How to Wire a Three-Phase Meter?

How to Wire a Three-Phase Meter? . Wiring a three-phase meter is an essential task for ensuring the proper functioning of large electrical systems. This guide will provide a step-by-step walkthrough for safely and effectively wiring a three-phase meter, emphasizing safety, accuracy, and compliance with electrical standards.

Understanding Three-Phase Power

Three-phase power is the backbone of industrial and commercial electrical systems. Unlike single-phase systems, three-phase power distributes electricity across three alternating currents, providing consistent energy delivery.

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Key Components:

• Three live wires (L1, L2, L3): Carry the alternating currents.
• Neutral wire (N): Balances the load.
• Earth wire (E): Provides grounding for safety.

Advantages:

• Greater efficiency in power distribution.
• Supports higher loads.
• Reduces energy losses in long-distance transmission.

What Is a Three-Phase Meter?

A three-phase meter measures electricity consumption in three-phase systems, crucial for accurate billing and system monitoring.

Types:

1. Electromechanical Meters: Traditional, analog meters using rotating disks.
2. Digital Meters: Modern, precise devices with features like remote monitoring and data logging.

Three Phase Meter Wiring for 400V AC – (UK & EU) – IEC

In UK, EU, Asia and IEC following countries, the three phase supply of 400V AC is provided by four wires systems (Three number of Phases (Lines) & Neutral) from the Three Phase 400/230V Transformer to the meter box and further to the main distribution board in the residential buildings.

Tools and Materials Needed

Before starting, gather the necessary tools and materials:

• Screwdrivers (flathead and Phillips)
• Wire strippers and cutters
• Insulated gloves and goggles
• Circuit tester
• Electrical connectors
• Insulating tape
• Multimeter for testing voltage and current

Step-by-Step Guide to Wiring

1. Preparation

1. Turn off the power supply at the main circuit breaker.
2. Obtain and review the wiring diagram specific to your three-phase meter model.
3. Confirm that all tools are functioning properly.

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2. Identifying Terminals

Three-phase meters typically have clearly labeled terminals:

• Input terminals: For incoming power (L1, L2, L3, N, and E).
• Output terminals: To connect to the load or consumer system.

3. Connecting the Input Wires

1. Strip the insulation from the ends of the three-phase wires.
2. Connect L1, L2, and L3 to their respective input terminals, ensuring secure and tight connections.
3. Attach the neutral wire (N) to its designated terminal.
4. Ground the system by connecting the earth wire (E).

4. Securing the Output Wires

1. Repeat the process for output terminals.
2. Ensure that the phase sequence matches the input.

5. Finalizing and Testing

1. Double-check all connections for tightness and correctness.
2. Use a multimeter to test for proper voltage and continuity.
3. Restore the power and observe the meter for any irregularities.

Installation of Three Phase kWh Meter (3-Phase, 4 Wires, 400V AC Energy Meter)

1. First of all, make sure to disconnect the main power before working on electrical installations.
2. Starting from the left side for MAIN, connect the first incoming (from transformer) Phase (Line) wire to the 1st slot on the meter (Main).
3. Connect the second incoming phase wire in the 3rd slot
4. Connect the third incoming phase wire in the 5th slot.
5. Connect the incoming Neutral (N) wire to the 7th slot on the meter.
6. On the Load side, connect the Outgoing Neutral in the 8th slot.
7. Now connect the remaining outgoing three phase wires in the 2nd, 4th and 6th slots respectively and connect them to the distribution board as shown in the fig.

Below is the basic connection diagram for installation of a three-Phase, 4-Wires, Wye-400V) kWh meter (Digital or Analog Energy Meter) from the 400VAC supply to the main distribution board in home.

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Common Wiring Configurations

Star Configuration

• Neutral wire is present, ideal for systems requiring a mix of single and three-phase loads.
• Connections: L1, L2, L3, N, and E.

