Be careful you don't run afoul of the co-op board. Best to get their permission, in writing. Also, whoever you use get a copy of his State license and a copy of his insurance certificate that has an endorsement that covers your unit. Those documents should be in hand at least 48 hours before any work is done. That way, when he blows out the master panel for the building you will know damages are covered, assuming his coverage is at least $10 million. Can't be too careful in these matters. My guess, $500 in NYC.