Disconnect Switch - Type

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Charz

Member
Location
Texas
Disconnect Switch:


The disconnect switch provided according to the code 430.102(B) Motor. A disconnecting means shall be provided for a motor in accordance with (B)(1) or (B)(2).


What is the type of disconnect switch to be provided?


This disconnect switch is to be capable of disconnecting the power supply when the motor is operating (or) just be able to be in open position when the motor is switched off.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
The two common types of disconnect switches are UL98, or UL508, but as Augie said, there are multiple ways of providing a disconnect DEVICE as laid out in 430.109.

A UL98 listed disconnect switch can be used anywhere and it will be listed with a HP value for opening the circuit under load. UL98 switches can be fused, in which case the entire unit can be the Branch Over Current Protective Device (BCPD), or non-fused. But a non-fused switch means you need an OCDP somewhere else, i.e. a circuit breaker or ANOTHER fused switch in the circuit. So the only time you would use a non-fused switch is if the BCPD is part of a motor starter that is not within sight of the motor.

A UL 508 listed disconnect is typically cheaper but can ONLY be used in a circuit that has a BCPD elsewhere. They too must have a HP rating equal to or greater than your motor.

The only time you can get away with using a switch that does not have a HP rating is if it is used as an isolator and is mechanically interlocked with something else that prevents it from opening the circuit under load. Those are uncommon in LV equipment, but fairly common in Medium Voltage.
 
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