Terms
Volts – The common name for measuring the energy level in a circuit or conductor or the rating of the energy required by a device.
Amps – The common name for the measurement of the current in a conductor, the amount or current a device requires or the maximum rating for a conductor or wiring device.
Watts – The common name for the amount of energy consumed by a device or produced by a generator.
Kw or Kilowatts – Watts divided by 1,000. Example: 10Kw = 10,000 watts
Power Factor – The amount of power transmitted in a multi phase system. The power factor depends on the number of phases and cycles. The power factor of a three phase 60 cycle systems is .8.
KVA – KiloVoltAmps – Used to quantify the output of three phase transformers or generators. To get the Kw output, multiply the KVA value by the power factor .8. Example, a 45KVA generator (3 phase) produces 36Kw (45Kva X .8 = 36Kw).
Load – The amount of wattage either a device or an entire system uses.
Load Diversification -An operating theory which states that not all loads will be present in a system (turned on) at the same time.
Formulas
WATTS = VOLTS x AMPS
To solve for unknown watts – volts x amps = watts 120v x 10a = ?w or 1,200 watts
To solve for unknown amps – watts / volts = amps 1,500w / 120v = ?a or 12.5 amps
To solve for unknown volts – watts / amps = volts 1,200w / 5a = ?v or 240volts
KiloVoltAmps x Power Factor = Kilowatts
Assuming 60hz North American System
To solve for unknown Kw: KVA x Power Factor = Kw 20Kva x .8 = ? Kw or 16 Kw
To solve for unknown KVA: KW x 1.25 (reverse of .8) = KVA 36Kw x 1.25 = ?Kva or 45Kva
Systems & Wiring
Single phase – Most common for residential and light commercial. This system requires two hot conductors, a neutral & a ground for a total of four wires.
Three phase “star” or “Y” – Common in industrial & commercial location and for three phase generators. This type of system is found in the 208/120vac three phase in many restaurants, 480/277vac is found in many large commercial buildings (600/347vac is found in Canada ). Five (5) wires are required for these systems, three (3) hot conductors, a neutral and a ground.
Three phase “Delta” – Common in industrial & some commerciall locations. These system are either 240vac, 480vac or 600vac ( Canada ). This type of system does not require a neutral because there is none. However, they cannot be used for 120vac unless a transformer is used for create a single or three phase system as described above. Four (4) wires are required for this type of system, three (3) hot conductors and a ground.
Panel or Distribution panel (box) – Common names for a (large) box containing circuit breakers or fuses. All panels have a maximum rating for the number of amps & volts they can handle.
Disconnect – A device, either a circuit breaker or switch, that opens all hot conductors. A disconnect is required from the main power source and is also required in or for any sub panel that is not in view of, physically separated from or is more than fifty feet (50′) from the supply panel.
Supply or Feeder Cable – The wire that runs from the power source (like a generator) to a panel.
AWG – Average Wire Gauge, when preceded by a number gives the size of the wire. Sizes run between 22 and 2awg.
Ought – When preceded by a number gives the size of a larger wire. Sizes run between 0 and 4 ought. Symbol is /o or also denoted as size /o or 2/0 is 2 ought wire.
Inrush (Motor) – When a device with a motor starts up there is an initial surge of current greater than the full load current during normal operation, this is known as motor inrush. This inrush depends on the type of motor but it is generally not greater than 50% more of the full load of the motor when running. Example: A motor uses 10amps when running it would have a starting inrush of 15amps.
Fuse or Circuit Breaker – A device to prevent overloading of the wiring in a system. The fuse or Breaker has a maximum load limit. Do not use a larger fuse or breaker than the conductor is rated for.
NEMA – National Electrical Manufacturers Assoc. has standardized many wiring devices such as plug & receptacles. These devices have “NEMA” numbers. Standard 120vac plug as a NEMA number of 5-15 (15 is for amps). The number can be followed by a letter as follows: P – Plug R- receptacle C- Connector (inline receptacle)
Straight Blade or Edison – A style of connector that plugs into a receptacle without any mechanical securing method. Limits connectors to no more than 60 amps.
Twistlock – A style of connector that turns in order to mechanically lock together. In NEMA styles, this type of connectors does not exceed thirty (30) amps.
Pin & Sleeve – A style of connector than also mechanically locks together but carries more amps than twistlocks, up to 100.
Cam Lock or ETC – A single conductor connector that can carry up to 400amps depending on rating.
Rain Tight – A style of cover that keeps water out of a receptacle.
Rain tight in use – A style of cover that keeps water out of receptacle when something is plugged in.
GFCI – Ground Fault Circuit Interruption – A device that detects when electricity is not remaining in the circuit and “interrupts” the circuit to prevent injury. NOT A CIRCUIT BREAKER.
Codes & Authorities
NFPA – National Fire Protection Assoication
NEC – National Electric Code part of the NFPA code.
Local Codes – Additional requirements to NEC based upon local jurisdictions.
Local Authority having Jurisdiction – Local government representative authorized to enforce codes. This could be a Building or Electrical Inspector and/or the Fire Marshal.
Testing Authorities – Third party Organization has been created to independently test Manufacturers products and wiring methods to determine if they meet sections of the NEC and NFPA Codes.
Underwriters Laboratories (UL) – Best known testing authority in the US . Tests products & methods for adherence to NFPA, NEC , US building codes and develops its own testing standards to guide manufacturers on its procedures. UL does not “approve” anything, instead it “Lists” (or UL Listed) a product or device as satisfactorily passing its standards.
ETL & FM – Other lesser known test laboratories that also test products for compliance to Codes.
List of Common Devices & Their Loads
Description Volts Amps Watts 100
Cup Coffee Urn 120 13.75 1650
Hot Box – Single Door 120 16.67 2000
Refrigerated Box – Single Door 120 12.50 1500
Frying pan 120 12.50 1500
Commercial Blender 120 12.50 1500
Household Electric Oven 240/208 25/29 6000
Household Electric Dryer 240/208 25/29 6000
Air Conditioner – 5000 BTU/h 120 10.00 1200 L B White 80,000 BTU/h
Heater 120 7.50 900 L B White 170,000 BTU/h Heater 120 10.00 1200
