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What wiring gauge and type of wire should I use?

Stranded wire AKA multicore is always recommended.
 
There's no maximum gauge, as long as you can find a terminal lug that fits it.  Click to search terminal lugs on Digikey
 
There is a minimum gauge, and that is determined by the maximum current you intend to draw.    At 15A, you should use a minimum of 14AWG for the output wiring, as shown in the wiring table below.

 

The table shows current ratings of PVC-insulated single and multicore wiring cables. Click to search for hookup wire at Mouser.   The current load depends somewhat on installation method - the enclosure - and how well the resistance heat is removed from the cable. Operating temperature of the conductor, ambient temperature and type of conductor insulation is important. Check the manufacturer's data for detailed engineering.

AWG Diameter
(mm)		 Diameter
(in)		 Square
(mm2)		 Resistance
Copper
(ohms/1000m)
 (Ohms/1000 ft)
 Typical Max. Current Load Ratings - Copper (amps)1)
Single Core Multicore
up to 3 cores 4 - 6 cores 7 - 24 cores 25 - 42 cores 43 and above
40 0.08 . 0.0050 3420            
39 0.09 . 0.0064 2700            
38 0.10 0.0040 0.0078 2190            
37 0.11 0.0045 0.0095 1810            
36 0.13 0.0050 0.013 1300            
35 0.14 0.0056 0.015 1120            
34 0.16 0.0063 0.020 844            
33 0.18 0.0071 0.026 676            
32 0.20 0.0080 0.031 547            
30 0.25 0.010 0.049 351            
28 0.33 0.013 0.080 232            
27 0.36 0.014 0.096 178            
26 0.41 0.016 0.13 137            
25 0.45 0.018 0.16 108            
24 0.51 0.020 0.20 88 3.5 2 1.6 1.4 1.2 1.0
22 0.64 0.025 0.33 52 5.0 3 2.4 2.1 1.8 1.5
20 0.81 0.032 0.50 34 6.0 5 4.0 3.5 3.0 2.5
18 1.0 0.040 0.82 22 9.5 7 5.6 4.9 4.2 3.5
16 1.3 0.051 1.3 13 20 10 8.0 7.0 6.0 5.0
14 1.6 0.064 2.1 8.5 24 15 12 10 9.0 7.5
13 1.8 0.072 2.6 6.8            
12 2.1 0.081 3.3 5.4 34 20 16 14 12 10
10 2.6 0.10 5.3 3.4 52 30 24 21 18 15
8 3.3 0.13 8.3 2.2 75 40 32 28 24 20
6 4.1 0.17 13.3 1.5 95 55 44 38 33 27
4 5.2 0.20 21.2 0.80 120 70 56 49 42 35
3     26.7   154 80 64 56 48 40
2 6.5 0.26 33.6 0.50 170 95 76 66 57 57
1 7.4 0.29 42.4 0.40 180 110 88 77 66 55
0 (1/0) 8.3 0.33 53.5 0.31 200          
00 (2/0) 9.3 0.37 67.4 0.25 225          
000 (3/0) 10.4 0.41 85.0 0.20 275          
0000 (4/0) 11.7 0.46 107 0.16 325          
250     127   345          
300     152   390          
400     178   415          

1) Current ratings for up to 1000 V, PVC-insulated single and multicore wiring cables, ambient temperature up to 30oC

The higher the gauge number, the smaller the diameter, and the thinner the wire.

Because of less electrical resistance a thicker wire carries more current with less voltage drop than a thinner wire. For longer distances it may be necessary to increase wire diameter - reducing the gauge - to limit voltage drop.

 

Correction-factors at ambient temperature above 30oC

  • ambient temperature 31 - 40 oC: correction factor = 0.82
  • ambient temperature 41 - 45 oC: correction factor = 0.71
  • ambient temperature 45 - 50 oC: correction factor = 0.58
 

For the input wiring to the DLI DC power switch, you want #6 or #8 at 50A.  If you are wiring over a long distance, say a few hundred feet, you may want to go down a gauge (thicker) to reduce thermal loss in the cable.  If you are running over a short distance and operating at lower currents, or if you anticipate frequent overloads, high temperature insulation like PTFE may be helpful.



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