Construction and Electrical Wiring Terms Defined

January 8th, 2010 by admin Leave a reply »

110/220 or 120/240?

110 volt and 220 volt designations are old familiar terminology, but are no longer commonly used in either product design or by electric utilities.

The 115 volt and 230 volt terminology comes from equipment design standards. Equipment is usually designed to operate at 115 or 230 volts with a plus or minus 10% acceptable variation.

Utility companies deliver electric service at 120 / 240 volts plus or minus 5%.

Thus, the correct terms are usually 120 and 240, but for practical purposes 110=115=120 and 220=230=240.

AFCI – Arc Fault Circuit Interrupter

AFCI Breakers are designed to protect your home from fires which are cause by arcing as well as over current conditions. Normal breakers are only effective against over current conditions. Arc Fault Breakers are now required by new construction codes to protect receptacles which are located in bedrooms (and possibly other locations according to local codes variants). Arc Fault breakers may not be 100% effective against all fires caused by arcing because there is a certain amount of arcing which is normal, and the arc fault breaker would be unusable if it tripped every time that a normal arc were detected. For example if you ever noticed a spark when you unplug an appliance or flipped a wall switch, then that is normal arcing. Abnormal (and Dangerous) arcing often is caused by a poor connection, or damaged wire. Unfortunately, dangerous arcing “looks” an awful lot like normal arcing to the breaker, so it is possible for a fire to be started without tripping the breaker. Nonetheless an arc fault breaker, even if less than perfect, is a lot better than no protection at all. By the way, arc faults are one of the big reasons that electrical connections should never be made outside of an approved wiring device.

Arc Fault Breakers like GFI devices have “test” and “reset” buttons and should be tested periodically according to the manufacturer’s specifications (usually once a month).

Approved Wiring Device

This term refers to any of a number of devices which are “approved” by Underwriters Laboratory or some other codes sanctioned testing organization for the purpose of mounting electrical fixtures and equipment, or for containing connections. Appliances and some fixtures are considered as approved wiring devices also. Wiring supply connections may only be made inside of approved wiring devices, and for several good reasons. The wiring device protects the connection from tampering, abrasion or other damage, and also protects the home from electrical fires which are most likely to start at connections.

Buck Boost Transformer

is a small single phase transformer which reduces (buck) or raises (boost) line voltage a small amount. The most common example is boosting 208 volts (derived from 3 phase service) to 230 volts (equivalent to single phase service) to operate a 230 volt appliance such as an HVAC compressor or fan motor from a 208 volt supply line. A buck-boost transformer does not alter the phase signature of the power supply.

GFCI devices

GFI or GFCI (Ground Fault Circuit Interrupter) devices help to protect people from being shocked or electrocuted. They work by very quickly detecting a “Ground Fault” (for example the ground fault that happens when a person is being shocked, one caused by a short, or a voltage “leak” caused by dampness in and around electrical equipment) and interrupting the current. GFI devices are usually either in the form of a receptacle or a breaker, although some equipment (hot tubs for example) may sometimes have GFI protection built in, but not usually. A single GFI receptacle or breaker often protects many additional receptacles or fixtures, which sometimes causes confusion because a homeowner doesn’t know that a tripped GFI receptacle in another part of the house could be interrupting the current to a regular receptacle.

In many codes jurisdictions an old fashioned two prong outlet can be replaced with a three pronged GFI receptacle in order to safely allow the use of modern appliances with three pronged plugs. GFI protected circuits and devices are usually found (and required by codes) outside, and in damp locations such as bathrooms, kitchens, and basements. Wet conditions around a GFI protected device may trigger the GFI and prevent it from being reset able.

All GFI devices have “Test” and “Reset” buttons on them. The test button causes a ground fault within the device and trips the reset button causing it to pop out and protrude slightly, thus interrupting the current to any devices which are protected by the GFI in question. Pushing the reset button in until it catches will restore current to the circuit. If the “test” button fails to function as described then the GFI device must be replaced. As mentioned previously, a continuous ground fault (like one cause by excessive water around the electrical equipment) will prevent the GFI from being reset able, and must be remedied before the circuit will be usable. A nonfunctioning GFI device is an extremely dangerous situation, which must be remedied immediately.

Ground loop

All residential electrical systems should have a single point ground. Grounding to multiple places will cause all kinds of problems with noise, hum, snow, and generally bad audio video signals. Intuitively it would seem that having redundant grounds would be a good thing, but it is not, because voltage is a relative value. If you did an experiment where you connected a long conductor to your house current, and then checked the voltage to ground at different locations (different places in the yard, water pipes, the ground rod, etc..) you would find that there would be different voltage potentials at different spots. In fact if you measured the voltage potential between two spots of earth in the yard you might find that current would actually flow through a conductor between two spots of earth. Those different voltage potentials and the current they cause are why ground loops are bad. Especially troublesome ground loops can be cause when a length of coaxial wire connects two pieces of audio video equipment (cable box, TV, etc…) which are plugged into different outlets. One great way to fix this problem is to use surge protectors which incorporate coax protection.


An electrical term which is short for “line voltage” and indicates wires which bring power into a device, and the terminals that such wires connect to. Incoming Power.


An electrical term which indicates an additional electrical load, the wires that carry current from a device to the load, and the terminals on a device that such wires connect to. Outgoing power.


Wild-wire or red-leg delta properly referred to as high leg delta is a type of three phase transformer winding connection sometimes found in older electrical installations. A transformer wound in this fashion will have four wires coming out of the secondary: the three phases, plus a neutral that is a center-tap of one of the windings. The voltages between the three phases are relatively the same; however the voltage magnitudes between a particular phase and the neutral vary. The phase-to-neutral voltage of two of the phases will be half of the phase-to-phase voltage. The remaining phase-to-neutral voltage will be 1.7 times the phase-to-phase voltage. Typically, the transformer is designed such that the ‘B’ phase is the ‘high’ leg. According to Article 110.15 of the 2005 National Electrical Code, panel boards connected to this type of transformer must explicitly identify as the high leg, preferably by coloring it orange. Generally the high-leg can not be used for loads requiring a neutral such as lighting because of the high voltage potential. In other cases such as three phase motors which do not utilize a neutral the wild-leg is irrelevant because it has the same phase to phase voltage potential as the other two legs.



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