I think I would know this answer- wire is wire.
The Travel Trailer project I'm working on needs power wires, and I'm doing a 12V fridge (more efficient, no gas, more space, etc)- the requirement for just about the length of wire I need is 12G, and it specifically says twisted pair.
When I search for 12g twisted pair wire, all I come up with is speaker wire.
That's ok to run 10A 12V through, right? It's just wire.
Sounds fine, as long as the wire is legit 12 gauge, it's intended use is quite irrelevant. And it sounds like you've factored in the length of run, so you should be good.
What's the length of the wire run, as routed, from the power source (the fuse) to the fridge?
There are definitely other sources for 12ga pair besides speaker wire, but as a general rule, this should be fine. There's probably the question of wire jacket melting temp but we really should just up the gauge to stay away from that being a question we need to answer.
Here's a nice article I just found with a table to figure out if you're doing okay on this or not.
http://www.offroaders.com/technical/12-volt-wiring-tech-gauge-to-amps/
If you want I can run this through a spreadsheet I use at work for aircraft wiring installations. The length question is important either way.
In reply to pres589 (djronnebaum) :
Somewhere between 12-20ft. It has to route from the box around a small channel that will hold the wires, and then to the fridge.
It's probably actually shorter than that, and the fridge specs 14g for shorter.
But the key spec to the fridge is that it's a twisted pair to reduce noise. Which is interesting. And the twisted pair 12 or 14g wire I can find is for speakers.
You could use two individual wires and twist up your own!
We've all done it, it's fine. I have a free roll of speaker wire ready to do the lighting on my crappy new trailer. Whoever here won't admit to using speaker wires for power is a liar.
Just twist your own. I use a cordless drill on one end and a bench vice on the other.
If you really want to know, get a roll of string, and run it out. It might be wise to step up to 10ga wire. Agreed on using a drill and a vise to twist the two conductors together if you want. That will also soak up some length so take that into consideration.
I used a fair amount of low voltage landscape lighting wire in SanFord. Lowes/Depot carries it in their garden lighting section. It's stranded and well insulated for direct burial.
It's available all the way up to 10/2. Plenty large enough for what you are doing. It's also fairly cheap.
APEowner said:Just twist your own. I use a cordless drill on one end and a bench vice on the other.
I kind of like the idea of going farther and getting shielded wire. These RV fridge's cost a fortune, so going farther with a shield can't hurt.
In my design work I do not put power and ground through shielded wire because if it gets cut the metallic shield can then serve as a sneak path for the power to find ground and let the smoke out of the wire. The metallic shield is not going to "help" the fridge and the point of the twisting is to try and harness EMI that being radiated by the + lead to the - lead. I like the stranded 10/2 suggestion Toyman made.
YMMV and I do not hold myself out as the world's best aircraft electrical engineer; others are invited to weigh in.
alfadriver (Forum Supporter) said:APEowner said:Just twist your own. I use a cordless drill on one end and a bench vice on the other.
I kind of like the idea of going farther and getting shielded wire. These RV fridge's cost a fortune, so going farther with a shield can't hurt.
The point to twisting the power wire isn't to protect the fridge, it's to protect other things in the RV from electrical noise produced by the fridge.
In reply to codrus (Forum Supporter) :
Not according to it. Which is really odd.
Still, a twisted, shielded pair would help with any noise it made, too. Especially since it will run in a bundle of wires from the box to the unit- both A/C and DC.
pres589 (djronnebaum) said:In my design work I do not put power and ground through shielded wire because if it gets cut the metallic shield can then serve as a sneak path for the power to find ground and let the smoke out of the wire. The metallic shield is not going to "help" the fridge and the point of the twisting is to try and harness EMI that being radiated by the + lead to the - lead. I like the stranded 10/2 suggestion Toyman made.
YMMV and I do not hold myself out as the world's best aircraft electrical engineer; others are invited to weigh in.
That's good to know. Thought it would help- didn't think about the sneaky ground short.
The twists would probably be more helpful than adding a shield to the equation. Really the only kinds of systems that are going to be impacted are things like radios. Nothing else is going to be fixed by adding shielding to the fridge power wires.
