Eaton Cutler-Hammer C306DN3 Size 1 Overload Relay

Description

Product Introduction

The Eaton Cutler-Hammer C306DN3 is a three-pole, bimetallic thermal overload relay from the industry-standard Freedom Series product line. Engineered to mount directly to Freedom Series NEMA Size 1 contactors (or standalone via a mounting base), the C306DN3 delivers dependable ambient-compensated overcurrent protection for electric motors running across critical commercial and industrial applications.

Designed to prevent costly motor burnout from sustained overloads, phase loss, or mechanical jams, the C306DN3 utilizes interchangeable heater elements (Class 20 or Class 10) to precisely tailor the trip curve to full-load current (FLA) ratings. Its rugged construction includes isolated auxiliary contacts (1 NO / 1 NC), a manual/automatic reset selector, and a visual trip indicator—making it a core protective component in motor control centers (MCCs) and pump panels worldwide.

Key Technical Specifications

Application Scenarios & The “Trench” Experience

When a heavy-duty conveyor or wastewater pump jams, an unprotected motor will overheat and burn its stator insulation in minutes. To be honest, I’ve seen plant technicians spend hours troubleshooting complex PLC logic for an unannounced motor trip, only to realize the thermal overload relay did its job and cleared a bound impeller. Swapping out a worn-out C306DN3 or inserting the proper heater pack takes ten minutes and saves thousands in motor rewinding costs.

• Wastewater & Municipal Pumping – Submersible & Surface Pump Protection – Cuts power during dead-head or clogged impeller events to prevent motor winding destruction.
• Manufacturing & Assembly Conveyors – Jammed Line Overcurrent Trips – Provides Class 20 time-delay protection, allowing normal high-torque starting inrushes without nuisance tripping.
• HVAC Chiller & Air Handling Units – Fan & Compressor Motor Protection – Ambient compensation ensures accurate trip points even in hot mechanical rooms.
• Industrial Machine Tools & Presses – Hydraulic Power Unit (HPU) Protection – Works seamlessly in NEMA Size 1 starters across heavy industrial automation cabinets.

C306DN3

C306DN3

Transparency SOP: Quality Assurance & Testing

We don’t just ship electrical gear blindly; every C306DN3 relay goes through strict physical and functional bench checks before leaving our facility:

1. Inbound & Housing Inspection: Checking the plastic housing, DIN/contactor mounting prongs, and screw terminal threads for mechanical integrity, stress cracks, or stripped threads.
2. Auxiliary Contact Resistance Test: Measuring contact resistance across the 95-96 (NC) and 97-98 (NO) terminal points using a low-ohm digital multimeter to ensure clean, low-resistance switching.
3. Trip Mechanism Handshake Test: Manually triggering the red test/trip arm to verify positive snap-action mechanism response and mechanical trip flag operation.
4. Reset Functionality Check: Cycling between Manual and Auto reset modes to confirm spring retention and latch alignment.
5. Final Cleaning & Packaging: Solvent cleaning terminal lugs, applying protective terminal covers, and packaging in ESD-safe / shock-absorbent boxes.

The Veteran’s Tech Trap Guide (Crucial Value-Add)

⚠️ Heater Packs Are Sold Separately! The C306DN3 chassis does not include thermal heater elements out of the box. You MUST install three matching H2000-series heater packs tailored to your motor’s exact Full Load Amps (FLA) service factor rating, or the relay will not carry load or trip correctly.

❗ Check Your Reset Setting! The reset button can be set to Manual (M) or Automatic (A). One thing to watch out for is leaving it in Automatic mode on a two-wire control circuit (like a float switch)—if the overload trips and cools down, the motor will restart automatically without warning, posing a severe safety hazard to field personnel.

⚠️ Tighten Terminal Screws to Spec: Loose wire connections on Size 1 overload terminals generate localized resistance heat. This trick heat transfers directly into the bimetallic strips inside the C306DN3, causing false nuisance trips even when the motor’s actual running current is completely normal.

Frequently Asked Questions (FAQ for Conversion)

Q: Does the Eaton C306DN3 include the heater packs?

A: No. The C306DN3 is the overload relay base block. You must select and install three individual Cutler-Hammer H2000 series heater packs corresponding to your motor’s nameplate FLA.

Q: Can I mount the C306DN3 standalone on a DIN rail without a contactor?

A: Yes, but you will need the standalone DIN-rail / panel mounting adapter base (Eaton Part Number C306TB1) to secure the terminal lugs and mount it independently.

Q: What is the difference between Class 10 and Class 20 trip settings on the C306DN3?

A: Trip class designates how fast the overload opens under 600% locked-rotor current. Class 20 trips within 20 seconds (standard for general industrial motors), while Class 10 trips within 10 seconds (used for submersible pumps or hermetic motors requiring faster shutoff).

Q: Is the C306DN3 interchangeable with older Westinghouse Freedom Series overloads?

A: Yes. Eaton acquired Cutler-Hammer and Westinghouse’s distribution and control business. The C306DN3 is a direct form, fit, and function replacement for legacy Westinghouse Freedom Series Size 1 thermal overloads.

Q: What warranty coverage do you offer on new surplus C306DN3 units?

A: All C306DN3 overload relays supplied carry a full 12-month replacement warranty. If a unit experiences mechanical or electrical failure under rated conditions within one year, we replace it or refund your purchase.