Dual Voltage and Single Voltage MCB

The type-test regime.

Oh, and the knob is a different shape.

Is there a prize for getting it right?

Here is a link that gives a very good explanation per the NEC:

https://www.ecmweb.com/content/understanding-circuit-breaker-markings

could you please explain reason to say that "Single-pole breakers are always slash rated"?

What was the outcome of the various telephone calls to the manufacturers?

You have to read the manufacturer's data sheets (aka cut sheet) on the product to truly know what is the technical difference. This document will also allow you to decrypt the other cryptic markings that will identify critical factors like time to trip, temperature range, arc flash limit, environment, etc. Many vendors will make it easy to locate this document.

I suspect the dual voltages of the MK breaker identify the maximum voltage the breaker can safely interrupt under overload condition for DC (230V) and AC (400V~).

I never heard of any dual-voltage circuit breaker...If you're referring to the voltage range of 230v- 400v, that is because the breaker is designed for use with circuits with inductive and capacitive loads ...

..."In the case of Type C MCBs, the magnetic operating limits are between 5 and 10 times the current rating of the MCB. Under these conditions the mechanism of a 10A MCB will operate between 50A and 100A in an overcurrent situation. Type C devices are capable of supplying the majority of inductive and capacitive loads such as motors, transformers and tungsten or fluorescent lighting."...

https://storage.electrika.com/manu/man-0290/pdftech/0290-mk49-16-a-581-585.pdf

The reason for the marking is to indicate that they can be installed in either a single-phase 230V system (as found in most houses here) or in a 400V-3-phase system. If they are not so marked, then they cannot be used in the 3-phase.

In other words, there's no difference except the marking. Dual voltages markings are just 3ph phase-to-neutral / phase-to-phase voltage. In the example, 230/400, 400v = 230v x sqrt(3).

Wrong! Read and understand the National Electrical Code (NEC) article above to find out why.

You are correct, should be "ground", not "neutral". Thanks.

The breaker doesn’t know about the neutral, though.

The single voltage rated MCBs are acceptable for line to line or line to neutral loads at voltages up to 240 VAC.
The double voltage rated MCBs are acceptable for line to neutral loads at voltages up to 230 VAC, and line to line voltages up to 400 VAC.

WRONG! The article above clearly explains the difference.

The breaker must be able to clear a fault to GROUND,as well as a line to line fault, and ground is not the same as NEUTRAL.

The lower voltage rating is the rating of the voltage to GROUND.

People tend to think of neutral and ground as the same,but they are not.

The higher voltage is the rating LINE to LINE.

Keep these facts in mind when you read the NEC article above.

Please read carefully the quote from the NEC:

"Voltage markings for breakers with slash voltage ratings are separated by a slash — for example, 208/120V or 480/277V. Each pole of the breaker is suitable when the line-to-ground voltage does not exceed the lower voltage marking, while the higher voltage marking is the value the line-to-line voltage may not exceed. Single-pole breakers are always slash rated."

Line to neutral is not the same as line-to-ground.

what are the instances where line-to-ground voltage and line-to-neutral voltage difference matters?

Read and understand the following from my previous post.

"Although the Code permits you to install a 120/240V slash-rated breaker on a 120/240V 3-phase, high-leg delta system, you cannot install it on the “B” phase (high-leg), because the nominal line-to-ground voltage of the high-leg is 208V. This exceeds the 120V line-to-ground voltage rating of the 120/240V slash breaker.

Be careful when installing slash-rated breakers on a solidly grounded high-leg delta system. Do not install them on corner-grounded, resistance-grounded, or ungrounded systems."

"You cannot use a slash-rated 480/277V breaker on a 480V corner-grounded delta circuit because the line-to-ground voltage from two of the conductors would be as high as 480V. This exceeds the breaker's 277V line-to-ground voltage rating."

Check these link for more info.

https://en.wikipedia.org/wiki/High-leg_delta

corner-grounded, resistance-grounded, or ungrounded systems.

https://ctlsys.com/support/electrical_service_types_and_voltages/

There is 400V, 3-ph system with 230V as Ph-N voltage and then, there is 690V, 3-ph system with 400V as Ph-N voltage.

The dual voltage rating I think means that the single pole MCB can be used in either of the systems.

What you think is wrong.

Read the article from the NEC(National Electrical Ccde).

This explains it very clearly.

Thanks for correcting me.

It means that the single pole breakers rated 400/230V can be installed only in 400V neutral point earthed systems where Phase-to-ground voltage during healthy conditions doesn't go beyond 230V.

In case of single phase to ground fault, the unfaulted phase to ground voltage may go over 230V (until the fault is cleared) but that is not a concern.

Hope I have understood correctly.