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

installation of single-phase wiring & 3 phase, 120v & 208v & circuits circuit breakers in main service panel

in the usa In the US, 208V single and three phase voltage is one of the standard voltage levels used for commercial applications. can be derived from the star-star (star-to-star), delta-wye, or high branch delta configuration of the primary and secondary windings of the transformer.

In this post, we will consider star-star connection for 208v single phase and 3 phase distribution panel wiring and additionally 120v single phase. the other type of connection will be discussed in future posts.

Reading: How to connect 208v single phase

Electric power providers typically install three transformers to achieve 208v and 120v supply voltage levels. The primary side of these three step-down transformers is connected to the 7.2 kv supply. the transformers then step down the voltage level to the desired 208v and 120v applicable to commercial buildings and industrial facilities.

In this type of configuration, the following different voltage levels are available on commercial transformers.

  • 208v three-phase, 4 wires (three live wires + ground wire)
  • 208v single-phase, 3 wires (two live wires + ground wire)
  • 120v simple phase, 3 wires (one live wire + neutral wire + earth wire)

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This is the general configuration and may vary (ie additional wiring depends on appliance requirements), e.g. A neutral wire may be required on both single and three phase 208v circuits as shown in the figure below.

Three-phase power from the secondary of the distribution transformer through insulated cables enters the meter box and safety switch and finally enters the main distribution panel. each live line or cable connects to a separate busbar in the panel box for further distribution. Three pole, two pole and one pole circuit breakers can be slotted (i.e. metal tracks hold the cb firmly) over three busbars drawing heat from each busbar.

in 120v and 208v, single phase & For three phase wiring systems, the available voltage levels are as follows inside the main breaker panel.

  • voltage between three active wires (active 1, active 2 and active 3) = 208 v three-phase
  • voltage between two active wires = 208 v single-phase
  • voltage between any hot and neutral wires = 120v single phase.

Almost all panel boxes designed for star and delta by different manufacturers are the same, i.e. there are live busbars for 3-pole breakers and a separate busbar for neutral and ground. note that all 208v-120v panels have the neutral wire, especially in the star configuration, except if it is not necessary to use a 120v single phase system or a special type of 3 phase motors (such as a sewage pump) that you don’t need a neutral wire.

also, there are some cases in delta connection where neutral is not needed. except this, grounding is needed in almost all configurations (whether delta or star), regardless of whether a neutral wire is needed in wiring or not applied to circuits.

  • related post: how to connect 277v & 480v, single phase & 3-phase commercial main service panel?

click on the image to enlarge

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

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Let’s see how to wire 208v and 120v single and three phase switches and charging points as follows.

how to wire 208v & breakers?

The following tutorial shows how to wire a 208v 3 phase breaker box installation in applicable commercial or residential apartments.

As shown in the figure, a three-pole circuit breaker is connected to three live busbars, i.e. (three live lines or cables). the three hot wires outgoing from the 3 pole mcb breaker, ground (as well as neutral if needed) connect to the 3 phase load, such as a 208v 3 phase motor.

if local codes allow, you can use three single pole breakers for 208v 3 phase circuits if they are all connected to separate hot busses and main breakers for all cbs are connected together (one breaker must be on/off all switches at once). we have shown this case in the previous figure.

On 208v 3 phase appliances you may need four or five wires, where three wires are so hot and the rest are ground and neutral. For example, you can connect 4-pole, 4-wire, ungrounded 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. the same goes for ag208c3 surge protectors and you can follow the same wiring connection, ie four wires with no neutral. in some cases, a grounded neutral is needed. consult the user manual for proper connection.

on the other hand, 5 poles, 5 wires, the ground can be connected to the three hot wires and neutral + ground wires like l21-20r and l21-30r, etc.

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how to wire 208v & breakers?

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

As shown in the figure, connect a two-pole circuit breaker to either of the two live busbars, i.e. (live 1 and live 2, live 2 and live 3, or live 3 and live 1). the two hot wires coming out of the 2 pole breaker, ground (as well as neutral if needed) connect to the single phase load, such as a 208v water heater.

