Understanding DC Breakers: The MNEPV and Off-Grid Solar Systems

What's the deal with the MNEPV, our trusted DC circuit breaker? I've spent a lot of time researching and talking to Midnite Solar experts about these changes.

If you've worked with off-grid solar and battery setups, you've probably encountered the Midnite Solar MNEPV DC circuit breaker. For those new to DC overcurrent protection, these breakers look like slim versions of the ones in your home's electrical panel. The MNEPV line has been around for years, mostly unchanged - until now.

I've done the deep dive into the MNEPV lineup changes so you don't have to. Let's explore what the MNEPV breaker does, what's changing, and how this affects your off-grid (or sometimes grid-tied) system design.

Overcurrent Protection Basics

Overcurrent protection, whether fuses or breakers, safeguards current-carrying wires. When too much electricity flows through a circuit, the wire heats up and can catch fire. Properly sized protection disconnects the circuit before it becomes dangerous.

Solar Panel Connections and Combiner Boxes

Solar panels can be wired in series, parallel, or both. Many systems use separate overcurrent protection for each series string. A popular method to connect series strings in parallel is using a combiner box.

A combiner box is a metal enclosure that houses:

• Overcurrent protection
• Bus bars for neutral and ground wires
• A transition point from PV wire to conduit

Combiner boxes feature a din rail, where MNEPV breakers attach. When shopping for DC breakers, note the difference between din rail and panel mount types. The box also has a positive busbar connecting breakers in parallel, joining the solar array's series strings. Ensure the busbar only connects the strings specified in your design.

Additional combiner box components:

• Negative and ground bus bars
• Surge protection device (SPD)
• Strain relief for each string and system ground

Choosing Between Circuit Breakers and Fuses

Traditionally, available DC breakers were rated for 125-150 volts DC (Vdc). This worked for low-voltage strings, but as system voltages increased, higher-rated fuses became necessary. Fuse holders allowed the use of 1000v-rated fuses similar to circuit breakers.

Higher voltage DC breakers emerged to address some issues:

1. They serve as both overcurrent protection and disconnects
2. They're resettable, avoiding system downtime from blown fuses

The MNEPV DC Breaker

The MNEPV is a din rail mounted DC breaker rated for 150Vdc and up, available in 1-63 amp sizes. These breakers are used in:

• Combiner boxes
• DC load centers as disconnects

DC load centers may be far from combiner boxes, requiring:

• PV disconnect
• Charge controller disconnect
• Battery disconnects 
• DC load disconnects

Many DC load centers can use MNEPV breakers for all these functions.

Choosing the Right DC Breaker

Selecting the appropriate DC breaker for your system involves several factors:

1. System voltage: Ensure the breaker's voltage rating exceeds your maximum system voltage.
2. Current rating: Choose a breaker rated slightly above your expected maximum current.
3. Interrupt rating: Select a breaker capable of safely interrupting the maximum fault current in your system.
4. Environmental conditions: Consider temperature ratings and enclosure types for outdoor installations.
5. Compliance: Verify the breaker meets relevant electrical codes and standards.

Always consult with a qualified professional or electrician when designing your system and selecting components.

Key breaker features you need to know:

There are both AC and DC breakers (and Outback's handy AC & DC combo). Knowing what type of electrical circuit you're working on should go without saying, but you know the phase, "common sense ain't so common". Unless you have one of those ACDC breakers, you'll want to makes sure your breaker matches the type of electrical circuit you're using.

Next up are voltage and amp ratings. We won't go deep into breaker sizing at this time, but make sure to match your breaker amp rating to your wire for proper protection. Breaker voltage can be higher, but not lower, then your current carrying conductor (aka wire), so a string that never goes above 150 Vdc can still use a 600v rated breaker. Another difference between breakers is the mounting style: panel mount vs din rail mounting, that we've already covered.

Then there's the number of poles - simply put, how wide is the breaker? 1 pole is narrow, while 2, 3, and 4 poles get progressively wider, taking up more box space. Lastly, there's polarization. (I'll get more details from Midnite). In a DC circuit, electricity flows positive to negative. Reversing this can destroy equipment. Some devices have protection, but a polarized breaker ensures correct flow. Non-polarized allows flow both ways. So which do you need? 99% of the time, it doesn't matter - just get what's in stock. If your local authority requires a specific type, include that in your design and order.

