Form 4s Meter Wiring Diagram

The form 4s meter is the meter form used to meter single phase three wire services. Below is the form 4s meter wiring diagram. As always remember that there is no standard on colors in the metering field. So, always use your company standard as far as the color code goes. The colors here are chosen at random so they show up in the drawing.

Form 4s Meter Wiring Diagram

For the form 4s meter wiring diagram let’s start at the bottom. Notice that we are going to be metering a single-phase three-wire service. We have two phase wires and a neutral. Make note that this is the same type of service that you find on most homes. The only difference is that it is larger. Homes are typically metered with a 200 amp meter base. Furthermore, anything above that normally requires CT’s.

Ok, so we have two phases. Using Blondel’s Theorem we know that since we have three wires we are going to need two CT’s. However, each CT is installed on a different phase. Remember that the orientation of the CT’s are important. The polarity marking needs to face back towards the line side or the transformer. Hence the old adage, “dot to the pot.”

Going up the diagram from the CT’s we have wires X1 and X2 on each CT. It is also important to note that X1 is connected to the meter socket terminals labeled “current in,” and X2 is connected back to the neutral. Wire these backwards and the meter will not register correctly.

Staying in the CT circuit we go to the current return terminals. These wires connect back to the neutral to create a return path for the current.


After tracing out all of the current wires we trace out the voltage wires. Notice that in this case the voltage wires connect directly to the service wires. If we were using PT’s in this service we would connect the voltage wires to the PTs.

What voltage should you expect in this service? You should expect to see a voltage of 240v between each phase. Also from each phase to ground or neutral you should expect to see 120v. Now there are some odd 480v services out there that use this service so be aware.

Where do we normally see the form 4s?

The form 4s meter is a transformer rated, also known as a CT meter, and is typically installed on large residences who have 400 amp or larger services.

It is also found on large businesses with the same requirements. Also, it can also be found on temporary services. These can include saw services or temporary trailers for schools.

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  1. Would it be advisable to fuse the voltage tap that feeds the 4S meter?
    and in a 120/240v installation, what current should I select >

    • Some utilities fuse their metering equipment installations others do not. There is no reason not to but I would say that generally most utilities do not use fuses. If you are going to use fuses then it depends on what size wire you are using. If you are using #12 then you would want to use 20 amp fuses.

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