Disconnect Symbol
Definition: The Disconnect symbol represents a manually operated safety switching device in wiring diagrams that provides visible, lockable isolation of electrical equipment from its power source, depicted as a single-pole or multi-pole switch symbol with a gap indicating the open position, referenced in IEC 60617 and ANSI Y32.2 / IEEE 315; it is designated QS or DS in industrial schematics and S in residential diagrams.
Also known as: safety switch, cutoff switch, main disconnect, service disconnect, isolation switch, lockable disconnect, fused disconnect.
What the Disconnect symbol means
The Disconnect symbol marks a point in the electrical circuit where a physical, visible break in all ungrounded conductors can be established to allow safe maintenance, inspection, or replacement of downstream equipment. Unlike a circuit breaker, which also provides overcurrent protection, a disconnect is primarily an isolation device—its defining feature is that its open state must be visually confirmable and its contacts lockable in the open position under OSHA and NEC requirements.
In residential wiring diagrams the Disconnect symbol typically appears at the service entrance or as a means of disconnect for HVAC equipment, pools, or spas. In industrial single-line and schematic drawings it marks the isolation point for motor feeders, sub-panels, and machinery supply circuits. The Line pin connects to the supply and the Load pin connects to the protected equipment.
How to identify the Disconnect symbol
The Disconnect glyph is drawn as one or more single-pole switch symbols—a fixed contact and a movable blade—arranged in parallel for multi-pole versions, with the blade shown in the open (off) position. A box or rectangle enclosing the switch elements is common in industrial symbols to indicate a housed disconnect unit. Some versions include a small padlock symbol or a dashed enclosure box to emphasise the lockout/tagout (LOTO) capability. The symbol is distinguished from a circuit breaker by the absence of the trip element indicator and from a fuse by the absence of the fuse element.
Function in a circuit
A disconnect switch provides a safe, reliable means of de-energising electrical equipment for maintenance or emergency shutdown. In its open position the disconnect creates a visible air gap in the circuit conductors, confirming to maintenance personnel that the circuit is de-energised. The lockout/tagout mechanism (hasp or padlock lug) allows the open position to be secured against accidental re-energisation. Most disconnects also accept fuses in the switch-blade holders, providing both isolation and overcurrent protection in a single device (fused disconnect).
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617 represents the disconnect switch (isolator) using the standard switch symbol with an added isolation qualifier; IEC 60947-3 governs the performance requirements for switches, disconnectors, and switch-disconnectors. The designator is QS in IEC-based industrial schematics. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315-1975 defines the disconnect switch symbol as a single-pole switch blade with a fixed contact, enclosed in a box for housed units. NFPA 70 (NEC) Article 230.70 and 422.31 mandate a disconnect means for services and appliances. The designator is DS or S in North American drawings. |
| Key difference | IEC symbols use the 'isolator' or 'switch-disconnector' classification with QS designator; ANSI/NEC uses 'disconnect switch' or 'safety switch' with DS designator. Both standards require the open state to be visually confirmable. IEC 60947-3 specifies the switching-duty categories (AC-23, AC-22, etc.) not present in the ANSI symbol definition. |
Terminals / pins
| Pin | Name |
|---|---|
| line | Line |
| load | Load |
Typical values
Residential disconnects: 30 A to 200 A, 120/240 V single-phase. Industrial disconnects: 30 A to 1200 A, 240 V to 600 V AC, three-phase. Enclosure ratings: NEMA 1 (indoor), NEMA 3R (outdoor), NEMA 4/4X (watertight/corrosion-resistant). Fused types accept Class J, RK1, RK5, or CC fuses depending on AIC rating required.
Where the Disconnect symbol is used
- Service entrance disconnect (main disconnect) at the utility meter to isolate the entire building electrical system
- HVAC equipment disconnects required by NEC Article 440 within sight of the equipment
- Pool and spa equipment disconnects per NEC Article 680 providing LOTO capability for maintenance
- Industrial motor feeder disconnects providing isolation prior to the motor starter
- Sub-panel feeder disconnects separating branch-circuit panels from the main service
- Outdoor signage and rooftop equipment disconnects providing local isolation for service personnel
Example
In a residential air-conditioning installation wiring diagram, a Disconnect symbol is placed outdoors within sight of the condensing unit; the Line pin is connected from a 240 V two-pole circuit breaker in the main panel via a feeder, and the Load pin feeds the condensing unit's contactor. The disconnect is shown as a 60 A fused safety switch in a NEMA 3R enclosure, satisfying NEC Article 440.14 requirements.
