POST a QUESTION or READ FAQs about the definitions of AC, DC current, amps, watts, volts, ohms, and other electrical terms common to residential buildings and their mechanical systems. Photographs and sketches in this article illustrate and help explain concepts and definitions of electrical voltage, electrical resistance, and other electrical wiring concepts.
In most places in the world, electrical service brought to a building is at either of two voltage levels: 240V or 120V. Most modern buildings receive 240V service, a total achieved by the provision of two individual 120V incoming power lines as we discuss below. Amperage or Amps provided by an electrical service is the flow rate of "electrical current" that is available. Also see AMPS MEASUREMENT METHODS for a description of using a clamp-on ammeter to make actual electrical usage measurements.
Ampacity, in the electrical code, refers to the current, measured in amperes, that a conductor (a wire) can carry continuously under the conditions of use without exceeding its temperature rating - in other words, the ampacity of a #14 gauge copper wire intended for residential electrical wiring is 15 Amps because that's the amount of current that the wire can carry without getting too hot. Volt, formally, is defined as the potential difference across a conductor when a current of one ampere dissipates one watt of power.
Amps,as we discussed above, is a measure total current flow (or "gallons per minute" or "gpm" using the popular water analogy) available from an electrical service. A ten-amp 240V electrical service is capable of delivering, speaking roughly, twice the energy to the end-user than a ten-amp 120V electrical service. Volts (continuing the same water analogy) is the "pressure" in an individual electrical conductor. Some people explain volts as similar to water pressure in a pipe, and amps as water current or total quantity flow.
The total current ("gpm") that will flow through a conductor is doubled if the pressure is doubled.
Doubling voltage and also doubling the amperage will deliver four times the power or energy. Why we need circuit breakers or fuses: In either case, if we exceed the current rating of an electrical wire, it will get hot, risking a fire.
Most (but not all) modern electrical equipment can handle small voltage variations and differences without a problem. The two (in this case) phases are arranged so that connecting a circuit across the two "hot legs" produces "240V" in for that circuit. An electrician or engineer, trained in safe volt-ohm meter (VOM) or digital multimeter (DMM) use can easily demonstrate this fact. Watts is a measure of the amount of electricity being used - a rate of electrical power consumption. How do we calculate watts, volts, and amperage for an electrical device like an air conditioner? Watts (W) as used in a simplified manner here and by electricians, is a measure of electrical power and is expressed by any of the formulas shown below. At SEER RATINGS & OTHER DEFINITIONS we include additional examples of calculations of electrical usage by air conditioning equipment, including how we calculate watts, volts, and amperage for an electrical device like an air conditioner. In the above watts, volts, amps calculations, these simplified formulas are for DC voltage. If pf - power factor - = 1, then 1 VA of apparent power transferred in a circuit will produce 1 W of real power. It is interesting that in an electrical circuit, a load that causes a low power factor will draw more current than a load with a high power factor for the same a mount of usable or useful power actually transferred. Lots of electrical appliances include a label providing the appliance's wattage, and in the case of heating and air conditioning equipment, lots of other details are provided too. Watt (1736-1819), credited with developing a useable steam engine, for WATT which was named for him in 1882. To factor in time, as the electrical utility wants to do in sending us an electrical bill, the electric company's meter calculates the number. We list these common electrical terms roughly in the order that they are observed, from the electrical utility company's overhead wires and pole to the building receiving electrical power to its electrical panel, and in the panel to individual circuit breakers which provide power to and protect individual electrical circuits that distribute electrical power throughout a building. ELECTRICAL SERVICE DROP: the overhead electrical service conductors from the last electric utility pole (or other aerial support) to and including splices if any, connecting to the service entrance conductors at the building. Service-Entrance Conductors, overhead system: the service conductors (wires) between the terminals of the service equipment (main electrical panel) and a point usually outside of the building, clear of building walls (usually the electrical masthead, visible in this sketch), where the wires are joined by tap or splice to the service drop (the wires from the utility company). Service Conductors: wires connecting service point (such as the outside electric meter) to the main service disconnect (such as the main breaker in the main electrical panel). Service Equipment: usually the circuit breaker(s) or switches and fuses used to connect to the load end of service conductors coming to the building.
