Objectives Review conductor and conduit selection Learn about protection systems (basic rules) Learn to design Residential Electrical Systems

Current-Carrying Capacity Ref: Tao and Janis (2001)

Tubing size

Other Issues In general, no more than 40% of raceway can be filled with wiring Why? To prevent extensive heat up To prevent physical installation of wires

Conductor Rules Explain each of the following: No more than 4 90 ° bends are allowed between pull boxes In the same conduit: No mixing of high- and low-voltage conductors No mixing control and power conductors No mixing phone and power conductors Do place all three phases in the same conduit

Receptacles and switches Receptacles (duplexes) Number Shape Voltage rating Current Rating Number of poles and wires Switches Type (NEC rating) Contact method Speed of operation Voltage rating Number of poles Method of operation Enclosure Duty Other (dimming)

Protective Devices What are we protecting from? Overcurrent Overvoltage Circuit breakers Switch that responds to thermal or short circuit loads Can be bimetal, magnetic, or electronic Reusable, remote control, compact, can be used as disconnect switch Fuses Melting metal Self destructive, larger

Why use fuses instead of circuit breakers? A.Fuses can be used multiple times B.Fuses are more aesthetically pleasing C.Fuses are safer D.Fuses cause less damage to equipment

Ref: Tao and Janis (2001)

Motor starters ON-OFF switches are NOT for motors Motor circuit-rated switches Reduce the current during the start until the motor rich full speed Protect the motor form overload Emergency power systems Batteries Power generators

Residential Systems Very little variation between different houses Many similarities to commercial buildings Particularly as you get close to end uses Need to be watchful for unusual circumstances

Procedure 1.Analyze building needs 2.Determine electrical loads 3.Select electrical systems 4.Coordinate with other design decisions 5.Prepare plans and specifications

List of needs Appliances (incl. HVAC) Receptacles Ground fault protected (GFI/GFCI) Switched Lighting Switches Ceiling Fans

Example House Master Bedroom Bathrooms Entry and Outdoor (AC compressor) Bedrooms Dining and Mechanical Closet (resistance heat) Kitchen (appliance circuits, range, oven) Family Garage/Laundry/Closet (resistance water heater, dryer)

Master Bedroom Bathroom Bedroom 2 Bedroom 3 Garage Laundry Closet Kitchen Family room Dining Mechanical closet Entry Outdoor

NEC about receptacles No longer approve non-polarized and ungrounded receptacles in new installations. Each receptacle (duplex) is rated for 1.5 A. For 120 V: Each duplex 1.5×120 = 180W

Residential system sizing Typically 3 wire 1 phase system 120/240 V Procedure defined by NEC article 220: Identify characteristic electrical loads Add lighting (3W/ft 2 ) Add two 20 Amps circuits for kitchen Add one 20 Amps circuit for laundry Electricity for HVAC equipment based on requirement for heating or cooling

Summary of Power Sizing Include enough capacity for heating and cooling Work through kitchen and then other rooms Include any items that are unusual Take first 10 kVA and then 40% of remaining load

Panel Sizing Find panel power usage and neutral usage Size panel conductors and associated conduit and switches

Electric panel - 3 wire 1 phase 120/240

Homework 5 - problem 2 Sizing the residential electrical system Defined by NEC article Similar to the example we worked out You need to collect the data for several characteristic consumers Includes conductor sizing