Electrical Metering for Linemen and Techicians


Three Phase 3 Wire Delta 


(Form 12S Meter)


This type of configuration is the most appropriate service for customers that do not require 120V but do require 240V three phase service.  120V is not available because the customer does not have access to any of the X2 transformer bushings.  Therefore, 240V is the only voltage available for the customer and in the meter socket.

Key Points for Metering:

  1. Grounded phase (neutral) conductor must go through the center of the meter socket and must be connected to the bottom of the potential coils.
  2. Hot (240V) conductors must go through each current coil in the meter.


Common Mistakes:

  1. Don’t run the grounded phase (neutral) conductor through one of the current coils.  A parallel path through earth ground may inadvertently bypass the current coil with a portion of the current flow.  The result will be a partial loss of revenue!  See below:
  2. In addition to a loss of revenue, connecting the meter as shown below may set up a death trap!  Many electricians and linemen believe removing a meter will disconnect all sources of electrical energy from the service beyond the meter.  As shown below, a hot 240V conductor will still be providing energy through the meter socket even when the meter has been removed!


  3. The “L” shaped blade on the back of the meter provides a connection for the bottom of the both potential coils.  It can optionally be placed in the two positions shown below.  If the “L” shaped blade is not positioned correctly it will not make the appropriate connection to the lug in the meter socket.  Registration on the meter will be reduced to 50% for balanced load conditions.  For example, a consumer paying $500 per month for energy should be paying $1,000 per month.  The result will be an annual revenue loss of $6,000.

  4. The Form 12S meter is often miss-applied in a 4W Delta configuration.  Although it will meter three phase loads accurately.  Phase to ground loads will not be metered correctly.  In addition, a death trap will be created just as in example 2 listed above.  See below: