3-phase 4-wire systems have 3 hot wires and a neutral wire. This could be a 480/277 volt system, or a 120/208 volt system. In the case of a 480/277 volt system, if you measure from any hot wire any other hot wire you will measure 480 volts and if you measure from any hot wire to neutral you will get 277 volts. Metering of these systems can be done with any of our EKM Omnimeters. For metering 3-phase 4-wire systems above 480VAC you will need to use the Omnimeter HV v.5, which is capable of metering such systems up to 600VAC.
The images and diagrams shown here are in no way exhaustive. These are just a few examples of how you might set up a metering system, and are simply intend to show what is possible. These are the options that you might consider for your metering setup:
- Do I want to read the meter(s) locally with computer or do I want a cloud based solution (EKM Push).
- What diameter and amperage rating will I need for the Current Transformers? You will need three CTs for your 3-phase 4-wire electrical system.
- Do I need to go wireless?
- Do I have a need to daisy chain multiple Omnimeters together? This allows you to connect multiple Omnimeters in series, which can then be connected to a single communication device.
The answers to these questions should help you narrow down your options and allow you to select the products that you will need for your particular application.
For a 3-phase 4-wire system you will need to use 3 CTs. You will have 3 hot wires (usually black or red) and a neutral wire (usually white). Depending on which wires you measure between you will get different voltages. If for example you have a 120/208 3-phase 4-wire system and you measure the voltage between any of 3 hot wires you will get 208 volts, when you measure from any hot to neutral you will get 120 volts.
- Turn off power to the sub-panel.
- Mark one of the hot wires as L1 and mark the another hot line as L2 and mark the last hot wire as L3. You can pick these wires randomly.
- Connect the L1 hot line voltage reference wire to port 7 on the Omnimeter, connect the L2 hot line voltage reference wire to port 8 on the Omnimeter, connect the L3 hot line voltage reference wire to port 9 on the Omnimeter, and connect the Neutral line voltage reference wire to port 10 on the Omnimeter.
- Connect the CT1 so that the L1 hot wire passes though it and the arrow on the CT points towards the load. Connect the CT2 so that the L2 hot wire passes though it and the arrow on the CT points towards the load. Connect the CT3 so that the L3 hot wire passes though it and the arrow on the CT points towards the load.
- Connect the CT1 black wire will go to port 1 on the Omnimeter and the CT1 white wire will go to port 2 on the Omnimeter. Connect the CT2 black wire will go to port 3 on the Omnimeter and the CT2 white wire will go to port 4 on the Omnimeter. Connect the CT3 black wire will go to port 5 on the Omnimeter and the CT3 white wire will go to port 6 on the Omnimeter.
This video tutorial provides an example of how to install an Omnimeter Pulse v.4 on a 120/240v electrical system. You can use this video to infer how a three phase, four wire installation might go. The only absolute difference for this type of electrical system is that there will be three CTs and three voltage reference wires:
See this model for reference of how to properly connect an Omnimeter to a 3-phase 4-wire system: