Special Purpose GFCI Protection (SPGFCI)

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What You Need to Know About Special Purpose GFCI Protection (SPGFCI)​

When most inspectors and electricians hear “GFCI,” they immediately think of the standard Class A device that trips at 6 milliamps to protect people from shock. But as we continue to see more high-voltage lighting systems, temporary power setups, and pool equipment circuits operating above 150 volts to ground, we also need to talk about the device that fills the gap where Class A GFCIs are not permitted: the Special Purpose Ground-Fault Circuit Interrupter, or SPGFCI.

This article explains what SPGFCIs are, how they differ from other forms of ground-fault protection, where the 2023 NEC now requires them, and why correct installation, including the neutral connection, is critical to proper function.

Definition and Purpose​

According to the 2023 NEC:

Ground-Fault Circuit Interrupter, Special Purpose (SPGFCI) — A device intended for the detection of ground-fault currents, used in circuits with voltage to ground greater than 150 volts, that functions to de-energize a circuit or portion of a circuit within an established period of time when a ground-fault current exceeds the values established for Class C, D, or E devices.
(CMP-2, NEC 100)

Informational Note: See UL 943C, Outline of Investigation for Special Purpose Ground-Fault Circuit Interrupters, for more information on Classes C, D, and E.

Unlike Class A GFCIs, which are limited to 150 volts-to-ground and trip at 4–6 mA based on the human body’s "let-go" threshold, SPGFCIs are designed to trip at higher currents (up to 20 mA) and handle higher voltage systems. Their primary safety goal is to prevent ventricular fibrillation, not just prevent involuntary muscle contractions. These are personnel protection devices—not equipment protection—and should not be confused with GFPE (Ground-Fault Protection of Equipment), which often trips at 30 to 1200 mA and has no intent to protect human life.

Classes of SPGFCIs Under UL 943C​

• Class C: For circuits ≤300 volts to ground. Trip threshold: 20–100 mA.
• Class D: For circuits >300 volts to ground. Trip threshold: 20–100 mA.
• Class E: Custom-engineered applications that fall outside Class C or D.

Many people wrongly assume SPGFCIs are only Class D or E. Class C is very real and very relevant, especially on 277V lighting circuits where voltage to ground exceeds 150V, but the total system voltage remains below 300V.

2023 NEC Requirement: Article 680.5​

The biggest change in the 2023 NEC is the explicit requirement for SPGFCIs in Article 680, which covers swimming pools, fountains, and similar installations. This is where wet conditions, people, and elevated voltages intersect—making proper fault protection absolutely critical.

NEC 680.5(C) – SPGFCI Requirement:​

“Where required in this article, ground-fault protection of receptacles and outlets on branch circuits operating at voltages above 150 volts to ground, not exceeding 480 volts phase-to-phase, single- or 3-phase, shall be provided with SPGFCI protection not to exceed 20-mA ground-fault trip current.”

This means if you have a branch circuit supplying lighting, pumps, or receptacles in a pool area, and that circuit operates over 150V to ground (like a 277V or 480V system), you are now required to use an SPGFCI. The trip threshold of 20 mA is mandatory—no more, no less. This requirement is not about protecting conductors or panels—this is life safety in an extremely hazardous environment.

680.5(B) – Where Class A GFCIs Still Apply​

For systems 150V or less to ground and 60 amps or under, you are still required to use a Class A GFCI. These are your standard bathroom, kitchen, and wet-location devices. They trip quickly (in about 25 milliseconds) and shut down the circuit at low current to prevent both "let-go" and fibrillation.

SPGFCI ≠ 240V GFCI Breaker​

A major source of confusion in the field is the assumption that a 2-pole, 240V GFCI breaker is the same as an SPGFCI. It is not.

• A standard 240V Class A GFCI breaker is still rated for 120V to ground. It protects two hot legs going to something like a water heater or dryer, tripping at 4–6 mA, but does not protect against faults on systems with higher voltages to ground.
• An SPGFCI, on the other hand, is listed under UL 943C, not UL 943. It is intended specifically for use in circuits where voltage to ground exceeds 150V, which includes 277V lighting and many commercial and industrial systems.

Do not confuse a high-voltage circuit with high phase-to-phase voltage alone. SPGFCI requirements are based on the voltage-to-ground, not line-to-line voltage. So a 240V residential split-phase circuit (120V to ground) does not require an SPGFCI. But a 277V branch lighting circuit (277V to ground) does, if located in a setting covered by Article 680.

Neutral Requirements​

Like Class A GFCIs, SPGFCIs require a connection to a neutral conductor to operate correctly. This is often overlooked in installations, especially with 277V lighting where the presence of neutral may not seem obvious or necessary.

The microprocessor and sensing circuits inside both standard and special purpose GFCIs need a grounded reference to power the logic, test/reset functions, and fault detection. If neutral is missing or not bonded properly, the device may fail to test or trip correctly—and that is a critical failure in any personnel protection device.

TBCF Final Thoughts​

SPGFCIs are not optional anymore. The 2023 NEC now mandates their use in specific applications—particularly around water and elevated voltage-to-ground systems. They’re not substitutes for GFPE, and they are not just Class A GFCIs rated for more current. They’re their own class of devices, with their own UL standard, their own use case, and now, their own code mandate.

As inspectors and code professionals, we need to know this. Too many people still don't. The goal is to prevent electrocution—not just from the “let-go” threshold of a 6 mA fault, but from deadly ventricular fibrillation when someone is exposed to higher current in an already dangerous environment. SPGFCIs are the answer when traditional GFCIs can't do the job.

Make sure your field crews understand this. Make sure the neutral is connected. Make sure the breaker says UL 943C, not just UL 943. And most of all, make sure that if you're dealing with circuits above 150V to ground, you're not relying on the wrong protection. Lives depend on it.