Category: Wiring Diagrams

The form 12s meter can be one of the more confusing meter forms out there. So, here I want to provide a form 12s meter wiring diagram in two different configurations. One is the 120/208 network service.  The other form 12s meter wiring diagram is the form 12s meter in a delta service.

Form 12s Meter Wiring Diagram Network Service

The form 12s meter can be used with the network service. The network service comes from taking two legs off of a three phase wye transformer and using the neutral. So, if you measure voltage from each phase to ground you should get 120v. Also, if you measure voltage from phase to phase you should get 208v.

This service is typically found in businesses that are located in a downtown area or businesses that are located in an industrial park. The reason for this is that many of these businesses do not require a full three phase service. So, the utility will pull two legs and a neutral off of the nearest wye transformer and call it a day.

Looking at the diagram you notice that there are two yellow terminals. These are either or terminals. Meaning that you connect the wire to one or the other in the meter socket. Also, some meter sockets do not come with this 5th terminal pre-installed. You have to purchase a 5th terminal separately and install it yourself.

With some form 2s meter sockets there are provisions to install a 5th terminal. The form 12s is also known as a self-contained meter. This means that the meter is installed in series with the load. Pulling the meter will also turn off the power.

Form 12s Meter Delta Wiring Diagram

For the form 12s delta wiring diagram we are going to talk about the service. This is the diagram for using a 12s with a delta service. Note that this is a three phase service. If you notice there is no difference in how it is actually wired. I used different colors here to denote the difference but it is actually physically wired the same way.

This could be a 120v, 240, or 480v delta service. My recommendation, as always, is against using a self-contained meter for voltages above 240v however. In the center of this diagram following the blue wire again this is an either or connection. You can connect the wire to the left center terminal or the bottom center terminal. Also note that the stab on the back of the meter is interchangeable.

Since this is a three phase service when measuring voltage across any of the three phases you should get the same voltage.

As always remember that the colors in the diagram are for illustration purposes only. You should always use the colors your utility uses.

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.

Voltages

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.

By far the most commonly used meter in the United States is the form 2s meter. Here is a form 2s meter wiring diagram. I also want to offer some notes about the form 2s service here.

Where is the Form 2s Meter Installed

Being the most popular meter out there it comes as no surprise that the form 2s meter is installed on both residences and businesses. It comes in both regular Kwh only format and is available with a demand register as well. Regardless the meter socket for the form 2s meter is wired the same way.

The Form 2s Meter Wiring Diagram

Ok, now that we know where the form 2s meter is installed let’s take a look at the form 2s meter wiring diagram. Notice that the form 2s meter is what is known as a self-contained meter form. This means that the meter is in series with the load. So, when the meter is pulled out of the meter socket the power to the service will go off. Of course, this happens so long as there is not a bypass meter base installed.

Alright, the power comes in from the utility on the line side of the meter base which is the top side. There are two terminals that the two phase wires will attach to. These terminals connect to the jaws that hold the meter in the socket. The next thing that you notice is the neutral wire. The neutral connects to a lug that is normally but not always in the center of the meter socket. Continuing on we see the ground connection. Most meter sockets now contain terminals specifically for the ground wire. This wire is connected to a driven ground rod.

On the bottom side of the meter socket we have the load side terminals. This is where you connect the wires that go into the house and connect to the panel. Notice that you also have both phase wires and a neutral.

I also want to make note of the colors in this diagram. The colors were chosen so they show up on the diagram. Always be sure to follow local and national codes with regard to wire color codes.

Voltages

The most common voltage for this type of service is 120/240. This means that if you check the voltage between the two phase wires you should get 240v. And if you check the voltage from each phase to ground or neutral you should get 120v. If you are having problems with the voltage on this service check out this post on flickering and dimming lights to help you with troubleshooting.

One of the questions that I often get is about how to wire a form 9s meter and how to do a load check. Since I get this question so often I thought I would put up a form 9s meter wiring diagram. Here it is with comments about the form 9s meter wiring diagram below.

About the Form 9s Meter Wiring Diagram

The form 9s meter is one of the most commonly used meter forms. So, as you begin to study the wiring diagram I want to make note of a few things. First is that the colors that I chose were chosen at random. That is because there is no universally accepted color code. You need to make sure that when you are doing the wiring that you adhere to your utilities color code.

If you do not have a color code then create one. You can use the colors above with some important changes. If you use colors that are the same you need to make sure you have a way to tell the difference between them. One way to do this is to use a red wire for one and a red wire with a black or white tracer for the other. This helps with troubleshooting especially down the road.

Remember that the form 9s is typically used to meter a 4 wire wye service. If you notice you have phases 1, 2, and 3 labeled as well as the neutral. You will also connect the metering equipment back to ground.

Wire Groups

So, what are the different wires? When wiring a form 9s meter you can think about the different wires in groups. You have phase groups and you have voltage a current groups. This means that each phase will have two wires. The voltage wire connects directly to the service wire in this example. The current wire connects to X1 on the CT.

Follow the black lines. The smaller black line connects to the voltage terminal in the form 9s meter socket and the thicker black line comes from the CT and connects to the current terminal. These make up one phase.

Remember that with the CT’s you need to make sure that the polarity marking or “dot” as it is often called needs to point back towards the Line. Remember dot to pot.