Fusing/Power Wire Ratio

Power Wire:

10 gauge: ~35 amperes
Class D (~70% efficiency) - <350 watts
Class A/B (~50% efficiency) - <250 watts

8 gauge: ~55 amperes
Class D (~70% efficiency) - <550 watts
Class A/B (~50% efficiency) - <400 watts

6 gauge: ~87 amperes
Class D (~70% efficiency) - <875 watts
Class A/B (~50% efficiency) - <625 watts

4 gauge: ~140 amperes
Class D (~70% efficiency) - <1400 watts
Class A/B (~50% efficiency) - <1000 watts

2 gauge: ~220 amperes
Class D (~70% efficiency) - <2200 watts
Class A/B (~50% efficiency) - <1500 watts

1/0 gauge: ~350 amperes
Class D (~70% efficiency) - <3500 watts
Class A/B (~50% efficiency) - <2500 watts

2/0 gauge: ~440 amperes
Class D (~70% efficiency) - <4400 watts
Class A/B (~50% efficiency) - <3000 watts

4/0 gauge: ~700 amperes
Class D (~70% efficiency) - <7000 watts
Class A/B (~50% efficiency) - <5000 watts

Speaker wire:

22 gauge: ~2.2 amperes
8 ohms - <36 watts
6 ohms - <27 watts
4 ohms - <18 watts
3 ohms - <13.5 watts
2 ohms - <9 watts
1 ohm - <4.5 watts

20 gauge: ~3.4 amperes
8 ohms - <96 watts
6 ohms - <72 watts
4 ohms - <48 watts
3 ohms - <36 watts
2 ohms - <24 watts
1 ohm - <12 watts

18 gauge: ~5.5 amperes
8 ohms - <240 watts
6 ohms - <180 watts
4 ohms - <120 watts
3 ohms - <90 watts
2 ohms - <60 watts
1 ohm - <30 watts

16 gauge: ~8.7 amperes
8 ohms - <600 watts
6 ohms - <450 watts
4 ohms - <300 watts
3 ohms - <225 watts
2 ohms - <150 watts
1 ohm - <75 watts

14 gauge: ~13.7 amperes
8 ohms - <1500 watts
6 ohms - <1125 watts
4 ohms - <750 watts
3 ohms - <563 watts
2 ohms - <375 watts
1 ohm - <188 watts

12 gauge: ~21.8 amperes
8 ohms - <3800 watts
6 ohms - <2850 watts
4 ohms - <1900 watts
3 ohms - <1425 watts
2 ohms - <950 watts
1 ohm - <475 watts

10 gauge: ~34.6 amperes
8 ohms - <9600 watts
6 ohms - <7200 watts
4 ohms - <4800 watts
3 ohms - <3600 watts
2 ohms - <2400 watts
1 ohm - <1200 watts

8 gauge: ~55 amperes
8 ohms - <24000 watts
6 ohms - <18000 watts
4 ohms - <12000 watts
3 ohms - <9000 watts
2 ohms - <6000 watts
1 ohm - <3000 watts

Maximum Fuse Size

00 awg 400 amps
0 awg 325 amps
1 awg 250 amps
2 awg 200 amps
4 awg 125 amps
6 awg 80 amps
8 awg 50 amps
10 awg 30 amps
12 awg 20 amps
14 awg 15 amps
16 awg 7.5 amps

These are the recommended maximum fuse ratings for the corresponding wire size. Using a smaller fuse than what's recommended here will be perfectly safe.

Hope this makes sense.