When sump pump goes on or we use Microwave then voltage goes down for a second then comes back to normal. Electric service provider says its problem at my end. What it can be and how much approximately it will cost me to fix? Please reply & thanks in advance for any reply.
Thanks

Start by checking your main panel, insure all wires and connections are tight. Put your test leds on the mains from the utility compnay and see if there is any actual drop from their feed.

Thank you Ballen.