480V, 1-phase, 300W Heater length without casing for machines older than 1981 is L=945 Heater length without casing for machines yonger than 1981 is L= 1050.
Note, cooling system have roughly 200 times higher capacity than heater! To avoid condensation within the machine it's important that the heaters system is fully functional and switched on and the cooling system is switched off, when the machine is stand still or in turning gear.