{"id":4244,"date":"2026-09-25T00:00:00","date_gmt":"2026-09-25T00:00:00","guid":{"rendered":"https:\/\/chac-electric.com\/?p=4244"},"modified":"2026-10-19T03:37:15","modified_gmt":"2026-10-19T03:37:15","slug":"ung-dung-va-lua-chon-cac-loai-duong-cong-ngat-mach-kieu-b","status":"publish","type":"post","link":"https:\/\/chac-electric.com\/vi\/blog\/what-is-type-b-mcb-tripping-curve-applications-and-selection\/","title":{"rendered":"Lo\u1ea1i MCB lo\u1ea1i B l\u00e0 g\u00ec? \u0110\u01b0\u1eddng cong ng\u1eaft \u0111i\u1ec7n, c\u00e1c \u1ee9ng d\u1ee5ng v\u00e0 l\u1ef1a ch\u1ecdn"},"content":{"rendered":"

A M\u00e1y bi\u1ebfn th\u1ebf MCB lo\u1ea1i B<\/strong> is a miniature circuit breaker with a B time-current characteristic. Its instantaneous magnetic operating band is commonly 3\u20135 times rated current in the IEC-based product families covered by the manufacturer\u2019s curve. That band is not the normal load allowance, and \u201cType B\u201d here does not mean a Type B residual-current device. Select the breaker from the load\u2019s starting behavior and the circuit\u2019s fault-clearing requirements together.<\/p>\n

\"\u1ee8ng<\/p>\n

Understand the magnetic band and the thermal curve<\/h2>\n

A thermal-magnetic MCB responds to sustained overload through its thermal mechanism and to sufficiently high current through its magnetic mechanism. Schneider Electric\u2019s Acti9 FAQ gives a B-curve band of 3\u20135 times rated current. For a hypothetical B20 device using that characteristic, the band corresponds to 60\u2013100 A. This is an illustration of the multiplier, not a guaranteed trip point at every temperature or duration.<\/p>\n

Below the magnetic region, the thermal curve still matters. A breaker carrying somewhat more than its rating does not necessarily open instantly. Read the complete manufacturer time-current curve, including tolerances and test conditions, when checking overloads and disconnection time.<\/p>\n

Check the actual inrush before calling a load low-inrush<\/h2>\n

B-curve devices are often considered for resistive loads and circuits with modest starting currents. \u201cLighting,\u201d however, is not a complete electrical description: a bank of LED drivers can draw a short charging pulse at switch-on. Obtain the driver\u2019s inrush information and any manufacturer limit on the number of drivers per protective device.<\/p>\n

The useful design question is whether the combined startup stays within the breaker\u2019s acceptable operating envelope. A low running wattage does not prove low inrush. Group switching, simultaneous restart after a power failure and replacement driver types can all change that envelope without changing the circuit\u2019s everyday current.<\/p>\n

Compare B and C curves against the fault conditions<\/h2>\n

Ph\u1ea7n B-curve tripping characteristic<\/strong> has a lower magnetic threshold than the C characteristic in the cited Acti9 guidance, which gives C as 5\u201310 times rated current. Moving to C can tolerate a larger startup pulse, but it also changes the current needed for rapid magnetic operation. Check the fault path and required disconnection time before accepting that change.<\/p>\n

For a long cable run, inspect the minimum fault-current condition as well as the maximum fault level at the board. A device must interrupt the largest credible fault within its rating and operate quickly enough at the fault conditions relevant to the installation. Raising the threshold solely to stop a nuisance trip can leave that second check unresolved.<\/p>\n

\"CHAC:<\/p>\n

Keep the curve letter separate from other ratings<\/h2>\n

A B marking does not establish breaking capacity, AC\/DC suitability, residual-current sensitivity or arc-fault detection. Those are separate characteristics. In particular, a Type B RCD classification concerns residual-current waveforms, whereas a B-curve MCB characteristic concerns overcurrent operation. Similar wording is not evidence of equivalent protection.<\/p>\n

Review the available curves in CHAC\u2019s miniature circuit breaker range<\/a> and the exact variant on the CQB2-63 MCB page<\/a>. Confirm the model curve and rating instead of transferring a competitor\u2019s threshold or application approval to a CHAC catalogue number.<\/p>\n

Diagnose unwanted trips before changing the breaker<\/h2>\n

Record when the trip occurs, which loads switch together and whether the event follows maintenance or a change of equipment. Immediate startup trips and delayed overload trips call for different investigations. Check the circuit and connections before assuming the selected curve is the only problem.<\/p>\n

A replacement MCB curve selection<\/strong> should document the load inrush, cable protection and disconnection-time review. The 20 A MCB selection guide<\/a> shows how the current rating and curve remain separate decisions. Keep that record so a later technician understands why the replacement was chosen.<\/p>\n

