Dear Mr. electrical429 (Electrical)
"...I always specify DC, since in the event of AC supply failure you can still operate the switchgear for 6-12h until the battery runs down. Are there any other points that should be taken into account?.."
Che. 1. Sir, what is the [voltage] level (<1kV) or (>1kV) and what is the [wattage] level (<1W), (<100W), (<1 kW), (<100 kW), (<1 MW) etc., are you talking/concerned about?
2. AC can be in single-phase or three-phase with (voltage) being easily [transformed up/down] very efficiently. But not DC. AC Single-phase or three-phase motors are very robust and efficient, which DC motors impossible to match; unless under special condition/requirement.
3. There are transmission lines with three-phase voltage (>400kVac). There are also EHV DC (>400kVdc)transmission lines but eventually invert back to AC; for ease of voltage transformation.
4. Domestic, commercial and industry electrical equipments with 99.99% operate on AC. But EV, forklift , torch-light etc., operate on DC.
Che Kuan Yau (Singapore)