Feature: Components
Yet, there are now much better and, above all, more reliable
protection mechanisms, such as electronic circuit breakers (ECBs); see Figure 1.
MCB or eFuse? – Which one is best for properly securing DC circuits
By Abdul Ücüncü, Application Engineer, PULS
I
n times of unregulated transformer power supplies, traditional miniature circuit breakers (MCB) have established themselves as the main protection modules. However, when switched-mode power supplies (SMPSs) were introduced in the 1990s, they quickly replaced transformer power supplies in industrial applications.
Te new technology enabled more efficient and compact power supplies that better met the increased demands of the industry. Te era of transformers was thus over, but the MCBs remained and continued to be used in conjunction with SMPSs, even on the DC side.
30 September 2025
www.electronicsworld.co.uk
MCB vs. eFuse Te biggest challenge is that miniature circuit breakers were originally designed for the AC side of the application and require multiple times the nominal current for a few milliseconds to trip. Many SMPSs cannot provide this, as they shut down on the DC side during a high current pulse, to protect themselves and the connected loads. Te alternative to the classic MCB is an ECB with integrated
eFuses. Tese modules, such as our PISA models, are optimised for the distribution and protection of DC loads and do not require peak current for reliable and quick tripping. Te reaction time, even with slight overload, is within 1ms.
Approval: MCB on the DC side only, with IEC 60947-2 Most circuit breakers were developed for the protection of AC circuits. Te idea that the same technology can also protect DC circuits is a misconception. Te main reason is that the arc burning and arc extinguishing properties of AC and DC systems are different. An AC circuit breaker may not reliably trip in a DC circuit. Terefore, if you want to use an MCB on the DC side in industrial low-voltage systems, it must comply with the IEC 60947- 2 standard. Tis standard applies to MCBs whose main contacts are intended for connection to circuits with rated voltages in the low-voltage range of 1,000VAC or 1,500VDC.
Tripping characteristic: B, C or Z? When selecting a circuit breaker, it is important to look at the tripping characteristic. Tere are different tripping characteristics suitable for various industrial applications. However, to reliably protect a DC circuit, it is advisable to use an MCB with the Z tripping characteristic. Since circuit breakers with this tripping characteristic are more
expensive, MCBs with the B or C tripping characteristic are mostly used in practice.
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