Overloads required for heaters?

[Pitt123]

Are overloads required in a starter that is feeding a 3 phase heater? The heater is a 20kW heater. I dont think overloads are required since the heater load is a fixed resistance. I'm not sure what the NEC says about this.

In the starter there are 30A fuses and a #8 wire feeding the heaters. I'm guessing the heaters or cables dont need overload protection since the load is fixed. The 30A fuses then would provide short circuit protection for the branch circuit. Are the fuses alone adequeate protection?

I have a heater circuit that keeps tripping overloads (probably wrong size need to check). Instead of replaing overloads I was thinking about just removing them all together.

 

[jbelectric777]

Thermal overloads are for motors only, someone must be using the motor starter as a contactor. The heating units have their own thermal protection, just bypass the thermal overload relay which is normally closed and install jumper heaters also called dummies. Or just take it out like you said and go direct to the coil of the contactor part of the controller.

 

[Dennis Alwon]

I am assuming you have a 480 circuit here. Either way I don't believe overloads are necessary. The fuses will protect from short cir. or overload.

20000/830 = 24.1

24*1.25 = 30.
Not sure what the heater is but if it is a water heater then you could fuse up to 150% so 24*1.5 = 36 amps, so you could use a 40 amp breaker-- art. 422.11(E)(3). if you need to.

 

[kwired]

A resistive load is "fixed" and will not draw a different current amount unless the input voltage is changed. An overcurrent device on this type of circuit is not protecting the heater, it is protecting the conductors and devices feeding the heater.

A motor is entirely different. If you increase the amount of work being done the motor is going to try to do it. It will draw more current while trying to do so, along with the increased current comes increased heating in the motor windings which will deteriorate the insulation on the windings. If enough load is put on the motor that it stalls - that is when it will draw 'locked rotor current'.

With a motor circuit you have two types of protection. Branch circuit overcurrent devices protect the conductors and other devices just like in the heater circuit. Motor overload protection devices protect the motor from overload conditions but not from short circuits and ground faults.