Electricity: Understanding How It Works: Distribution


Modern services are rated from 100 to 400 amps. After passing through the electric meter, the three-wire, 120/240-volt service-entrance wires enter the service panel. The two black hot wires (each supplying 120 volts) are attached to the terminals of the service disconnect, which feeds the two hot bus bars. Single-pole breakers plug into one bus bar and supply 120- volt circuits. Double-pole breakers plug into two adjacent bus bars sup plying 240-volt circuits. The neutral wire (marked white) attaches to the neutral bar, which is bonded to the metal enclosure and the ground bar with a screw or strap. Grounding wires from ground rods and water pipes and in the branch-circuit cables connect to the ground bar.

Service Panel

Modern services are rated from 100 to 400 amps. After passing through the electric meter, the three-wire, 120/240-volt service-entrance wires enter the service panel. The two black hot wires (each supplying 120 volts) are attached to the terminals of the service disconnect, which feeds the two hot bus bars. Single-pole breakers plug into one bus bar and supply 120- volt circuits. Double-pole breakers plug into two adjacent bus bars sup plying 240-volt circuits. The neutral wire (marked white) attaches to the neutral bar, which is bonded to the metal enclosure and the ground bar with a screw or strap. Grounding wires from ground rods and water pipes and in the branch-circuit cables connect to the ground bar.


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Older-style fuse box When to Upgrade the Fuse Box

Older 60-amp services are only adequate in smaller homes with no more than one 240- volt appliance, like a water heater or range. Home-loan programs and insurance companies often require existing homes to have a minimum of 100-amp service. Upgrading old fuse boxes enhances your safety, adds convenience and value to your home and allows you to easily add circuits to accommodate modern appliances.

Consult a licensed electrical contractor to evaluate the load supplied by your service to determine if an upgrade is necessary.


Branch circuits carry electricity from the service panel's breakers or fuses to receptacles, light fixtures and appliances.

Branch Circuits

Branch circuits carry electricity from the service panel's breakers or fuses to receptacles, light fixtures and appliances. There are three categories of branch circuits. General-purpose cir cults supply two or more outlets for lighting and appliances, appliance circuits supply only appliances, and individual circuits supply only one item, such as a water heater. A 120-volt circuit consists of a black hot wire connected to the breaker, a white neutral wire connected to the neutral bar and a bare cop per or green insulated equipment grounding wire connected to the ground bar. A 240-volt circuit will have two hot wires and a grounding wire and may include a neutral wire if required by the appliance served. Unlike hot wires that are interrupted by light switches, neutral and grounding wires must never be switched.

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Recommended Reading

American Electricians' Handbook

Book Description:

OVER 750,000 COPIES SOLD! THE “ELECTRICIANS’ BIBLE” SINCE 1913

Filled with practical advice and facts, the American Electricians’ Handbook is the best single source for essential information on designing, installing, operating, and maintaining electrical systems and equipment. For over 85 years, there has been no better or more trusted way to keep up with the latest developments in the electrical field.

Revised and updated in compliance with the most recent National Electrical Code and National Electrical Safety Code, as well as the current standards of NEMA the American National Standards Institute, and the Underwriters Laboratories, this one-stop reference enables you to tackle even the most complex job with total confidence. Using the clear language and diagrams that have made the Handbook the industry’s definitive resource, the expanded Fourteenth Edition brings you the latest data on:
* Advances in fiber optic cables, grounding, arc-fault circuit interrupter devices, and transient voltage surge suppressors
* The National Electrical Code, the National Electrical Safety Code, and NEMA motor and generator standards
* High-efficiency motors and electronic control of motors
* Circuits and circuit calculations, transformers, wiring tables, lamp application tables, and much more.

Topics include:

incoming black wire, house grounding system, protector box, incoming power cable, splice box, grounding block, incandescent floodlights, grounding slot, one service call, nonmetallic boxes, meter base, grounding electrode conductor, bonding jumper, grounding terminal, ceiling box, grounding bus, pancake box, utility transformer, grounding screw, fan box, main panel, cfm rating, metal water pipes, equipment grounding conductor, professional electrician

Reviews:

Focus on quality and safety: In "Safe Home Wiring Projects," Rex Cauldwell focuses on two things: quality and safety. He shows you how to choose quality receptacles, light fixtures, tools, and other equipment. He also shows you how to do safe, high-quality wiring. While most of us are tempted to buy the cheapest equipment that will get the job done, or buy light fixtures based on looks only, Rex Cauldwell provides good reasons to consider other criteria. The book is well-written and very easy to understand, and the illustrations are numerous and clear. This book is best for those looking for an introductory text -- it covers mostly basic projects, and doesn't cover anything that would involve opening the main panel.

When it comes to electrical wiring, you can't afford to skimp on quality or safety. Armed with the knowledge in this guide, a homeowner can do home wiring confidently, and rest easy with the knowledge that the job was done correctly.

Recommended Products



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Codes, Permits and Inspections

The National Electrical Code (USA) and the Canadian Electrical Code contains rules necessary for safeguarding people and property from hazards associated with electricity use. Before doing any electrical work, contact your local, county, state or province inspector for up-to-date information.

Except for minor repairs, such as replacing a broken receptacle, you usually need to apply for a permit, submit plans or pass a simple proficiency test to do the work. Wiring usually must be inspected before it's covered or concealed; final inspections ensure the wiring is complete and safe to use. Electricity can be deadly—when in doubt, hire a licensed electrical contractor to handle the tough jobs.

All electrical equipment should be third-party certified. Look for the Underwriters Laboratories (UL), Underwriters Laboratories Canada (ULC) or Canadian Standards Association (CSA) mark or label.

A Few Projects You Need Permits For:

  • Wiring new homes
  • Upgrading electrical services
  • Room and porch additions
  • Finishing basements
  • Replacing light fixtures and ceiling fans
  • Installing or replacing appliances, furnaces and air conditioners
  • Installing wiring to detached garages and sheds
  • Installing outdoor wiring and wiring for hot tubs and swimming pools

Last modified: Wednesday, 2013-06-05 0:04 PST