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is High Leg Delta E-mail: geno03245w@gmail.com |
| Use only 600 volt wire. Lamp cord, extension cords are not rated 600 volt. Use copper wire only. Aluminum wire is fire risk and should be avoided or installed by professional. 30 amp breaker use 10 gauge / 120-240 volt 30 amp outlet can be installed on 30 amp breaker only/ use 10 gauge wire ... cannot be connected to 15-20-40 amp breaker.  Orange/ #10 gauge wire, with ground ... 30 amp capacity. Safe maximum: 30 x 80% = 24 amps. Buy: 10-2 gauge/ 30 amp 10-3/ 30 amp Southwire electric tools |
Yellow
12 gauge 20 amp 120 volt 20 amp outlet can be installed on 20 amp breaker, but not 15 amp breaker/ use 12 ga wire. ... cannot be connected to 30-40 amp breaker. 1  Yellow/ #12 gauge wire, with ground ... 20 amp capacity. Safe maximum 16 amps. Buy: 12-2 gauge/ 20 amp 12-3/ 20 amp NMB is house wiring UF is underground Rolls of stranded wire HOOK UP Wires |
White
14 gauge 15 amp 120 volt 15 amp outlet, AFCI, GFCI, timer, switch etc can be installed on 15 or 20 amp breaker. Never connect 15 gauge wire to 20-30-40 amp breaker.  White/ #14 gauge wire, with ground ... 15 amp capacity. Safe maximum 12 amps. Buy: 14-2 gauge/ 15 amp 14-3/ 15 amp NMB is house wiring UF is underground |
| 50-60
amp breaker use 6 gauge / 240 volt 50 outlet can be installed on 50 amp breaker only  Buy: 6-2 wire Southwire electric tools NMB is house wiring UF is underground |
40-50
amp breaker use 8 gauge / 240 volt 40 amp outlet can be installed on 40 or 50 amp breaker only  Buy: 8-2 wire Southwire electric tools NMB is house wiring UF is underground |
  Copper ground wire. Every device, load, metal enclosure etc must be grounded. Ground wire must be continuous throughout installation, never switched on-off, never used as a Neutral wire. Generally ... use same size as other wire in circuit Buy: 12 gauge copper ground wire Ground wire Green ground wire Ground pigtails Ground rods/ ground clamps at Amazon |
 Non metallic flexible cables must carry ground wire, but do not have hazard of short circuit causing injury from shock. Armored steel cable can be used as a grounded connection, and will protect wires from damage. Metal can be energized from an insulation failure. All conduit ...metal, plastic ... flexible and rigid ... must be attached to structure, and attached to enclosures, boxes. Movement, damage and deterioration are major cause of electrical failure. Buy: Non-metallic flexible conduit Power whip Armored cable Southwire armored cable cutter Pull boxes |
 Electrical tools must be insulated. Always best to disconnect power, but insulation failure, lack of proper grounding, grounded neutral, lack of GFCI, out-of-code wiring, generator operating without transfer switch, and other problems still pose a risk to anyone working on electric power ... even when breaker is off. Buy: Electrician tools kits KLEIN TOOLS Tools kits IRWIN tools KNIPEX Telephone cable knife Low Voltage Mounting Bracket for Telephone |
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 Multimeters Voltage is tested across two separate wires. Ohms or resistance is tested across both ends of same wire. Amperage is tested along one or two points on same wire. Buy: Analog multimeter Multimeters at Amazon Klein multimeter Electric testers at Amazon Clampmeter for testing amp flow on line |
 GFCI circuit breaker A GFCI circuit breaker will protect all boxes on circuit. Circuit must be grounded. Ground wire must be continuous and connected to each piece of equipment. White wire on circuit breaker must be connected to Neutral busbar inside the breaker panel. Buy GFCI circuit breakers |
Push down 1" wide Push down breaker Plug-in breaker Buy single-pole: Choose from 15 to 60 amp Eaton CL series Siemens 15-60 amp Single-pole tandem breaker Tandem breakers |
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| High Leg Delta is a type of
3-phase, 4-wire, electric service available at some commercial
buildings It supplies 120-208-240 volts to the building, allowing electrician to choose from the following combinations: 120 volt single phase with 1 Hot and 1 Neutral (Math: 240 divided by 2 = 120) 208 volt single phase with 1 Hot from the high leg and 1 Neutral (Math: 240 volt divided by 2 x square root 3 = 208) 240 volt single phase with 2 out-of-phase Hots 240 volt 3-phase with 3 out-of-phase Hots "High leg Delta systems provide increased voltage flexibility over similar Wye systems because, in addition to a ground wire and 120 Volt single phase, they offer a higher (240 volt) three phase connection" ... meaning that Delta can deliver more power (wattage) per amp than WYE. High Leg 240-415-480 A variant of the same supplies 240-415-480 volts, allowing electrician to choose from the following combinations: 240 volt single phase with 1 Hot and 1 Neutral (480 volt divided by 2) 415 volt single phase with 1 Hot from the high leg and 1 Neutral (480 volt divided by 2 x square root 3 = 415.6) 480 volt single phase with 2 out-of-phase Hots 480 volt 3-phase with 3 out-of-phase Hots -Why are voltages standard? There are many types of 3-phase services, including High Leg Delta variants, plus other services like 208-208-208-120, 480-480-480-480-347 etc. The 3-phase voltages are standardized. For example in the US, a commercial building cannot select 365 volt service because it is not a standard voltage, while in other countries, standard voltages differ, but methods for generating and transmitting power are the same. Voltages are a function of the power generator, mathematics of electricity, transformer configuration,  availability
