{"id":2049,"date":"2026-08-27T14:45:12","date_gmt":"2026-08-27T06:45:12","guid":{"rendered":"https:\/\/jutrion.com\/?p=2049"},"modified":"2026-08-27T15:11:24","modified_gmt":"2026-08-27T07:11:24","slug":"rcbo-selection-guide","status":"publish","type":"post","link":"https:\/\/jutrion.com\/pt\/rcbo-selection-guide\/","title":{"rendered":"Guia de Sele\u00e7\u00e3o de RCBO para Circuitos Reais: Tipo A\/AC, 30mA, Curvas B\/C e Polos"},"content":{"rendered":"\n

A request for \u201c32 A, 30 mA RCBO\u201d is not ready for ordering. It identifies a load-current class and a residual-current threshold, but it does not identify the fault waveform, starting current, cable limit, supply conductors or available short-circuit current. The same two numbers could describe a general socket circuit, a bank of LED drivers or an inverter feeder\u2014and those circuits may need different RCBOs.<\/p>\n\n\n\n

The practical answer is to choose the RCBO around the protection job<\/strong>. For a typical modern final circuit, Type A and 30 mA are often the starting point. The finished choice still depends on whether the load produces electronic leakage, whether B curve can tolerate startup, which conductors must be disconnected and whether 6 kA is sufficient at the board.<\/p>\n\n\n\n

This guide follows three project files rather than a catalogue sequence. Each project starts with a different risk, then ends with a complete RCBO description that a contractor, panel builder or distributor can actually use.<\/p>\n\n\n\n

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Three Circuits That Should Not Receive the Same RCBO<\/h2>\n<\/blockquote>\n\n\n\n
Project file<\/th>Main uncertainty<\/th>Likely starting point<\/th>Decision that controls the result<\/th><\/tr><\/thead>
Office socket circuit<\/td>Future electronic loads and continuity<\/td>Type A, 30 mA, individual RCBO<\/td>Cable rating, fault level and board interface<\/td><\/tr>
LED lighting and small pump panel<\/td>Short startup current<\/td>Type A, 30 mA, B or C curve<\/td>Measured\/declared inrush versus fault-disconnection conditions<\/td><\/tr>
Inverter-backed three-phase circuit<\/td>Residual-current waveform, reverse power and neutral<\/td>Equipment-defined Type A\/F\/B and 3P\/3P+N\/4P<\/td>Converter instructions, supply topology and bidirectional approval<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
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Three different final circuits requiring RCBO selection based on their actual load and conductor arrangement<\/em><\/code><\/figcaption><\/figure>\n\n\n\n

These examples are illustrative, not records of completed JUTRION projects. Their purpose is to show how one parameter changes because the circuit changes.<\/p>\n\n\n\n

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Project File 1: An Office Socket Circuit<\/h2>\n<\/blockquote>\n\n\n\n

The first circuit supplies general socket outlets in a 230 V office. Today the connected equipment includes laptops, monitors, chargers and a printer. Tomorrow the occupants may connect different electronic appliances. The designer therefore cannot prove that the circuit will remain a simple sinusoidal AC load.<\/p>\n\n\n\n

Type A is the defensible starting point<\/h3>\n\n\n\n

Type AC responds to sinusoidal alternating residual current. Type A also responds to pulsating DC residual current. Modern single-phase electronics commonly contain rectifiers and switched-mode power supplies, so Type A is normally the more practical starting point for an unspecified socket circuit.<\/p>\n\n\n\n

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Type AC and Type A RCBO residual-current waveform comparison<\/em><\/code><\/figcaption><\/figure>\n\n\n\n

Type A is not a universal substitute for every RCD type. Equipment capable of producing smooth DC or particular mixed-frequency residual currents may require Type F, Type B or another declared arrangement. For a general office socket circuit, however, Type A addresses a more realistic load population than Type AC.<\/p>\n\n\n\n

Why 30 mA and 20 A answer different questions<\/h3>\n\n\n\n

The office specification proposes a 30 mA residual-current rating for additional protection under the applicable installation rules. That 30 mA value is I\u0394n; it describes the residual-current function. It does not describe the load current the circuit can carry.<\/p>\n\n\n\n

Assume the calculated design current is 17.2 A and the installed cable has a corrected current-carrying capacity of 24 A. A 20 A device passes the initial conductor-protection relationship:<\/p>\n\n\n\n

Ib \u2264 In \u2264 Iz<\/strong><\/p>\n\n\n\n

17.2 A \u2264 20 A \u2264 24 A<\/strong><\/p>\n\n\n\n

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RCBO 20 amp overcurrent protection compared with 30 milliamp residual-current protection<\/em><\/code><\/figcaption><\/figure>\n\n\n\n

Here, Ib is design current, In is RCBO rated current and Iz is corrected cable capacity. Ambient temperature, grouping, insulation, installation method, harmonics and national rules must already be reflected in Iz. Choosing 25 A because it is the next catalogue size would exceed the stated cable capacity.<\/p>\n\n\n\n

Individual RCBOs protect continuity as well as people<\/h3>\n\n\n\n

If several office circuits share one RCCB, leakage from their electronic filters accumulates at the shared device. One earth-fault event may also disconnect every downstream MCB. Individual RCBOs divide the leakage by circuit and usually contain a residual-current trip to the affected branch. That makes fault location easier and reduces unnecessary loss of service.<\/p>\n\n\n\n

