Ac Mcb Vs Dc Mcb The Complete Selection Guide Korlen

A practical selection guide for solar, storage, EV and building panels — by Korlen

Choosing between an AC miniature circuit breaker (MCB) and a DC MCB looks like a one-letter decision. It is not. The physics of the current they switch is fundamentally different, and using the wrong type where DC is present is a documented fire hazard. This guide explains the difference in plain terms, then gives you a practical checklist and Korlen’s real product data so you can specify with confidence.

AC vs DC in one minute

Alternating current reverses direction 50 or 60 times per second. Direct current flows one way and stays there. That single fact drives everything else about breaker design.

The blue curve is AC: it passes through zero voltage regularly. The red line is DC: it never crosses zero. When a breaker opens, an electric arc forms as the contacts separate. For AC, the next zero-crossing arrives within milliseconds and the arc dies naturally. For DC, nothing forces the arc to stop — it keeps burning until the breaker mechanically stretches and cools it into extinction.

A short history of the MCB

The MCB replaced the rewireable fuse in the early 20th century because it is resettable and far safer to maintain. Early units were AC-only, designed for the 50/60 Hz grids that powered homes and factories. As photovoltaic arrays, battery storage and EV chargers pushed DC into everyday installations, manufacturers had to redesign the breaker for a current that never lets go. The result is the DC MCB — visually similar, internally very different.

How an AC MCB breaks the arc

An AC MCB trips on two independent principles:

• Thermal: a bimetallic strip heats and bends under sustained overload, tripping after seconds to minutes.
• Magnetic: an electromagnet slams the mechanism shut instantly on a short circuit.

Once the contacts part, the arc is drawn into a stack of splitter plates (the arc chute). Because the AC current is about to hit zero anyway, the plates only need to cool and divide the arc briefly. That is why an AC MCB can be compact and inexpensive. Korlen’s KNB5-63 AC MCB is a 6 kA device built on exactly this principle, rated to 415 V AC across 1–4 poles.

Why a DC MCB is a different animal

With no zero-crossing to help, a DC MCB needs three extra design moves to extinguish the arc:

• Larger arc chamber — more splitter plates to stretch the arc longer.
• Wider contact gap — a bigger physical distance the arc must jump.
• Magnetic blow-out coil — a permanent magnet sweeps the arc upward into the chute instead of letting it linger at the contacts.

That same magnet makes DC MCBs polarity-sensitive. The + and − terminals must be wired as marked; reversed wiring defeats the blow-out and can leave the arc burning — a real fire risk. Korlen’s KNB2-63DC is rated up to 1000 V DC and complies with IEC/EN 60947-2, the standard written for DC switching.

Six factors that decide your choice

Where each type actually lives

IEC vs UL — which standard applies

Most export markets (Europe, Asia, Middle East, Latin America) follow IEC. North America follows UL. Korlen products are built to IEC/EN, which is what the majority of global buyers specify:

If you sell into the US, confirm the UL 489 / UL 1077 listing separately — that is a different certification track from IEC.

Seven-step selection checklist

1. Current type — Confirm AC, DC, or mixed.
2. Voltage — AC up to 415 V; DC up to 1000 V per pole.
3. Current rating — Match the load (Korlen: 1–63 A).
4. Trip curve — B for resistive, C for general, D for motors.
5. Breaking capacity — 6 kA covers most builds.
6. Poles — 1P, 1P+N, 2P, 3P, 4P as needed.
7. Standard — IEC 60898 (AC) or 60947-2 (DC).

Four mistakes that start fires

Korlen AC & DC MCB product line

Korlen manufactures both sides of the line, so you can standardise the panel:

Note the DC unit’s 20,000 mechanical operations versus 10,000 on the AC unit — DC mechanisms are built tougher because the arc is harder to kill.

FAQ

Can one MCB handle both AC and DC?

Some dual-rated breakers exist, but the DC voltage rating is far lower than the AC one (e.g. 277 V AC ≈ 60 V DC on the same pole). For real DC work — PV, storage — use a purpose-built DC MCB such as the KNB2-63DC.

Why is my DC MCB bigger?

The larger arc chamber and blow-out magnet take space. That bulk is the price of safe DC interruption.

Does polarity really matter?

Yes. Reverse the terminals on a DC MCB and the magnetic blow-out works against the arc instead of with it. Always follow the marked + / −.

Talk to our engineers

Specifying a mixed AC/DC panel? Korlen’s engineering team can confirm ratings, polarity and standards for your market — including DC surge protection with the KNY-40 Type 2 SPD and DC isolation with the KNH2-100 isolator.