If anyone thinks the following post is too long for readability, please PM me and I'll try to break it up.
...Have been meaning to ask the question which guage wires to use. Hopefully someone can help decipher the diagram and let us both know what guage the different color wires would be.
Wire sizes are usually identified by the "gauge", by which people normally mean the American Wire Gauge (AWG)
scale - you go to the store, ask for "10-gauge wire", and they sell you some thick stuff which says 10 AWG on the package.
Fundamentally, you need thicker wire if you have more current, so if you know how much current, and you have some sort of rule to follow, you can pick a wire size. Fortunately, that same Wikipedia page has a handy table
with a reasonable guide. It seems to match common practices in trailers; for instance,
- everyone recommends 10-gauge for the supply from the tow vehicle battery to the trailer, with a 30 A circuit breaker, and the table says 10-ga wire is good for 30 amps - that's the black wire from the tug to the battery and the power converter in the Scamp diagram
- running lights use only a few amps in total, so the table says 16-ga wire would do, and I suspect that's what's in the trailers, although big truck trailers (with lots of lights) use 14-ga - that's the red, brown, yellow, and green wires to the tail lights and markers in the Scamp diagram
- according to Tekonsha/Cequent Prodigy brake controller wiring instructions, up to two trailer axles of brakes needs 20 A of circuit breaker capacity and 14-ga wire (or 30 A and 12-ga for three or four axles), while the table says 20 A is 12-ga, which is close - that's the blue wire in the Scamp diagram
For the circuits from the power converter to stuff like the refrigerator
, each circuit has a fuse (or breaker) to limit current to some level, such as 10 A or 15 A. That tells you how big the wire has to be. Of course, thicker wire is harmless, so I vote for erring on the side of [b]thicker-than-necessary rather than almost-thick-enough. The rule is based on keeping heat (due to resistance to current flow) down so the insulation doesn't melt or break down, but there's no need to let wires get hot.
I notice that the Scamp diagram is really [b]schematic: that is, it tells you what is connected to what, but not really how the wires run. For instance, it shows that the power to everything goes out on some coloured wire and returns on a white wire, which is likely true. It also suggests that everything is connected to the same
white wire, which is almost certainly not the case. I would expect to see a few white "ground" (or "neutral", or "return", or "negative", whatever you want to call it) wires coming together in one point somewhere inside a cabinet. That makes it a little tough to figure out how much current might be in that wire - you have to total up everything actually running through it.
And one last note: thicker wire means less resistance, which means less power loss, which means more endurance from the battery or more performance from the device (e.g. brighter lights). Thick is good, within reason.
By the way, for alternative rules, I did a Google search for
wire gauge current capacity DC
and followed the very first link to a page from Powerstream
which had a table. In their table they have two "maximum" columns, depending on which rule you want to follow. The Wikipedia one looks reasonable to me, and falls between the two rules at Powerstream, tending to the more conservative side at larger sizes. That's all I did for comparitive research, because what I found in that first table all seemed reasonable to me based on other experiences.