The circuit breaker — foundation of protection
The circuit breaker (MCB) is the basic element of any electrical installation. Safety of people and equipment depends on correct selection.
Step 1: Rated current
MCB rating In is selected by design current: In ≥ Icalc. For a kitchen outlet group (3.5 kW): Icalc = 3500 / 230 = 15.2 A → select C16.
Step 2: Trip curve (B, C, D)
B — 3-5 In (lighting, general outlets), C — 5-10 In (universal, outlets, small motors), D — 10-20 In (large motors, transformers, welders).
Step 3: Breaking capacity
Icu must exceed the maximum short-circuit current at the installation point. For apartment panels: 4.5-6 kA. For main switchboards: 10-15 kA.
Step 4: Selectivity
The upstream breaker must be rated at least 1.6× the downstream one for current selectivity.
Frequently asked questions
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The site offers 21 free calculators: cable sizing, breakers, RCD, voltage drop and more.
The site offers 21 free calculators: cable sizing, breakers, RCD, voltage drop and more.
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In GorkyCAD Pro: plans, panels, calculations and a PDF set for free.
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