Cutler-Hammer KT3315TA | Molded Case Circuit Breaker 150A 3-Pole In Stock

Description

Key Technical Specifications

• Frame Size: K-Frame (Max 250A frame, 150A trip unit)
• Poles: 3
• Rated Current (In): 150 Amperes
• Rated Voltage (Ue): 600 VAC (50/60 Hz)
• Interrupting Rating (Icu): 25 kA @ 480VAC; 18 kA @ 600VAC
• Trip Unit Type: Thermal-Magnetic (Fixed)
• Frequency: 50/60 Hz
• Operating Temperature: -40°C to +70°C (-40°F to +158°F)
• Mounting: Panel Mount / Bolt-on or DIN Rail (with adapter kit)
• Terminal Type: Line and Load Lugs (Aluminum/Copper compatible)
• Standards: UL 489, CSA C22.2 No. 5, NEMA AB-4
• Dimensions: Approx. 5.5″ W x 7.0″ H x 3.5″ D (Varies by terminal cover)

Product Introduction

Walking into a substation built in the late 90s, you see rows of these K-Frame breakers. They aren’t fancy. They don’t have Ethernet ports or cloud connectivity. But I’ve pulled ones out of panels covered in oil mist and coal dust that still clicked shut with the same solid snap as the day they were installed. The KT3315TA is the workhorse of that era—a fixed thermal-magnetic breaker designed to take abuse and clear faults without needing a laptop to reset it.Engineers stick with this specific model because the trip curve is predictable. Unlike modern electronic trips that can get confused by harmonic distortion from VFDs, the bimetallic strip inside the KT3315TA reacts purely to heat and magnetic force. It handles 150 amps continuous, and its 25kA interrupt rating at 480V is enough for most branch circuits in heavy manufacturing. Just be warned: the thermal element is sensitive to ambient temperature. If you mount this inside a cabinet hitting 60°C (140°F) in July, it will nuisance trip below 150A. That’s physics, not a defect.

Quality SOP & Tech Pitfalls (The Reality Check)

The Lab Report (SOP)
Before we ship a KT3315TA, it goes through a brutal check. First, we inspect the casing for cracks or UV damage—old plastic gets brittle. We verify the UL/CSA labels aren’t peeling (a sign of refurbishment). Then, we hook it up to a primary injection test set (like an Omicron or Doble). We push 300% of rated current (450A) to ensure the magnetic trip hits within the specified cycles (usually <0.1 seconds). We also megger the insulation resistance between phases and ground; anything under 100 MΩ gets rejected. Finally, we log the serial number and seal it in anti-static foam.The Engineer’s Warning (Pitfalls)
Here is where people mess up. They swap a KT3315TA into a panel originally designed for a different frame or a different interrupt rating without checking the bus stab depth. I once saw a junior tech force a breaker onto a bus that wasn’t quite aligned. It seemed fine until the first high-fault event—the poor contact arced internally, welded the stabs, and took out the entire bus section. Another common disaster: ignoring the torque specs on the lugs. These are large conductors. If you don’t torque them to the spec stamped on the breaker (usually around 250-300 lb-in for this size), the connection heats up, melts the insulation, and starts a fire. Use a calibrated torque wrench. Don’t guess.

Installation & Configuration Guide

Phase 1: Pre-Installation
⚠️ LOCKOUT/TAGOUT. Verify zero energy with a multimeter. Wait 5 minutes for capacitors to discharge if upstream VFDs exist. Take a high-res photo of the existing breaker’s wiring and label every wire with tape. Do not trust the old labels; they are often wrong.Phase 2: Removal
Remove the phase barriers. Unbolt the line and load lugs carefully—do not let the heavy copper drop and damage the bus insulation. Release the mounting clips or unbolt the frame from the panel backplate. Lift the old unit straight out. Clean the bus stabs with a lint-free cloth and electrical contact cleaner if they look oxidized.Phase 3: Installation
CRITICAL: Check the new KT3315TA for any factory-installed shunt trips or auxiliary switches. If the old unit had them and the new one doesn’t (or vice versa), your control circuit won’t work. Seat the breaker firmly onto the bus stabs. It should slide in smoothly; never hammer it. Bolt the frame down securely. Reconnect line and load conductors. Torque the lugs to the manufacturer’s specification immediately. Install phase barriers.Phase 4: Power-On & Testing
Visually inspect for tools left in the panel. Close the breaker. Measure voltage across the load side (A-B, B-C, C-A) to confirm proper phasing. If possible, perform a secondary injection test or a “push-to-trip” mechanical check to ensure the mechanism isn’t stuck. Monitor the breaker with a thermal camera after 1 hour of full load to catch loose connections early.

Compatible Replacement Models

• ✅ Drop-in Replacement: Eaton KDB3150 or KDB3150T.
  • Note: Eaton absorbed Cutler-Hammer. The KDB series is the direct modern equivalent. Same dimensions, same bolt pattern, same electrical specs. You might need to update the panel schedule label to reflect the new brand name.
• ⚠️ Software Compatible: N/A.
  • Reason: This is a thermal-magnetic breaker. There is no firmware or software to configure. It is purely electromechanical.
• ❌ Hardware Mod Required: Eaton L-Frame (LD/LG) or E-Frame (ED).
  • Warning: These frames have different physical dimensions and bus stab locations. Installing one requires cutting the panel backplate, modifying bus bars, and rewiring. Do not attempt this unless you are doing a full panel retrofit. It creates liability issues with insurance inspectors.

Frequently Asked Questions (FAQ)

Q: Can I hot-swap this breaker while the bus is live?
No. Absolutely not. Even if you have arc-flash suits on, removing a molded case breaker from an energized bus exposes the live stabs. One slip with a screwdriver and you create a phase-to-phase fault that will kill you. Shut the main feeder down.Q: Is this a genuine Cutler-Hammer or an Eaton rebrand?
It’s the same thing. Eaton bought Cutler-Hammer years ago. If you buy “New Surplus,” it might have the old orange Cutler-Hammer logo. If you buy new stock, it will likely say Eaton but carry the same UL file number. Electrically, they are identical.Q: My old breaker was a KT3315TA with a shunt trip. Does this model have one?
Check the suffix carefully. The base “KT3315TA” usually implies just the breaker with standard terminals. Shunt trips, auxiliary contacts, or alarm switches are often factory-installed options with different suffixes (e.g., KT3315TA-ST). If your control circuit expects a shunt trip and the new unit doesn’t have one, the breaker won’t trip remotely. Verify the internal accessories before installing.Q: What kind of wire lugs do I need?
The KT3315TA typically comes with standard box lugs suitable for copper or aluminum wire. Check the label on the specific unit you receive. For 150A, you are likely running #1/0 or #2/0 AWG. Ensure your lug kit matches the wire type (AL9CU is standard for both). Don’t mix aluminum wire with copper-only lugs; it causes galvanic corrosion and fires.Q: Why does it keep tripping on a cloudy day?
Thermal-magnetic breakers react to ambient heat. If your panel is in direct sunlight or a non-ventilated room, the internal bimetallic strip heats up faster. A 150A breaker might trip at 135A if the air temp inside the cabinet is 60°C. Check your panel cooling. If the load is actually under 150A and it still trips, the breaker mechanism might be worn out from years of fault clearing. Replace it.Q: Can I use this for DC applications?
No. This unit is rated for AC only (600VAC). Using it on DC requires special arc chutes and pole configurations to extinguish the arc. DC arcs don’t cross zero like AC does. Using an AC breaker on DC is a fire hazard and violates NEC/UL codes. Look for a specific DC-rated breaker if your application involves solar arrays or battery banks.