HUM9NEZ DC 2P MCCB Breaker

HUM9NEZ DC MCCB Breaker – High Current DC Circuit Protection for Storage and Solar Applications

The HUM9NEZ DC MCCB breaker from HUYU Electric’s NE NEW ENERGY SERIES incorporates molded case circuit breaker (MCCB) technology into high current DC circuit applications. Designed for the main DC incomer and larger feeder protection applications in photovoltaic (PV) combiner boxes and battery energy storage systems; capable of handling currents from 63A up to 630A at voltages of up to 1500V DC, this unit comes into play when your DC MCB has reached its overload limit at a given current rating which may be either 250A (at the combiner output) or 630A (as a DC Bus Disconnector).

This unit is available in a 2 pole configuration on all frame sizes, providing simultaneous disconnection of both positive and negative conductors maintaining a low temperature rise design that will prevent increased contact resistance at continuous loads. The IP65 handle with extended travel facilitates manual operation in dusty or humid conditions. HUYU Electric also provides original equipment manufacturer (OEM) and original design manufacturers (ODM) factory direct with full certification for utility scale solar and storage EPC projects.

Technical Information and Breakage Information

The HUM9NEZ format provides specifications for breaking capacity across multiple DC voltage levels with time constants applied. The Icu level at 1500V will be 20kA with τ=2ms giving a suitable rating for most PV string combiner outputs with the fault current limited by the arrays. The 40kA Icu rating then allows for handling of much higher fault levels where battery storage is used on DC Bus applications operating at 500V–1000V. When we consider 400A or 630A frame breakers with a 70kA Icu rating for 250V–500V, the HUM9NEZ will have sufficient interruption margin for large battery racks where there is a large short-circuit risk. As a result of the breaking capacity being defined based on voltage levels, specifiers will be able to select the correct frame size for the fault level at each location within the DC system.

Designed for Use as a DC Main Incomer

In a large-scale PV system, DC MCBs provide protection of individual strings with continuous ratings up to 63A or 80A. The maximum output of several strings working in parallel (i.e., 150A, 200A, or 250A) will require the use of a DC MCCB breaker that has the ability to handle both the continuous and available fault current. The HUM9NEZ has been designed to fill this requirement. The main disconnect for all downstream circuits in a combiner box or battery cabinet typically consists of a 400A DC circuit breaker or a 630A DC breaker.

Designed to operate under load for extended periods of time, these circuit breakers have a low rise in temperature when under load, which means that they won’t create thermal bottlenecks. When installed outdoors in conditions where there could be moisture and dust, the IP65-rated handle provides for consistent mechanical operation.

OEM/ODM Supply – DC MCCBs for Utility-Scale Solar and Storage

Buyer’s Guide

How to Select a DC MCCB for Solar and Battery Storage

Key selection criteria for the HUM9NEZ in high-current DC applications.

1. When to Move from DC MCB to DC MCCB

DC MCBs are compact and cost-effective up to 125A. When the DC circuit current exceeds this — common in combiner box outputs, battery rack feeds, and main DC bus connections — a DC MCCB breaker is required. The HUM9NEZ covers 63A–630A, overlapping with the upper end of DC MCBs and extending into the range where only molded case construction provides the necessary thermal capacity and breaking performance.

2. Voltage and Time Constant Matching

Select the breaker’s voltage rating to match the system: DC 1500V for next-generation PV, or DC 1000V for existing installations. The time constant (τ) in the breaking capacity specification indicates the circuit inductance the breaker has been tested with — τ=2ms represents a mostly resistive circuit, τ=5ms includes inductive energy typical of battery storage DC buses with filter reactors.

3. Frame Size and Breaking Capacity

For combiner outputs up to 250A, the HUM9NEZ-250S provides 20kA at 1500V. For larger battery storage DC bus protection, the HUM9NEZ-400 and -630 frames provide 70kA Icu at 500V — necessary where multiple battery racks in parallel can deliver substantial fault current. Always verify Icu exceeds the calculated prospective short-circuit current at the installation point.

4. Low Temperature Rise and Continuous Duty

In battery storage, DC breakers carry rated current for hours during charge and discharge cycles. The HUM9NEZ’s low temperature rise design ensures contact resistance remains stable during extended high-current operation, preventing nuisance trips from thermal drift. Combined with the IP65-rated handle, this makes it suitable for outdoor containerized battery installations.

Frequently Asked Questions

What is the difference between AC MCCB and DC MCCB?

An AC MCCB relies on the alternating current’s natural zero-crossing — 100 or 120 times per second — to help extinguish the arc when the contacts open. A DC MCCB faces continuous current with no zero-crossing, so it uses magnetic blowout coils and larger arc chutes to stretch, cool, and collapse the DC arc. The HUM9NEZ DC MCCB breaker is purpose-built for DC with voltage-dependent breaking capacities up to 70kA and defined time constants (τ=2ms or 5ms) that confirm its DC interruption capability. AC and DC MCCBs are not interchangeable — using an AC MCCB on DC risks contact welding and failure to interrupt the fault.

What is a DC MCB breaker?

A DC MCB is a compact, DIN-rail-mounted circuit breaker for DC circuits, typically rated up to 63A or 125A with breaking capacities up to 10kA. It is designed for string-level protection in PV systems and branch circuits in DC distribution. A DC MCCB — such as the HUM9NEZ — is a larger molded case breaker rated from 63A to 630A, with breaking capacities up to 70kA. It serves the main DC incomer and feeder protection roles where MCB capacity is exceeded. DC MCBs protect individual strings; a 250A DC MCCB or 400A DC MCCB protects the combined output.

How to install DC MCCB breaker?

Installing a DC MCCB breaker requires attention to polarity, cable sizing, and torque specifications. DC MCCBs have marked “+” and “−” terminals that must be connected according to the wiring diagram to ensure proper arc extinguishing during a fault. Cable sizing must account for the continuous DC current and the voltage drop over the circuit length. All connections must be torqued to the manufacturer’s specification to prevent hot spots at the rated current. Installation must be performed by a licensed electrician in compliance with local electrical codes. The HUM9NEZ includes an IP65-rated operating handle that can be installed through an enclosure door for external operation without opening the panel. Always consult the product manual for specific wiring diagrams and torque values.

What does MCCB mean in electrical terms?

MCCB stands for Molded Case Circuit Breaker. It is an overcurrent protection device housed in a molded insulating case, rated from approximately 16A to 1600A with breaking capacities that can exceed 100kA. In electrical terms, an MCCB sits between miniature circuit breakers (MCBs, typically up to 63A) and air circuit breakers (ACBs, above 630A) in the protection hierarchy. A DC MCCB like the HUM9NEZ is a molded case breaker specifically designed and tested for DC circuits — it uses magnetic arc extinguishing technology to safely interrupt DC fault currents with no zero-crossing. The HUM9NEZ covers 63A–630A at up to 1500V DC, placing it in the DC MCCB category for main incomer and large feeder protection in photovoltaic and battery storage systems.