of conductive materials, cost,
safety, and need for
standardization.Standardization makes it possible to mass produce electric wire, switches, appliances etc. For example light fixtures are widely available for 120 or 277 volt, but not available for a non-standard voltage like 365 volts. If
a building has high leg delta service, then 277 volts is not available
without having electrician install a separate 240-to-277 step-up/
step-down, or buck-boost transformer to the electric service. However,
277 volt troffers are rated 120-277, so a building with high leg could
use the 120 volt circuit for this type of lighting.
ResourcesWhat is 277 volt Buck-boost transformers Buy: 120-277 volt troffer Commercial voltages are 3-phase: -Typical buildings, businesses and factories receive 3 phase electric power that is derived from 3 sets of transformer coils, and sometimes 2 sets transformer coils. Residential homes receive single phase power derived from one set of transformer coils. Difference between single-phase and 3-phase |
|
| Why use 3-phase? 3-phase is generated at the power plant. ''Three-phase circuits are the most economical for AC power transmission (from power plant to substations) and distribution (from substations to local homes and businesses).'' "In a balanced 3-phase system, the wires can be about 75% the size of conductors (wires) for a single-phase two-wire system of the same KVA (power) rating. This helps offset cost of supplying the third wire required by 3-phase systems." Terminology: KVA is Kilo volt amps, or 1000 volt amps. Since volts x amps = watts (power), the KVA rating means kilowatts and how much power is produced by a motor, transformer, heating element etc. KVA (kilowatt) is a static number for comparing available power, and not to be confused with KWH (kilowatt-hour), which is a measurement of billable wattage (power) consumption over 1 hour of time. Difference 3-phase and single-phase "Industrial and commercial 3-phase electric systems differ from residential single-phase: 3-phase power is more complex, but more efficient in motor applications, and large area uses. Higher voltages of 277/480v and 347/600v distribution systems are more efficient, but considerably more dangerous, and should only be maintained and modified by trained and qualified electricians." With 120 or 208 volt single-phase, it requires 1 Hot and 1 Neutral .... and has efficiency of pedaling bike with 1 leg With 240 volt single-phase, it requires 2 out-of-phase Hot wires, ... and has efficiency of pedaling bike with 2 legs The problem with single-phase ... when both pedals are briefly at top and bottom at same time, the power drops to zero. Commercial 3-phase requires 3 out-of-phase Hot wires, ... and has efficiency of pedaling bike with 3 legs due to higher average power compared with single phase. 3 phase delivers more power than single phase because no two pedals are at the top and bottom at same time, so 3-phase delivers smoother, more continuous power. Result the average power is greater with 3-phase. Resource: What is 3-phase: power plant to end user Difference between single-phase and 3-phase |
Fig-1 Full image |
Fig-1: 3-phase arrives
at building Identify High Leg transformer bank: 3 wires come off one transformer and 1 wire (the high leg) comes off another transformer -Typical buildings, businesses and factories have 3 transformers that provide three-phase service. Some services that require less power have 3-phase from 2 transformers. The 3-transformer 3-phase service is the source for High Leg Delta, but not every commercial installation has High Leg, unless specified for the service. How it happens: If High Leg Delta service is specified by the architect, builder, end user or electrical engineer, then the power company brings the correct transformers, and connects three-phase 4500-7200 volt distribution line to the three transformers on the primary side in a WYE configuration as shown. Primary side can also be wired in Delta. To achieve high leg, the transformers on the secondary, or the service side, are wired in Delta configuration. |
| Why
