Description
The Siemens Furnas 45FG20AG is a Class 45 Definite Purpose (DP) magnetic contactor engineered to regulate high-current inductive and resistive loads in industrial and commercial HVAC, refrigeration, and heating systems. Acting as an electrically controlled heavy-duty switch, it features a 2-pole configuration designed to make or break dual-line power circuits upon command from an active thermostat or low-level control loop.
Initially manufactured under the Furnas Controls brand (Centurion 2000 series) and subsequently brought under the Siemens portfolio, this specific product line has been officially discontinued by the OEM but remains widely utilized as a field replacement block.
Commercial and Logistics Summary
| Commercial Parameter | Status / Value |
| Condition | New Surplus (Legacy Stock) or Refurbished (Tested Contacts) |
| Availability | Discontinued by OEM; available through specialized electrical distribution networks |
| Typical Lead Time | 1 to 3 business days worldwide |
| Warranty | 12-month standard supplier warranty |
| Pricing Note | Price is subject to secondary market conditions; contact us for a firm quote. |
Technical Specifications
| Parameter | Specification Value |
| Contactor Type | Definite Purpose (DP) Magnetic Contactor |
| Product Line | Class 45 / Furnas Centurion 2000 Series |
| Number of Poles | 2-Pole (Double Pole, Single Throw – DPST) |
| Full Load Amperage (FLA) | 35 A continuous |
| Resistive Amperage (Rating) | 50 A continuous |
| Operational Voltage Block | 120 V, 240 V, 277 V, 480 V, 600 V AC max |
| Coil Voltage Spec | 190 to 220 V AC at 50 Hz / 208 to 240 V AC at 60 Hz |
| Locked Rotor Amps (LRA) | 200 LRA at 277 V AC; 135 LRA at 480 V AC; 110 LRA at 600 V AC |
| Phase Count | 1-Phase load control capabilities |
| Regulatory Standards | UL listed, CSA certified, CE compliant |
Engineering Considerations and Field Retrofitting
1. Coil Voltage Compatibility
The “AG” suffix code explicitly indicates a high-voltage AC operating coil rated for 208 to 240 V AC at 60 Hz. Field technicians must not apply common 24 V AC residential thermostat control lines directly to these coil terminals. Doing so will fail to generate the magnetic force required to pull down the armature, resulting in contact chattering or outright failure to energize.
2. Contact Overheating and Inrush Management
When sizing replacements for heavy condenser fan motors or compressor packages, ensure the application’s locked rotor amperage (LRA) does not exceed the graded metrics (e.g., 200 A at 277 V). Exceeding these limits during high-inertia motor start-ups induces high-temperature electrical arcing across the silver-cadmium oxide contacts, accelerating pitting and leading to catastrophic contact welding.
3. Interchangeable Drop-In Replacements
Because the 45FG20AG features standard straight-through wiring architecture and a universal baseplate configuration, it can be directly swapped with modern 40 A rated definite purpose contactors (such as the Mars2 17427, Resideo/Honeywell PowerPro DPL2040C1001, or Hartland/Packard DPC50-240 variations) provided the replacement unit matches the 2-pole construction and contains a 240 V AC coil assembly.
Frequently Asked Questions
What are the main field indicators of a failing contactor?
Failure points typically present as a loud mechanical buzzing or humming sound originating from the laminated iron core pieces due to dirt build-up or a weak internal shading coil. Additionally, if the internal coil burns out or develops an open-circuit fault, the main contact blocks will refuse to drop in when control voltage is applied.
Can this unit be mounted in an outdoor environment without protection?
No. The 45FG20AG features an open-chassis construction with an IP00/Open type environmental rating. It must be installed within a protective NEMA 3R or NEMA 4 rated weatherproof electrical box or outdoor condenser housing assembly to prevent rainwater intrusion and environmental debris from shorting the terminal paths.
