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Quick Disconnects Speed Motor Changeouts

Jul 1, 1998 12:00 PM, By Jerry Woodward, Thomas & Betts Corp.

Unique device has contact rings with high conductivity and high contact force.

Many facilities have dozens, possibly hundreds, of motors, some driving a variety of equipment or even continuous-operation machines and systems. Because downtime on many processes is so costly, a fast changeout of a faulted motor is an important advantage. At the Ponderay Newsprint Co., Usk, Wash., some connectors and boots simplify and speed motor changeouts. With motor maintenance and troubleshooting maximized, modern quick disconnects and insulating boots save time and money.

Motors, motor controllers, and related equipment should receive regular preventive maintenance and testing. Usually, we perform these tests with test instrument probes connected at the motor controller. If necessary, you can quickly isolate the controller from a motor with the quick-disconnect arrangement.

Plant electricians at the Ponderay facility find quick disconnects install much more quickly than the wire connector/tape method. This is because you can easily assemble the quick-disconnect terminating components, permitting much more space in the motor terminal box. The insulating boots provide a fast, clean insulation, because you can apply or remove them with such ease.

Five years ago, Charles Green, manager of electrical service, chose the disconnects to speed installation of more than 800 460V motors. Since the project's completion, there have been no termination failures or reports of "hot" connections. And because high motor reliability is essential, infrared tests of all mill motor connections, which are done every nine months, reveal only normal, reliable terminations. The selection of the quick disconnects proves to be the best choice.

Quick-disconnect system. This system consists of two- and three-part connectors (see Photo 1, original article). These connectors snap and unsnap easily, yet form a highly reliable connection; even after numerous connect and disconnect operations.

The quick-disconnect motor connectors come in sets that accommodate one line to one load (two wires); or one line to two loads (three wire). Four "body sizes" allow matching of different wire sizes, because line supply cables are often larger than the motor leads. For example, you can properly connect a No.12 motor lead wire to a No. 1 supply line cable with one particular body size, or a No. 2 motor lead to a 4/0-supply cable with another body size.

These connectors offer numerous advantages over conventional motor lead connectors. They eliminate nuts, bolts, washers, torquing procedures, and the danger of mismatching bolt-holes on-line and load cable lugs. They save a great deal of labor time.

Contact ring improves conductivity. The quick connector is dependable because of a high-amperage capability of an interface ring or band. This band, which occupies the female portion of the connector, has raised louvered edges, tin-plated for low contact resistance. (See Photo 2, on page 50 of original article). The band is made of beryllium copper, which creates its high conductivity. It also has excellent spring characteristics, aiding the reliability of the termination.

When you insert the male pin into the female socket containing the contact band, all the raised edges of the louvered band are deflected, producing a multitude of high-force contact points. Each contact point is typically in the force range of 8000 psi to 10,000 psi. High currents, caused by short circuits or sudden surges, tend to make the interface even more efficient by increasing the contact pressure.

Multiple high-force contacts are more efficient electrically than two flat surfaces bolted together. For example, two lugs bolted together generally produce good contact only in the immediate area of the bolt-holes. You can install the connectors using a mechanical crimping tool, creating a larger area of high-pressure contact between the cable, motor lead, and connector. This assures low resistance and high pullout strength.

Boots add reliability. Insulating boots protect the connectors. This eliminates taping and "knuckle-busting" work in tight spaces. The boot and connector are also more compactthan two lugs bolted together and taped. Installing the boot takes only seconds, versus up to 10 min for taping. Unlike tape, the insulating boot is reusable. It slips on and off quickly and easily.

In cases where dirt, corrosion, condensation, and humidity are a problem, you can add a tape sealant over the connectors before you install the boot. Supplied in 10-ft rolls, the tape sealant is removable and reusable.

The insulating boot, (see Photo 3, original article) also eliminates an installation variable: the skill of the installer assigned to tape the connection. Moreover, there is less chance of failure due to insulation breakdown from heat and vibration. When disconnecting the leads, the boot also eliminates cutting away of insulator tape. Since a knife isn't used, motor leads can't be damaged.

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© 2012 Penton Business Media, Inc.

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