Must DC circuit breakers always be bipolar?

For a 24V switch-mode power supply branch, I used a single-pole DC circuit breaker, with the negative pole subjected to equipotential bonding (previously, I even directly used AC breakers as substitutes—the main difference being arc-extinguishing performance, but how significant can the arc be in a few-amp low-current short circuit?).

During a design review, an expert stated that DC circuit breakers must be bipolar, arguing that DC has positive and negative poles, unlike AC!

I'm puzzled—where is this regulation specified? Later, I wondered, why would manufacturers even produce single-pole versions? What is the rationale for requiring switching of the negative pole as well? According to available information, if a DC breaker is connected in reverse, the primary impact should only be on arc-extinguishing performance. Also, when I mentioned that the negative pole is equipotentially bonded, another expert claimed that "equipotential" doesn't apply to DC systems—only to AC. Is that true? It's strange—many sensors clearly mark their power supply negative terminal with the "GND" symbol.

For the incoming PE (protective earth) wire in the electrical cabinet, I directly used the PE green-yellow terminal on the mounting rail, but was told it's not acceptable and must be connected to a dedicated grounding busbar. It's hard to question the experts we've invited, especially those from the maritime field—marine applications are quite special, right?

User A's View:
Probably just being overly cautious. DC arc extinction differs from AC, but for low-voltage circuits, it might not be such a big concern. In my opinion, if it's not a critical application, a single-pole breaker, as long as it's reliable and won't cause contact welding, should be acceptable. Marine electrical systems primarily emphasize fire and safety. So safety must be prioritized.

User B's View:
In special cases, such requirements may be stricter. The intent is likely to ensure both poles are disconnected. If 0V is grounded, there could be risks of high-voltage intrusion, causing problems.

User C's View:
I relate to the point about the incoming PE wire. I directly used the PE terminal on the rail, but was told it's not allowed and must go to a grounding busbar. I understand this—it's a code requirement to ensure reliable and safe grounding.

User D's View:
Don't blindly follow outdated standards. I believe that any conductor carrying current or voltage should be controllable and interruptible. Standards from decades ago aren't necessarily safe today. Technology advances, and so should some standards.

User E's View:
For specified DC loads, polarity (+/-) is always clearly marked—reversing connections can lead to serious consequences. I'm not sure how exactly equipotential bonding is implemented, but I once modified an American machine where they kept saying the PLC wasn't sending signals, causing disputes and even involving the equipment department head. He simply used a multimeter—one probe on the chassis, one on the terminal—and concluded to "check the downstream side" (it turned out the software had disabled it). The issue was resolved by implementing equipotential bonding. Since you're dealing with marine applications, just follow the experts' recommendations.

User F's View:
If you use a bipolar breaker, it implies the negative terminal is not grounded—i.e., an isolated system. In such cases, a positive-to-ground short won't immediately cause a trip. The method of grounding the negative pole and using equipotential bonding isn't suitable for all situations. For equipment that can stop immediately, this method can help locate fault points and resolve issues. However, it's inappropriate for applications like medical or lifting equipment. Also, experts aren't omnipotent—they're only deeply familiar with certain areas. If you specialize deeply in a field, you can become an expert too.

If you have other suggestions or insights, feel free to share and discuss!