Umair Gaines
A wild leg in electricity is a term used to refer to a type of electrical service known as a high-leg delta or wild-leg delta. It is a three-phase power configuration where one of the phases, typically labelled as Phase B, has a higher voltage compared to the other two phases when measured to neutral. This phase with an elevated voltage is referred to as the high leg or wild leg. In a four-wire delta system, the voltage between any two phases is 240V, but the voltage between Phase B and the neutral point is 208V, making it the wild leg. This type of electrical service is commonly found in older manufacturing facilities and areas with ageing electrical infrastructure.
| Characteristics | Values |
|---|---|
| Type of electrical service | Four-wire delta (4WD) |
| Type of load | Three-phase delta service with a center-tap on one of the transformer windings to create a neutral for single-phase loads |
| Voltage | 240 volt, three-phase, three-wire delta service |
| Phase | B phase, also known as the "high leg" or "wild leg" |
| Voltage between phases | 240V |
| Voltage between phase and neutral point | 208V |
| Safety | Requires special markings or labeling to alert technicians and users of the increased voltage and the need for extra caution |
| Use case | Commonly used in older manufacturing facilities with mostly three-phase motor loads and some 120-volt single-phase lighting and plug loads |
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What You'll Learn
- The wild leg is also known as the high leg, stinger leg, bastard leg, etc
- It is a three-phase, 4-wire, delta-connected system
- It is usually identified as Phase B, but can be labelled as Phase C
- It is marked orange to alert users of the increased voltage and the need for caution
- It is supplied using 240 V line-to-line and 120 V line-to-neutral
The wild leg is also known as the high leg, stinger leg, bastard leg, etc
The "wild leg" is a term used to refer to a specific type of electrical system configuration known as a "high-leg delta". It is a three-phase power configuration where the centre point of one phase is grounded, resulting in three ungrounded phase conductors and a neutral. This configuration is commonly used in older manufacturing facilities with mostly three-phase motor loads and some single-phase lighting and plug loads.
The "wild leg" is also referred to as the "high leg", indicating that it has a higher voltage compared to the other phases. This higher voltage poses a greater safety risk if not handled properly, and electrical codes often require special markings or labelling to alert technicians and users. The term "wild leg" likely originated from the early days of electrical systems when this higher-voltage phase was considered more unpredictable or "wild".
The "wild leg" is also known as the "stinger leg", a term that may come from the potential danger of the high voltage. Additionally, it has been referred to as the "bastard leg", possibly due to the unconventional nature of having one phase with a higher voltage. These terms are used to distinguish this phase from the others and to indicate its unique characteristics and potential hazards.
The "wild leg" or "high leg" is usually labelled as "Phase B" to indicate its higher voltage. However, with the change in the 2008 NEC (National Electrical Code), it can now also be labelled as "Phase C" in certain situations, such as when metering is part of the switchboard or panel board. This change provides more flexibility in the system configuration while still ensuring proper identification and safety measures.
The "wild leg" configuration offers advantages such as providing a higher line-to-line voltage than typical three-phase services, while also offering a sufficient line-to-neutral voltage for connecting appliances and lighting. This dual capability allows for efficient power utilisation and can result in reduced current draw, requiring smaller wire and breaker sizes.
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It is a three-phase, 4-wire, delta-connected system
A wild leg in electricity is a term used to refer to a specific type of electrical system known as a three-phase, 4-wire, delta-connected system. This type of system is commonly used in older manufacturing facilities with mostly three-phase motor loads and some single-phase lighting and plug loads.
A three-phase, 4-wire, delta-connected system is characterised by its unique configuration of voltage sources and loads. It consists of three voltage sources connected together in a delta configuration, resembling the Greek letter delta (Δ). This setup offers greater reliability in the event of winding failure compared to other configurations like the "Y" or "star" configuration.
In a three-phase, 4-wire, delta-connected system, one of the transformer windings has a centre tap, creating a neutral connection for single-phase loads. This centre-tapped winding results in varying voltages between the phases and the neutral. Motors loads are typically connected to phases A, B, and C, while single-phase loads are connected to either phase A or C and to the neutral.
Phase B, also known as the “high leg” or "wild leg," is an important aspect of this system. It has a higher voltage to ground compared to the other phases. This high leg allows for the connection of appliances and lighting without requiring an additional step-down transformer. However, it is crucial to be aware of the higher voltage when connecting single-phase loads to avoid supplying excess voltage.
The three-phase, 4-wire, delta-connected system offers advantages such as higher line-to-line voltage than typical three-phase services and sufficient line-to-neutral voltage for connecting appliances. It provides improved efficiency by requiring smaller wire and breaker sizes. Additionally, this system exhibits unusual power factors when metering a 4-wire delta circuit with a resistive load, resulting in varying reactive power from phase to phase.
