8.3 OCPD Location, Breaker Voltage Ratings, Handle Ties & Arc Energy Reduction

Where overcurrent devices may be installed (240.24)

240.22 Grounded conductor: an OCPD may not be connected in series with a grounded conductor unless it opens all conductors of the circuit simultaneously, or unless it is a motor overload device permitted by Article 430.

Circuit breakers as overcurrent protection

Handle ties and common trip (240.15(B))

Single-pole breakers with identified handle ties may protect each ungrounded conductor in these cases:

• multiwire branch circuits that serve only line-to-neutral loads;
• line-to-line loads on single-phase circuits; and
• line-to-line loads on 3-phase, 4-wire systems or 5-wire, 2-phase systems, where the system has a grounded neutral and the voltage to ground does not exceed the breakers' rating.

Handle ties make the breakers open together manually. Where a load requires all ungrounded conductors to trip together on a fault, use a multipole common-trip breaker.

Marking (240.83)

Breakers must be durably marked with their ampere rating, and with their interrupting rating where it is other than 5000 A. A breaker used as a switch for 120 V or 277 V fluorescent lighting must be marked SWD or HID; a breaker used to switch high-intensity discharge lighting must be marked HID.

Voltage ratings (240.85)

A 480Y/277 V slash-rated breaker is correct on a 480Y/277 V wye system. It may not be used on a 480 V ungrounded or corner-grounded delta system, because a conductor can be 480 V to ground. A 120/240 V slash-rated breaker on the high leg of a 120/240 V, 4-wire delta system would see about 208 V to ground, which exceeds 120 V, so a straight-rated 240 V breaker is required there.

Other circuit breaker rules

• 240.8 Parallel devices: fuses and circuit breakers may be connected in parallel only where factory assembled in parallel and listed as a unit.
• 240.86 Series ratings: a tested combination may be used where a downstream breaker's interrupting rating is lower than the available fault current, with the 110.22(C) field marking.
• 240.13 and 215.10 GFPE for buildings and feeders: like 230.95, a building or feeder disconnect rated 1000 A or more on a solidly grounded wye system over 150 V to ground needs GFPE, unless it is provided on the supply side.

Arc energy reduction (240.87 and 240.67)

Where the highest continuous current trip setting that a circuit breaker is rated for, or can be adjusted to, is 1200 A or higher, the documentation must show the breaker's location and the arc energy reduction method used. Methods include:

1. zone-selective interlocking;
2. differential relaying;
3. an energy-reducing maintenance switch with a local status indicator;
4. an energy-reducing active arc-flash mitigation system;
5. an instantaneous trip setting below the available arcing current;
6. an instantaneous override set below the available arcing current; or
7. an approved equivalent means.

The arc energy reduction system must be performance tested by primary current injection or another approved method when first installed, and a written record kept. Section 240.67 sets a parallel rule for fuses rated 1200 A or more: the fuse must clear the available arcing current in 0.07 second or less, or another listed method must be used.

Selective coordination

Certain systems require that only the OCPD closest to a fault opens, so critical loads stay energized. Selective coordination is required for emergency systems (700.32), legally required standby systems (701.32), critical operations power systems (708.54), elevator circuits with more than one driving machine disconnect on a feeder (620.62). Health care essential electrical systems have their own coordination rules in Article 517, which the 2026 NEC extended to Type 2 systems. The 2026 NEC also adds rules requiring elevator coordination to be re-evaluated when overcurrent devices are replaced or the system is modified. An engineer usually selects the devices, but the electrician must install the specified fuse classes, breaker frames, and trip settings exactly.

Worked example: choosing the right breaker

A plant has three systems: a 480Y/277 V wye feeding lighting panels, a 480 V corner-grounded delta feeding a press line, and a 120/240 V high-leg delta in an old shop.

1. 480Y/277 V lighting panel: 480Y/277 V slash-rated breakers are permitted: 277 V to ground, 480 V between conductors.
2. 480 V corner-grounded delta: two ungrounded conductors are 480 V to ground, so straight 480 V-rated breakers are required.
3. 120/240 V high-leg delta: the B phase (high leg) is about 208 V to ground. A 120/240 V slash-rated breaker on that phase violates 240.85; use breakers with a straight 240 V rating for circuits that include the high leg.