are transformers used? "Three-phase transformer banks are used in three-phase AC power circuits for the same reasons as single-phase power transformers in single-phase ac circuits, i.e., to step-up or step-down the voltages in the circuit and to provide electrical isolation (separation) between the primary windings (coils) and the secondary windings."  Transmission and distribution lines from the power plant are high voltage, low amperage to reduce heat loss. Heat occurs when voltage pushes amperage (current of electrons) against the matrix, or atomic structure, of the conductor. Using high voltage and low amperage means more force is pushing fewer electrons against the conductor matrix, which means less resistance from the conductor and less heat. Ampacities of power lines By reducing heat loss, electricity can be transmitted longer distance without losing power. To prevent electricity from jumping (arcing) to other wires, or to the transmission tower, or to the earth, high voltage conductors (wires) are suspended high above the ground and spaced far apart, utilizing air as an insulator. The higher the voltage, the more space is needed to keep the voltage under control. High voltage also requires large and expensive switchgear, and is extremely dangerous, making it impractical and hazardous for residential and commercial use. To solve the problem, transformers are used throughout the grid to step up or step down voltage. Since amps and volts are inversely proportional, when volts are stepped down by the transformer at local home or business, amps are stepped up. The lower voltage can be controlled at home and business using small switches contained inside metal or plastic enclosures while amps are controlled with properly sized circuit breaker and wire. Why 3 transformers? ''A three phase transformer may be a single unit (all windings wound around the same core, immersed inside one tank) or it may be made up of three single-phase transformers (as shown in illustrations on this webpage). In practice the choice between one or another type is governed mainly by economical reasons, transportation, future expansion, reliability.'' If 3 individual transformers are used, and one goes bad, then a lower-power version of High Leg can be achieved using 2 of the 3 transformers until a replacement transformer is installed. |
|
Fig-2 Larger image |
Fig-2 ... High leg delta service
at local
business 7200 volt distribution power comes from across the street on 3 Hot lines and 1 Neutral The Neutral can be at the top if there is higher risk of lightning. The Neutral will redirect a lightning strike into the ground wire at each pole. Otherwise, the Neutral is installed below the Hot lines as shown in Fig-2. If lightning or surge impacts the Hot wires, the lightning arrestor and fuse will protect transformers. If surge on the Hot wires exceeds rating of wire and grounding, the breaker at substation will trip and protect the distribution and transmission systems. While wires on the secondary side going to the customer service panel are always insulated, the distribution Hot wires in this picture are bare, stranded aluminum or aluminum alloy, approximately .8-.9" in diameter. Wire size and material used for the grid are a balance of cost and performance. For example, copper offers less resistance and less expansion and contraction than aluminum ... and steel is very strong and resistant to heat ... but aluminum and alluminum alloys are the choice for most overhead electrical conductors. Copper is best choice for interior wiring inside business and home. Inside home or business, aluminum wire will expand and connections come loose with high-amp loads, creating high risk of fire unless properly installede with special AL-rated compression fittings. Types of electric cable pdf  15/16" diameter, 500-1000 amp 37-strand aluminum-alloy distribution wires with my finger and shoes. Wires were being installed along freeway widening project and carried no power. |
 Larger imageFig-3: WYE and Delta Services To identify High Leg Delta: 3 wires come off one transformer, and 1 wire (the high leg) comes off 1 transformer. To identify WYE : 2 wires off center transformer, 1 wire comes off other 2 transformers Local auto dealership has 2 types of service: WYE and High Leg Delta The secondary WYE service might provide 208-208-208-120V or 480-480-480-277V to the automotive service center for compressors and hydraulics etc, and 120 or 277 volt for lights. The High Leg service goes to the customer service building, which would use multiple 120 volt circuits for computer terminals, and then 240 volts for lights. Resources What is 208 volt What is 277 volt |
|
 Fig-4: WYE-Delta transformer bankLarger image Illustration on the left describes wiring for 3-phase WYE-Delta service, same as shown in Fig-1 Fig-2 Fig-3 above. It is a representation of 3 transformers and the coils (windings) located inside each transformer, plus the wiring connections on both the 7200 volt primary (or distribution) side and the high leg delta secondary (or customer) side. JEA pdf To achieve High Leg on the secondary, or customer side, or service side, the correct transformers with the correct turns ratio (30:1)  must be installed by the power company, and then the
transformers are wired in WYE configuration on the primary
side, and
