The Watertown (Wis.) Wastewater Treatment Plant is saving time with a combination plug/receptacle and disconnect switch that makes motor and generator connections safer and faster in the plant and at lift stations around town.

The Decontactor Series switch-rated motor plug from Meltric Corporation allows workers to make and break electrical connections safely even under full load and provides the line-of-sight disconnect as required by the National Electrical Code (NEC).

The activated sludge secondary treatment plant (5.2 mgd design flow, 3.5 mgd average) serves a city of about 23,000. Submersible mixers in the aeration basins originally were hard-wired. When one of the mixers had to be replaced, the project put the tank out of service for about a day while the mixer was disconnected and a new one re-wired.

To resolve that issue, the facility staff installed DSN30 (30A, 480V, 10 hp rated) Decontactor plugs on all its aeration tank mixers. The devices allow the mixers to be connected and disconnected safely with plug-and-play simplicity.

Simple disconnect

Now, technicians can easily replace or service the mixers without needing an electrician and without electrical personal protective equipment as required by NFPA 70E. “When the first mixer failed, we had to shut everything off and disconnect all the wiring before we could pull it out and drop in a replacement,” says Kevin L. Freber, assistant water systems manager-wastewater. “Now we just pull the plug, crank the mixer up, and plug in a new one. We’re ready to go in minutes, and there’s never any exposure to live power.”

Disconnecting a motor is now a simple operation, initiated by pressing a pawl on the Decontactor plug, which causes it to break the circuit and eject the plug to its rest position. Then, a quarter-turn of the plug allows it to be totally withdrawn from the receptacle in complete safety, since the circuit is already dead. When the plug and receptacle are separated, a safety shutter prevents access to live parts.

The plugs incorporate spring-loaded, silver-nickel, butt-style contacts that provide consistently high electrical performance over thousands of operations. They also resist wear, corrosion, oxidation and other conditions that contribute to failure of pin-and-sleeve devices.

To the lift stations

Success with the aeration basins led the utility to equip its portable emergency generators and remote lift stations with similar connectors. Typically, the lift stations are located below ground level with a control panel above ground.

A power failure may make it necessary to bring the portable generators to power the pumps at some lift stations. Previously, the stations were equipped with conventional pin-and-sleeve connectors and could not be locked easily to prevent tampering or entry by children or vandals. “The generators deliver 100-amp service, and with the plugs we had before, there was no way of locking the two parts together,” says Freber. “Any child could walk up and pull it apart.”

The Decontactor plugs are easy to lock to prevent tampering and also are safe when separated. “You have to twist it to open it, and even if someone could get it apart, they never could get at the live contacts,” Freber says.

That is because the devices have dead-front construction and enclosed arc chambers. Easily accessible contacts on the previous connectors had the potential to expose workers or others to live power. Switching to the Decontactor plugs also helped the utility simplify compliance with NFPA 70E arc flash requirements.