Tag: watts

What is the difference between voltage and current?

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Voltage and current are two different measures that are found in electricity. They are both present in every electrical circuit from the flashlight all the way to refrigerators. But, the question is what is the difference? To illustrate the difference between voltage and current we will look at the age old comparison of electricity to water.

Current Flow

Current is a bit easier to illustrate. We can compare it to water in a garden hose. Imagine you have a simple water wheel. To make this water wheel turn you need to pour water over it. Let’s say we have two different sized water hoses. One is 3/4″ and the other is 1″. Now, let’s pour the water over the water wheel with the smaller hose and see what happens. The water wheel turns. Now, the larger hose. What happens? The water wheel turns faster.

This is a result of more water flowing in the larger water hose. More water = faster water wheel. Pretty simple. We need to make sure that when we think of current in the same way as water in a hose that we always think of the hose as full all the time. That way when you turn the hose on you instantly have water flow.

In the early days of electricity it was a commonly held belief that electricity was a fluid. This fluid was made up of tiny particles that would flow into different materials.

Voltage, the Driving Force

Again we are going to compare voltage to the water system. First remember that voltage is the driving or electromotive force that is a part of electrical circuits. How does this translate to water? Think of the voltage as the pressure in a water system.








With the two hoses from the example above how can we make the smaller hose move the water wheel faster? With more pressure of course. So, with more pressure the smaller hose can make the water wheel turn faster. How does this relate to voltage?

Example

Look at the distribution lines above your head next time you are out and about. The wires on these lines carry thousands of volts. However, they are not very big. Remember Ohm’s Law? Let’s say you have a 2,500 watt motor. This is a multi-voltage motor. Meaning that you can wire it a couple of different ways depending on the voltage available. You need to run new wires to this motor, but what size do you need? That depends on the voltage.

Wait, I know what you are saying. Wire is sized by the number of amps. You are correct. However, depending on the voltage we may be able to run a smaller wire therefore possibly saving money. If the voltage in this case is 120 then the amperage will be 2,500/120 = 20.8 amps requiring a 10 gauge wire. If the voltage is 240 then the amperage will be 2,500/240 = 10.4 amps requiring a smaller 12 gauge wire.

Conclusion

Voltage and current are two different quantities that go hand in hand. Voltage is the driving force while current is the flow of electrons in the circuit.









What is Electric Current and how it relates to Metering

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What is electric current? A good question indeed. What is the unit of measure for electric current? How can we measure electric current and the difference between current and voltage? And finally how does it relate to metering? These are the questions that will be tackled in this post. So, let’s get started with the first one.

What is electric current?

Electric current is the flow of electrons in a circuit. It is also what is used to power our stuff. Remember that in a circuit we have both voltage and current available. But, without the current flow our electrical stuff does not move. So, now that you know that electric current is the flow of electrons in a circuit what is the unit of measure used?

What is the unit of measure?

Current is measured using what are known as amperes, or amps for short. This is typically notated as an “A” in formulas but can also be notated as an “I”. This “I” stands for intensity of current. As with any unit of measure amps can be smaller or larger. So, it is not uncommon to see milliamps or kiloamps. Milliamps is typically notated as mA and kiloamps as kA. So, now that you know the unit of measure, how do you measure amps?

How do you measure Amps?

Amps, or electric current, are measured using what is known as an ammeter. An ammeter can come in a couple of different varieties. There is the common clamp on ammeter. The clamp on ammeter comes with a spring loaded jaw that enables you to open the jaw and place it around the conductors. This places the ammeter in parallel with the circuit. Clamp on ammeters can be found in digital and analog variants.

Another type of ammeter is placed in series with the circuit. These are typically found on multimeters. Also, when an ammeter is placed in series in the circuit it typically is not able to measure a very substantial load. Make sure you read the specs on your meter before you place it in series in any circuit.







How does electric current relate to Metering?

Ah yes, finally, the meat of the article. Electric current is very important to metering. This is because we are essentially measuring the changes in current flow. Remember that using Ohm’s law and the power formula that Watts = Volts x Amps. This means that the amount of watts used are in direct proportion to the amount of current that is being used. As the amps go up, so does the watts. As the amps go down so do the watts.

We as meter techs should know how amps relates to watts and how to convert amps to watts. We should also know how to go the other way and convert watts to amps. This will help us in troubleshooting with customers. Let’s have an example.

A customer is complaining of a high bill. You go to the meter and notice it is spinning pretty fast. So, you take the cover off the meter base and check the amperage. Let’s say that it is 30 amps. How do you convert this 30 amps to watts? Using Ohm’s law we plug in the numbers. Assume this is a 240v service. W = 240 volts x 30 amps = 7,200 watts. Let’s convert that to kilowatts and divide 7,200 by 1,000. We get 7.2 kw. This means that whatever the customer has on is pulling 7.2 kw and if left on for one hour it will use 7.2 kwh. A load like this could mean that an appliance like the air conditioning is not functioning properly and is running all day.

Conclusion

Electric current is one of the most important units we have in metering. It is measured by using ammeters and its unit of measurement is the amp. Using Ohm’s law we can convert amps to watts and back again.








