An insulating cap and method of using the same is disclosed. The insulating cap has one or more slots sized to accept edges of a rib of an arrester bracket so that the cap may be affixed to the rib by sliding the cap over the rib. Tabs at lower portions of the slotted side portions provide for snap fitting the cap to the rib. A cover portion of the cap extends forward from the slotted portion and is sized to at least partially cover a bolt or fastener that connects the arrester bracket to a mounting bracket that is, in turn, affixed to a transformer tank. The cover portion has curved or rounded upper surfaces to serve as a perch deterrent. The insulating cap is formed from a UV stabilized, polypropylene copolymer.