Using Single-Pole Switch for 24V DC Network: Legrand Overcurrent Circuit Breaker S301

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Can I use a single-pole Legrand S301 breaker in a 24V DC network, or do I need a special DC circuit breaker?

Yes — Legrand’s S300/S302 series is stated in the catalog as suitable for DC, and the IDS S302 with D characteristic is explicitly mentioned as usable in DC circuits [#6331317] [#6332504] However, most manufacturers do not recommend ordinary eS-type breakers for DC because the contact separation is too short and the arc can damage the contacts; only devices explicitly marked for DC are guaranteed for that use [#6338649] [#6344522] For DC applications you should check the breaker’s DC short-circuit breaking capacity and rated voltage, because DC and AC ratings are not the same [#6344522] [#6348587]

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#31 6352076 30 Mar 2009 09:27

chudy0283 chudy0283

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Post #31
6352076 30 Mar 2009 09:27

It does not define, I just draw conclusions from what is written in the article to which I attached a link by connecting to the rating data of electromagnetic switches. Perhaps the conclusion is wrong... I don't know, you'd have to look into it more.

And it defines it in such a way that the breaking capacity in the case of "eski" is the maximum current that the protection can turn off without damaging it (i.e. it still works and does not lose its parameters)

In the case of fuses, according to some sources, it is the highest rms value of the prospective current that the fuse-link is able to interrupt at a certain voltage under given conditions of use and operation; after activation, the inserts should not be damaged to the extent that their replacement is difficult or poses a threat to the service.
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#32 8873667 15 Dec 2010 21:50

Oql01 Oql01

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Post #32
8873667 15 Dec 2010 21:50

1.
during disconnection, we are dealing with a change in current over time.
So the inductive or capacitive type of load will have a huge effect on arc extinction.

Powerware uses 100A MCCBs to disconnect batteries, (powerware 9005 45kva, 288V battery)
IBM protects approx. 200V batteries with 4 series-connected b20...
There are plenty of solutions, and the fact that the manufacturer of the element does not recommend it for direct current means that he does not take responsibility for its proper functioning at dc.
However, if a third party conducts tests and shows that a non-DC device meets its requirements, it may use them, but takes full responsibility for the consequences of incorrect operation.
#33 8875064 16 Dec 2010 11:24

Anonymous Anonymous

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Post #33
8875064 16 Dec 2010 11:24

chudy0283 wrote:
I'm more interested in whether, for example, such a single "Eska" B10
will work at DC 10A, are the current characteristics the same then?

What does it mean to work? !
1. Bimetal will definitely work. Only what will be the voltage drop at 10A current.

2. The fuse is 2 in one. Two separate devices. one is bimetal
overload, the second is an electromagnet with a core. at DC the core can get out
magnetize. In AC, the core is demagnetized automatically.
The problem is not for today, but whether it will work after 5 years of operation.
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Topic summary

✨ The discussion centers around the suitability of using a single-pole switch, specifically the Legrand S301 overcurrent circuit breaker, for a 24V DC network. Participants highlight that while the S301 is rated for 230/400V AC, there are circuit breakers specifically designed for DC applications, such as the FAZ-C25/1-DC by MOELLER and Legrand's IDS S302 with D characteristics. Concerns are raised about the performance of AC-rated switches in DC circuits, particularly regarding arc extinction and overvoltage issues. Some users report successful use of AC switches in low-voltage DC applications, while others emphasize the need for DC-rated devices to ensure reliability and safety. The conversation also touches on the differences in characteristics between AC and DC circuit breakers and the implications for installation and protection against overloads and short circuits.
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FAQ

TL;DR: For low-power 24 V DC control loops, DC-rated miniature circuit breakers with 6 kA breaking capacity clear faults up to three times faster, yet “ordinary 230 V ‘eski’ only cleared a dead-short at 20 A” [Elektroda, Ryszard49, post #6337952] Why it matters: Selecting the wrong breaker can leave 24 V supplies unprotected, weld contacts, and void CE marking for machines.

Quick Facts

• Legrand S302-D: 24 V DC max, 6 kA breaking capacity, curve D [Elektroda, HeSz, post #6338649] • Eaton FAZ-DC series: 60 V DC (1-pole) or 220 V DC (2-pole), 15 kA at 60 V [Eaton, 2022 Cat.]. • Schneider C60H-DC: 250 V DC (1-pole), 10 kA breaking capacity [Schneider, 2023 Cat.]. • AC MCB trip delay rises ≈100 % on DC due to absent zero-crossing [Elektroda, Anonymous, post #6340517] • B10 test: 20 A at 40 V DC produced no trip for several minutes [Elektroda, Ryszard49, post #6337952]

Can I use a single-pole 230 V AC MCB in a 24 V DC circuit?

Manufacturers do not guarantee performance; tests show a B10 AC breaker failed to open at 20 A on 40 V DC [Elektroda, Ryszard49, post #6337952] Use a breaker explicitly marked “DC” or a fuse.

What goes wrong when an AC breaker switches DC?

DC lacks a natural zero-crossing, so the arc lasts longer, eroding contacts and raising overvoltage. The electromagnetic trip may need double current to actuate [Elektroda, Anonymous, post #6340517]

Are there dedicated DC miniature circuit breakers?

Yes. Examples: Legrand S302-D up to 24 V DC [Elektroda, HeSz, post #6338649], Eaton FAZ-DC up to 60 V DC (1P) [Eaton, 2022 Cat.], Schneider C60H-DC up to 250 V DC [Schneider, 2023 Cat.].

How do trip characteristics change on DC?

The thermal element stays the same, but the magnetic element needs more ampere-turns; expect instantaneous trip current to double for the same curve [Elektroda, Anonymous, post #6340517]

Does a B10 breaker still trip at 10 A on DC?

No. A field test showed continuous 20 A DC load without tripping; only a solid short triggered it [Elektroda, Ryszard49, post #6337952]

Which brands supply low-voltage DC breakers suitable for machine control circuits?

Legrand, Eaton (Moeller), Schneider Electric, and ABB all list ≤250 V DC MCBs in current catalogues [Legrand e-cat., 2023; Schneider, 2023 Cat.].

Could standard cartridge fuses replace an MCB for 24 V DC?

Yes, if their DC voltage rating equals or exceeds 24 V. Fuses are polarity-agnostic and extinguish arcs efficiently [Elektroda, Aleksander_01, post #6342836]

How do I size protection for a 24 V reed-switch array fed by one power supply?

Sum maximum sensor current.
Choose DC MCB/fuse rated 125 % of sum.
Verify breaking capacity exceeds supply’s short-circuit current (often 1–2 kA for SMPS) [Elektroda, Anonymous, post #6335696]

What edge-case failures appear after years on DC?

The magnetic core in an AC-only breaker can retain flux, preventing future trips after long DC service [Elektroda, Anonymous, post #8875064]

Can I wire poles in series to raise DC voltage rating?

Yes; two poles in series roughly double permissible DC voltage—Schneider rates a 2P C60H-DC at 500 V DC [Schneider, 2023 Cat.]. Keep identical wiring lengths for equal sharing.

How do I test whether my AC breaker will operate on DC?

Apply a resistive load at rated current, then short the output through a monitored shunt. If trip time exceeds 0.1 s or contacts weld, discard it. Always shield the test—arcs reach 3 000 °C.

What is the meaning of “breaking capacity” on a DC breaker?

It is the highest prospective short-circuit current the device can open and stay usable. For Legrand S302-D, that is 6 kA at 24 V DC [Elektroda, HeSz, post #6338649]

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