What is Voltage and how it relates to Metering

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What is voltage? This is certainly an important term to know in the electrical field. You hear it all the time. What is the voltage on the machine? Or, can you check the voltage on that circuit? We hear it, we say it but, what is voltage and how does it relate to metering?

What is voltage?

The most commonly used voltage definition states that voltage is the difference in potential between two points in a circuit. What a definition of voltage right? Another way that voltage is defined is by talking about water. Some find it easier to understand the voltage definition when we talk in terms of water pipes. Voltage is the driving force in an electrical circuit. We can think of it as the pressure in the circuit. So, what is voltage? It is the driving force in an electrical circuit.

How is voltage measured?

Voltage is measured using a voltmeter. With a voltmeter we can choose two different points in the circuit to measure the difference in potential across those two points. The unit of measure for voltage is known as the volt. The volt is named after Alessandro Volta who created the first battery known as a voltaic pile.

How does voltage relate to metering?

Ah yes, the big question is, how do we use voltage in metering? Well, we have to remember that meters measure kilowatts. So, what does that have to do with voltage? To find the kilowatts, we first need to find the watts. To calculate watts we need to know the current and the, you guessed it, voltage. Using Ohm’s Law we know that power is equal to voltage times current or stated mathematically, P = I x E. There are several ways you can remember this formula. One is by remembering the word PIE. Another is to change the letters to W = V x A.








In the first example, P = power measured in watts, I = current measured in amps, and E = voltage measured in volts. Just a quick fact here, E is the letter used because it stands for electromotive force which is a fancy way to say voltage.

In the second example, W = watts, V = voltage, A = amps. So, the two equations are equal they are just using different terms. The easy way to remember W = V x A is to think of West Virginia or W VA. Pretty simple right.

So, now that we know the terms we need to know how they relate to metering. Well, the nominal voltage in a typical metering circuit remains pretty much constant. A common household voltage is 120/240. So, the meter measures this voltage and then multiplies the voltage times the current in the circuit to get watts. And then as if by magic the readout is in kilowatts.

What?

Look at the equations again and go back to algebra I. If the voltage stays constant and the amperage goes up that means that the wattage will go up. If the amperage goes down, the wattage goes down. To get kilowatts from watts, divide the watts by 1000. In the older electromechanical meters the voltage coil, also known as potential coil, produced a magnetic field in the meter. When current flows through the meter it produces a magnetic field as well. The interaction between these two fields are what causes the disc to turn. So this is why it is important to make sure that the meter chosen for each installation is crucial.

Conclusion

Voltage is the driving force behind each and every electrical circuit. We can use Ohm’s law to calculate watts using the power formula. It is the interaction of voltage and current in a circuit that causes the meter disc to spin. To check the voltage in a circuit we use what is called a voltmeter.









Meter Multipliers

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Watthour meter multipliers are used whenever current transformers and/or voltage transformers are used in a metering circuit. The most often question that I am asked about watthour meter multipliers is how to calculate the watthour meter multiplier. It really is a simple thing to do and this article will explain.

Current Transformers and Potential Transformers

CT’s and PT’s are used to step down current and voltage in a metering circuit to a safe and measurable level. But this leaves us with a little bit of math to do to accurately calculate the number of KWH or kilowatt hours the customer has used.

To calculate the meter multiplier we need to know what the CT ratio and PT ratio are. The best way to explain this is with an example.

Meter Multiplier Example 1

Let’s say for instance that you have a 120/208 three phase 4 wire wye service that is using 400/5 CTs.

How would you determine the watthour meter multiplier? You would simply do the math. 400/5 means 400 divided by 5 and if we do this math we come up with an answer of 80, this is our watthour meter multiplier. What if we had 600/5 CTs? 600 divided by 5 is 120, so our watthour meter multiplier is 120.




Now what if the service that we are metering is a 480v service and we are using PTs? For this example let’s assume we are metering a 480v three phase 4 wire wye service by using 400/5 CTs and 2.4/1 PTs. How do we come up with the watthour meter multiplier in this example? We would use the same method as before to find the CT ratio and do the math of 400 divided by 5 which equals 80 but we are not finished because in this example we also have PTs. Before we do the math let’s remember Ohms’s law which says that Watts = volts x amps. Let’s also remember what we are trying to figure out. We are trying to find the multiplier for the WATThour meter. So to find watts we need to multiply volts x amps. We already know the amps part of the equation equals 80 so what is the volts part? It is 2.4 because 2.4 divided by 1 is 2.4. So, we now multiply 80 x 2.4 and we come up with 192 which is our watthour meter multipler.

Meter Muliplier Example 2

Another example with PTs and CTs. Say you have a 480v three phase three wire service with 200/5 CTs and 4/1 PTs. What is the watthour meter multiplier? 200 divided by 5 equals 40. 4 divided by 1 equals 4. So, 40 x 4 = 160. Thus, the watthour meter multiplier would be 160.

When you divide out the CT ratio and PT ratio and multiply them together this is also known as the transformer factor.

Conclusion

So, there you have it.

To calculate watthour meter multipliers first you need to determine whether there are CTs and PTs or only CTs in the circuit. Next, divide out the ratios. And lastly, multiply the ratios to determine the watthour meter multiplier.