01Calculate the change before discussing compatibility
For an approximately constant resistance with unchanged connections, use P₂ = P₁ × (U₂ / U₁)² as a preliminary estimate. Compare voltage at the same location in both cases: line-to-line supply voltage, for example, or the voltage across the same element.
Resistance changes with temperature. The calculation below illustrates the effect of voltage; it does not approve the element, terminal assembly, control panel or protective devices for a different supply.
02What happens to a nominal 30kW load?
| Nameplate and supply | Constant-resistance estimate | Process consequence |
|---|---|---|
| 400V, 30kW → 480V | 30 × (480/400)² = 43.2kW | About 44% more power; heated-surface watt density also rises |
| 480V, 30kW → 400V | 30 × (400/480)² ≈ 20.8kW | About 69.4% of rated power; the original temperature rise or flow duty may not be met |
| 380V, 30kW → 400V | 30 × (400/380)² ≈ 33.2kW | Even a smaller change needs a check against the permitted operating range |
03Line voltage is not necessarily element voltage
In a balanced wye-connected load, branch voltage is line voltage divided by √3. In delta, branch voltage equals line voltage. A branch may contain series-connected elements, so its voltage is not necessarily the voltage across one element.
Use the complete wiring diagram. Six terminals and the position of a few links do not establish all internal connections. Changing between wye and delta changes the load and is not a general-purpose way to convert every heater to another voltage.
04Review more than the heating elements
The control supply, contactor coils, SCR controller, fuses, cables and motors each have ratings. Compatibility of the heating load with another voltage and compatibility of a pump or fan with another frequency are separate checks.
Send the supplier the unit and element nameplates, wiring diagram, actual voltage and frequency, and panel component list. Ask for the permitted supply, revised kW and current, required component changes and an updated drawing. Wiring and measurements belong with qualified electrical personnel using the appropriate isolation procedures.
↗Sources and scope
References support the design principles discussed here. Product-specific limits must come from the selected equipment and fluid documentation. Illustrative values are not purchase specifications.