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What are L7 Disconnect Switch Auxiliaries Used For?

Question: What are LA7-P-D10, LE7-P-D10, LA7-16-P-D10 and LE7-16-P-D10 auxiliary contacts used for when attached to an L7 UL508 “At Motor Disconnect” Switch? These auxiliaries are labeled as N.O.E.B. (Normally Open Early Break). What does this description mean?

Answer: These contacts are actually a N.O. (Normally Open) auxiliary contact with an Early Break function that occurs when the switch is turned from On to Off.

When these are installed on an L7 switch, they function as follows:

• When the L7 switch is tuned On, the 3 normally open power contacts will close slightly before the normally open auxiliary contact does.
• When the L7 switch is turned Off, the auxiliary contact will open slightly before the 3 power contacts do.

Essentially, N.O.E.B. auxiliary contacts are used to break control power before line power.

There are certain applications which benefit (such as the isolation function for many VFDs) from removing the control power (or run signal) prior to the removal of 3-phase power. If the line power is removed before the control power the result is a fault condition in the drive due to a line loss being detected.