How to Wire 120V & 208V – 1 & 3-Phase Main Panel? 3-Φ Load Center Wiring

Electrical Technology

Wiring Installation of Single Phase & Three Phase, 120V & 208V Circuits & Breakers in Main Service Panel

In the USA, 208V single phase and three phase voltage is one of the standard voltage levels used for commercial applications. It can be derived from Wye-Wye (Star to Star), Delta-Wye or High leg delta configuration of primary and secondary windings of the transformer.

In this post, we will consider the Wye-Wye connection for the single phase and three phase 208V and additionally 120V single phase distribution panel wiring. The other type of connection will be discussed in upcoming posts.

Generally, the electric power supply providers install three transformers to obtain 208V and 120V supply voltage levels. The primary side of these three step-down transformers are connected to the 7.2kV supply. The transformers then reduce the level of voltage to the desired 208V and 120V applicable to the commercial buildings and industrial installations.

In this kind of setup, the following different levels of voltage are available from the commercial transformers.

208V Three Phase, 3 Wires (Three Hot wires + Ground wire)
208V Single Phase, 2 Wires (Two Hot wires + Ground wire)
120V Single Phase, 2 Wires (One Hot wire + Neutral wire + Ground Wire)

These are the general setup and may vary (i.e. the further wiring depends on the appliance requirement) e.g. neutral wire may be needed in both single phase and three phase 208V circuits as shown in the fig below.

The three phase power from the secondary of the distribution transformer via insulated wires enters the meter box and safety switch and finally enters in the main distribution panel. Each line or hot wire connects to a separate bus-bar in the panel box for further distribution. Three poles, two poles and single pole circuit breakers can be snapped (i.e. metal tracks hold the CB tightly) over three busbars which draw hot from each busbar.

In 120V and 208V, 1-Phase & 3-Phase wiring systems, the available voltage levels are as follows inside the main breaker panel.

Voltage between three hot wires (hot 1, hot 2 & hot 3) = 208V Three Phase
Voltage between any two hot wires = 208V Single Phase
Voltage between any hot wire and Neutral = 120V Single Phase.

Almost all the panel boxes designed for Wye and Delta by different manufacturers are the same i.e. there are hot busbars for three pole breakers and a separate busbar for Neutral and Ground. Keep in mind that all the 208V-120V panels have the neutral wire especially in Wye configuration except if there is no need to use 120V single phase system or special kind of three phase motors (such as wastewater pump) which does not need a neutral wire.

In addition, there are some cases in delta connection where neutral is not needed. Except this, ground is needed in almost all the configurations (either Delta or Wye), no matter if neutral wire is needed in the wiring or not applicable to the circuits.

Related Post: How to Wire 277V & 480V, 1-Phase & 3-Phase, Commercial Main Service Panel?

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Let’s see how to wire 208V and 120V single phase and three phase breakers and load points as follows.

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How to Wire 208V Three Phase Circuits & Breakers?

The following tutorial shows how to wire 208V three phase breaker box installation in commercial or applicable residential apartments.

As shown in the fig, a three pole circuit breaker is connected to three hot busbars i.e. (three lines or hot wires). The outgoing three hot wires from the 3-Pole MCB circuit breaker, ground (as well as neutral if needed) is connected to the three phase load such as 208V three phase motor.

If allowed by local codes, you may use three single pole circuit breakers for three phase 208V circuits if all of them are connected to separate hot busbars and the main switches of all CBs are connected together (one switch must Switch ON/OFF all the breakers at once). We have shown this case in the above fig.

In three phase 208V appliances, you may need four or five wires where three wires are as Hot and the rest are ground and neutral. For instance, you may connect 4-poles, 4 wires, non-grounding outlets such as 18-15R, 18-20R, 18-30R, 18-50R, 18-60R, L18-20R, L18-30R etc. These outlets can be connected without neutral wires. Same is the case for AG208C3 Surge protectors and you may follow the same wiring connection i.e. four wires without neutral. In some cases, grounded neutral is needed. Refer to the user manual for proper connection.

On the other hand, 5-poles, 5 wires, grounding outlet can be connected to all three hot wires and neutral + ground wires such as L21-20R and L21-30R etc.

How to Wire 208V Single Phase Circuits & Breakers?

The following tutorial shows how to wire 208V single phase breaker box installation for commercial uses.

As shown in the fig, connect a two pole circuit breaker to any two hot busbars i.e. (Hot 1 & Hot 2, or Hot 2 & Hot 3 or Hot 3 & Hot 1). The outgoing two hot wires from the 2-Pole circuit breaker, ground (as well as neutral if needed) is connected to the single phase load such as 208V water heater.