Delta Configuration

• No neutral wire, suitable for high-power equipment.
• Connections: L1, L2, L3, and E.

Testing and Commissioning

After wiring, follow these steps:

1. Power on the system and verify meter readings.
2. Check for phase sequence correctness using a phase sequence meter.
3. Monitor for unexpected voltage drops or surges.

Read More : Why Three-Phase Power Systems Are More Efficient Than Single-Phase

Requirement for 400V, 3-Phase Meter Installation

• You must contact and inform the electricity providers before any kind of service installation/modification or wiring a meter.
• You must use single core PVC & double insulated cables for all phases.
• Use proper marking for all phase cables such as “L1”, “L2”, “L3” and “N” respectively.
• 900mm clearance space in width should be provided in case of electric meters and Low voltage panels and switchgears with a rating of +100 Amps.
• Use minimum of 4mm² (stranded copper wire) between the consumer unit and electric meter or based on the load ampacity.
• The meter tails (cables used to connect your meter to the cut out o or main breaker) should be double insulated in size of 25mm and properly terminated in to the meter slots.
• The meter tails should be the shortest possible, or at least, the length of meter tails from the cut-out through the metering equipment to the consumer unit) should always be no more than 3 meters of cable (more on BS7671 Reg. 434.2.1).
• You will have to contact a licensed electrician to connect wires from the distribution board to the electric meter. The electricity will be provided later by power service providers by showing them the BS7671 certificate signed by your electrician.
• The meter box must be installed on the external side of the wall which can be easily accessible from the front and unlikely to be damaged.
• There should not be a gas meter, telephone and other utility equipment above or below the electric meter box.
• The meter cabinet (surface mounted or flush mounted) approved by UK power networks can be used based on the proper guidelines and codes.

An 38 mm hockey stick (performed tube) with the meter cabinet must be installed according to the following minimum specifications.

• Meter cabinet from the ground level: 600 mm Min &1100 mm Max
• Meter tails: 25mm
• Clearance from front of cabinet: Min 1000 mm
• Hockey stick (preformed tube): 38 mm ( min 1450mm high &  310mm long) and 500 mm minimum depth in garden.
• Cable access hole: 20/30 mm

The overall three phase meter wiring (IEC Color Coded) from the utility power supply to the main distribution board will look like this.

Read More : Three-Phase Electrical Power

Common Mistakes to Avoid

• Misidentifying wires: Always label wires clearly during the preparation phase.
• Loose connections: Double-check terminal screws to prevent sparking or overheating.
• Ignoring safety: Never bypass safety protocols to save time.

Maintenance Tips for Longevity

• Conduct routine inspections to identify loose connections or signs of wear.
• Clean terminals and surrounding areas to prevent dust accumulation.
• Recalibrate digital meters periodically to maintain accuracy.

Legal and Compliance Aspects

• Adhere to national and local electrical standards, such as IEC codes or NEC guidelines.
• Schedule inspections to ensure compliance and avoid penalties.

Three-Phase Meter Wiring for Different Level of Voltages – US – NEC

The story is totally different in the North America as compared to the UK, EU and the rest of the world. For example, the single phase and three phase voltage levels in the US – NEC are different as compared to the IEC following countries such as the level of common single phase voltages are 120V, 240V. Additionally, both single phase and three phase voltages levels of 120V, 208V, 240V, 277V & 480V are available from the 7200V utility pole mounted transformer.

The level of three phase voltages in the US are as follow:

• 240V, Three Phase, 4 Wires (High Leg Delta) Between Three Hot (Line) wires and Ground.
• 208V, Three Phase, 4 Wires – Between Three Hot (Line) wires and Ground.
• 480V, Three Phase, 4-5 Wires – Between Three Hot (Line) Wires + Neutral and Ground.
• 600V, Three Phase, 4 Wires – Between Three Hot (Line) Wires + Ground.

In the following sections, we will show how to wire an electric meter for 240V, three phase, and 208V three phase & 480V three phase & 600V Three Phase according to NEC.

