A problem with raising taps on distribution transformers to compensate for secondary-cable voltage drop is simply poor voltage regulation. During light-load periods, 130V is murder on lamps and consumer electronics, where 110V or less during heavier-load periods is tough on motors. {Don’t forget to consider the significant additional load of motor starting, if applicable.} Flicker from poor voltage regulation can be bothersome to intolerable for some. [In North America, utilities and appliance producers have sort of a “treaty” agreeing on a range of around 110-125V.] The best solution is to size the cable for acceptable voltage drop over the range of anticipated loads, although secondary cables can get quite large.
Consider using an online voltage-drop calculator like those at
www.electrician.com Remember that if 120V loads are split by using 3-wire 120/240V servce, that will effectively lower “120V” voltage drop by one-half, if a reduced neutral is not used.
Another fix may be to move the distribution transformer {extending the primary cables} to a location closer to half way between the two residences, but that may not be acceptable to the utility.