Which part of the specification answers each question?<\/h2>\n\n\n\n\n\n\n\n\n
Question<\/th>\nRelevant characteristic<\/th>\nDo not confuse it with<\/th>\n<\/tr>\n<\/thead>\n
Will it tolerate startup?<\/td>\nFull time-current curve and load inrush<\/td>\nRunning current alone<\/td>\n<\/tr>\n
Can it clear the fault?<\/td>\nBreaking capacity at the declared voltage<\/td>\nThe B curve letter<\/td>\n<\/tr>\n
Does it detect leakage?<\/td>\nA separate residual-current function<\/td>\nA Type B MCB marking<\/td>\n<\/tr>\n
Can it operate on DC?<\/td>\nExplicit DC rating and wiring instructions<\/td>\nIts AC trip curve<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\n

C\u00e1c c\u00e2u h\u1ecfi th\u01b0\u1eddng g\u1eb7p<\/h2>\n

Kho\u1ea3ng ph\u1ea1m vi ho\u1ea1t \u0111\u1ed9ng c\u1ee7a m\u1ed9t b\u1ed9 c\u00f4ng t\u1eafc MCB lo\u1ea1i B l\u00e0 bao nhi\u00eau?<\/h3>\n

Theo ti\u00eau chu\u1ea9n IEC 60898-1, v\u00f9ng ho\u1ea1t \u0111\u1ed9ng t\u1ee9c th\u1eddi th\u01b0\u1eddng \u0111\u01b0\u1ee3c x\u00e1c \u0111\u1ecbnh \u1edf kho\u1ea3ng 3\u20135 l\u1ea7n d\u00f2ng \u0111i\u1ec7n \u0111\u1ecbnh m\u1ee9c, nh\u01b0ng c\u00e1c gi\u1edbi h\u1ea1n ki\u1ec3m tra ch\u00ednh x\u00e1c v\u00e0 d\u1eef li\u1ec7u s\u1ea3n ph\u1ea9m lu\u00f4n \u0111\u01b0\u1ee3c quy \u0111\u1ecbnh ri\u00eang. Lu\u00f4n s\u1eed d\u1ee5ng \u0111\u01b0\u1eddng cong c\u1ee7a m\u1eabu \u0111\u01b0\u1ee3c cung c\u1ea5p.<\/p>\n

When should I use a B-curve MCB?<\/h3>\n

Consider it where the load\u2019s inrush is compatible with the B characteristic and the circuit meets the required disconnection conditions. Resistive and some lighting circuits may fit, but LED drivers, transformers and other electronic loads need an actual inrush check.<\/p>\n

T\u00f4i c\u00f3 th\u1ec3 thay th\u1ebf \u0111\u01b0\u1eddng cong C b\u1eb1ng \u0111\u01b0\u1eddng cong B \u0111\u01b0\u1ee3c kh\u00f4ng?<\/h3>\n

Ch\u1ec9 sau khi ki\u1ec3m tra l\u1ecbch s\u1eed s\u1ef1 c\u1ed1, t\u00ecnh tr\u1ea1ng d\u00f2ng \u0111i\u1ec7n r\u00f2 r\u1ec9 v\u00e0 d\u00f2ng \u0111i\u1ec7n qu\u00e1 t\u1ea3i. M\u1ee9c ng\u01b0\u1ee1ng t\u1eeb t\u00ednh th\u1ea5p h\u01a1n c\u00f3 th\u1ec3 c\u1ea3i thi\u1ec7n vi\u1ec7c gi\u1ea3i quy\u1ebft s\u1ef1 c\u1ed1, nh\u01b0ng c\u00f3 th\u1ec3 g\u00e2y ra s\u1ef1 c\u1ed1 khi kh\u1edfi \u0111\u1ed9ng.<\/p>\n

Lo\u1ea1i B c\u00f3 t\u01b0\u01a1ng th\u00edch v\u1edbi DC kh\u00f4ng?<\/h3>\n

Kh\u00f4ng. \u201cB\u201d l\u00e0 ch\u1ec9 \u0111\u1ecbnh v\u1ec1 \u0111\u01b0\u1eddng cong d\u00f2ng \u0111i\u1ec7n trong th\u1eddi gian c\u1ee7a m\u1ed9t d\u00f2ng r\u01a1le, kh\u00f4ng ph\u1ea3i l\u00e0 ch\u1ec9 s\u1ed1 \u0111\u1ecbnh m\u1ee9c DC. Vui l\u00f2ng ki\u1ec3m tra \u0111i\u1ec7n \u00e1p, c\u1ef1c v\u00e0 d\u1eef li\u1ec7u th\u1eed nghi\u1ec7m DC ri\u00eang bi\u1ec7t.<\/p>\n

What is the difference between B and C curve circuit breakers?<\/h3>\n

In the cited Acti9 guidance, B has a 3\u20135 times rated-current magnetic band and C has a 5\u201310 times band. Both also have thermal overload behavior. Choose using the exact model curve, load inrush and fault-clearing requirements rather than an application label alone.<\/p>\n<\/section>\n

Tham kh\u1ea3o<\/h2>\n