There is a specific case where three-pole circuit breakers can be used for 208v single-phase circuits and loads. To do so, simply connect the two output hot wires from the cb and plug them into the charging point. connect the neutral also if necessary. in this way, a three pole circuit breaker will feed a 208v single phase circuit as shown in the figure above.

Good to Know: It is good practice to keep the system on all three-phase systems as balanced as possible for reliable operation of the transformers. If only 3-pole breakers are installed in the 3-phase breaker box, it is easy to manage the unbalanced system, but the situation is complex if 3-pole, 2-pole and 1-pole breakers are installed.

for example, a 120v single phase breaker will draw very little power compared to a 3 phase water heater circuit. in this way, one of the transformers will supply more power with respect to the rest of the two transformers.

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Similarly, if most of the breakers are installed on the same busbar, the same problem of an unbalanced system will occur. while management makes every effort to maintain load balance and equal amp draw on each live wire for reliable operation of the power generation plant and distribution network system.

In the event of a voltage imbalance, the common point in the star connection (known as the neutral that carries the resulting current) is properly grounded (system grounding). this is because the loads are not nearly balanced compared to the ideal cases. also, the neutral wire size is smaller than the three live wires (see local area codes for details).

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how to wire 120v & 208v panel breakers?

The following tutorial shows how to wire a 120v single phase breaker box installation to a 208v three phase panel box for residential applications such as lighting or ceiling fan etc.

As shown in the figure below, connect a single pole circuit breaker to any active busbar i.e. (Active 1, Active 2 or Active 3). 1 pole breaker outgoing hot wire, neutral and ground wire is connected to single phase load such as 120v outlet, light bulb or ceiling fan etc.

Note that in some cases you can use a 3 pole breaker for 120v single phase if you only pull a single hot wire from the breaker output and connect the neutral wire from the neutral bus to the load point. this should be according to the amperage capacity of the connected device.

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how to wire 120v & 208v, single phase & three-phase load?

The following figure shows the three possible wiring connections in a 208v three-phase configuration.

  • a 208v 3-phase motor is connected to the three live bus bars plus the neutral and ground wires.
  • a 208v single-phase water heater is connected to the hot 1 and hot connections 2 plus the ground wire.
  • a standard 120v single phase outlet is connected to the hot 1, neutral and ground wires.
  • a 208v 20a 3 phase outlet l21- 20r is connected to the three live wires plus ground and neutral wires.

click on the image to enlarge

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

208v wiring color codes:

In this tutorial, we have used different colors of wires for illustration purposes only. follow national electrical codes i.e. nec wiring color codes or other local area color codes.

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

  • black = active 1 or line 1
  • red = active 2 or line 2
  • blue = active 3 or line 3
  • white = neutral wire
  • green = bare conductor as ground wire

Recommended colors for live wires on a 208v 3-phase system are black, red, and blue for three live wires. If white wire has been used on 208v for hot wire carrying voltage, it should be covered with a black strip or tap wrapped around it. this way it can be easily identified as a live wire being used as a live wire and not a neutral wire.

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Do not use green, green with yellow stripes, or bare conductors for live wires. use only copper wire to reduce resistance and heat instead of aluminum wire in main panel box wiring.

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safety precautions

  • Disconnect the power supply (and make sure it is completely clean) before servicing, repairing, or installing electrical equipment. to do so, turn off the main switch at the main panel box.
  • never stand or touch wet or metal parts during repair or installation.
  • carefully read all precautions and instructions and strictly follow them while performing this tutorial or any other practical work related to electrical work.
  • Always use the correct size wire and cable, the correct size plugs and switches, and the correct size circuit breakers. You can also use the Wire and Cable Size Calculator to find the correct gauge size.
  • Never attempt to play with electricity (as it is dangerous and can be fatal) without proper guidance and care. perform installation and repair work in the presence of experienced people with extensive knowledge and good practices who know how to handle electricity.
  • Doing your own electrical work is dangerous and in some cases illegal. contact your licensed electrician or power supply supplier before making any changes/modifications to electrical wiring connections.
  • the author will not be responsible for any loss, injury, or damage from viewing or use of this information or if you test any circuit in the wrong format. so please! be careful because it’s all about electricity and electricity is too dangerous.

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