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It is usually identified as Phase B, but can be labelled as Phase C
In a 4-wire delta system, the three phases are connected in a triangle (delta) configuration. The voltage between any two phases is 240V. However, the voltage between one phase (usually labelled B) and the neutral point is 208V. This phase is referred to as the "high leg" or "wild leg".
The high-leg or phase with the higher voltage as measured to neutral has traditionally been designated “Phase B”. This is because, in a three-phase transformer, the three phases, plus a neutral, are connected as a centre-tap on one of the windings. The phase-to-neutral voltage of two of the phases will be half of the phase-to-phase voltage.
However, a change to the 2008 NEC now allows the high leg of a four-wire three-phase delta service to be labelled as the “C” phase instead of the “B” phase. The NEC Code requires that the high leg be identified by an orange colour (it was often referred to as a red-leg delta) or by other effective means and is usually the “B” phase. But, to accommodate utility meter configurations, the high leg is permitted to be the “C” phase where metering is part of the switchboard or panel board.
The "wild" label serves as a visual reminder of the increased voltage and the need for extra caution. The term "wild" likely originated from the early days of electrical systems when the higher voltage phase was considered more unpredictable or "unruly".
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It is marked orange to alert users of the increased voltage and the need for caution
In a 4-wire delta system, the three phases are connected in a triangle (delta) configuration. The voltage between any two phases is 240V. However, the voltage between one phase (usually labelled B) and the neutral point is 208V. This phase is referred to as the "high leg" or "wild leg". The higher voltage of the B phase can pose a safety risk if not handled properly.
The term "wild" likely originated from the early days of electrical systems when the higher voltage phase was considered more unpredictable or "unruly". Electrical codes often require special markings or labelling for the wild leg to alert technicians and users. The "wild" label serves as a visual reminder of the increased voltage and the need for extra caution.
The "high leg" in electrical systems has been referred to as the wild leg, the stinger leg, the bastard leg, and so on. The NEC uses the terms 4-wire, delta-connected systems, or the simple term, high leg. The high leg or phase with the higher voltage as measured to neutral has traditionally been designated "Phase B".
A change to the 2008 NEC now allows the high leg of a four-wire three-phase delta service to be labelled as the "C" phase instead of the "B" phase. The NEC Code requires that the high leg be identified by an orange colour (it was often referred to as a red-leg delta) or by other effective means and is usually the "B" phase. Therefore, it is marked orange to alert users of the increased voltage and the need for caution.
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It is supplied using 240 V line-to-line and 120 V line-to-neutral
A wild leg, also known as a high leg, is a type of electrical service connection for three-phase electric power installations. It is used when both single and three-phase power is supplied from a three-phase transformer or transformer bank.
The three-phase power is connected in a delta configuration, and the centre point of one phase is grounded. This creates both a split-phase single-phase supply (L1 or L2 to neutral) and three-phase (L1-L2-L3).
In a 240 V line-to-line and 120 V line-to-neutral system, the line-to-line voltage magnitudes are all the same. The line-to-neutral voltage of two of the phases will be half of the line-to-line voltage. The remaining line-to-neutral voltage will be greater than the line-to-line voltage.
For example, if A-B, B-C, and C-A are all 240 volts, then A-N and C-N will be 120 volts, but B-N will be 208 volts. This is because the winding between the A and C phases is centre-tapped.
A high-leg delta service provides a higher line-to-line voltage than the usual 208 V that most three-phase services have. It also provides a sufficient line-to-neutral voltage for connecting appliances and lighting. This means that large pieces of equipment will draw less current than with 208 V, requiring smaller wire and breaker sizes. Lights and appliances requiring 120 V can be connected to phases A and C without requiring an additional step-down transformer.
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Frequently asked questions
A wild leg, also known as a high leg, stinger leg, or bastard leg, is a type of three-phase power configuration where one of the phases has a higher voltage than the others. This phase is typically labelled as "Phase B" or "the B phase" and has a voltage of 208V compared to the other phases' 120V.
A three-phase power configuration is a type of electrical power transmission where three conductors carry three separate alternating currents with a phase difference of one-third of a cycle between them. This allows for a more stable and efficient power supply than a single-phase power configuration.
In a wild leg configuration, the three phases are connected in a triangle (delta) configuration. The voltage between any two phases is typically 240V. However, the voltage between one phase (usually Phase B) and the neutral point is higher, at 208V. This higher voltage phase is referred to as the wild leg or high leg.
Wild leg configurations are commonly used in older manufacturing facilities with mostly three-phase motor loads and some 120-volt single-phase lighting and plug loads. They can also be used in residential and commercial settings with older electrical infrastructure. Wild leg configurations provide a higher line-to-line voltage than typical three-phase services, while also providing a sufficient line-to-neutral voltage for connecting appliances and lighting.
