Electrical Metering for Linemen and Techicians


Single Phase 120V 2 Wire - FM2S (Alternate 1)


(Form 2S Meter)


Form 1S meters are not required as often as form 2S meters. This metering diagram allows the more popular form 2S meter to accurately meter a 120V 2 wire service. To make a form 2S 240V meter equivalent to a form 1S 120V meter, the meter socket must be re-wired. The form 2S meter has two half-current coils. These half-current coils can be wired in series, to create the equivalent full current coil contained in a form 1S meter. Next, the test link must be opened to allow access to the right end of the potential coil. The right end of the potential coil can then be connected to ground. Compensation has been added to the design of this meter to allow the 240V potential coil to be operated at only 120V while maintaining accuracy.

Key Points for Metering:

  1. Half-current coils should be wired in series by re-wiring the meter socket.
  2. Open the test link to gain access to the right end of the potential coil. Be certain you attach the ground wire to the appropriate screw on the back of the meter. Connecting to the wrong test link will create a dangerous short circuit when the meter is installed!

Common Mistakes:

  1. As stated above, this meter is designed to accurately operate at half voltage when connected in this configuration. Do not use other meters at other than their designated nameplate voltage.
  2. Installing the form 2S 240V meter in a meter socket wired for a form 1S meter will usually result in a loss of revenue. Revenue is lost when one of the current coils is inadvertently bypassed through an earth ground.