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How to Wire 120V & 208V – (Wye) 1-Φ & 3-Φ Electric Meter?

Let’s see how to wire a 3-phase, 4 wires, 120V & 208V AC energy meter.

1. First of all, make sure to disconnect the main power supply before working on electrical installations.
2. Connect the three incoming Lines (L1, L2 & L3) from the transformer as “HOT” wire to the top lugs (Black, Red & Blue Colors).
3. Connect the three outgoing Lines (L1, L2 & L3) as “HOT” wire (to the load side) from the bottom lugs to the load center or panel box main breaker (Black, Red & Blue Colors).
4. You may connect the neutral to the left center lug labeled as (G & N) if needed according to the design. Just connect the load side Lines (Hot wires) and Neutral wires to the main breaker box.
5. Connect the ground wire to the small lug (located left to the Line number 3). If there is no Neutral in the terminal box, the ground is still connected to this point.
6. You may use minimum #10AWG (Copper) or #8 AWG (Aluminum) for the 120V circuits (see details below).
7. #4 AWG (American Wire Gauge) copper wire is suggested for the ground (protective earth) connection.
8. Now carefully install and fix the meter in the meter box (i.e. 7 meter prongs to 7 jaws in the meter box cabinet).

From this configuration of service lines, the following 1-P & 3-P voltages are available as follow.

Three Phase:

• 208V – Three Phase, 4-Wires (3 Hot Wires + Ground)

Single Phase:

• 208V – Single Phase, 3-Wires (2 Hot Wires + Ground Wires)
• 120V – Single Phase, 3-Wires (2 Hot Wires + Neutral + Ground)

Note: If the Neutral Wire is not available in the meter box, then Only 208V available. If there is Neutral Wires, then both 120V & 208V are available to the panel box i.e.

• Neutral Available: Both 208V & 120V is available
• Neutral Not Available: Only 208V is available

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Precaution: If lines are not properly connected to the meter cabinet, or meter prongs are not tightly fixed in the lugs, it will not read the kWh reading and you may not be able to do electric bill calculations based on energy consumption. Additionally the wrong connection of the meter may trip the breaker or may cause a flash, damage to the meter or even serious injury with hazardous fire.

Read More : Maintenance of Transformer

How to Wire 120V, 208V & 240V (High Leg Delta) for 3-Φ & 1-Φ Electric Meter?

Let’s see how to wire a 1-phase & 3-phase, 4 wires or 3 wires, 120V, 208V & 240V AC electricity meter.

1. First of all, make sure to disconnect the main power supply before working on electrical installations.
2. Connect the three incoming Lines (L1, L2 & L3) from the transformer as “HOT” wire to the top lugs (Blue, Black & Orange Colors). Keep in mind that the 3rd line (as Line 3) on the right in orange color is Power leg (Wild Leg) or High Leg Delta and should be connected to terminals on right of Neutral prong.
3. Connect the three outgoing Lines (L1, L2 & L3) as “HOT” wire (to the load side) from the bottom terminals to the load center or panel box main breaker (Blue, Black & Orange).
4. You may connect the neutral to the left center terminal labeled as (G & N) as Neutral is available in high leg delta for 208V single phase.
5. Now connect the load side Lines (Hot wires) and Neutral wires to the main breaker box.
6. Connect the ground wire to the small terminal (located left to the Line number 3). If there is no Neutral in the terminal box, the ground is still connected to this point.
7. You may use minimum #10AWG (Copper) or #8 AWG (Aluminum) for the 120V circuits (see details below).
8. #4 AWG (American Wire Gauge) copper wire is suggested for the ground (protective earth) connection.
9. Now carefully stab and fix the meter with a strong push and restore the power to verify everything is well and working properly. Done.

From this configuration of service lines, the following 1-P & 3-P voltages are available as follow.

