SEL-551C 0551C0DX5X1X | Overcurrent & Reclosing Relay

The SEL-551C P/N 0551C0DX5X1X is an overcurrent and automatic reclosing relay from Schweitzer Engineering Laboratories (SEL), designed primarily for distribution feeder protection and control. It combines instantaneous and time-overcurrent protection for phase, ground, and negative-sequence faults with programmable autoreclosing functions. The SEL-551C also provides SELogic® control equations, event recording, demand metering, programmable inputs and outputs, and serial communications.

The exact 0551C0DX5X1X ordering code specifies a particular hardware configuration, including the power/control-input arrangement, 5 A phase and neutral current inputs, horizontal rack-mount packaging, and an EIA-232 rear communications port. The SEL-551C is now discontinued, although SEL states that it continues to support and warranty the product.

SEL-551C

⚙️ Product Datasheet

Parameter	Specification
Brand	Schweitzer Engineering Laboratories (SEL)
Model	SEL-551C
Part Number	0551C0DX5X1X
Series	SEL-551C
Product Name	Overcurrent / Reclosing Relay
Application	Distribution Feeder Protection & Control
Protection Functions	Phase, Ground, Neutral & Negative-Sequence Overcurrent
Current Input	5 A Phase / 5 A Neutral
Communications	EIA-232 Rear Port
Mounting	Horizontal Rack Mount
Condition / Status	Used / Surplus — verify actual unit condition
Power Supply	Configuration-dependent; ordering code must be matched
Country of Origin	USA / SEL manufacturing configuration dependent

🔧 Key Features

⚡ Instantaneous overcurrent protection
🛡️ Phase, ground, neutral, and negative-sequence protection
⏱️ Time-overcurrent protection with multiple curve options
🔄 Programmable automatic reclosing, up to four shots
🧠 SELogic® Control Equations
📊 Demand and peak-demand current monitoring
📝 Sequential Events Recorder and event reports
🔌 Six digital inputs and three outputs
💻 EIA-232 / EIA-485 communication options depending on configuration
🔗 Modbus RTU protocol support
🛠️ Designed for distribution feeder protection and legacy system maintenance

❓ Common Questions & Answers

Q: What is the SEL-551C used for?
A: It is an overcurrent and reclosing relay primarily used for distribution feeder protection and control.

Q: What protection functions are available?
A: The SEL-551C provides instantaneous and time-overcurrent elements for phase, ground, neutral, and negative-sequence protection.

Q: Does it support automatic reclosing?
A: Yes. The relay can be programmed to automatically reclose a circuit breaker up to four times before lockout.

Q: What does the 5X configuration indicate in the supplied part number?
A: The SEL ordering information identifies 5 as the 5 A phase / 5 A neutral secondary-current configuration.

Q: What communication interface does 0551C0DX5X1X specify?
A: The ordering information identifies the configuration with an EIA-232 rear port.

Q: Is the SEL-551C still manufactured?
A: SEL currently lists the SEL-551C as no longer in production and identifies the SEL-851 and SEL-751 as newer alternatives. SEL also states that it continues to support and warranty the SEL-551C.

Q: What should be checked before replacing a SEL-551C?
A: Verify the complete part number, control power rating, CT secondary rating, mounting arrangement, communication interface, wiring, firmware, and protection settings before installation.