1. Introduction
The MidNite Solar MNDC250 Plus Mini-DC Disconnect is designed for use in various renewable energy installations. This manual provides detailed instructions for installation, operation, and maintenance of the MNDC250 Plus, ensuring safe and efficient integration into your solar or wind power system.
The MNDC Plus version expands upon the popular MNDC by incorporating an additional DIN rail, accommodating up to ten DIN rail mount breakers. It includes two DIN rail cover plates and two panel mount plates, allowing for the installation of 3/4" 125VDC breakers ranging from 60 amps to 100 amps. The enclosure can also house an MNDC-GFP80 along with four additional panel mount breakers, or a configuration of one MNDC-GFP, one 3/4" panel mount breaker, five DIN rail breakers, and a large 125-250A inverter breaker. Provisions are made for mounting a 500 amp shunt and an MNTBB-R terminal bus bar. A battery negative stud and a ground busbar are also included.
Figure 1.1: MidNite Solar MNDC250 Plus Mini-DC Disconnect with the door open, revealing the internal layout, including breaker slots, bus bars, and mounting points.
Figure 1.2: Views of the MNDC enclosure, showing the unit with its door open (left) and closed (right), illustrating its compact design.
2. Features
The MNDC250 Plus Mini-DC Disconnect offers several key features designed for durability and ease of installation:
- Aluminum Chassis: Constructed from aluminum, providing resistance to rust, even in humid or salty environments.
- Hinged Door: Features a hinged door for convenient access to internal electrical circuits during installation and maintenance.
- DIN Rail for DC Circuits: Includes a DIN rail suitable for various DC circuits, such as PV input, charge control output, DC loads, and PV combiners.
- Ground Bus Bar: Equipped with a 14-pole ground bus bar for comprehensive grounding.
- Shunt Mounting Spots: Provides six mounting spots for 500 amp, 50mV shunts.
- Negative Connection Point: Dedicated mounting spot for an insulated bus bar, ideal for PV negative connection points.
- Knockouts: Pre-drilled knockouts for inverter and battery cables, charge control mounting, and DC input/output.
- Battery Negative Tie Point: Features a 5/16" diameter stud for the battery negative tie point.
- ETL Listed: Listed by ETL for compliance with safety standards in both the US and Canada.
- Compact Size: Dimensions of 17"L x 9"W x 4"D and a weight of 8 lbs.
- Made in the USA: Manufactured in the United States.
3. Setup and Installation
3.1. Dimensions and Layout
Understanding the physical dimensions and internal layout is crucial for proper installation planning.
Figure 3.1: Detailed dimensional drawing of the MNDC250 Plus, including measurements for various components and mounting points. All dimensions are in inches.
- The enclosure is made of white powder-coated aluminum.
- Breaker covers are supplied for 5 DIN rail or 3 panel mount breakers.
- Reverse all internal components for left-hand versions.
3.2. Conduit Knockout Locations
The MNDC chassis features various knockout sizes and locations for conduit entry. Plan your conduit runs carefully based on your system's requirements.
Figure 3.2: Top and side views illustrating the various conduit knockout locations and their respective sizes on the MNDC enclosure.
- The top view shows three 1" knockouts. The left two knockouts are designed to fit charge controllers such as the Classic, MX60, C-40, and Tristar controllers.
- The left side of the MNDC chassis has three 2" knockouts and two ½" knockouts. The 2" knockouts are intended for inverter DC cables. If installing to a Trace or Xantrex SW inverter, use a 2" offset nipple to attach to the SWCB conduit box.
- If routing cables directly through the hole without conduit, ensure a plastic grommet is installed to prevent chafing.
- The bottom surface is typically where battery cables enter. The 1" knockout can be increased in size to accommodate a second 2" conduit opening if required. This is suitable for connecting to a Trace or Xantrex DR Series conduit box.
3.3. Wire Type Considerations
Due to the compact size of this box and limited wire bending room, the use of super flexible type battery cable, such as Cobra Cable X-Flex, is recommended. While welding cable is not listed for use in residential wiring, it may also offer the necessary flexibility. For DIN rail mount breakers, 6AWG THHN or similar type wire is suitable for PV circuits.
3.4. Wiring Diagram
Refer to the wiring diagram provided on the inside of the MNDC door for correct connections.
Figure 3.3: Wiring diagram located on the inside of the MNDC door, illustrating the various electrical connections within the system.
