Disconnect leaves mobile home park without electricity

Site, system and components
600 Amp single phase overhead service supplying electrical power to a mobile home park.

A wooden 8X8 post attached to an electrical distribution room was used to support the attachment point for the 600 Amp overhead service. Three 250 MCM (1) aluminum armoured cables are fastened to the wooden post, these cables are then terminated into threaded conduit bodies with wet location connectors. Threaded rigid conduit is then used to connect the conduit body to the 600 Amp fused service disconnect. The rigid conduits have been entered at the top back side of the service disconnect directly above the conductor termination terminals. From the load side of the disconnect conductors are connected to other sub distribution equipment located in an electrical room.

MCM: unit of dimension, thousands of circular or 1.25 in cable.

Failure scenario(s)
Oxidization (rust) occurred at the bottom of the fused disconnect from moisture entering through an old connector at the top of the conduit body (Photo 1). The bottom of the conduit body where the rigid conduit is terminated showed signs of corrosion causing a hole (Photo 5). The disconnect blades, knife switch and fuse also showed signs of heat damage.

Facts and evidence

• Armoured cable exposed to wet conditions with connectors wrapped in electrical tape to prevent moisture from entering the conduit body.
• Conduit bodies showed signs of moisture damage.
• Rigid threaded conduit showed signs of moisture damage.
• One conduit was terminated directly above the connection terminal that suffered the heat damage.
• Moisture damage is prevalent in the service disconnect.

Causes and contributing factors
It is likely that moisture had been entering the conduit body from the improperly terminated or sealed armoured cable connector exposed to wet conditions. Moisture dripping directly onto the effected terminal would have caused heating and cooling of disconnect blades and knife switch and eventual failure.