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The Basics of Connecting Loads

Jan 1, 2000 12:00 PM, By Paul Frank, PRIMEDIA Workplace Learning

Even if you connect electrical loads often, reviewing basic load connection principles can save you time and money -- or even your life.

Typical electrical connections are for lighting and motor loads. But other loads, like ovens, heaters, and dryers are also common. Most lighting requires single-phase power. Often, there are just two supply terminals or leads. One (usually black) is the hot conductor. The other (usually white or gray) is the grounded neutral. Check the voltage at the terminals before locking out to make connections. Know which is the neutral conductor; never connect a single-phase load between one of the phase conductors and ground on a 3-phase system. The neutral's job is to handle the unbalanced load; making the ground do this will cause excessive current to flow through ground.

Many single-speed, single-phase motors can operate on either 115V or 230V by connecting different terminals or adding or removing a jumper. A 115V motor may have a terminal or lead that requires a grounded conductor. If so, wire according to the motor's wiring chart. The motor's insulation arrangement determines this, so don't swap the wires.

Whenever you have a choice, use a voltage higher to reduce current draw and line losses. When connecting the motor for high-voltage operation, both conductors will be hot. For many single-phase motors, polarity makes no difference; the motor will run equally well and in the same direction with the leads reversed. In 3-phase motors, you can change motor direction by changing the wiring connections.

Multiple-speed single-phase motors may have six or more terminals or leads. You can refer to a standard chart for connecting wye-wound and delta-wound motors, but you should always check the data on the nameplate before making any connections.

Whether you have a wye or delta motor, it has nine leads (or terminals). Each motor has three T-leads, (1, 2, or 3): You can swap any two of them to reverse the motor's rotation. Use a rotation tester prior to making connections to leads, and apply properly sequenced voltages of the correct polarity to each of the other leads. If you have clear markings, follow the connection chart. Otherwise, you'll need to use a diagram, ohmmeter, and low-voltage source to identify the leads and their polarity, prior to following the chart. Guessing can burn up the motor.

Industrial ovens, heaters, and dryers may all require single-phase or 3-phase power. Some dual-voltage devices may require you to add or remove jumpers. Make sure you read and understand the manufacturer's installation instructions when connecting such equipment.

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