When on-site maintenance personnel replace a sheathed electric heater, a common problem is that after the new unit is connected to the same power supply, its heating rate differs from the original, and the shell temperature may even be higher. In most cases, the cause is not the heater itself, but the failure to check three parameters item by item: rated voltage, grounding, and carbon deposit condition. The following is presented in an order that can be followed on site.
The rated voltage of a sheathed electric heater must match the on-site supply voltage; 220V and 380V must not be mixed. Before wiring, confirm that the circuit voltage, circuit breaker capacity, and cable cross-section match, and ensure that the metal sheath is reliably grounded, with grounding resistance meeting on-site electrical safety requirements. For parts that need to wrap objects of irregular shape, flexible sheathed units can be installed closely, but the bending radius should not be too small, so as to avoid stress deformation of the internal resistance wire.
This model can be configured with power according to installation space and medium conditions, with common single-unit power ranging from 0.5kW to 3kW. When power density is high and heat dissipation is insufficient, the sheath surface temperature will rise quickly. During installation, the heating section should be fully immersed in the medium or tightly attached to the heated body to avoid local dry burning; when used for pipeline tracing, heat-conducting measures should preferably be added between the sheath and the pipe wall to reduce the thermal resistance caused by air gaps.
For heaters used for a long time in heat transfer oil or other organic media, a carbon deposit layer will gradually form on the sheath surface. The carbon deposit layer has poor thermal conductivity and will hinder heat transfer outward, causing the internal resistance wire temperature to rise and accelerating insulation aging. On site, the degree of carbon deposition can be judged by observing the surface color and measuring changes in no-load current; if necessary, shut down and clean, avoiding scratching the sheath during cleaning.
Measure cold insulation resistance before commissioning, and during operation regularly check whether the wiring terminals are loose and whether the sheath is deformed or leaking. During shutdown, keep the junction box dry to prevent moisture intrusion from affecting insulation. When replacing spare parts, recheck the above parameters item by item to reduce repeated shutdowns.
