Overload Relay Sizing for Star-Delta Starters
How to size a thermal overload relay for a star-delta starter using the FLC divided by √3 delta-leg current calculation.
8 min read
Technical
Sizing guides
Guides and notes on industrial electrical and automation parts: selection, wiring, settings and ordering.
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- Latest
MPCB Sizing for Star-Delta and Soft Starting
How to size an MPCB's thermal dial and magnetic trip for star-delta and soft-start motor circuits, including the 58% winding-current rule and soft-starter coordination.
10 min read
How to Size an RCBO for a Final Circuit
How to size an RCBO for a final circuit: matching In to design current and cable capacity, setting IΔn and type by load, and checking discrimination with the upstream device.
9 min read
VFD Sizing for Constant vs Variable Torque Loads
How to match a VFD's Normal Duty or Heavy Duty overload rating to constant-torque and variable-torque loads, with the sizing steps, overload-margin formula, and derating factors that keep a drive...
10 min read
Soft Starter for High-Inertia Loads: Sizing and Start Profile
How to size a soft starter for a high-inertia load: the torque-vs-voltage sizing trap, WK² acceleration time, current limit versus torque control, and AC-53a duty-rating checks.
11 min read
How to Size an MCB for a Circuit
How to size an MCB using the Ib ≤ In ≤ Iz coordination rule, curve matching, and breaking-capacity verification, with a worked example.
9 min read
How to Select and Size a Soft Starter for a Motor
How to size a soft starter correctly by full-load current, IEC 60947-4-2 duty class, starting torque against the load, control method, wiring topology and protection features.
10 min read
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