Sanity check: Inverter input current, wire size, fusing, and ampacity

citysnaps

I’m considering going with a 12 volt Exeltech XP 1100 for my van conversion AC power requirements. The inverter output will provide 1,100 watts of power with three second surges to 2,000 watts. It will be driven by 200 ah of AGM battery and provide occasional short duration power for a small “600 watt” microwave (a few minutes a day), a small computer printer (a few minutes a day), and various laptop/camera battery chargers (a few hours a day) - and not all at once.

Right now I’m trying to determine input wire size and fusing requirements.

The Exeltech user manual ( http://exeltech.com/Manuals/xp600-1100-2000manual.pdf ) in Appendix A recommends 0 AWG wiring for runs less than five feet. No problem on the length. Appendix A also lists rated current at 94 amps and peak current at 220 amps.

Checking the NEC Ampacity chart for 0 AWG THHN wire shows 170 amps. That’s fine for the inverter’s rated output. It’s shy for peak current (220 amps for 3 seconds), but that is not continuous so I suspect that's not an issue.

My question is what Class T fuse rating should I use?

If I fuse for 170 amp ampacity I’ll not be able to handle occasional startup peaks. If I fuse for occasional peaks, I’m not protecting the input wiring for unforeseen situations.

I suspect there’s something I’m not understanding, so any help or insight would be appreciated!

Cariboocoot

Re: Sanity check: Inverter input current, wire size, fusing, and ampacity

Amperage ratings for wire, fuses, and breakers are almost always for continuous current.
What's more, the application will have an effect on the rating because much of it has to do with the ability to dissipate the heat generated by the current: wire in conduit has a lower Amperage rating than the same wire in 'free air'.

Normally you ignore peak current demands because they are momentary; not long enough to generate heat or trip a breaker or blow a fuse.

O AWG can take 245-250 Amps momentarily. What you want to look at for sizing the over-current protection is your expected continuous current. It will be lower than that, and usually only the rated power for the inverter. In this case 1100 Watts / 12 Volts (or LVD point) = 92 Amps, plus the inverter draw. Hence Exeltech's 94 Amp rating. If you really intend to run at full output you will need OCP >94 Amps and <250 Amps. A bit of fudging is in order: call the continuous current 100 Amps and using the NEC derating factor you get 150 to 200 Amp fuse/breaker.

I would not worry about the 220 Amps for 3 seconds.

citysnaps

Re: Sanity check: Inverter input current, wire size, fusing, and ampacity

Thank you for your help - very much appreciate it!