Three Phase:

• 240V – Three Phase, 4-Wires (3 Hot Wires (including the High Leg Delta) + Ground)

Single Phase:

• 208V – Single Phase, 3-Wires (1 Hot Wire (Must be High Leg Delta) + Neutral + Ground Wire)
• 240V – Single Phase, 3-Wires (2 Hot Wires + Ground)
• 120V – Single Phase, 3-Wires (1 Hot Wire + Neutral + Ground)

Note: If the Neutral Wire is not available in the meter box, then 208V single phase is not available. If there is a Neutral Wires, then 120V, 208V & 240V are available to the panel box i.e.

• Neutral Available: 208V Single Phase is also Available
• Neutral Not Available: Only 120V & 240V is Available

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How to Wire 277V & 480V – (Wye) 1-Phase & 3-Phase Meter?

Let’s see how to wire a 1-phase & 3-phase, 5 – wires or 4 wires, 277V & 480V energy meter.

1. First of all, make sure to disconnect the main power supply before working on electrical installations.
2. Connect the three incoming Lines (L1, L2 & L3) from the transformer as “HOT” wires to the top terminals (Brown, Orange & Yellow Colors).
3. Connect the three outgoing Lines (L1, L2 & L3) as “HOT” wire (to the load side) from the bottom terminals to the load center or panel box main breaker (Brown, Orange & Yellow).
4. You may connect the neutral to the left center terminal labeled as (G & N).
5. Now connect the load side Lines (Hot wires) and Neutral wire in Gray color to the main breaker box.
6. Connect the ground wire to the small terminal (located left to the Line number 3). If there is no Neutral in the terminal box, the ground is still connected to this point.
7. You may use minimum #10AWG (Copper) or #8 AWG (Aluminum) for the 120V circuits (see details below).
8. #4 AWG (American Wire Gauge) copper wire is suggested for the ground (protective earth) connection.
9. Now carefully stab and fix the meter with a strong push and restore the power to verify everything is well and working properly. Done.

From this configuration of service lines, the following 1-P & 3-P voltages are available as follow.

Read More : Difference Between Single Phase and Three Phase Transformer

Three Phase:

• 480V – Three Phase, 4-5 Wires (3 Hot Wires + Neutral (If needed) + Ground)

Single Phase:

• 480V – Single Phase, 3-Wires (2 Hot Wires + Ground Wire)
• 277V – Single Phase, 3-Wires (1 Hot Wires + Neutral + Ground)

Note: If the Neutral Wire is not available in the meter box, then 277V single phase is not available. If there is a Neutral Wires, then 277V & 480V are available to the panel box i.e.

• Neutral Available: 277V Single Phase is also Available
• Neutral Not Available: Only 480V (1-P & 3-P) is Available

How to Wire 600V / 347V – (Wye) & 480V – Delta 3-Phase Meter?

The following fig shows the wiring for two configurations as follows.

480V Delta Metering (Left Side)

This is only three phase meter wiring i.e. no neutral and single phase system included. There are 5 jaws in the meter cabinet without Neutral but ground is still connected according to the NEC.

347V / 600V – Wye Metering (Right Side)

This meter wiring diagram is the same as for 277V & 480V (1-P & 3-P). There are 7 Jaws i.e. Neutral is included for single phase supply of 347V.

• Three Phase: 600 Volts, 3-Phase across three hot lines + ground wire.
• Single Phase: 347 Volts, 1-Phase across One Hot wire + neutral + ground.

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FAQs

1. What is the purpose of a three-phase meter?

A three-phase meter measures electricity usage in three-phase systems, ensuring accurate billing and monitoring.

2. Can I wire a three-phase meter myself?

While possible for experienced individuals, it is advisable to hire a licensed electrician to ensure safety and compliance.

3. What happens if the phase sequence is incorrect?

Incorrect phase sequencing can lead to equipment malfunction or damage.

4. How do I identify the input and output terminals?

Refer to the wiring diagram provided with the meter, as terminals are usually labeled.

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