Греющий кабель является резистивной нагрузкой, но линии часто длинные, а дальний участок может недогревать при большом падении напряжения. Считайте реальную длину в одну сторону, мощность, напряжение и материал проводника.

Резюме

Check voltage drop from real one-way route length, not just heating-cable length.
For the same watts, 240V draws half the current of 120V and usually cuts percent drop sharply.
NEC 426, NEC 427, IEC 62395, GFCI/GFPE, and manufacturer listings must be checked together.
Voltage drop cannot compensate for insufficient watts per foot, missing insulation, or poor sensor placement.

Definitions That Matter on Heat-Trace Circuits

Heat trace is an electric heating cable or tape installed along pipe, valves, tanks, roofs, or gutters to replace heat lost to the environment.

Roof deicing cable is a fixed electric heating system that melts ice paths on eaves, gutters, downspouts, ramps, or slabs.

Voltage drop is the voltage lost in branch-circuit conductors because resistance rises with length, current, temperature, and conductor material.

Self-regulating heating cable is a heat-trace cable whose output changes with temperature, but its branch circuit still needs overcurrent, GFCI, manufacturer, and voltage-drop checks.

Design Workflow Before You Pull Cable

Step 1

Add every heating cable segment served by the branch circuit. A 120V, 960W roof-edge zone draws 8A; a 240V, 3,840W snow-melt zone draws 16A.

Step 2

Treat long-duration heating as a continuous-load planning problem unless the adopted code, controller sequence, and manufacturer instructions justify a different assumption.

Step 3

Measure panel-to-controller-to-junction-box routing one way. Include attic detours, roof transitions, downspout loops, maintenance disconnects, and weatherproof box offsets.

Step 4

Run voltage drop at the expected design current, then check the manufacturer minimum operating voltage for cold starts and long energized periods.

Step 5

Coordinate the electrical answer with heat-loss design. A larger conductor cannot fix too few watts per foot, poor insulation, missing sensor control, or a cable installed outside its listing.

NEC and IEC Checkpoints

NEC Article 426 covers fixed outdoor electric deicing and snow-melting equipment, and NEC Article 427 covers fixed electric heating equipment for pipelines and vessels. IEC projects commonly reference IEC 62395 for electrical resistance trace heating systems and IEC 60364 installation rules. For public background, see the National Electrical Code and the International Electrotechnical Commission .

NEC 426.28 and related GFPE rules are commonly encountered on outdoor deicing and snow-melting equipment.
NEC 427 work also needs pipeline/vessel heating cable listing, branch-circuit protection, and installation instructions from NEC 110.3(B).
IEC 62395 does not replace local cable-sizing, RCD, segregation, enclosure, and environmental requirements under IEC 60364 or national rules.

Worked Voltage-Drop Examples

The following examples are planning checks. Enter the final route, conductor, voltage, and load into the voltage-drop calculator before installation.

Circuit	Voltage-drop issue	Practical decision
120V pipe heat trace, 960W, 8A, 140 ft one-way	12 AWG Cu can land near 4.7% drop	Move to 10 AWG Cu, shorten the controller feed, or split the zone
240V roof deicing, 3,840W, 16A, 180 ft one-way	10 AWG Cu is roughly half the percent drop of a comparable 120V layout	Use 240V where product listing and control equipment allow it
208V commercial gutter zone, 2,496W, 12A, 220 ft one-way	Low system voltage makes long routes sensitive	Put the contactor panel closer to the roof junction boxes
400V IEC process pipe trace, 6 kW, 15A, 95 m one-way	Voltage drop may be acceptable while protective device and RCD selection still control	Coordinate IEC 62395 heating design with IEC 60364 cable sizing

Field Checklist

Confirm the heating cable listing, watts per foot or meter, maximum circuit length, and branch-circuit protection from the manufacturer.
Check NEC 426 or NEC 427 as applicable, plus GFCI/GFPE, wet-location boxes, bonding, disconnecting means, and controller listing instructions.
Use the actual one-way route length to the last junction point, not the visible length of heating cable alone.
For 120V circuits, review voltage drop early because the same wattage draws twice the current of a 240V circuit.
For IEC work, coordinate IEC 62395, IEC 60364 cable sizing, protective devices, RCD requirements, and local inspection practice.

Common Questions

Should heat trace voltage drop use breaker size or load current?

Use the installed heating load current for voltage drop, then confirm breaker, GFCI/GFPE, controller, and manufacturer maximum circuit length separately.

Why is 240V often better than 120V for long deicing runs?

For the same watts, 240V uses half the current of 120V. Lower current produces less voltage drop on the same conductor and route length.

Does self-regulating cable eliminate voltage-drop checks?

No. Self-regulating cable changes heat output with temperature, but the branch circuit still has conductor resistance, terminal limits, and manufacturer voltage limits.

Which code articles apply in the NEC?

NEC 426 is used for fixed outdoor electric deicing and snow-melting equipment, while NEC 427 covers fixed electric heating for pipelines and vessels.

What IEC references matter for heat tracing?

IEC 62395 addresses electrical resistance trace heating systems. IEC 60364 still controls installation wiring, protective devices, voltage drop practice, and local adaptations.

Рассчитайте цепь до монтажа

Пока место контроллера можно изменить, сравните 120V/240V, медь/алюминий и реальный маршрут.

Открыть калькулятор Continuous Load Voltage Drop

Падение напряжения для греющего кабеля и антиобледенения