5.3 NEMA Arc Welding Power Source Classifications
The National Electrical Manufacturers Association (NEMA) has classified electric arc welding machines primarily by duty cycle. Duty cycle is “the length of time that a welding machine can be used continually at its rated output in any ten (10) minute period.” The classification of electric arc welding machines is as follows:
|
5.3.1 Arc Welding Power Source Specifications
An arc welding machine is described and specified by the following:
The power requirements are called the rated load voltage or welding voltage. For Class I and II power sources under a 500A rating, the rated load voltage is calculated as follows:
Voltage (E) = 20 + 0.04 × rated amperes.
As an example, using a Class I machine with an output current rating of 300A, the rated load voltage would be:
Voltage= 20 + 0.04 × 300 = 20 + 12 = 32V
The welding rated output current rating for this welding machine is 300A at 32V. For welding machines with output currents above 600A, the rated load voltage used is 44 volts.
- Rated output current rating.
- Power requirements.
- Duty cycle.
The power requirements are called the rated load voltage or welding voltage. For Class I and II power sources under a 500A rating, the rated load voltage is calculated as follows:
Voltage (E) = 20 + 0.04 × rated amperes.
As an example, using a Class I machine with an output current rating of 300A, the rated load voltage would be:
Voltage= 20 + 0.04 × 300 = 20 + 12 = 32V
The welding rated output current rating for this welding machine is 300A at 32V. For welding machines with output currents above 600A, the rated load voltage used is 44 volts.
Electrical power input requirements for NEMA Class I and II transformer arc welders are as follows:
The electrical power input requirements for a NEMA Class III transformer is at 60Hz, 230V.
Most welding machines are not required to operate 100% of the time. If they are used to weld one hundred percent of the time, a machine with a 100% duty cycle would be required. Work must be loaded and unloaded, and electrodes must be changed. Metal must be chipped, cleaned, and inspected. The duty cycle normally recommended for manual welding is 60%. Automatic and semiautomatic welding operations usually require 100% duty cycles. Light duty work, such as that done in the home hobby shop, could possibly be done using a machine with a duty cycle as low as 20%. When purchasing a welding machine, the maximum duty cycle requirement must be considered.
If an arc machine is used at lower than rated current outputs, the duty cycle may be increased under certain conditions. A graph supplied by the manufacturer will indicate how the duty cycle can vary with a given current setting. Figure 5-30 is an example of a graph showing welding amperage and duty cycle.
- 50Hz (cycles)—220V, 380V, and 440V.
- 60Hz (cycles)—200V, 230V, 460V, and 575V.
The electrical power input requirements for a NEMA Class III transformer is at 60Hz, 230V.
Most welding machines are not required to operate 100% of the time. If they are used to weld one hundred percent of the time, a machine with a 100% duty cycle would be required. Work must be loaded and unloaded, and electrodes must be changed. Metal must be chipped, cleaned, and inspected. The duty cycle normally recommended for manual welding is 60%. Automatic and semiautomatic welding operations usually require 100% duty cycles. Light duty work, such as that done in the home hobby shop, could possibly be done using a machine with a duty cycle as low as 20%. When purchasing a welding machine, the maximum duty cycle requirement must be considered.
If an arc machine is used at lower than rated current outputs, the duty cycle may be increased under certain conditions. A graph supplied by the manufacturer will indicate how the duty cycle can vary with a given current setting. Figure 5-30 is an example of a graph showing welding amperage and duty cycle.