Available in several sizes and voltage ranges, RoMan grounding reactors can be used with any resistance welding transformer, regardless of make, model, or age.

The grounding reactor is used where direct grounding of the welding circuit is not practical to protect the operator from electrical shock hazard, caused by capacitive coupling or insulation failure between primary and secondary coils of the welding transformer. Typical applications are portable welding gun installations, transgun installations for robots or series welding and push-pull welding circuits in multispot welders. The AWS publication ANSI/ASC Z49.1-1983 entitled "Safety in Welding and Cutting" lists under paragraph 12.4.6 the grounding reactor as the recommended safety device for these applications.

Rating
The grounding reactor is designed for an operating voltage which will be equal to or higher than the maximum secondary voltage of the welding transformer and a ground conductor size which must be equal to or larger than required by the National Electric Code. Series RGR24/4 grounding reactors have an operating voltage of 24 volts maximum at 60 Hertz and a ground conductor size of No. 4 AWG copper wire.

Construction
The grounding reactor consists of a center tapped coil installed on a magnetic core which is placed in a sheet metal enclosure and fully potted with an epoxy resin. This construction prevents damage to the insulation from contaminants such as oil, water, weld spatter etc. and protects the device from mechanical damage.

Electrically, the lead ends of the grounding reactor coil are connected to the secondary terminals of the welding transformer and the center tap lead is connected to ground. Under normal conditions the impedance of the grounding reactor limits the flow of ground loop circulating currents but provides a ground path for capacitive charges of the secondary. In case of an insulation failure between the primary windings and the secondary of the welding transformer, the secondary assumes an electrical potential to ground or in more common terms, becomes electrically "live". The resultant current flows in both parts of the center tapped coil which "buck" each other creating a low impedance path to ground and causing the primary protection device to open.

Selection Table

In multi-spot welding systems, equal weld currents are expected in the two weld circuits powered by one multi-spot transformer. For this reason, impedance balanced transformers are used and the designer of welding tools exercises great care to make the geometry of the two welding circuit identical. Regardless of these efforts, unbalances in weld currents of 10% and above exist due to uncontrollable differences between the welding circuits and deterioration of welding loop components causing unacceptable weld quality. The weld current equalizer balances the weld currents by transformer action. Other applications of the weld current equalizer are to balance the weld currents between two welding circuits operated by two single secondary transformers and to use the device as a weld current splitter to power two weld circuits from one welding transformer having a single secondary. Typical equalizer connections are shown on drawing R1959.

The advantages of the weld current equalizer are:

• Eliminates equalization of currents by trial and error
• Compensates for deterioration of welding loop componen
• Easy to install on new or existing machines
• No adjustments required
  
• No regular maintenance
• Rugged device

Rating
The curves on the rating graph represent the maximum unbalance of weld currents expressed in percent (%), which the weld current equalizers can balance as a function of the maximum secondary voltage available from the welding transformer. The process of determining the required rating is shown in the following examples.

Example 1

• Maximum Secondary Voltage 7.5 Volts
• Welding Current in Loop 1 15,500 A
• Welding Current in Loop 2 14,000 A
• Unbalance 15,500-14,000 = 1,500 A
• % Unbalance 1,500 / 14,000 X 100 = 10.7%*
• From Rating Curve: Use RWE 7/15
  

Example 2

• Maximum Secondary Voltage 11.5 Volts
• Welding Current in Loop 1 16,200 A
• Welding Current in Loop 2 18,400 A
• Unbalance 18,400-16,200 = 2,200 A
• % Unbalance 2,200 / 16,200 X 100 = 13.6%*
• From Rating Curve: Use RWE 12/15
  

*The percent unbalance must be based on the lower weld current representing 100%

Rating Graph

Selection Table