I have a 36 KW infrared heater 240 Volts has 3 hot lines,what size the portable generator I need and amps also?

**Our answers**

*Answer by Frank*

That sounds like a GIANT heater. it would take 15 amps of 240v if 36kw is the electrical wattage. You would probably want a 5000w generator.

*Answer by billrussell42*

You need a 40 kW or 50 kW generator.

this is 150 amps. You will need a plug and socket rated at that current (and I don’t know of any) and wire rated at 150 amps, such as #3 AWG.

.

**We encourage our readers to submit their feedback**

{ 3 comments… read them below or add one }

Hard to believe there are so many different answers given. I’ll base mine on US practice.

If you truly have a 240V 3-phase load (3 hots, no neutral), then the load amperage is calculated as follows:

I = 36kW/0.24kV/sqrt(3)=86.6A=87A

For resistance heat, minimum conductor size (ampacity) is 125%, or 125% x 87A = 109A. Select wire with 90degC insulation but apply it at its 75degC ampacity. Select 2 AWG, type THWN-2 or THW-2 (for wet or dry locations) or optionally THHN (for dry locations only).

Your circuit breaker should be loaded to 80% maximum (=109A). The next standard size up is 110A. Select 110A breaker (or fuses).

Resistive loads do not have a significant starting kVA, unlike motors. But it is a good idea not to load generators up to 100%. Limit it to 80%. Then the minimum generator size is:

36kW/80% = 45kW

Be careful when selecting a generator. Generators are rated in both kW and kVA, using an 80% power factor, where the kVA = kW/PF = 45kW/.80 = 56.25 kVA. So the minimum size generator should be rated:

56kVA/45kW (or larger).

If you are running the generator in stand-alone mode, then you will need to ground either the common point of a wye output (240/138V generator), or the midpoint of one winding of a delta output (240/120V generator).

=====

Note: Since this is a purely resistive device, you can choose to power it from a 208V generator. The power will decrease with the square of the voltage, to a new value of:

P=36kW x (208/240)^2 = 27kW

This would require a 208V generator (probably configured 208/120V) with a minimum power rating of:

42kVA/34kW

Load is 27kw/.208kV/sqrt(3)=75A

Wire ampacity = 75Ax125%=94A

select 3 AWG, same types as above

Breaker or fuses: 94A minimum, select next size up: 100A

You will need a 45 kVa 230 volt 3-phase generator. Amperes = 46000/230(0.8)(1.732}

If you really need 36KW in three phase load, you’re out of the ‘portable’ class.

You’d need a pick-up or trailer to move it around.

You’re looking for about 90A. at 240 three phase delta.

That’s a pretty rare configuration though, (rural, industrial).

Are you sure you’re reading the nameplate right?

You’d have a 100A. load at the more noraml 208V. 3 Phase.

Unless the unit ‘comes on’ in stages, you’d need at least a 50KVA

M/G set to handle the ‘start’ surge.

Careful. An infra-red heater that big requires a lot of clearance

from ‘combustibles’ and personnel for safe operation.