Some installations of the M-2001 series Tapchanger Control may experience interposing relay buzzing, chatter (severe buzzing), or in extreme cases, lock-up and runaway tap changer operation.

With sensitive coil configurations, even though the pull-in current is usually in excess of 10 mA, the “maintain” or “holding” current can be as low as 1-2 mA. At that level, the leakage current from protective components in the M-2001 series control, can cause the relay armature to buzz or lock-up the interposing relay. Adding shunt resistance to each of the output relay circuits will minimize the interposing relay’s sensitivity to small leakage currents, thereby eliminating the relay buzz, chatter, and lock-up.

For this reason, the B-2048 Resistor Assembly is provided with some adapter panels.