UPS neutral problem

salam alikum, on eids third day i have a strange problem in my ups wiring.

i have desi made 2000VA 24 VDC UPS with two ags 165 batteries. i have connected my ground floor and upper portion on it which are from two different meters. at night there is trip in the main supply and voltage fluctuates and remains on 120 to 150v for a brief moment of 20 min. then it shifts to ups. after few min i have a very strong smell of burning near ups. i called the ups company and the electrician came and said neutral wire is burnt after checking he replaced the whole wire from outlet since it is placed at distance.

Now the problem is whenever supply is on ups there is a flickering in the upper portion connection while ground floor connections are ok i .e no flickering.

is there some neutral wire problem since its running fine before this problem.

help in this reqrd is required from wp member. thanks.

to further understand the problem, do confirm if following is correct;

Given that meter A and meter B are for two different/separate wapda connections.

lets say;

Upper floor is on meter A

Ground floor is on meter B

UPS is connected to meter B

is the UPS output wired for both Line and Neutral or Line only.

when UPS is on battery mode, there is flickering only on Upper floor, while the Ground floor is alright.

is everything alright when on wapda.

Ups output connected to only live wire from both portions i.e line only.

Flickering only on upper portion ground floor is alright.

Yes every thing is ok on ke, since iam in karachi and there is k electric here.

thanks for the suggestion . Today installed the ups back. the guy told me there was some problem of AVR insid the ups since inside ups neutral is connected with ground.. now working ok.