Short answer: you cannot use an AC miniature circuit breaker on a solar PV string. An AC MCB such as the CHINT NB1-63 follows IEC/EN 60898-1 and is designed around alternating current that crosses zero one hundred times a second at 50 Hz and one hundred and twenty times at 60 Hz; the arc drawn when the contacts open is extinguished at one of those zero crossings. A PV string delivers direct current with no zero crossing at all, so the arc has no natural moment to die on its own. The correct device is a DC breaker built and tested to IEC/EN 60947-2 for the string’s DC voltage — in our range the CHINT NB1-63DC, where the pole count sets the voltage: 1 pole = DC 250 V, 2 poles = DC 500 V, 4 poles = DC 1000 V, rated current up to 63 A, breaking capacity Icu 6 kA.
Why an AC MCB is the wrong device for a PV string
Two things separate an AC from a DC breaker, and neither of them is the label printed on the front.
First, the physics. On an AC system the current passes through zero many times per second. When a breaker trips on a fault, its job is to hold the arc briefly and then let it go out at the next zero crossing. On a DC string there is no next zero crossing. The arc has to be pushed into an arc chute and stretched until the voltage across it can no longer sustain it. That is a deliberate mechanical and magnetic design problem, and a device that was never built or tested for it is not the place to find out where your design assumptions were wrong.
Second, the standard. A household MCB is certified to IEC/EN 60898-1. The DC device in our range, the NB1-63DC, is certified to IEC/EN 60947-2 — an industrial circuit-breaker standard with its own DC test regime and its own DC voltage ratings. Two standards mean two different test setups. A 60898-1 certificate says nothing about how the device behaves with a unidirectional arc that never reaches zero.
Pole count is the voltage rating, not a current rating
On the NB1-63DC the rated DC voltage is a function of how the poles are used, which is why one product family appears at three different voltages. A single pole interrupts DC 250 V; two poles used in series interrupt DC 500 V; four poles in series interrupt DC 1000 V. The rated current is not what changes with the pole count — all three configurations are available up to In 63 A.
| NB1-63DC configuration | Rated DC voltage (Ue) | Rated current (In) | Breaking capacity (Icu) | Standard |
|---|---|---|---|---|
| 1 pole | DC 250 V | ≤ 63 A | 6 kA | IEC/EN 60947-2 |
| 2 poles | DC 500 V | ≤ 63 A | 6 kA | IEC/EN 60947-2 |
| 4 poles | DC 1000 V | ≤ 63 A | 6 kA | IEC/EN 60947-2 |
The same datasheet also states an electrical life of more than 1,500 operations, IP20 and pollution degree 3. Those are manufacturer figures for the series; as always, the value that governs your order is the row for the exact ordering code you buy, at the exact voltage you operate at.
AC assumptions versus DC reality
The table below is the difference in one view. It is the reason a procurement list that says “63 A, 6 kA” is not enough to describe a PV breaker.
| Assumption | AC circuit (IEC/EN 60898-1 MCB) | DC PV string (IEC/EN 60947-2 DC MCB) |
|---|---|---|
| Current waveform | Sinusoidal, crosses zero 100 (50 Hz) or 120 (60 Hz) times per second | Unidirectional, no zero crossing |
| How the arc is cleared | Naturally, at the next current zero | Forced: pushed and stretched in an arc chute built for DC |
| Device type | Modular household MCB, In 1–63 A | DC breaker, In ≤ 63 A |
| Voltage region | Ue 230/400–240/415 V AC | DC 250 V (1P) / DC 500 V (2P) / DC 1000 V (4P) |
| Breaking capacity figure | Icn (for example 6 kA) | Icu 6 kA at the stated DC voltage |
| Governing standard | IEC/EN 60898-1 | IEC/EN 60947-2 |
Polarity is not decoration
A DC arc is direction-sensitive. The arc chute is shaped to receive the arc from a defined direction, and the blow-out force that drives the arc into the plates depends on which way the current is flowing. Land the string’s positive and negative conductors the wrong way round and the arc is pushed toward the wrong side of the chamber, where it may not be split and cooled as intended.
