Thermolec Application &Technical Notes - Manual (Page 7)

THREE EASY STEPS
STEP 1 - (continued)
Power and Voltage Requirements
Nominal and Standard Supply Voltages
While a utility's voltage may be referred to by means of a nominal figure, actual applied voltage may vary
over a fairly wide range depending on factors like the system's power distribution lines, and many others.
For instance, a nominal voltage of 575V / 3PH / 60Hz may variously be called 550V, 575V or 600V
depending more on what the specification writer is accustomed to calling it than on the actual voltage
supplied to the heater. Designing a heater for 550V when in fact 600V is supplied to it will result in almost
10% more current and 20% more KW capacity since current is proportional to the voltage and KW is
proportional to the square of the voltage. Conversely, application of a lower voltage results in a
corresponding under-performance of the heater. It is therefore of the utmost importance to ensure that
the correct voltage is specified.
For safety reasons Thermolec standard supply voltages have been chosen to be the highest for each
voltage range, as shown in the table below. Heaters designed for lower voltages in each range are
available and will be supplied when customer expressly specifies a lower supply voltage.
STANDARD VOLTAGES
This standardization reduces the risk of overheating due to a heater subjected to an overvoltage with the
resulting nuisance tripping of high-temperature cut-outs.
Examples of risk:
Example 1:
A 575V/3 PH heater in a 600V/3PH installation would carry 5% more current and produce 10% more KW
than it is designed for.
Example 2:
A 220V/1 PH heater in a 240V/1PH installation would carry 10% more current and produce 20% more
KW than it is designed for.
Under such conditions, these heaters would overheat and thermal cut-outs would trip.
In order to avoid any risk of overheating, it would be advisable to verify the existing conditions
on the job site.
In case of doubt about the required voltage, always specify one of the Thermolec Standard Voltages.
Common 110 230 318 440 550
Nominal 115 208 220 240 277 332 380 416 460 575
Voltages 120 347 480 600
Thermolec
Standard 120 208 208 220 240 240 277 347 380 380 416 416 480 480 600 600
Voltages 1 Ph 1 Ph 3 Ph 1 Ph 1 Ph 3 Ph 1 Ph 1 Ph 1 Ph 3 Ph 1 Ph 3 Ph 1 Ph 3 Ph 1 Ph 3 Ph