Circuit Breaker: a device designed to open and close (turn off or on) an electrical circuit by non-automatic means (a physical toggle switch) and to open the circuit automatically (internal trip mechanism) on a predetermined overcurrent without damage to itself when properly applied within its rating. Branch circuit: is the conductors (electrical wires, hot, neutral, ground) between the final overcurrent device protecting the circuit (a circuit breaker or fuse in the electrical panel) and the outlet(s).
A general purpose branch circuit is an electrical circuit that supplies two or more receptacles or outlets for lighting and appliances.
Alternating current is almost universally used for home electric power and is, therefore, the kind this article is primarily concerned with. Because voltage is the pressure that causes current to flow, the current will also change from zero to maximum to zero and will reverse direction and repeat. See our Electric Power Frequency Table for a table showing the voltage and frequency for nearly every country in the world, provided courtesy of Paul Galow, Galow Consulting. Direct current is most commonly found in homes in the form of electrical energy stored in batteries.
The real world is a little more complex; lots of devices draw more current when they're starting-up, especially air conditioners and refrigerators.
Electrical potential, a concept used to explain electrical voltage or volts, is illustrated at left, courtesy of Carson Dunlop Associates.
The word potential is used to explain that the capacity to do work is present, but not that work is necessarily being performed.
Water in the bucket in our sketch at left is a capacity to do work (move water, or exert pressure) but until water actually flows out of the bucket (say when it's tipped), no water is moving and no work is being performed. Electrical resistance can be thought of as how easily electricity flows through a material. A reason that the light bulb filament has high resistance is that it is very small in diameter. Electrical circuits, alternating current (AC), direct current (DC), short circuits, and other basics of electrical wiring are defined further in our series of articles on electricity for homeowners starting at ELECTRICAL CIRCUITS, SHORTS. What are the Definitions of Electrical Ground, Grounding Electrode, Grounding Conductor, Grounded Conductor, Ground Wire, Neutral Wire (Grounded conductor wire), Ground Rod?
Grounding to trip the circuit breaker or blow the fuse: Electrical grounding is necessary to protect people from electric shock by providing a good electrical path to route a faulty electrical connection (such as a short circuit) to ground (literally, to the earth) so that current will flow through and thus trip the circuit breaker or blow the fuse, safely and quickly turning off the electrical circuit.
Grounding to route stray electricity from static electricity, electrical power surges, lightning, etc. Grounding to provide a normal path for electricity to flow: energy flows in an building's electrical circuit from a power source (the utility pole through electrical panel, though building circuits and electrical devices connected to them) to the ground, to earth.
If there is no good connection to earth, electricity does not flow, though it might if you stand on wet ground and touch a live electrical wire - an action that could be fatal.
Here are some elementary electrical ground, grounding, and ground wire definitions to help us get our terms straight when discussing electrical grounds, grounding, and ground bonds. Grounding electrode or ground electrode: a metal conductor, usually a solid copper-alloy rod of specified length, driven into the ground in order to provide a point for electrical connection between the building grounding system and ground or earth. The grounding electrode conductor is the conductor (a wire) used to connect the grounding rod(s) to the equipment grounding conductor (the ground bus and ground wires in the electrical panel) OR to the grounded conductor (the neutral bus and neutral wires) OR to connect both of these to the grounding electrode (which is usually the case in residential electrical systems). Grounded Conductor: by traditional convention the grounded conductor or neutral wire is white or gray. In the electrical code, a grounded conductor is one which has been intentionally grounded - connected to the earth. Details and extensive definitions of the terms used in electrical grounding & ground systems for buildings are found at ELECTRICAL GROUND DEFINITIONS and at GROUND SYSTEM INSPECTION.
Also see our Electric Power Frequency Table for a table showing the voltage and frequency for nearly every country in the world, provided courtesy of Paul Galow, Galow Consulting. Continue reading at ELECTRICAL GROUND DEFINITIONS or select a topic from the More Reading links or topic ARTICLE INDEX shown below.