Summary of the various types of breakers

• AC vs DC 
• Voltage 
• Amperage 
• Mounting style 
• Number of poles 
• Polarization 
• Relevant safety listings (RoHS, ETL) 

Recent Changes to the MNEPV Breaker Lineup

Midnite Solar has introduced significant updates to their MNEPV DC breaker line. These changes aim to improve performance, reliability, and versatility in various solar applications.

Key updates include:

1. Increased voltage ratings
2. New size options
3. Wider range of options 

These modifications address evolving industry needs and stricter safety standards.

Implications for System Design

When planning your off-grid or grid-tied solar system, consider these changes carefully. They may allow for more efficient designs or open up new possibilities in your setup.

The MNEPV is a DC din rail breaker, rated 150-600 Vdc, 1-200 amp, with one to four poles, either polarized or non-polarized. In the past, we just had MNEPV# (# being amp rating). A MNEPV15 was 15 amps - all were polarized, 150 VDC rated, so no need to specify. With more options now, we need better naming, new part numbers, and more stock (and design choices).

Midnite's new system looks like this: MNEPV##-###-#. MNEPV means din rail mounted. First numbers are amp rating. Second set is voltage rating. Third set shows poles and polarity. So, MNEPV15-600-2PP is din rail, 15 amps, 600 Vdc, two poles (each half-inch wide), and polarized. MNEPV20-150-1PNP is din rail, 20 amps, 150Vdc, one pole, non-polarized. Simple, right?

While the naming is straightforward, the transition has been tough. Some MNEPV breakers are being replaced, some discontinued, some unchanged. Some discontinued ones can still be ordered while in stock, like MNEPV4, while others are gone for good. Some are now 300Vdc (like MNEPV20), others only non-polarized (like MNEPV1). Some (like MNEPV15) come in polarized (quick shipping) or non-polarized (special order, may take time - and you probably don't need it). This makes ordering tricky. We've made a handy guide to help: Midnite MNEPV Breaker Update

It's a big list, but you'll likely only use about 15 breakers. Five new 600v breakers can replace fuses in many systems. If you're sticking with fuses, it's down to only ten. Generally, ignore polarity unless you know you need it. Some 150v breakers are now 300v, some polarized, some not.

The top 15 MNEPV Breakers

MNEPV15-300-1PP
MNEPV15-600-2PP
MNEPV20-150-1PNP
MNEPV20-300-1PP
MNEPV20-600-2PP
MNEPV30-300-1PP
MNEPV30-600-2PP
MNEPV40-300-1PP
MNEPV40-600-2PP
MNEPV50-300-1PP
MNEPV50-600-2PP
MNEPV60
MNEPV63
MNEPV80
MNEPV100

Most MNEPV breakers will be one of these once old stock runs out.

The MNEPV DC circuit breaker continues to evolve with the industry's changing needs. Understanding these updates is crucial for anyone working with solar power systems, whether you're a DIY enthusiast, professional installer, or just interested in solar tech. Staying informed about components like the MNEPV breaker helps ensure safe, efficient, and reliable solar power systems.

As solar technology advances, we can expect further improvements in DC protection devices, driving sustainable energy growth. Always prioritize safety and seek expert advice when in doubt. With the right knowledge and tools, you can harness solar power while protecting your investment and the environment.

Conclusion

The MNEPV DC circuit breaker has been a staple in off-grid and solar installations for years. With the recent updates, it continues to evolve to meet the changing needs of the industry. Understanding these changes and how they affect system design is crucial for anyone working with solar power systems.

Whether you're a DIY enthusiast, professional installer, or just curious about solar technology, staying informed about components like the MNEPV breaker helps ensure safe, efficient, and reliable solar power systems. As the industry continues to innovate, we can expect further improvements in DC protection devices, driving the growth of sustainable energy solutions.

Remember, proper system design and component selection are key to a safe and efficient solar installation. Always prioritize safety and consult experts when in doubt. With the right knowledge and tools, you can harness the power of the sun while protecting your investment and the environment.