I currently have a Gentran 3028 subpanel connected to a 12,000 watt generator over a 30 AMP branch and the utility/main panel over a 60 AMP branch. I want to replace the Gentran with a APC UTS10BI. I would like to mount the APC more than the recommended one foot distance away from the utility/main panel. The APC can use a UPS as an alternate power source until I can get the generator running. This is also the reason I need to mount the APC away from the utility/main panel. There isn't enough floor space for a rack mounted UPS system near the main panel. My question is how much of a gauge drop do I need to make to cover the 18 to 20 foot distance? The installation manual recommends a utility line of "Circuit: 12 AWG Two Neutral:10 AWG". If I drop the circuit to 10 AWG and the two neutral to 8 AWG would that be safe?
According to the Manufacturers Installation Guide (PDF)...
According to National Electrical Code (NEC)...
I'm guessing the unit has permanently attached wires in a raceway, which is of a limited length. So mounting the unit further from the panel would require you to extend these wires and raceway, which requires knowledge of wiring methods to do properly. It's not likely you'll have to upsize the wires, but you will have to understand basic wiring methods (Chapter 1-4 of NEC).