Description
Product Overview
The DEIF RMC-122D is a combined short-circuit and over-current protection relay from the DEIF Uni-line series. It is designed for generator protection in both marine and land-based electrical installations.
Unlike a simple short-circuit relay, the RMC-122D provides two protection functions: over-current protection I> and short-circuit protection I>>. DEIF specifies the RMC-122D under ANSI codes 50/51.
The relay measures three-phase current and activates its associated relay output when the configured protection threshold and time delay are reached. Front-panel potentiometers are used to adjust the protection settings, while LEDs provide operating and fault indication.
Technical Specifications
| Parameter | Specification |
|---|---|
| Brand | DEIF |
| Model | RMC-122D |
| Product Type | Short Circuit & Over-current Protection Relay |
| Protection Function | I> Over-current + I>> Short-circuit |
| ANSI Code | 50 / 51 |
| Measurement | 3-phase current |
| Over-current Setting I> | 50–150% of In |
| Short-circuit Setting I>> | 100–400% of In |
| Current Input | Specific configuration; 0.4–5.0A AC versions available |
| Frequency | 40–70 Hz range |
| Relay Outputs | 2 maximum contacts |
| Mounting | 35 mm DIN rail or screw mounting |
| Protection | Case IP40; terminals IP20 |
| Application | Generator, feeder and electrical protection systems |
DEIF documentation specifies I> adjustment from 50–150% of In and I>> adjustment from 100–400% of In. The RMC-122D provides two maximum relay contacts corresponding to its two protection functions.
Protection Functions
The RMC-122D combines two current-protection levels in one relay.
Over-current protection — I>
The over-current function is adjustable from 50% to 150% of the rated measuring current In. A separate time delay can be configured according to the relay version.
Short-circuit protection — I>>
The short-circuit function is adjustable from 100% to 400% of In. When the measured current exceeds the configured threshold, the associated timer starts. If the fault remains until the timer expires, the relay contact changes state.
This arrangement makes the RMC-122D suitable where both overload/current protection and high-current short-circuit protection are required without using two separate protection relays.
Typical Applications
The RMC-122D is intended for applications such as:
- Generator protection
- Marine generator systems
- Land-based generator installations
- Main and auxiliary switchboards
- Feeder protection
- Industrial power distribution
- Generator control and alarm circuits
- Engine-driven generating equipment
DEIF specifically lists the RMC series for generator protection and states that the relays are applicable to both marine and land-based installations.
Installation & Configuration
Before installation, verify the complete relay label rather than relying only on the basic model number. RMC-122D units can have different measuring-current and auxiliary-supply configurations.
Recommended checks:
- Verify the RMC-122D model and complete nameplate information.
- Confirm the installed current module and measuring-current range.
- Check the auxiliary supply voltage.
- Verify CT secondary current and wiring.
- Confirm the I> and I>> settings against the protection coordination study.
- Set the corresponding time delays.
- Check the relay contact logic before connecting it to a trip circuit.
- Test the relay using a suitable secondary-current injection setup.
- Confirm LED indications and output contact operation.
For a replacement unit, matching the measuring-current configuration and auxiliary supply is particularly important.
Inspection & Maintenance
For a spare RMC-122D, inspect:
- Front adjustment potentiometers
- Transparent protective cover
- LED indicators
- Terminal blocks
- Housing condition
- Mounting clips
- Current-input terminals
- Relay output contacts
- Nameplate and configuration markings
A functional test should verify both protection stages independently. Apply a controlled test current to confirm the I> and I>> pickup levels and verify the corresponding time-delay and relay-contact operation.
For critical generator applications, record the measured pickup values and trip times together with the unit’s serial number.
440VAC / 5A Identification Note
The eBay listing describes this unit as 440VAC / 5A. The 5A designation is consistent with available RMC-122D measuring-current configurations, but the 440VAC figure should be treated as the specific installation/application or configuration information, not as the relay’s current-input rating. DEIF’s documentation shows that the RMC-122D uses a configurable measuring-current arrangement and that the exact relay label identifies the measuring current, current module and supply voltage.
For a replacement purchase, compare the physical label and terminal configuration with the original relay before installation.
Condition
The condition should follow the actual eBay listing and physical unit. For a used unit, inspect the housing, terminals, adjustment controls, and nameplate carefully before shipment.
If the unit has been removed from working equipment, it is still recommended to perform a current-injection and relay-output test before placing it into critical service.
Compatibility Notes
The RMC-122D belongs to DEIF’s Uni-line protection relay family. Related models such as RMC-111D, RMC-121D, RMC-131D and RMC-132D have different protection functions and should not be treated as automatic replacements. DEIF identifies RMC-122D specifically as the combined I> + I>> version.
When replacing an existing unit, verify:
- Complete RMC-122D part/configuration information
- Measuring current
- Current transformer ratio
- Auxiliary supply
- Frequency
- Relay contact logic
- Protection settings
- Time-delay ranges
- Mounting arrangement
Ordering Information
For quotation or replacement inquiries, provide the following information:
- Model: RMC-122D
- Measuring current / CT secondary rating
- Auxiliary supply voltage
- Complete nameplate information
- Required quantity
- Existing generator or switchboard application
A clear photo of the relay nameplate is useful when confirming the exact configuration.
Recommended eBay Title
DEIF RMC-122D | Short Circuit & Over-current Protection Relay | 5A AC