The architecture does not eliminate leakage planning. Normal protective-conductor current still needs margin below the device threshold, particularly where many IT power supplies or long cables are connected.<\/p>\n\n\n\n

The office result<\/h3>\n\n\n\n
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230 V AC, 1P+N RCBO, 20 A, Type A, 30 mA, B or C curve subject to inrush and fault verification, breaking capacity above the measured\/calculated board fault level, compatible with the declared consumer-unit busbar.<\/p>\n<\/blockquote>\n\n\n\n

The curve and breaking capacity remain open because neither can be chosen from \u201coffice sockets\u201d alone.<\/p>\n\n\n\n

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Project File 2: LED Lighting Beside a Small Pump<\/h2>\n<\/blockquote>\n\n\n\n

The second panel contains two outgoing circuits with similar normal current. One feeds a group of LED drivers; the other feeds a small direct-on-line pump. Both can produce a brief current peak during energization, but the source and duration of that peak differ.<\/p>\n\n\n\n

B curve versus C curve is an inrush and fault-path decision<\/h3>\n\n\n\n

For common IEC miniature-breaker characteristics, B curve typically has an instantaneous operating range around 3\u20135 times In, while C curve is around 5\u201310 times In. D curve, often around 10\u201320 times In, is reserved for higher-inrush duties that have been specifically engineered. Exact operation must be checked against the applicable product data.<\/p>\n\n\n\n

A C-curve RCBO can tolerate a larger short-duration startup current before its magnetic element operates. That does not make it a better general-purpose choice. The higher threshold also means the circuit must deliver more fault current to ensure instantaneous disconnection.<\/p>\n\n\n\n

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B-curve and C-curve RCBO instantaneous trip ranges compared with LED-driver and pump inrush current<\/em><\/code><\/figcaption><\/figure>\n\n\n\n
Evidence from the circuit<\/th>What it suggests<\/th>What must be verified next<\/th><\/tr><\/thead>
Low or controlled startup peak<\/td>B curve may remain suitable<\/td>Manufacturer curve and normal switching events<\/td><\/tr>
Short, repeatable peak above the B magnetic region<\/td>Consider C curve<\/td>Fault-loop\/disconnection conditions and cable protection<\/td><\/tr>
Very high transformer or motor inrush<\/td>Engineered C\/D solution or different starting method<\/td>Available fault current, coordination and equipment protection<\/td><\/tr>
Trip occurs after running for minutes<\/td>Likely thermal overload rather than inrush<\/td>Load current, enclosure temperature, terminals and cable<\/td><\/tr>
Trip indication shows residual-current operation<\/td>Changing B to C will not solve it<\/td>Leakage, insulation, moisture, neutral routing and RCD type<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

This distinction prevents a common diagnosis error. A B-curve and C-curve RCBO with the same 30 mA marking have the same nominal residual-current sensitivity. The curve letter belongs to the overcurrent section; it does not make the RCBO more tolerant of earth leakage.<\/p>\n\n\n\n

LED drivers and pump motors also change the RCD-type question<\/h3>\n\n\n\n

LED drivers contain electronics, so Type A is a sensible baseline. A conventional single-phase motor circuit may also include an electronic controller, soft starter or variable-speed drive. Once power electronics are introduced, the equipment instructions\u2014not the word \u201cmotor\u201d\u2014determine whether Type A remains suitable or whether Type F\/B behavior is needed.<\/p>\n\n\n\n

The two circuit results<\/h3>\n\n\n\n

After verifying a modest LED-driver inrush and adequate fault current, the lighting circuit may finish as:<\/p>\n\n\n\n

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230 V AC, 1P+N, 16 A, Type A, 30 mA, B curve, 6 kA where the verified prospective fault current is below that rating.<\/p>\n<\/blockquote>\n\n\n\n

If the pump starting record exceeds the B-curve region but the circuit satisfies C-curve disconnection requirements, the pump circuit may finish as:<\/p>\n\n\n\n

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230 V AC, 1P+N or 2P as required, 16 A, Type A (or equipment-specified type), 30 mA where required, C curve, breaking capacity matched to the board fault level.<\/p>\n<\/blockquote>\n\n\n\n

The difference was not \u201clighting versus motor\u201d by label. It was the measured or declared startup behavior, residual-current waveform and fault path.<\/p>\n\n\n\n

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Project File 3: An Inverter-Backed Three-Phase Circuit<\/h2>\n<\/blockquote>\n\n\n\n

The third project connects a three-phase power-electronic system. It may import power, export power or operate differently when a backup source is active. A catalogue shortcut such as \u201cfour-pole, Type B\u201d is unsafe because the converter design and supply topology have not yet been established.<\/p>\n\n\n\n

Let the converter documentation define the residual-current type<\/h3>\n\n\n\n

Type F extends Type A behavior for defined mixed-frequency conditions associated with selected single-phase inverter loads. Type B covers a wider residual-current range, including smooth DC under its applicable characteristics. Some EV chargers and inverters incorporate residual direct-current monitoring; others require a particular upstream device.<\/p>\n\n\n\n

The choice cannot be made from product category alone. Confirm:<\/p>\n\n\n\n