Security Service covered under category 65(105)(w) i.e. 'Security/ detective agency service' and the corresponding accounting code is '00440108'
As far as payment made for labour charges for painting in office concerned, these are not covered under the definition of works contract, hence not chargeable under reverse charge. However you can check your own case by referring to the definition of works contract service (which is reproduced below).
Payment made to electrical contractor is covered under works contract (if it involves transfer of property in goods) and category of works contract is 65(105)(zzzza) and the corresponding accounting code is '00440410'.
Sec. 65(105) "taxable service" means any service provided or to be provided
(zzzza) to any person, by any other person in relation to the execution of a works contract, excluding works contract in respect of roads, airports, railways, transport terminals, bridges, tunnels and dams.
Explanation.—For the purposes of this sub-clause, “works contract” means a contract wherein,—
(i) transfer of property in goods involved in the execution of such contract is leviable to tax as sale of goods, and
(ii) such contract is for the purposes of carrying out,—
(a) erection, commissioning or installation of plant, machinery, equipment or structures, whether pre-fabricated or otherwise, installation of electrical and electronic devices, plumbing, drain laying or other installations for transport of fluids, heating, ventilation or airconditioning
including related pipe work, duct work and sheet metal work, thermal insulation, sound insulation, fire proofing or water proofing, lift and escalator, fire escape staircases or elevators; or
(b) construction of a new building or a civil structure or a part thereof, or of a pipeline or conduit, primarily for the purposes of commerce or industry; or
(c) construction of a new residential complex or a part thereof; or
(d) completion and finishing services, repair, alteration, renovation or restoration of, or similar services, in relation to (b) and (c); or
(e) turnkey projects including engineering, procurement and construction or commissioning (EPC) projects;