wired in the Delta configuration on the secondary side.The primary side can also be wired in Delta depending on power company needs. Primary: WYE is a description of the wiring configuration on the primary side where the high-voltage distribution wires (shown as A B C) are connect to the H1 tap on each of the 3 transformers. The H2 taps on each of the 3 transformers are connected together and connected to the Neutral (N). The Neutral wire on every pole and tower throughout the grid is always bonded to the ground wire that is connected to the ground rod. Secondary: Delta is a description of wiring on the secondary coils of the three transformers ... where each 3 Hot wires (shown as a b c) are connected to two transformers at the X1 X3 taps. The Neutral (shown as n) is connected at center of 1 transformer at X2 tap. This describes the basic connection on secondary side for High Leg Delta. So here you can see that WYE configuration has 3 hot wires, and that each Hot connects to a 1 tap on a transformer, while Delta configuration has 3 hot wires but each Hot connects to 2 separate taps or two transformers. Each transformer shell is also bonded to ground connection. Other Delta variants include: Delta with no Neutral wire, 2 transformer wiring for open Delta, un-grounded Delta without a ground connected to transformer coils, and Delta with grounding at the connection point of 2 coils. |
|
 Phasor diagrams
are simple way to show transformer connections.Phasor diagrams are used for Secondary or Primary, depending on what is being explained. Start with the secondary connections from Fig 4 above, and then simplify into the Phasor diagram that summarizes the wires coming off a transformer bank. There are 3 transformers. each with X1 X3 with center transformer having Neutral at X2 The phasor diagram represents the X1 and X3 taps as a single point at each corner of a triangle, and the X2 in center. The resulting 3-phase service is wired in delta (so each transformer is wired end to end, and the service has 3 Hot wires, 1 Neutral wire and a ground wire: Thus it is a 4-wire, 3-phase high leg delta service. Note that transformer #2 carries all the 120 volt loads, plus 1/3 of the 3-phase loads. The 120 volt loads cannot exceed 5% of transformer KVA, and the total KVA must be derated by 30%. Transformners 1 and 3 cannot carry any 120 volt loads since there is no Neutral tap. Resource: Federal Pacific transformer .pdf |
|
 Delta with center tap NeutralFig-8 on the left is a symbol (phasor diagram) that represents High Leg Delta. There are numerous ways that banks of two and three transformers can be wired to deliver 3-phase power to end user. These include 3-transformer WYE and Delta and High leg Delta, 2-transformer open Delta, 2-transformer High Leg open Delta. 2-transformer Open WYE does not deliver 3-phase, but is an option if a 3-transformer bank loses 1 transformer. High Leg Delta comes from one type of Delta configuration. See illustrations |
|
 2
transformer 3-phase open delta for smaller loadsIdentify High Leg open delta. There are 2 transformer, one is larger than other, 3 wires come off large transformer and 1 wire (the high leg) comes off another transformer High Leg Delta (or open delta) can be achieved using 2 transformers that pull 2 Hots and a Neutral off the distribution line, instead of 3 Hots and Neutral. Open Delta can also be identified by 3 drop wires (two Hots and a Neutral) connecting to 1 transformer, and 1 drop (Hot wire) connected to the smaller transformer. The secondary side still supplies 4-wire high leg to the business, with 3 wires coming off 1 transformer and 1 wire (the high leg) coming off the smaller transformer. This configuration is common for businesses that consume less power, but still want 3-phase, and/or want the selection of voltages found with high leg ... that is 240 volt, 120 volt, and 208 volt. For example, this service provides power to a windshield repair company, with an office and garage for dispatching trucks. This configuration is also used in case of emergency to restore power if one transformer goes bad in a 3-transformer bank. If the business needs more power, then a third transformer can be added at any time ... and this would change the high leg open delta into ordinary high leg delta. A 3-transformer service is more efficient at delivering high power than 2-transformer service. Two transformers can also be configured to deliver Open WYE, and can supply 4 wires, with 2 sets of single-phase, but not 3 phase. This would generally be found in a repair condition when 1 transformer in a 3-transformer bank fails. |
|
 Open Delta
is a form of 3 phase that can be wired to produce High Leg Delta.Instead of 3 transformers, the Open Delta (and Open WYE) variants of electric service use two transformers that draw power from just 2 of the 3 Hot wires on the primary side. If the business needs more power for electric service, a third transformer can be added. If business has 3-transformers and 1 transformer goes bad, temporary re-wire to two transformers will allow uninterrupted electric service until bad transformer is replaced. On the Secondary side, 1 Hot connects to X1 tap, another Hot connects to X3 tap, and one Hot wire connects to two taps X1 X3. Neutral comes from X2 center tap, same as the 3-transformer version, and the High Leg comes from the point farthest from the center tap Neutral. Two-transformer Open Delta "is not as efficient as a three transformer system and is normally reserved for smaller loads. Many three phase buck-boost applications are wired in Open Delta configuration."  |
