Space Heater For Electrical Motor

What is Space Heater in a Motor And Electric Panels?

A motor space heater, also known as an anti-condensation heater, is a device to heat a small area such as electrical panels, switch gears, and motors.

It’s an electrical heater with low energy but enough to heat the space around it.

Space heaters are powered by electrical energy but not the same source as the panel or the motor to heat space. This is because space heaters for motors or panels work while the panel or electrical motor is off.

Why space heaters Are being used in electrical motors?

electrical short circuit damaged an electrical generator
The electric generator burnt out due to moisture

The space heater for the motor keeps the temperature above the ambient dew point at a motor-off time.

The heater works to prevent condensation from forming in the motor which can cause motor windings damage.

In my work site, humidity and moisture are very high, In many cases, we face electric motors and generators winding burn out. Of course, these motors and generators have no space heater.

Humidity decreases the winding resistance causing it to break down. The result is, as you know, an internal short circuit between windings.

Motors insulation and electrical components of electrical panels and switch gears could get damaged and short-circuited because of high humidity and water condensation.

In the case of generators in my workplace, the windings are totally burnout and the fire catches all other generator’s parts.

Unfortunately, some generators continue running while the fire continues catching everything it can. The result is obvious, a totally destroyed electrical generator.

Working principle of motor space heater

A space heater is a simple heater, that usually works on a single-phase AC power source. It consists of a resistive coil that produces heat when an electric current passes through it.

It’s simply just like the electrical water heater in our houses. It’s connected to a simple control circuit to work in times the panel or the motor is stopped for any reason.

Usually, space heaters are connected to the motor starter. But keep in mind that space heaters need power while the motor is out of service.

So, its power supply is not the same as the motor. This is clear, in case of the motor main power source is disconnected, the space heater power should not be disconnected too.

Safety tip for working with anti-condensation heater

As mentioned above the heater has its own power source. i.e its power is not the same source as the panel or the motor.

This makes it tricky when you need to electrically isolate the panel for maintenance or inspection. You should pay attention to the right isolation of the heater.

Don’t just isolate the panel power source main circuit breaker.

Once I isolated a medium-voltage panel. The panel has a space heater, I didn’t realize that the space heater has a separate power source.

The situation was very risky for those who are working on the panel. You know what! my boss was working on the panel and he got shocked. Fortunately, he let the wire go very quickly.

Don’t worry, he was so kind to me and didn’t punish me. But, the most important thing is the lesson I learned, and I’m letting you know it now. Take care, your boss may not be kind to you.

Motor Space Heater Voltage Drop

In many cases, the motor power source and starter are located away from the motor itself. As the space heater voltage is usually 220V or 110V, this distance may cause some voltage drop in the space heater.

The question is what will happen? Will the space heater voltage drop affect its efficiency?

The answer is, the space heater voltage drop will of course affect its heating ability. But it still working. It will need a longer time to heat the space of the motor or the panel.

It’s a heater, not a motor. I mean it has no starting current. It will work on any voltage. But you should check its user guide data and make sure to keep this voltage within allowable limits.

Motor anti-condensation heater resistance calculation

Motor anti-condensation heater resistance is just like any other resistive load. You can measure it with a multimeter. The value varies from one to one.

The motor or the panel nameplate should tell you the motor’s anti-condensation heater resistance. If the value is not on the nameplate, then you will find the voltage and the power of the heater.

As the heater has no power factor, then you can calculate its resistance by applying the formula

R = V2 / P


  • R is the space heater resistance.
  • V is the space heater operating voltage.
  • P is the power in watts.


If the motor space heater is 500 watts and its voltage is 110 V then its resistance is 1102/500 = 24.2 Ohm

Do all Motors and Panels Have a Space Heater?

It’s not necessary to find a space heater inside every single motor and electrical panel you meet.

It depends on the design and needs. Also, small motors don’t have enough space to get a heater inside them.

If you are responsible for designing or purchasing a new motor or panel, make sure to order a proper space heater if the humidity is high in the workplace.

Space heaters are in larger-size motors and medium voltage panels. But you should be careful and check the wiring diagram of the motor and the panel.

Also, the nameplate should tell you if there is a space heater.