Originally Posted by dznf0g
By single run, you mean 1 b+ and 1 b- ? Bundled you mean multiple pos and neg in same proximity in the run?
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Since the table referenced ABYC standards, and specifically E-11 (which I am intimately familiar with having just completed my ABYC Master Marine Electrician certification course), the definition of a single conductor is one wire not bundled, sheathed or in conduit.
I just pulled up my E-11 wiring tables and the chart above seems to be a combination of the 2 pictorial (in an easier viewing form) of the E-11 charts for conductor length of a wire run of the 2 types of circuits (critical and non-critical) for the ungrounded (current carrying) conductors. For RV use, I would stick to using the critical designation (3% voltage drop) for all wiring.
ABYC CONSIDERS THE LENGTH OF A CONDUCTOR TO BE FROM THE SOURCE OF CURRENT TO THE LOAD DEVICE AND BACK
TO THE SOURCE!!
This means that if your converter is 10 feet from your battery, the circuit length is effectively 20 feet. This WILL change wire gauges used in many of the circuits at 3% voltage drop and should be carefully calculated.
The bundling, sheathing or use of conduit will further derate
the ampacity of the wire gauges, and specifications for those are contained in different tables. There are 2 tables that apply to DC circuits; one that considers a single conductor that is not bundled, sheathed or in conduit and up to 3 current carrying conductors that ARE either bundled, sheathed or in conduit. ABYC does not consider derating of ampacity over 3 bundled DC conductors, but does have further derating specifications for bundles of AC conductors up to 25 or more bundled
current carrying conductors.
I know what the next question is……………What is considered a current carrying conductor? In a DC circuit, BOTH positive AND negative are current carrying. In an AC circuit, only the hot (ungrounded), and neutral (grounding) conductors are considered current carrying. The actual ground conductor (grounded) is NOT considered current carrying, as in a properly wired and normal functioning AC circuit, the ground (grounding) conductor should have no voltage on it. The terminology in parenthesis is from ABYC, as they do not typically use the terms 'hot, neutral and ground' to describe AC circuits.
Now that you are probably totally confused, use the chart above from Blue Sea Systems, but remember to use the TOTAL length of your circuit (from the current source AND BACK) in your calculations. Since most RVs don't bundle their cables (Airstream actually does
with the DC wires that come from the fuse block), you really don't have to consider this type of derating of the cable's ampacity.
I have noticed though, that Airstream now fuses 12AWG DC cables from the fuse block at 15 amps, when one would normally fuse them at 20 amps (as they have done in the past). This is a result of derating the ampacity due to bundling and something that I did not mention, the temperature rating of the wire's insulation.
I use 105ºC rated cable, which is standard marine cable. Most RVs use cabling rated at 60ºC, which further derates the ampacity of the cables used.
Sorry to go on for so long, but there is MUCH MORE to figuring a wire's ampacity than just the AWG of the cable.
I'M DONE NOW!