In reply to pres589 (djronnebaum) :
What about it's own computer? Put the onus on the owner to make sure their computer stays safe.
It's kind of a neat thing- using a compressor instead of an absorbtion system- it have more fridge in less space, and it uses a ton less electricity... the only bad thing is if you run out of juice, it's all over. Having seen a few other travel trailers go all electric, that's kind of where I'm heading (other than a cool fire pit and maybe a gas grill outside.)
pres589 (djronnebaum) said:Here's a nice article I just found with a table to figure out if you're doing okay on this or not.
http://www.offroaders.com/technical/12-volt-wiring-tech-gauge-to-amps/
If you want I can run this through a spreadsheet I use at work for aircraft wiring installations. The length question is important either way.
Would the spread sheet itself be available to us non aircraft types? Os is that work proprietary stuff?
Speaker wire is pretty much regular lamp cord that isn't rated for high voltage. I think the main reason speaker wire is labeled as speaker wire is because it is designed for flexibility and (in car audio) scuff resistance.
At the theater, I have a roll of black speaker wire and a roll of black lamp cord. Both are 18AWG, and I can't really tell the difference in the conductors. The speaker wire might be a finer strand, and the jackets are marked differently. The lamp cord has printing on one insulator and ribs on the other, while the speaker wire has little embossed + and - symbols.
Otherwise, they are both fine-strand, vinyl-insulated wire, and I wouldn't hesitate to use them interchangeably.
Although it isn't a huge deal, one thing the AWG and SWG don't take into consideration is that finer strands tend to offer less resistance. When electrons flow through a conductor, they flow primarily on the surface of it, not as much in the middle. More strands for a given gauge has more surface area, and therefore more real estate for electrons to play. This doesn't change the amps it can carry necessarily, but it may make more juice end up at the far end with less loss.
As far as electrical noise is concerned, you can do a couple things to help it. It doesn't work as well for DC current, but you could try making the ground a different length than the power. You can also do a redundant ground to eliminate some electrical resonance in the wire
I'm curious about the requirement. It's a pretty poorly designed system that can't handle the types of transient that are likely to be induced in a 12 v DC power line. You can buy Shielded, twisted pair 12 ga wire. I only checked one source but they wanted $135/5 feet. If they're not calling for shielded I wouldn't bother. If you really want shielded you can add some aluminum polyester tape to you self twisted. If you're going to shield it you need to de-rate it as if it were in conduit which will require an even larger conductor.
In reply to 03Panther :
It's work proprietary having been created by an employee as part of his work. Sorry.
Alfa:
Not sure I follow your question. In general the smart way to do this is to put shield wires on the wiring that might bring EMI into components that are sensitive to it. Data, audio, video, those sorts of lines going into a piece of equipment.
In reply to APEowner :
The reason that it might be nice to put shielded power wire to and from a fridge is to try and get noise from the compressor motor itself from radiating out of the power wires as well as the "snap" RF generated when the compressor turns on and off.
Given the distance, a pair of 10 gauge conductors running to and from the fridge, kept together for as much of the run as possible, would be how I would deal with this. No EMI tape, no multi-ground thing, etc etc. Keep it simple. My 2 cents.
pres589 (djronnebaum) said:In reply to 03Panther :
It's work proprietary having been created by an employee as part of his work. Sorry.
Alfa:
Not sure I follow your question. In general the smart way to do this is to put shield wires on the wiring that might bring EMI into components that are sensitive to it. Data, audio, video, those sorts of lines going into a piece of equipment.
In my very limited knowledge of wiring, I had thought that a shield on a source would help. But you pointed out that it's a small benefit especially relative to the risk of a short- which makes a lot of sense. I was also wondering if the risk hardware was the computer mounted on the refrigerator- as there's very little radio stuff in an RV.
Anyway, I'll just twist a pair of wires and power it like that.
I *might* put a bluetooth receiver, but I doubt it, and all of the rest of the 12V need is lights, a water pump, and a couple of vent fans. Although a cell phone signal booster may be in order, too. And a rear view camera.
There will be a TV, so keeping the electrical noise low would be good.
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