Question: What do I need to hook up DC running lights and a porch light on a gutted Airstream International trailer? I have a 1967 Airstream International planted in the backyard and want to run an extension cord out to it to run basic electric. At your local electrical supplier or auto supply store or even at Radio Shack you should be able to pick up a small External AC to DC power converter (aka AC to DC Power Supply). I used the term "External AC to DC Power converter or power supply because you don't want to have to buy a separate cabinet or case and do assembly. For just a few running lights and a porch light, most likely you won't even be drawing 10 watts, but to be on the safe side and to allow for expanded use of your power supply once you figure out how useful it is, I'd look at a unit with 35 watts or larger output.

Take a look at our DEFINITIONS of ELECTRICAL TERMS beginning at the top of this page for help with AC, DC, Amps, and Watts. Run a weather-resistant outdoor-rated extension cord from an outdoor GFCI protected receptacle over to the Airstream and inside it where it will be weather protected. If you're going to use this electrical supply system frequently you might want to put together a suitable plug connection feeding the DC powered circuit and a suitable connector on the wires that you run from the AC-DC converter. For more permanent power conversion of an older Airstream or other mobile home or trailer, I'd look at what's offered by RV suppliers. No not as I understand it; the amps rating is the maximum amount of current draw or demand that can be asked of the inverter. Alan Carson is an ASHI Member, national home inspection educator, author and building failures researcher in Toronto, Ontario.
Daniel Friedman, an original author of this article and the editor and producer of InspectAPedia where this article now appears is an ASHI Member, first ASHI Technical Committee chairman, editor and publisher of the ASHI Technical Journal, licensed home inspector, educator, and building failures researcher in Poughkeepsie, NY. Robert Klewitz is a licensed professional engineer, a professional home inspector, an ASHI Member, and has served on the ASHI Technical Committee as well as in other ASHI activities. Arlene Puentes, an ASHI home inspector in Kingston, NY, suggested text on the importance of safe electrical grounding.
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Recommended books on electrical inspection, electrical wiring, electrical problem diagnosis, and electrical repair can be found in the Electrical Books section of the InspectAPedia Bookstore. The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. The nominal impedance Z = 4, 8, and 16 ohms (loudspeakers) is often assumed as resistance R.
P = power, I = intensity, E = electro motive force (EMF = voltage), V = voltage, potential difference, R = resistance. Formula 1: Electric power P = V ? I - where power P is in watts, voltage V is in volts and current I is in amperes.
We include basic formulas relating amps, volts, resistance, watts, and we explain what these electrical terms mean in practical applications such as for building or appliance electrical power, electrical wiring, and basic troubleshooting. Using a water-in-pipes analogy, volts is analogous to water "pressure" in the electrical system. So volts is a measure of the strength of an electrical source at a given current or amperage level. Twice the power or energy can be delivered on a # 12 conductor by doubling the voltage and holding the current to 20 amps. We've already said that "120V" and "240V" are "nominal" ratings, meaning that the actual numbers may vary. An electrical load in an AC circuit will typically use both real power - P - and reactive power - Q - (definitions below).
We include additional more technical explanation of power factor, real power, apparent power, complex power, and reactive power just below.
Due to energy stored in the load and returned to the source, or due to a non-linear load that distorts the wave shape of the current drawn from the source, the apparent power can be greater than the real power.
If pf = .5 then to produce 1 W of real power we would need to transfer 2 VA of apparent power.
If an electrical circuit is drawing higher current, there is more energy loss, larger transmission wires are needed, and thus costs of both the circuit and its operation are increased. These are the electrical wires coming down the building exterior from a mast-head connection point to the electrical meter, and continuing inside to the main electrical panel or service switch. These are wires bringing electrical power from the electric meter into the electrical panel.
This is the main electrical switch, fuse, or breaker, usually in the main electrical panel but sometimes installed as a physically separate switch before the main electrical panel. In other words, the wires that bring power from the electrical panel to one or more points in the building where it will be used to power an light, power something plugged into an electrical outlet, or to an individual appliance. In an AC circuit, the amount of voltage applied to the circuit is constantly changing from zero to a maximum and back to zero in one direction and then from zero to maximum and back to zero in the other direction. The maximum amount of current, however, is determined by the load resistance and can vary as the load resistance varies. The chemical energy can be in wet form, as in your car battery, or in dry form as in flashlight and transistor-radio batteries.