Key facts
- The Disconnect symbol represents an isolation switching device (not an overcurrent protective device) that provides a visible, lockable open circuit for safe maintenance; it is designated QS (IEC 60947-3) or DS (ANSI/NEC) in schematics.
- A disconnect has two terminals: Line (supply side) and Load (equipment side); it is always wired in series with the circuit and interrupts all ungrounded conductors when opened.
- The NEC (NFPA 70) mandates a disconnect means within sight of HVAC equipment (Article 440.14), within sight of motors (Article 430.102), and at each service entrance (Article 230.70).
- Fused disconnects combine isolation and overcurrent protection in one unit; unfused disconnects provide isolation only and rely on upstream overcurrent devices for fault protection.
- The lockout/tagout (LOTO) capability is a defining feature of a disconnect: the open position must be securable with a padlock to prevent accidental re-energisation during maintenance, per OSHA 29 CFR 1910.147.
- Disconnects are rated by voltage, current (amperes), and horsepower (for motor loads); motor-rated disconnects must be rated for at least 115% of the motor full-load current per NEC Article 430.
- Common disconnect enclosure types: NEMA 1 (open/indoor), NEMA 3R (rainproof/outdoor), NEMA 4 (watertight), and NEMA 4X (watertight + corrosion-resistant for wet or chemical environments).
Frequently asked questions
What does the disconnect symbol mean in a wiring diagram?
The Disconnect symbol means that a manually operated isolation switch is present at that point in the circuit, allowing all ungrounded conductors to be physically opened and locked out for safe maintenance or emergency shutdown. It indicates a required means of disconnect, not merely an on/off switch.
What does the disconnect switch symbol look like?
The Disconnect symbol is drawn as one or more single-pole switch blades (a fixed contact and a movable blade shown in the open position), often enclosed in a box or rectangle representing the switch housing. Multi-pole disconnects show parallel switch blades for each pole. Some versions include a padlock symbol to indicate lockout/tagout capability.
What is the difference between a disconnect and a circuit breaker?
A disconnect is a manually operated isolation device that provides a visible, lockable open-circuit position; it does not automatically trip on overcurrent. A circuit breaker is an automatic overcurrent protective device that also functions as a manual switch. Many disconnect enclosures are designed for fuses, not breakers—combining isolation with fuse overcurrent protection.
What is the designator for a disconnect switch in a schematic?
In IEC-based industrial schematics the disconnect switch designator is QS (per IEC 60947-3). In North American (ANSI/NEC) drawings the designator is DS or S. The designator appears next to the disconnect symbol on the schematic, followed by a circuit identifier number.
Where is a disconnect required by the NEC?
The NEC (NFPA 70) requires a disconnect means at service entrances (Article 230.70), within sight of motors and controllers (Article 430.102), within sight of HVAC equipment (Article 440.14), within sight of pool and spa equipment (Article 680), and for appliances exceeding certain power ratings (Article 422). 'Within sight' generally means within 15 m (50 ft) and visible from the equipment.
What is a fused disconnect?
A fused disconnect is a safety switch that incorporates fuse holders in the switch-blade cartridges, combining both isolation (disconnect) and overcurrent protection (fuses) in a single enclosure. When the handle is turned to the off position, the blades open the circuit and remove the fuses from the circuit simultaneously. Common fuse types include Class J, RK1, and RK5.
What IEC standard governs disconnect switches?
IEC 60947-3 governs switches, disconnectors, switch-disconnectors, and fuse-combination units for low-voltage applications. It defines performance requirements including utilisation categories (AC-21, AC-22, AC-23 for AC circuits), making and breaking capacity, mechanical endurance, and dielectric requirements.
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