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 |
High Leg Delta service Image shows general layout for above-ground 3-phase service drop. A drop is generally considered to be the wires that 'drop' down from the transformers, enter the service conduit that feeds into the main switch or safety switch. The safety switch is usually a non-fused disconnect that is located on outside of building. The disconnect must be available for service technician or emergency personnel. The wires pass through the meter box that records billable wattage before entering building and going into main breaker box or service panel. Amperage on delta service. If each phase (each coil on the transformer coil) is 50 amps for example, then each Hot wire will carry 87 amps. 50 x √3 (1.732) = 87 amps This means Delta delivers higher amp 240 volt vs WYE The wye differs from the delta connection in that it has two phases in series. The common point “O” of the three windings is called the neutral because equal voltages exist between this point and any of the three phases. ''When windings are connected wye, the voltage between any two lines will be 1.732 times the phase voltage, and the line current will be the same as the phase current. When transformers are connected delta, the line current will be 1.732 times the phase current, and the voltage between any two will be the same as that of the phase voltage.'' Resource Transformer Basics |
 Larger image3-phase Power leaves the transformer bank and passes through an electric meter that registers billable wattage. From the meter, the electric power goes through a safety cut-off switch and then enters the main breaker box or service panel, and connects to 3-pole main breaker. 3-pole means there are 3 places for wires to connect. And each pole is electrically insulated (separated) from other poles. Each pole on the main breaker connects to a separate busbar where the breakers snap down and draw power for individual circuits. Illustration on left shows High Leg Delta service panel. When wired for delta system, phase “B”, the middle busbar, must be the High Leg 208V to neutral. Wiring can be different, for example the Neutral might be on right side, or the orange-colored wire for High Leg shouldn't be, but might be on different bus. High Leg means the building wants 120-240 Volt service, but it indicates that 208 volt will not be used extensively. The reason is that power consumption across all 3 legs of a 3-wire service must be balanced. This means that each leg or Hot wire of the service supplies equal level of power, and that the usage is spread evenly. If 208 is needed as the primary voltage, then 4-wire 208-208-208-120 WYE service is generally used. What is 208 Volt |
|
 Larger image |
Example service panel The panel pictured here has the Neutral busbar on the right side (note the hex-head Lug with large wire to right of main breaker). White tape is added to Neutral wire to designate that it is a Neutral line and not Hot. The ground busbar is on left side (note the screw lug). The High Leg is the center busbar on this service panel. When wired for delta system, phase “B” must be High leg 208V to neutral. Opening link for larger image reveals -There are no triple pole breakers, except main breaker. -8 breakers are double pole, and deliver 240 volt. -8 breakers are single pole. Only 1 of the 8 single breakers is connected to the High Leg for 208 volt. The other 7 single breakers deliver 120 volt. This illustrates that 208 volt is not used extensively in the building, and the usage is mostly 120-240 volt. Adding total amps of breakers attached to each busbar reveals even or balanced draw from all three busbars. 30-25-20-50-50-20-20 = 215 amps 25-30-20-20-50-25-25-20 = 215 amps 20-20-20-20-50-25-20-20-20 = 215 amps "Connecting single phase loads line-to-line (240V) unevenly loads two windings (coils on the transformers), may unbalance the phases and derates the transformer more than connecting line-to-neutral (120 or 208V)." A double 20 amp breaker delivers 20 amps from each leg. Double 50 amp breaker delivers 50 amps from each leg. Power is doubled with a double breaker. A single breaker has one switch. Two single breakers cannot be used for a double, unless switches are connected. Each double breaker must have connected switches. Example of 2 single breakers combined to make a double breaker can be seen on bottom right of box ... note the two switches are connected together to meet code. Some ground wires are connected to Neutral busbar, and some Neutrals are connected to ground busbar. By code, the ground and Neutral wires should be separated despite both busbars being bonded (connected) together. On the other hand, adding a clutter of extra wires creates hazard and nuisance when working inside a service panel. |