There is a specific case where you can use three pole circuit breakers for 208V single phase circuits and loads. To do so, simply connect the two hot output wires of the CB and connect to the load point. Connect the neutral as well if needed. This way, a three pole circuit breaker will power up a single phase 208V circuit as shown in the fig above.

Good to know: It is a good practice to keep the system in all three phase systems as much as balanced for reliable operation of the transformers. If only three poles breakers are installed in the three phase breaker box, it is easy to manage the unbalanced system, but the situation is complex if all three poles, two pole and single pole breakers are installed.

For instance, a single phase 120V breaker will consume very low power as compared to the three phase water heater circuit. This way, one of the transformers will supply more power as compared to the rest of two transformers.

Similarly, if most of the breakers are installed on the same busbar, the same problem of an unbalanced system will occur. Whereas, the management try their best to maintain the balance load and same amperes flow on each hot wire for reliable operation of the power generation plant and distribution grid system.

In case of voltage imbalance, the common point in Wye connection (known as neutral which carries the resultant current) is properly grounded (earthing system). This is because loads are not practically balanced as compared to ideal cases. In addition, The size of the neutral wire is less than the three hot wires (refer to the local area codes for more details).

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How to Wire 120V Single Phase Circuits & Breakers in 208V Panel?

The following tutorial shows how to wire 120V single phase breaker box installation in case of 208V three phase panel box for residential application such as lighting or ceiling fan etc.

As shown in the fig below, connect a a single pole circuit breaker to any hot busbars i.e. (Hot 1, Hot 2 or Hot 3). The outgoing hot wire from the 1-Pole circuit breaker, neutral and ground wire is connected to the single phase load such as 120V outlet, light bulb or ceiling fan etc.

Keep in mind that in some cases, you may use a three pole breaker for single phase 120V if you only pull out a single hot wire from the breaker output and connect the neutral wire from the neutral busbar to the load point. This must be according to the connected device amperage capacity.

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How to Wire 120V & 208V, 1-Phase & 3-Phase Load?

The following fig shows the all three possible wiring connections in 208V three phase configuration.

A 208V three phase motor is connected to all three hot busbars plus neutral and ground wires.
A 208V single phase water heater is connected to hot 1 and hot 2 plus ground wire.
An 120V single phase standard outlet is connected to hot 1, neutral and ground wires.
A 208V three phase, 20A, L21-20R outlet is connected to all three hot wires plus ground and neutral wires.

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Wiring Color Codes for 208V:

In this tutorial, we have used different wire colors for illustration purposes only. Please follow the National Electric Codes i.e. NEC wiring color codes or other local area color codes.

For 208V single phase and three phase circuits, we have used the NEC + general practice wiring color codes as follows.

Black = Hot 1 or Line 1
Red = Hot 2 or Line 2
Blue = Hot 3 or Line 3
White = Neutral Wire
Green = Bare Conductor as Ground wire

The recommended colors for hot wires in a 208V three phase system are Black, Red and blue for three hot wires. If a white wire has been used in 208V for hot wire which carries voltage, it must be covered with a black strip or a tap wrapped around it. This way, it can be easily identified as hot wire which is used as hot wire, and not as a neutral wire.

Do not use green, green with yellow stripe or a bare conductor for wires carrying voltage. Only and only use copper wire to reduce the resistance and heat instead of aluminum wires in the main panel box wiring.

Disconnect the power source (and make sure it is really swathed OFF) before servicing, repairing or installing electrical equipment. To do so, switch off the main switch in the main panel box.
Never stand or touch wet and metal parts while repairing or installation.
Read carefully all the cautions and instructions and follow them strictly while doing this tutorial or any other work in practical related to electrical works.
Always, use the right size cable and wire, proper size outlets and switch and suitable size of circuit breakers. You may also use the Wire and Cable size calculator to find the right gauge size.
Never ever try to play with electricity (as it is dangerous and can be fatal) without proper guidance and care. Do the installation and repairing work in presence of experienced persons having vast knowledge and good practice who knows how to deal with electricity.
Doing your own electrical work is dangerous as well as illegal in some cases. Contact the licensed electrician or the electric power supply provider before practicing any change/modification in electrical wiring connections.
The author will not be liable for any losses, injuries, or damages from the display or use of this information or if you try any circuit in the wrong format. So please! Be careful because it’s all about electricity and electricity is too dangerous.