, just use the right fuse to protect it. For instance, a 20a fuse to protect #12 wire. Doesn't matter if you pull 10a with the lighter socket and 3a on the USB, as long as you don't overload the fuse that protects the supply wire.

So sure, go ahead and do a single run and split it to feed both, as long as the wire and fuse are big enough.

 

[doug720]

I have the same plug setup and ran a single wire to the area and added a second jumper. Works great.

Just run good size wire, at least a 12, I used 10g and make sure it's fused.

 

[freedomrider]

Thanks guys. If wired as a single run, my plan was to run 10G wire protected with a 20A fuse. The run is only gonna be 6 or so feet so 10 G may be overkill.
Regarding fuses/breakers, the way I learned it is that the fuse/breaker protects the hard wired circuit and not the end device (similar to what dwh wrote). But I was considering the sockets as part of that circuit and am not sure that each can handle 20A if there's a down stream short but I guess that's not a realistic concern.
Thanks again for the help.

 

[freedomrider]

I think it would be fine to make a single run, with the correct guage wire to handle the 10A.

BTW, where did you get this?

I had a hard time finding a source for what I was looking for but finally found a direct-from-China distributor called Banggood (no, really, that's their name). Online reviews for them are mixed but my purchase went fine.

 

[dwh]

Thanks guys. If wired as a single run, my plan was to run 10G wire protected with a 20A fuse. The run is only gonna be 6 or so feet so 10 G may be overkill.
Regarding fuses/breakers, the way I learned it is that the fuse/breaker protects the hard wired circuit and not the end device (similar to what dwh wrote). But I was considering the sockets as part of that circuit and am not sure that each can handle 20A if there's a down stream short but I guess that's not a realistic concern.
Thanks again for the help.

Yea, the fuse protects the supply wire.

Most anything you'll plug into the 12v socket will have a fuse in its plug to protect the device. The USB ports are current limited by their internal circuitry.

 

[rayra]

I was taught much the same but in opposite terms. It's that the fuse that cuts the risk of the branch circuit. That branch circuit is added risk / exposure. By placing the fuse at the head of that circuit, you ensure any damage / short anywhere along it is dealt with by the fuse. The fuse doesn't protect the line, it protects everything else from that line.

eta - Looking at the same outlet to retrofit in place of my Suburban's center console and rear cargo power ports. I've used the USB converters that plug into a cig lighter, but for almost the same price I'd rather have the extra ports.

 

[dwh]

I was taught much the same but in opposite terms. It's that the fuse that cuts the risk of the branch circuit. That branch circuit is added risk / exposure. By placing the fuse at the head of that circuit, you ensure any damage / short anywhere along it is dealt with by the fuse. The fuse doesn't protect the line, it protects everything else from that line.

No, it protects the wire. What you are describing would only apply in a "dead short" situation. But not all short circuits are dead shorts. Also, the fuse will protect the wire from an overload, which might have nothing to do with a short circuit.


Say a #12 wire, rated for a bit over 20a, and a 20a fuse to protect that wire.

Now you get a short circuit. Not a "dead short", but say your phone charger shorts out internally and draws 10a instead of 2a. The charger is melting, but the fuse doesn't blow.

The fuse is there to protect the wire by melting before the wire does in the case of a dead short or overload. It's not there to protect whatever else might be connected to, or come into contact with, that circuit.

The fuse is placed as close as possible to the source, to protect the maximum length of the wire.

 

[rayra]

we're expressing the same thing in opposite ways. 'Protect the source'. I'm talking about a branch circuit being a potential risk to the whole structure or vehicle. I'm not trying to protect the branch wiring. I'm trying to protect everything else from some unplanned damage to that added circuit, occurring anywhere on it. Be it too much current being drawn by a device, or an unplanned chafe or dead short. Regardless the reason or location of the dangerous event, anywhere on that circuit, the fuse is positioned to 'protect the source', in your own words.
We're saying the same thing, the fuse ought to go at the head / branching, not at the tail. Fuse panels are arranged that way for more than convenience.

