Lesson 1



Let us start by looking at a simple scenario involving residential wiring in your home.  The utility company brings their wires supported by a messenger cable to your home.  This is called a service drop.  If it was brought underground it would be called a service lateral.  The cables must be supported and attached to a point of attachment on the service mast or house so the cables will not fall below certain height requirements.  Once the utilities connect to the premises wiring at the weather head we now call these parts of the conductors, service entrance conductors.  The service entrance conductors will be those conductors up to the point where the service equipment will cut off the main supply.  This is where all your major grounding is addressed.


The conductors between the service entrance conductors and the over current protective device protecting the utilization equipment are defined as feeders.  In your home you may not have feeders unless you are feeding another panel.  Feeders deliver energy from the main service equipment to a point where equipment or other loads are protected by multiple over current devices in the panel board.  Feeder may free up space in your main panel board or you may compensate for voltage drop over long runs or save time and money from bring cables long distance back to your main service equipment.


Branch circuits are the conductors located between the last over current device and the utilization equipment.  Branch circuits may be located in the service equipment or in a panel supplied by a feeder.  When we look at voltage drop, remember the total of 5% allowed is between the Feeder and branch circuit.  If we compensate or size the wire for 3% volt drop on the feeder, then we must compensate for only 2% on the branch circuit, the total being 5%.  If we compensate or size the wire for 2% volt drop on the feeder, then we must compensate for only 3% on the branch circuit, the total being 5%.


Generally electrical installations require certain requirements.  Temperature limitations of lugs and conductors, the size and type of equipment and allowable spaces for equipment meeting installation guidelines all affect our layout of the job.  Coordinating electrical systems do not only rest upon the electrical engineer or architect.  As professionals we are to check the electrical design of the system and coordinate not only the method of installation or installer, but all professional recommendations.  Our purpose is to safeguard the protection of life and property.  This is a big responsibility and coordinating electrical systems should be taken seriously.


Electrical terminology is like studying another language for the first time.  Before having a conversation with fellow electricians, engineers, architects, etc, an individual should be familiar with the electrical terms presented in the definition portion of the code book.  If you are unfamiliar with the proper terminology, no other professional will take you seriously. 





When the square footage of space is known how do we as electricians prepare to accomplish what we do?  Yes we are installers but we must also think about how many luminaries, receptacles, and switches are needed as well as the location of our electrical equipment to be installed.  Allowances for panel design and room specifications must be met.  Working spaces required by the NEC with regards to electrical equipment promote safety:

·        For the operation and cooling of equipment.

·        Providing requirements for a means of egress and minimum distance to safely work on equipment.

·        Protecting customers from potential future fires due to improper electrical installation.  

·        By requiring receptacles every so many feet in certain locations thus reducing fires due to improper use of extension cords

·        The use of lighting switch location and smokes.

·        Requiring Arc fault and Ground fault protection.


Ground faults protection is most commonly used in areas in close proximity to wet or damp locations.  Kitchen countertops, bathrooms, garages, unused spaces not adaptable for future use as well as outdoor locations all require the use of this device to detect if the difference in current between the hot and neutral changes (4ma-6ma or .004a-.006a).  Basically all areas not protected by a GFCI (Ground fault circuit interrupter) need to be AFCI protected.  Arc fault circuit interrupters protect the circuit by detecting an arc if the insulation should break down by overloaded circuits or if one phase should come in contact with the neutral or a grounded metal surface.  With this in mind and what areas on the household need to be protected by which type of circuit we should remember we can not use a 3 wire circuit to protect one circuit through the use of an AFCI breaker and can not protect the other by a GFCI breaker.  Careful consideration should be implemented by determining the requirements of installation, working spaces, number of circuits needed depending on load calculations (3va per sq ft) which will be discussed later and what type of protection needed prior to installation.



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