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We have a motor control centre installed in garage for a commercial outlet.

The MCC has a SMC-Flex ( Low voltage soft starter).

The control relays (700 HA33) are connected to the SMC control terminals. Most of the time the control relays connected to the SMC control terminals are provided with the surge suppressors.

Is it necessary to provide the suppressors to all control relays within the circuit?

Is it essential to provide them to the timer relays? Please note that I am referring to the control circuit. All the components connected are in the control circuit.

K H
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DaSnipeKid
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1 Answers1

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If the control circuit power supply also powers electronic control equipment or if the relays are in the same enclosure with electronic control equipment, then every relay should have transient voltage suppression. For AC relay coils, RC suppression should be used. For DC coils, an anti-parallel diode should be used. If the soft starter is electronically controlled, that is electronic equipment in the same enclosure. Timing relays may also be electronic.