120V household electrical circuit uses #14 gauge copper wire and is protected (and thus limited) by a 15-amp circuit breaker. 120V 20A household circuits use #12 gauge copper wire and are protected and thus limited by a 20-Amp fuse or circuit-breaker.
The electrical engineer (during design) or electrician (during house wiring) choose a circuit breaker that can tolerate that temporary high current but that will trip off if high current continues to flow on the wire.
Beginning with Thomas Edison, researchers discovered that if resistance in a wire is high enough the wire will get hot enough to glow (produce light) or even to start a fire (which is why the inside of an incandescent light bulb is a vacuum - to deny oxygen and thus protect the filament from simply burning up). We can re-write Georg Ohm's law to describe each of amps, volts, or resistance in terms of the other parameters, as shown below. In 2014 the New York Times reported the electrification of an entire New York City block (surfaces, sidewalks, manhole covers, storm drain grates, even metal door knobs) due to stray voltage traced to the combination of water, salt used for melting snow and ice, and a faulty Con Edison electrical service main.
The Times cited a Con Ed 2012 survey reporting 41 cases of people being shocked and 16 cases of animals being shocked by stray voltage in that year.
In an electrical circuit the grounded conductor (white or in two-phase current systems the neutral wire) normally carries electrical current between the un-grounded (hot) electrical wire and (back through the main electrical panel and grounding system) earth. As reader WT Smith points out below, the grounded conductor is not necessarily synonymous with the neutral conductor.
What you need is a converter that will have high enough Amps output for the few trailer lights that you cited.
When shopping don't rule out existing computer or other electronic power supply "bricks" - just take a look at the DC Wattage output that the supply can provide.
Srinivasan, MSEE, is a senior member of IEEE with 30 years experience in the electrical industry.
The text is intended as a reference guide to help building owners operate and maintain their home effectively. Having higher "pressure" in a pipe (or electrical conductor) means that conductor is capable of delivering more energy to the user.
Because there may be energy stored in the load and returned to the source (picture a rotating flywheel energized by electrical power), or due to non-linear loads on the circuit (the load is varying over time), apparent power can exceed real power in an AC electrical circuit. Electrical engineers may design equipment to include components that improve the power factor to thus lower its operating cost. Each complete change from zero to maximum to zero in one direction and then zero to maximum to zero in the opposite direction is called one hertz (formerly cycle).
Cycles-per-second, which you will still see marked in some electrical devices, is abbreviated cps. Such a circuit can deliver about 350 watts of electrical power to devices plugged into it, and another roughly 10 watts is consumed by the resistance of the circuit and its devices (receptacles and switches).
A smaller-diameter electrical wire has more resistance to electrical flow than a larger-diameter wire.
In some circumstances grounding can protect the insulation on electrical wires from damage due to high voltage. There are about 20 battery chargers and batteries plugged into one AC circuit that is presumably a 15 amp circuit. For example if you are selecting an electrical switch capable of handling 5A at 125VAC, it should be fine to use that switch on a DC current since the actual DC amperage draw will be a bit under 5 amps. Puentes has served as Hudson Valley ASHI (American Society of Home Inspectors) chapter president, and is active in professional education in the home inspection field. The direction of current flow is also constant and, as in AC circuits, the amount of current flow is determined by the load resistance. But as some writers have pointed out, for safety, household circuits are intended to carry less current (about 20% less) than their theoretical maximum. The protection against static electricity helps reduce the chances of an un-wanted spark that can cause damage to electronic components or cause an explosion of nearby combustible gases. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order.
80% of 2400 Watts is 1920 watts - that's about what you should expect to obtain from such a circuit.
