Leslie, the ABYC ampacity is only concerned with safety, and how many amps you can put through the wire without overheating. #10 can safely handle 60A, but after 10 feet of wire the voltage will be reduced significantly, which can be an issue for battery charging.
The ProMariner manual I've got says #8 can be used with the 40A charger @ 10 feet. The 50 and 60A chargers require at least #6 or larger. Both the Blue Sea table and West Marine graph show the same for the 40A and that 60A requires #6 or larger.
#14 for the AC wiring is fine. The 60A charger only draws 11A. Most likely the AC breaker is 15 A anyway.
I generally aim for less than 2% with chargers inclusive of all fuses & terminations.. Just finished an installation of a 60A today and it got 2GA wire.
12V Nominal @ 2% Drop 40A Charger - (Circuit = total wire length for neg and pos)
10' Circuit = 8GA - 2.15% VD
12' Circuit = 8GA - 2.58% VD
12' Circuit = 6GA - 1.63% VD
14' Circuit = 8GA - 3.02% VD
14' Circuit = 6GA - 1.9% VD
16' Circuit = 8GA - 3.44% VD
16' Circuit = 6GA - 2.17% VD
18' Circuit = 6GA - 2.44% VD
18' Circuit = 4GA - 1.53% VD
20' Circuit = 6GA - 2.71% VD
20' Circuit = 4GA - 1.7% VD
24' Circuit = 6GA - 3.25% VD
24' Circuit = 4GA - 2.04% VD
Here's a real world example of "sizing for 3%"
Q: "RC I sized my alternator system for a 3% voltage drop but it is exceeding this by quite a bit. Did I calculate incorrectly? Tom"
A: "Tom,
It's called the real world. You sized for 3% which is already a -0.44V drop at 14.7V, not ideal for a performance charging system without voltage sensing, but that 3% sizing is for the wire only. Even good techs often forget that the charts for wire sizing completely ignore all the other things that add to the total voltage drop.
For most circuits a 3% volt drop is a fine target to aim for but it is not adequate for performance charging system where you expect your inverter to remain in bulk at near voltage parity with the battery terminals. Your early absorption issue is because the design calcs did not account for total
as installed voltage drop between the IC and the bank.. This is why your assumed target for bulk charging for an hour, on your multi day offshore racing passages, do not meet expectations. It is also why I suggested to aim for less than 2% drop. We will need to tweak it when you get back."
Real world also meant that when the wires were finally run, the length, according to the owner, "
was a tad longer." The wire passed through multiple lugs/terminals, a fuse, switch, busbar etc. and each and every connection adds more voltage drop to the wires loss.. For termination calcs I use 0.00025Ω when I make the terminations and 0.00040Ω when someone else does.
Each lug is; Wire to Lug as #1 > Lug to XX Point as #2.
For example an ANL fuse would have a total of 5 points of resistance.
Two connection points per lug then the fuse itself.
This 0.00040Ω seems to bear out quite often. Let's run the numbers on just the connection points at say 40A with the average connections I see on many battery charger installs:
12 *Connection points at 0.00040 = 0.0048
40A X 0.0048 =
-0.192V
This drop, 0.192V, would be added to the cable volt drop.
*0.00040 is still assuming the connections are clean, tight and not made with a dime store crimp tool.