 

[dwh]

we're expressing the same thing in opposite ways. 'Protect the source'. I'm talking about a branch circuit being a potential risk to the whole structure or vehicle. I'm not trying to protect the branch wiring. I'm trying to protect everything else from some unplanned damage to that added circuit, occurring anywhere on it. Be it too much current being drawn by a device, or an unplanned chafe or dead short. Regardless the reason or location of the dangerous event, anywhere on that circuit, the fuse is positioned to 'protect the source', in your own words.

I don't know where you got that. I never said, "protect the source".

Those are NOT my words - they are yours.


The purpose of the fuse is to protect THE WIRE.
This is why the fuse or breaker has to have a rating of less than the rating of the wire.
#12 can actually handle over 20a, but it's rated at 20a and you use a 20a fuse or breaker so that the fuse will melt, or the breaker will blow BEFORE THE WIRE MELTS.

You can use a 15a fuse to protect #12 wire, but you can't use a 20a fuse to protect #14 wire.

Because the fuse has to melt before the wire does.
Because the fuse is there to protect the wire.

We're saying the same thing, the fuse ought to go at the head / branching, not at the tail. Fuse panels are arranged that way for more than convenience.

We're saying the same thing about where to put the fuse.

We are NOT saying the same thing about WHY it is done that way.

It's not about protecting the source.
It's not about protecting the structure or vehicle from the branch circuit.

A 10a short on a 20a circuit can start a fire, but it won't melt the fuse or blow the breaker.
NOTHING is protected by the fuse or breaker except THE WIRE.

 

[rayra]

Sorry, I disagree completely. The fuse is to keep the house or vehicle from burning to the ground, not save a few bucks worth of wire. Every branch circuit added is an additional source of risk / danger to the house / vehicle. That's why they are fused.

 

[dwh]

Sorry, I disagree completely. The fuse is to keep the house or vehicle from burning to the ground, not save a few bucks worth of wire.

A fuse or breaker has no idea if a house or vehicle is burning to the ground. Doesn't know jack about fire. Only knows if the current exceeds the limit.

So how do you prevent fire?
Protect THE WIRE.



U.S. National Electrical Code, Article 240.1:

"FPN: Overcurrent protection for conductors and equipment is provided to open the circuit if the current reaches a value that will cause an excessive or dangerous temperature in conductors or conductor insulation."

 

[DaveInDenver]

Sorry, I disagree completely. The fuse is to keep the house or vehicle from burning to the ground, not save a few bucks worth of wire. Every branch circuit added is an additional source of risk / danger to the house / vehicle. That's why they are fused.

You can disagree but that doesn't change best practices. Fuses protect the branch wire. If there is more current flowing than the wire can handle the fuse open. Could be a load, a shorted outlet, a cut wire. Doesn't matter.

If an end load or the source itself are a risk in the case of a fault then they should also get current or voltage limiting, be that a fuse/breaker or active protection. This should typically be lower than the branch wire can handle. A vehicle battery is proportionally infinite compared to anything on your truck except for the starter or winch. That's why they don't put one, single main fuse for everything. They put a big fuse into the main distribution box to protect the main wire feeding it, they'll put a fusible link to the starter. But in the end whatever is faulty will almost always melt down and let the smoke out before the battery.

Same with your house wiring. The power company side will just keep feeding and feeding whatever you ask for, so you add breakers in smaller and smaller values as you keep going down the line.

Trying to size a load fuse on a cigarette lighter socket or USB port is a recipe for nuisance trips. Put a 15A fuse at the battery, run #12 AWG wire and use a solid crimp terminal on the socket and you have bought down all practical risk. Then just make sure anything you plug into it has a fuse and there is much higher chance of being struck by lightning than of a vehicle fire.

 

[freedomrider]

The USB ports are current limited by their internal circuitry.

I have no disagreement with what you wrote but will note that it's the quality of the internal circuitry in my cheapo USB port that I'm fretting over.

Then just make sure anything you plug into it has a fuse and there is much higher chance of being struck by lightning than of a vehicle fire.

Well now I'm really worried. The 12V or 120V transformers that came with my phone/tablet/etc. are appropriately fused like that but I'm not so certain about the port I'm installing. I have a some concerns that it wasn't QCed as tightly as the Samsung/Apple/JBL transformers it's replacing.

Ignorance breeds fear and I confess my ignorance regarding USB ports and the like. :snorkel:

Cheers!
Mike