If all of the batteries needed charging at the same time, drawing 40 amps, then the batteries would have to share the available 15 amps resulting in a very slow charge. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. To avoid this, designers use a gas safety valve that does not open until ignition is assured. Different manufacturers have designed different methods of keeping the gas safety valve closed until ignition is guaranteed. Carson Dunlop Associates' provides extensive home inspection education and report writing material.

Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order.
It is important to know which you are dealing with, because many of the valves look the same. How did we do?"A A "What are your thoughts on these new ways of; 'All-Green', All-Sustainable', and 'All-Climate' Community Living Styles? If you try to test a low voltage valve by putting high voltage across it, you will burn it out. Do not confuse the oven gas thermostat valve with the safety valve.
The oven gas thermostat valve is a valve you set by hand (the oven temperature knob) to control the oven temperature.
In some types of systems, the thermostat is not a valve at all; it is an electrical switch that opens or closes based on the oven temperature it senses. The gassafety valve, on the other hand, simply prevents gas from flowing to the burner until ignition is guaranteed.
In systems with an electrical thermostat, the safety valve opens and closes to cycle the burner on and off, but it still will not open if there is no ignition. The nice thing about gas ovens is that there aren't a whole lot of moving parts, so wear and tear is a relatively minor consideration. The sensing element sits right in the pilot flame. Just exactly where the sensor sits in the pilot flame is important.
All that's needed is a safety valve that will sense this tiny voltage and open the valve if it is present. To test, turn it on and test for continuity. Try cleaning the pilot orifice and pilot generator as described in section 6-5 and adjusting it a little higher.
The pilot generator needs to be sitting right in the hottest part of the flame as described in section 6-2. If that doesn't work, we have a minor dilemma in determining whether the problem is the pilot generator or the safety valve. The dilemma here is that the voltages are too small to be measured with standard equipment. And the safety valve, which is usually the problem, costs twice as much as the pilot generator. What I recommend is just to replace the gas valve first; that usually will solve the problem. Any tighter than that and you can damage the electrical contacts on the valve. 6-2 (b) CAPILLARY PILOT SYSTEMSIn some systems the sensor is a liquid-filled bulb, with a capillary to the safety valve or flame switch. When the liquid inside heats up, it expands and exerts pressure on a diaphragm, which opens the valve or closes the switch. It is important to know that these sensor bulbs do not cycle the burner on and off to maintain oven temperature.
If the pilot is out, the flame switch does not close and the 110 volt heating circuit is not complete, so the safety valve will not open. In hydraulic capillary systems, hydraulic pressure from the capillary physically opens the gas safety valve.
Gas for the primary pilot may come from either the thermostat or directly from the gas manifold. When the thermostat valve is turned on, the pilot flame gets bigger, heating the sensor bulb, which activates the safety valve (hydraulically) and the burner ignites.
Gas for the secondary pilot comes from the oven thermostat itself. When the oven reaches the correct temperature setting, the thermostat drops the pilot flame back to the lower level, the safety valve closes and the burner shuts off.
If you don't have a good strong pilot (secondary pilot, in two-level systems) that engulfs the pilot sensing bulb with flame, try cleaning the pilot assembly and sensor bulb as described in section 6-5. If it is a safety valve replace that. In a two-level pilot system, remember that the main oven thermostat supplies the secondary pilot with gas. So if you cannot get a good secondary pilot the problem may be the pilot assembly, or it may be the thermostat.
The spark module is an electronic device that produces 2-4 high-voltage electrical pulses per second. These pulses are at very low amperage, measured in milliamps, so the risk of shock is virtually nil.
The spark ignition module is usually located either under the cooktop or inside the back of the stove.
The same module is used for both the surface burner ignition and the oven burner ignition. However, the spark is not certain enough to light the oven burner, and the gas flow is too high, to rely on the spark alone.
These are the same switches as shown in section 5-3.The flame is positioned between the spark electrode and its target.
So when the pilot flame is burning, electricity from the spark electrode is drained off to ground, and sparking stops. Spark ignition, a pilot, a flame switch and TWO - count 'em - TWO safety valves; one for the pilot and one for the burner. When you turn on the oven thermostat, a cam on the thermostat hub closes the pilot valve switch.
