Power[1]
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Transcript of Power[1]
MEP FundamentalsPower
MEP FundamentalsPower
MEP FundamentalsPower
September, 2007
1. What is AIC?
2. If 3-phase is better, why not 4 or 5?
3. Do all tenants have a transformer? Why or why not?
Examples of Questions we will answer:
MEP TrainingPower
September, 2007
Electricity is created by:Nature - lightningBattery - chemicalGenerator- mechanical Creates alternating
current as it rotates Why three phases, why
not four?
Motor in reverse
MEP TrainingPower
September, 2007
Generation:Heat > steam > turbine > generatorVoltage boosted for distanceSubstations step down to 7,200-15,000vOn-site transformer steps down to 480 or 208v
MEP TrainingPower
September, 2007
Ground:
The earth safely absorbs electricityNot just one of those NEC things
MEP TrainingPower
September, 2007
Grounding and bonding:Ground is a connection to the earth that only carries current when there is a short (green wire)Bond is connection between components to the groundGrounding is required: At service initiation At low voltage side of transformer
Initiation of new voltage (480v to 208v)
Grounds need to be where inspectors can find them
MEP TrainingPower
September, 2007
Transformers:
MEP TrainingPower
September, 2007
Fault Current:How much current will flow when a fault (short) occurs?What limits the current?Common panel/breaker rating is 10,000 ampsHow do you know? Utility company transformer
available fault current Fuses in landlord or tenants main
MEP TrainingPower
September, 2007
Transformers Typically 480/277 to 208/120
30 KVA to 83 Amps (290 Lbs.) $ 2,300
45 KVA to 125 Amps (400 Lbs.) $ 2,800
75 KVA to 208 Amps (500 Lbs.) $ 4,000
MEP TrainingPower
September, 2007
Breakers vs. Fuses
MEP TrainingPower
September, 2007
Types of Landlord distribution equipment:Utility metered Wireway Switchgear Meter Center
Landlord redistribution, no meters Distribution Panelboard / Switchboard Buss duct
MEP TrainingPower
September, 2007
Wireway (Utility Metered)
MEP TrainingPower
September, 2007
Switchgear (Utility Metered)
MEP TrainingPower
September, 2007
MEP TrainingPower
Meter Center (Utility Metered)
September, 2007
DistributionPanelboard/Switchboard
MEP TrainingPower
(Landlord Redistribution, no meters)
September, 2007
Buss duct
MEP TrainingPower
(Landlord Redistribution, no meters)
September, 2007
CT’s / CT Cabinet
September, 2007
Load Center Residential Not bolt-on breakers Breakers not switch duty rated
Panelboards Grouping of 20A breakers
Distribution Panelboards Larger breakers, 60A – 400A
Switchboards Distribution panelboard with fused switches
Switchgear Large utility rated equipment
MEP TrainingPower
September, 2007
Breakers:
Rating (maximum continuous current)Some appliances create short duration surges at start-up(ex. electric motor)
MEP TrainingPower
September, 2007
Ground fault:
Hot conductor connected to groundCreate arc/sparkCaution: intermittent fault will not trip breakerGround fault interrupters
MEP TrainingPower
September, 2007
Common voltages:Single phase: 120v – household outlet
Three phase: 240v = 120v x 2 wires for larger load (dryer) 208v/120v/3ph/4w 480v/277v/3ph/4w
What’s the last number? Three wires are power Four wire – neutral Ground isn’t counted, it’s assumed
MEP TrainingPower
September, 2007
Neutral Another path to ground
(white wire) One hot (black) wire plus
neutral = single phase 277v or 120v
Why not 277v x 3 or 120v x 3 for three phase? Power triangle, really is
geometry.
MEP TrainingPower
September, 2007
Load calculation:NEC rules
No consideration for diversity permitted. Actual load rarely exceeds 65% of service size
Actual rating of equipment/lighting is required Equipment nameplates Lighting ballast inefficiencies must be considered
Continuous loads (operating for three + hours) Rated load x 1.25 Lights What about AC and heat?
Track lighting considered 75 watts per foot for service size, but not branching size
MEP TrainingPower
September, 2007
Loadcalculation:
MEP TrainingPower
September, 2007
Wire size:Sized like pipe (velocity, diameter and pressure)Continuous loads de-rate wire capacity
Heat Defined as 3+ hours (lights)
Multiple conductors de-rate wire capacity Heat (more wires = more heat)
Voltage drops Wire acts as resistor based on
length of wire Long distance with continuous
load = larger diameter
MEP TrainingPower
September, 2007
Wire size:
MEP TrainingPower
September, 2007
Wire size / Voltage Drop:How long? Wire can run as far as voltage (ex. 480v = 480 feet)
Single phase in out and back Three phase is out only Don’t ask why
Conduit sizing Never consume more than 40% of cross-sectional
area Heat Pulling wire through conduit 40%
Max
MEP TrainingPower
September, 2007
Electrical formulas:Energy = power for a period of time Energy = usage, watts x time Electric meters use this measurement Units are watt hours
Power = voltage x amperage Similar to auto horsepower Power = demand, kilowatts (1 kw = one thousand
watts) Voltage = the pressure (pushing) on the current Amperage = current, the flow rate
MEP TrainingPower
September, 2007
Electrical formulas continuedExamples of calculations Single Phase: 2.4 kw = 120v x 20 amperes
What is 115v or 110v? Three phase: 16.6 kw = 480v x 20 amperes x 1.73
1.73 is the square root of three (for three phase)
MEP TrainingPower
September, 2007
Rules of thumb:20 watts per square foot for retail tenants with their own rooftop units. 15 watts per square foot for retail tenants with landlord central air conditioning. 40 watts per square foot for sit-down restaurants. 100 watts per square foot for food court type tenants.
MEP TrainingPower
September, 2007
1. What is AIC?
2. If 3-phase is better, why not 4 or 5?
3. Do all tenants have a transformer? Why or why not?
MEP TrainingPower