Eaton C-Series Breakers: Sizing and Accessories

FACT: Eaton C-Series breakers were originally introduced as a modernization of the legacy Cutler-Hammer breakers, but Eaton designed them so that many parts, accessories, and even mounting footprints remained backward-compatible. That means you can often upgrade old panels with new Series C breakers without major rewiring or panel modifications—a huge time and cost saver for electricians!

The Eaton Series C breaker family was made with flexibility and compatibility in mind. Whether you’re installing a new system or upgrading an existing one, these breakers have the same footprint and accessories, so you won’t need to learn a new part number or accessory set every time you change ampacity or trip type.

In fact, these breakers are UL 489 compliant and come in thermal-magnetic, electronic, and magnetic-only (HMCP) configurations, all under the Eaton molded case circuit breakers Series C umbrella. That means there is a Series C breaker for any load or environment.

If you’re asking how to choose between an FD, KD, or PD frame, this chart gives you a snapshot of each Eaton C Series breaker and what it’s built for. You’ll also find a popular part number for each to help with sourcing:

Frame	Breaker	Amp Range	Typical Use Case	Popular Part Number
F	FD	15–250A	Panelboards, lighting, branch loads	FD3025
K	KD	70–400A	HVAC, commercial feeders	KD3400
L	LD	125–600A	Mid-size industrial equipment	LD3600
M	MD	200–800A	Large panels, generator feeds	MD3800
N	ND	300–1200A	Main switchboards, industrial mains	ND31200
P	PD	400–1600A	Heavy-duty switchgear	PD31600

No matter which frame, these breakers are part of the Eaton MCCB Series C family, which means your accessories, maintenance processes, and replacement workflows are streamlined across the board.

Unlike the other Eaton molded circuit breakers in Eaton MCCB Series C, the HMCP is a magnetic-only breaker developed for motors. That suggests it will not guard against overloads on its own; it needs to be linked with an overload relay. The HMCP is a go-to solution for motor control centers (MCCs). It still uses the Series C platform, so you’ll have the same mounting dimensions and accessory possibilities.

🔄 Streamline Projects with Shared Accessories

The beauty of the Eaton C-Series breaker platform is that most accessories — from handle locks to auxiliary switches to trip alarms — are compatible across the FD–PD frames. This makes installation and field modification a breeze. In retrofit jobs, this compatibility is even more valuable. You can usually drop in a new breaker without reconfiguring the panel or switchboard.

Looking for Eaton Breaker Replacements? You can find popular Eaton C-Series breakers, including HMCPs and larger PD-frame breakers, at trusted online distributors like Relectric. These pages let you quickly filter by frame size, interrupt rating, or amperage range.

⬛ What does Series C mean in Eaton breakers?
🟩 It’s Eaton’s family of modular molded case circuit breakers designed to cover 15–1600A with consistent form factors and accessories.

⬛ Are Eaton Series C breakers UL listed?
🟩 Yes, they meet UL 489 standards for molded case circuit protection.

⬛ Can I use Series C HMCP for general loads?
🟩 No — HMCPs provide short circuit protection only and must be paired with overload protection for motors.

⬛ What accessories are shared across Series C breakers?
🟩 Shunt trips, undervoltage releases, auxiliary switches, and handle mechanisms are often interchangeable.

⬛ Are Eaton C Series breakers compatible with Cutler-Hammer?
🟩 Yes. Series C is the modern version of many legacy Cutler-Hammer designs and maintains backward compatibility.

⬛ Where can I find the Eaton Series C breaker catalog?
🟩 You can view the official Eaton Series C breaker catalog PDF here.

⬛ How do I read Eaton breaker part numbers?
🟩 The first two letters denote the frame (e.g., FD, KD), the next digits specify amperage, and suffixes indicate poles or trip unit options.

MCCB (Molded Case Circuit Breaker): A circuit breaker with a solid, insulating outer shell.
Frame Size: The physical size and maximum amp rating of a breaker.
Trip Unit: The sensing component that detects overcurrent conditions.
Thermal-Magnetic: Uses heat and magnetic force to detect overloads and short circuits.
Electronic Trip Unit: Microprocessor-based protection offering adjustable settings.
Interrupt Rating: The highest current a breaker can safely interrupt.
TCC (Time/Current Curve): A graphed representation