4. Grounding
Proper grounding is essential for safety and system performance in renewable energy installations. The MNDC chassis should be grounded to your earth ground rod through a 6AWG wire connected to the ground bus bar located in the top left section of the MNDC chassis. This MNDC ground bus bar will become your primary system DC ground.
The ground bus bar also serves as the location where DC surge suppressors, such as the MNSPD, should be grounded. It is advisable to use one of the ¾" conduit knockouts to mount a DC lightning arrestor to the MNDC box. It is also common practice to run a ground wire from the PV panels to the MNDC ground. In dry climates, it is particularly advisable to run a ground wire from the PV panels to the MNDC ground. The MNDC ground bus bar is an ideal place to ground a DC-GFP when installed, as well as the inverter chassis and the charge control chassis. Do the grounds first since they normally lie in the bottom of the chassis.
Figure 4.1: Close-up view of the ground bus bar within the MNDC enclosure, showing connection points for grounding wires.
5. Battery Negative Connection
The wiring diagram indicates a 500 amp shunt. The voltage drop across this shunt is used to calculate the battery state of charge. If this shunt is not installed, you can use the 5/16" stud directly above the shunt area as a battery negative tie point. This tie point will ground the battery negative to the chassis. Grounding the battery negative is not required when employing a DC-GFP device. The inverter side of the shunt or the 5/16" stud also serves as an ideal tie point for PV negative or other DC negative circuits.
6. Operating Instructions
The MidNite Solar MNDC250 Plus is primarily a DC disconnect and enclosure for circuit breakers. Operation involves the proper use of installed breakers and understanding the system's electrical flow.
- Breaker Operation: Ensure all circuit breakers are correctly installed and rated for their respective circuits. To disconnect power, switch the corresponding breaker to the "OFF" position. To restore power, switch it to the "ON" position.
- System Monitoring: If a shunt is installed, monitor battery state of charge through your connected battery monitor.
- Safety First: Always ensure power is disconnected before performing any maintenance or modifications within the enclosure.
7. Maintenance
Regular maintenance helps ensure the longevity and safe operation of your MNDC250 Plus Mini-DC Disconnect.
- Visual Inspection: Periodically inspect the enclosure for any signs of damage, corrosion, or loose connections. Check for dust or debris accumulation.
- Cleanliness: Keep the interior and exterior of the enclosure clean. Use a dry, soft cloth to wipe surfaces. Do not use abrasive cleaners or solvents.
- Connection Checks: Annually, or as recommended by your system installer, verify that all electrical connections are secure and free from corrosion. Ensure all breakers are seated properly.
- Ventilation: Ensure that any ventilation openings are clear and unobstructed to allow for proper airflow.
8. Troubleshooting
This section provides basic troubleshooting steps for common issues. For complex problems, consult a qualified electrician or contact MidNite Solar support.
| Problem | Possible Cause | Solution |
|---|---|---|
| No power to DC loads/inverter | Breaker tripped or off; loose connection; faulty component. | Check all breakers and reset if tripped. Verify all wiring connections are secure. Inspect for damaged wires or components. |
| Enclosure feels hot | Overloaded circuit; poor ventilation; loose connection causing resistance. | Reduce load on circuits. Ensure ventilation is not obstructed. Check for loose connections at terminals. Consult a professional if problem persists. |
| Unusual noises from enclosure | Loose components; arcing. | Immediately disconnect power if safe to do so. Inspect for loose hardware or signs of electrical arcing. Contact a qualified electrician. |
9. Specifications
| Attribute | Value |
|---|---|
| Brand | MidNite Solar |
| Model Number | MNDC250 Plus |
| Product Dimensions (L x W x H) | 9" x 4" x 17" |
| AC Adapter Current (Max) | 250 Amps |
| Number of Circuits | 10 |
| Phase Type | Single Phase |
| Item Weight | 6 pounds |
| Manufacturer | Midnight Solar |
| ETL Listing | Listed for US & Canada |
10. Warranty and Support
For specific warranty information regarding your MidNite Solar MNDC250 Plus Mini-DC Disconnect, please refer to the documentation included with your purchase or visit the official MidNite Solar website. Warranty terms and conditions may vary.
For technical support, installation assistance, or any inquiries not covered in this manual, please contact MidNite Solar customer service directly. Contact information can typically be found on their official website or on the product packaging.
Manufacturer: Midnight Solar