 Larger image |
Example
single-pole
breaker in 3-phase panel Color added to busbars for illustration Single and double breaker can be added to 3-phase panel Or single-phase can be drawn from one or 2 poles of a 3-pole breaker. In this example, the breaker is stabbed onto phase C, and not the High Leg. This mean the circuit breaker supplies power to 120 volt circuit. |
 Why the High Leg measures 208
volt to NeutralElectric power is mathematical and some concepts can be shown geometrically. An example of geometrical description follows: ''The angular displacement of a transformer connection may be defined as the angle between the no-load line to line voltages of the corresponding primary and secondary terminals. There are two basic angular displacements: 0◦ and 30◦. Other angular displacements of 150◦, 180◦, 210◦, 330◦ (and -30◦, -150◦. etc.) can also be obtained by suitable connections of windings.'' .pdf resource To keep it simple, the triangle on left can explain why the High Leg measures 208 volt to Neutral. Delta comes from 3 transformer coils wired end-to-end that can be represented by equilateral triangle. So the blue line is one transformer, and the blue transformer has 2 connection points, 1 connection is to the green transformer, and one to the yellow-pink transformer. With High Leg Delta, there are 4 connection points on the triangle.... one point at each corner and one at the Neutral point on one side, which is a midpoint on the yellow-pink trandformer. Each side of the triangle is same length so voltages are same from corner point to corner point.... equal 240 Volt. Then from corner point to Neutral point is half length or 1/2 x 240 volt .... equal 120 Volt. But far corner point (the high leg) to Neutral point is shorter than sides of triangle ... but longer than half, so it cannot be 240 or 120 ... instead the formula becomes 1/2 x 240 volt x √3 (1.732) ... equal 208 Volt. |
|
 Delta and WYE differ from each
otherDelta coils are wired in series (end to end). WYE coils are wired in parallel (with a common point). In a 3-transformer Delta configuration Fig 12-14, the line voltage (measured across any 2 Hot wires) and phase voltages (measured across the transformer coil) are the same. But each Hot wire draws amperage (current) from two transformers, yielding higher amperage on the line. If each transformer coil in a Delta configuration delivers 10 amps (phase current), then each line receives 10 amps x √3 = 17.32 amps. This means Delta can deliver more amps per volt, giving higher power connection. Delta transformer calculations .pdf |
|
 WYE coils are wired in parallel (with a common point). Delta coils are wired in series (end to end). Electricity is a combination of voltage and amperage, where volts multiplied by amps equal watts (total power). Each coil on the generator can be called a phase. Each phase has a volt and amp rating called the Phase amperage and Phase voltage. Each line also has a volt and amp rating, called the Line voltage and the Line amperage. Volts and amps are measured differently. Voltage is a potential across any 2 points. Voltage can be measured across the 2 ends of any coil, or across 2 Line wires, or across the Line and Neutral point. Amperage is measured as a flow of current (current of electrons) at any point. Amperage can be measured along a Line wire, or along the coil inside the generator etc. The amperage on each coil of the generator (called the Phase Amperage) is the same as the amperage (current) that flows along each Line (called the Line amperage or Line current). In a WYE configuration, each Line has the same potential voltage (called the Line voltage) as the other Lines. There is also voltage potential between the any of the 3 Lines and the Neutral point (called the Phase voltage). The phase voltage for a WYE configuration is exactly √3 x 17321 of the Line voltage. Square root of 3 (1.732) is a common math found with 3 phase. Source: 3-phase power math .pdf |
|
| Question: My High Leg panel tests
for 220 volt instead of 208 volt Starting at the top left testing to ground, I get 220 then 120 then 120 then 220. That is both 50amps on the left. The 25amp has 220 on top and 120 on the bottom. Both are 120 on the right 25amp and the 30amp on the bottom right is 220 on the top and 120 on the bottom. 3 busbars: 120 the center is 220 and the right is 120. |
Answer: Overall it sounds like High Delta service, not
sure what else it would be from your description and tests. Your earlier tests on the double breakers showed 247 V instead of 240. That's within expected range, but the 220 instead of 208 sounds higher than expected.. It's possible that your service is running a bit higher on one transformer. The panel looks balanced. Maybe try another meter and see if you get same result, or call power company and ask about the issue. I suppose if it's not causing problems, it's not really a problem. |
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