% Current Rating Of Wire / Continuous / Intermittent /Ambient Temperature /De-rating
So I thought about explaining this at the same time as my last post, I was kind of tired and let it go, I have all this info in my brain and many times take for granted that everyone else does too.
You notice I say % current rating, that is are we running for example 20 amp on 16 ga shows 2 feet, you notice
wire length, that is total so really if you are carrying a ground the total distance source to load is 1 foot .
Next thing that isn't mentioned is ambient temperature, continuous rating is 30'C, on a motorcycle the heat from the engine if you ride in a warm climate can cause the ambient + heat from the motor to reach over 40'C. Therefore if you live in these warm climates you should de-rate the wire.
Two ways of explaining it, 80% load rating of a 10 amp fuse on 16ga wire = 8 amp. maximum. A second way of stating it, 10 amp load current @ 125%= 12.5 amp, there is no 12.5 amp table, go to the next rating of 15 amp, using a 12.5 amp fuse of 15 amp fuse, in this case the maximum distance for 16 is 2 feet or total wire length of 4 ft.
I bring in temperature rating, for a reason, as the copper heats up, it's resistance increases, something like the element in a toaster , it gets red hot due to resistance, it is composed of nickle and chrome, nichrome
https://www.google.ca/url?sa=t&rct=...iki/Nichrome&usg=AOvVaw17dBNvZ3LmLEZlJcI_G2iA.
So i mentioned using crimps, doubling over wire and surface area came up often, also oxide . Here is what happens, we run 16 ga wire with 8 amp on it off the regulator 3 phase stator, everything is fine, for months. One day we go for a ride, it is hot out, stop and go traffic , the weakest link is the connection points, one connector starts to heat up, which increases the resistance of the connection, a greater voltage drop which produces a increase in heat, that joint fails, we now have a single phase situation, the stator now outputs 13 amp on 18 gauge magnet wire, within 10 minutes we have burnt stator windings.
This may come as a surprise, however, using a oversize conductor, acts as a heat sink, pulling heat away from the connection points, it is forced upon electricians in industry and even residential services, the main safety switches have limited metal contact surfaces and the manufacturers have representitives on places like CSA and UL, which forces electricians to use a minimum wire size for the designated current rating of the switch, usually we need to supply a 125% wire size for the 100% rated switch** going to stop as it gets complicated and not all areas follow this rule.
So my point is, when possible , go 1 size larger.
How you start is what is the current of your load, take 125% of this value and that is your fuse size , example of 8 amp load =10 amp fuse.
Next look at the distance, I prefer to have a central grounding point with a oversize copper ground, as steel frame is a poor conductor. An example is I have a 10 gauge ground about 3 feet long, my Denali split sound bomb horn ( 20 amp fuse), my 15 amp fairing outlet, my Denali lights, my dash 10 amp outlet, my heated grips, and my Gerbing jacket outlet. Not all these loads are continuous , not all are used in warm temperatures. That ground is also tied to the frame though the threaded mounting bolts of my distribution.
Last as a rule,on a 12 VDC system, actual load current; I use 14 gauge for 10 amp [15 amp fuse]; 12 gauge for 15 amp [20 amp fuse]; 10 gauge for 20 amp
[ 30 amp fuse] If you look at the distance in the table, my values are going to be hard to exceed the distance / load rating.
Any questions feel free to ask, probably something wrong or missed. I am a
electrician not a magician >