Electrical Resistance Calculator — Ohms (Ω)

Methodology

The electrical resistance (R, in ohms) of a cartridge heater is needed to select the diameter of the internal heating wire, verify the consistency between voltage, current and power, and diagnose the element's condition in the field using an ohmmeter.

The three formulas derived from Ohm's Law

• R = V / I — from supply voltage (V) and measured current (A)
• R = V² / P — from voltage (V) and rated power (W)
• R = P / I² — from power (W) and current (A)

Where: V = supply voltage (V), I = current (A), P = rated power (W), R = electrical resistance (Ω).

Relation to cartridge heater manufacturing

In production, the R value is used to calculate the required length of heating wire using the formula R = ρ × L / A, where ρ is the resistivity of the material (NiCr80/20 or similar), L is the wire length and A its cross-sectional area. Every cartridge heater manufactured by Maxiwatt is bench-tested before dispatch.

Worked example

Cartridge heater rated 500 W at 230 V:

1. By voltage and power: R = V² / P = 230² / 500 = 52,900 / 500 = 105.8 Ω
2. Verification by current: I = P / V = 500 / 230 = 2.17 A → R = V / I = 230 / 2.17 = 105.9 Ω ✓

In three-phase heaters, the resistance per phase depends on the wiring configuration (delta or star). In star connection R_phase = R_total / 3; in delta connection R_phase = R_total × 3.