This opens the 110 volt pilot safety valve and energizes the spark module, igniting the pilot. As in the other spark system, the pilot flame provides a path that drains off the spark current, so the ignitor stops sparking while the pilot is lit. As long as the oven thermostat is turned on, the pilot valve switch stays closed, so the pilot valve stays open and the pilot stays lit. When the pilot heats the pilot sensing element of the flame switch, the flame switch closes. Is there sparking after the thermostat is shut off? IF SPARKING OCCURS(The pilot may or may not light, but the main burner is not lighting) Remember that the thermostat supplies the pilot with gas in these ovens, and only when the thermostat is on.
So if you don't have a primary and secondary pilot flame, odds are the problem is the pilot orifice or oven thermostat.
If that doesn't work, replace the pilot assembly. If you do have a good strong secondary pilot that engulfs the pilot sensing bulb with flame, then odds are that the oven safety valve (or flame switch, whichever is attached to the pilot sensing bulb in your system) is defective. Replace the defective component.IF SPARKING DOES NOT OCCURSomething is wrong with the high-voltage sparking system. If you are in a hurry to use your oven, you can turn on the oven thermostat, carefully ignite the primary pilot with a match and use the oven for now; but remember that the minute you turn off the thermostat, the pilot goes out. Are the cooktop ignitors sparking? What typically goes wrong with the sparking system is that the rotary switch on the valve stops working. If the switch does not test defective, replace the spark module. Remember that these switches are on 110 volt circuits.
If you get too fast and loose with pulling these leads off to test them, you might zap yourself.6-4 GLOW-BAR IGNITIONA glow-bar ignitor is simply a 110 volt heating element that glows yellow-hot, well more than hot enough to ignite the gas when the gas touches it. It is wired in series with the oven safety valve. When two electrical components are wired in series, they share the voltage (see figure 6-I) according to how much resistance they have. If the ignitor has, say, two-thirds of the resistance of the entire circuit, it will get two-thirds of the voltage. So unlike the flame safety switch system (which has a safety valve that looks almost exactly like this one,) this safety valve is a low voltage valve. Let's talk about honey for a minute. When the ignitor heats up, the resistance drops, and electricity is able to flow through it more easily, and the voltage across it drops. Now apply that fact to what we just said about the ignitor and gas valve splitting the voltage. When the ignitor is cold, its resistance is high, and it gets most of the voltage. So much, in fact, that there isn't enough voltage left to open the safety valve. When the ignitor heats up, the resistance drops, the safety valve gets more voltage, and bingo!
Usually the fuse is located down near the safety valve, but in some installations it's under the cooktop or inside the console. If the ignitor gets old and weak, it will still glow, but usually only red- or orange-hot, not yellow-hot.
It can throw you; since you see the ignitor working, you think the problem is the safety valve. And electrical parts are non-returnable. When diagnosing these systems, I recommend replacing the ignitor first. And over a long long period of time this ash can build up and clog tiny gas orifices, like pilot orifices.
In an oven, it usually also means that the pilot will not get hot enough to open the safety valve, and the burner will not light. Or the ash might build up on the pilot sensing bulb, and insulate it enough that the safety valve operates intermittently or not at all.You can usually clean them out with an old toothbrush and some compressed air, but pilot orifices are generally so inexpensive that it's cheaper and safer to just replace them. If you choose to clean them out, use a soft-bristle brush like a toothbrush, and not a wire brush; a wire brush might damage the orifice. All that's needed is a safety valve that will sense this tiny voltage and open the valve if it is present. If you don't have a good strong pilot (secondary pilot, in two-level systems) that engulfs the pilot sensing bulb with flame, try cleaning the pilot assembly and sensor bulb as described in section 6-5. When the oven thermostat is on, and there isn't a pilot flame, is the electrode sparking? So if you don't have a primary and secondary pilot flame, odds are the problem is the pilot orifice or oven thermostat. Usually the fuse is located down near the safety valve, but in some installations it's under the cooktop or inside the console. If you do have any crusty stuff from accidental contact with food, clean as described in section 5-4.?Copyright 2011 GOFAR Services, LLC.

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