In practice: read the polarity markings on the terminals, keep the same convention across every device in the array, and document it. A DC breaker that is correct on paper can still be installed incorrectly on the roof, and the failure only shows up on the day it has to interrupt a real fault.
String design basics that decide the device
Two numbers from the string design should be checked against the breaker’s nameplate before it is ordered:
- Maximum string voltage in cold weather. A PV module’s open-circuit voltage rises as cell temperature falls, so the highest voltage the string will ever present is a cold-morning figure, not the value at standard test conditions. That worst-case figure must stay below the breaker’s rated DC voltage, which is where the pole count (250 V / 500 V / 1000 V) becomes a design decision rather than a catalogue choice.
- Available fault current at the point of protection. This must sit below the device’s Icu rating. Icu is stated at a particular DC voltage; a rating quoted for one voltage is not automatically valid at another.
If the array has a combiner or an entry cabinet, surge protection is normally part of the same bill of materials. The NU6-I+II Class I+II SPD in our range is a TÜV and VDE certified line suited to PV combining and entry cabinets, and it is quotable alongside the DC breakers — again certified per exact ordering code.
Sourcing a DC breaker without a surprise
For a trading purchase the risk is not the design, it is the paperwork. When you are quoted a “1000 V DC breaker”, ask for the datasheet page showing the rated DC voltage and the Icu for the code you are buying, plus the certificate that covers that code. Different voltages and pole counts are different codes, and certificates follow codes, not families. Our verification checklist covers how we confirm this on every order.
FAQ
Q: Can I use a normal AC MCB on a solar PV string?
A: No. An MCB to IEC/EN 60898-1 is designed around alternating current that naturally crosses zero. A PV string is direct current with no zero crossing, so the arc has no natural moment at which it goes out. Use a device certified to IEC/EN 60947-2 for the DC voltage of the string.
Q: Why does the number of poles change the DC voltage rating?
A: Because the poles are connected in series to share the DC voltage. On the NB1-63DC one pole interrupts DC 250 V, two poles DC 500 V and four poles DC 1000 V. The current rating stays at up to 63 A across all three; only the voltage changes.
Q: What breaking capacity does the NB1-63DC have?
A: Icu 6 kA at the rated DC voltage of each configuration (1P / 2P / 4P). The figure is tied to the DC voltage that configuration is rated for, so quote it that way in a submittal.
Q: Is a DC MCB polarity-sensitive?
A: Yes. DC arc extinction depends on the direction of current relative to the arc chute, so the positive and negative conductors must be landed as marked on the terminals. Consistency across the array matters as much as the device itself.
Q: Can the NB1-63DC be used for telecom DC power as well as solar?
A: Yes. The manufacturer lists the series for photovoltaic DC systems and telecom power supplies. The voltage and pole-count logic is the same, so the string or bus voltage decides the configuration.
Q: Which certificate covers the DC breaker?
A: Certificates apply to the exact ordering code, not to the family as a whole. We send the certificate file that covers the code quoted, and we confirm the property against the datasheet before shipment.
Quote to the string, not to a headline figure
Send: array or string voltage · number of strings and their configuration · required pole count · quantity · destination country · the certificate your client needs. You get the datasheet page for the exact code, the certificate that covers it, and packing data, within 24 hours. Request a quotation.
Related: MCB and DC breaker catalogue · CHINT NB1-63 modular MCB · SPD, ATS and isolator range · Why grid voltage decides the device · How to read a breaker marking · Contact
CHINT is a trademark of its respective owner. HAZAM is an independent trading company; we are not the manufacturer and we are not an appointed distributor. Certificates and ratings always refer to the exact ordering code. Values above reflect manufacturer datasheets; the certificate for your code governs.