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Electricalaka: disconnect switchaka: safety switchaka: fusible disconnect

Disconnect

In Plain English

A switch or device that cuts power to a piece of equipment so it can be serviced safely.

Definition

A device that opens an electrical circuit so that equipment can be safely de-energized for maintenance or emergencies. The NEC requires disconnects within sight of equipment they serve, such as HVAC units, motors, and appliances. Disconnects can be fusible or non-fusible and may include lockout/tagout provisions.

Why It Matters in Bidding

Disconnects are required by code at most powered equipment, so the electrical estimator must count one for each HVAC unit, motor, water heater, and similar load, plus the conductors and connections feeding them. Whether a disconnect is fusible or non-fusible, and its NEMA rating for outdoor use, changes unit cost, and overlooking these required devices during takeoff creates both a code violation and a coordination gap with the mechanical scope.

Example

Reviewing the mechanical schedule against the electrical drawings, an estimator adds a weatherproof non-fusible disconnect at each rooftop condensing unit because the NEC requires one within sight of the equipment, even though the architect's plans did not show them.

Related Terms

Circuit BreakerSwitchgearNEC (National Electrical Code)Electrical Panel

Frequently Asked Questions

They cross-reference the mechanical and equipment schedules against the electrical plans, adding a disconnect for each motor, HVAC unit, and appliance that code requires, even when not drawn. Each device is priced with its conductors, terminations, and rating, since outdoor or fusible units cost more than indoor non-fusible ones.
A fusible disconnect includes fuses that provide overcurrent protection, costing more and requiring the correct fuse class to be carried in the bid. A non-fusible disconnect only opens the circuit and is cheaper. The equipment's protection requirements and the specs determine which to price for each connection.
Equipment often appears on mechanical drawings while the required disconnect is implied by code rather than shown on electrical plans. During scope review, confirm the electrical sub carries disconnects, whips, and final connections so they are not assumed by the mechanical contractor or omitted from both proposals.

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