Electrical Wiring

Reactive power is well known as that component which is shunted back and forth from the source to the load over the AC cycle. However, this does not mean the system has no reactive power losses. In fact they would be quite high. Loss is always measured with respect to load and not the source. When we term it reactive power loss, it is not the amount of power taken away from the source and not returned. That way, there would absolutely be no reactive loss at all because all the energy stored in the reactive elements are anyway returned. The idea is after all to provide the power to the load. So, the loss represents the amount of power unable to reach the load. The power lines are not purely resistive. They comprise considerable level of reactive elements especially line inductance.

Now, the active power which actually runs the load is never a separate entity. It co-exists with reactive power because the reactive (more so inductive) components of the load need to be energized in order to power the load. Reactive power loss is thus that amount of power which is deficient or 'not supplied' to the storage (reactive) elements of the load because of the reactive elements on the line. Thus the loss is always to be visualized in terms of load. That is why the complete return of reactive power to the source in the negative cycle has got nothing to do with loss understanding actually.

Hope this helps!

If you have 12/2 wiring in this circuit and a 20-amp breaker controlling it, you can THEORETICALLY do it, but you've got another problem: according to code, if you've got a 20-amp breaker and a 20-amp outlet, you're only allowed to have one outlet in the circuit on the theory that a 20-amp outlet is going to have a 20-amp appliance plugged into it. If you want more than one outlet, you'll need to use 10/2 wire and a 30-amp breaker.

If you are asking this question, it implies you are not qualified to do the work. Hire a licensed electrician!

If the breaker is not already 20A, then absolutely not! An existing 15A breaker will have #14AWG wire to the outlet(s). For a 20A circuit, you must have a MINIMUM of #12AWG. If you try to push 20A through #14 wire, you could start a fire, not to mention it is illegal.

15A and 20A outlets are wired exactly the same, one just has a higher rating than the other.

A regular 120V outlet is already single-phase.

So, your question really is: Can an existing 15A, 120V circuit be converted to a 20A circuit by simply changing the breaker and receptacle to 20A? : No, the breaker, wiring, and receptacle(s) must ALL be changed to be safe and legal.

If the breaker is already 20A, and the wiring is already #12, then no modification is necessary. You are good to go as-is.

Tip: If your house has an outlet for a washing machine, check the breaker for it. Washing machines are supposed to have their own dedicated circuit, and that circuit is required to be 20A according to NEC article 210-11. You could use that outlet temporarily to do your welding.

IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB

SAFELY AND COMPETENTLY

REFER THIS WORK TO QUALIFIED PROFESSIONALS.

If you do this work yourself, always turn off the powerat the breaker box/fuse panel BEFORE you attempt to do any work AND always use a meter or voltage indicator

to insure the circuit is, in fact, de-energized.

if the wire is #12 or higher, then yes you can swap the breaker and receptacle. however, without ripping your drywall apart there is no guarantee that is #12 the entire run. back to your panel. if ihe wiring is open and you can verify its indeed 12 gauge....go for it.

A two-phase system is archaic and you are unlikely to find it in use anywhere these days, so it is mainly of historical interest. A two-phase, three-wire system, consists of two phase voltages, displaced from each other by 90 electrical degrees, and a phase voltage which is 1.414 x phase voltage.

A three-phase system consists of three phase voltages which are displaced from each other by 120 electrical degrees. In the case of a three-phase, three-wire, system, the line voltages are numerically equal to the phase voltages; in the case of a three-phase, four-wire, system, the line voltages are 1.732 x phase voltage.

Answer Take all phases into account. Voltage is measured between two phases of the three phases at one time, so what this means is this...first you read voltage between line 1 and line 2...then you read voltage between line 2 and line 3...and then from line 1 to line 3. Each phase of a 3 phase system is 120 degrees from the other in a 360 degree pattern. It takes all 3 phases to start a 3 phase motor but can run on two. If a 3 phase motor tries to start on two phases it is refered to as single phasing and can damage the motor.

Another Answer

First of all, let's get the terminology correct. The wires that join a three-phase load to its supply are called 'LINE conductors', not 'phase conductors'! This is very important. Phases, which are normally inaccessible, are either the generator windings, the transformer windings, or the individual loads, connected to the line conductors -this can make measuring phase voltages very difficult unless you can access the interior of these machines/loads.

The voltage of a three-phase system is normally defined in terms of its line voltage, not its phase voltage, so one normally measures its line voltage by connecting a voltmeter between any two line conductors or terminals. As the line voltages are determined by the supply system, all line voltages should be the same, regardless of which line conductors you choose to place the voltmeter between.

The important thing, however, and this is something your voltmeter will NOT tell you, is that the three line voltages are out of phase with each other -each lagging its predecessor by 120 electrical degrees. And this is important, because it is the phase displacement between these voltages, not the magnitude of each voltage, that allows -for example- a three-phase motor to self-start.

With a delta connection, picture a triangle. Each side of the triangle is a transformer or motor winding. Call the 3 corners of the triangle A, B, and C. There are only 3 wires except for a safety ground, which has no connection to, nor is any part of, the power transmission service lines.

All 3 windings have the same voltage, say for example 208V. If you take a meter, you will measure 208V between A and B, between B and C, and between C and A.

With a wye connection (also called a star connection) take our triangle above and use your wire cutters (literally) to cut the triangle apart at the corners. rearrange the three sides (transformer or motor windings) to form a Y. Where the three sides join in the center, connect a fourth wire. Call this wire "neutral". Call the three ends A, B, and C. Connect the 3 supply service lines to A, B, and C.

Now if you measure with your meter you will see 120V between the neutral and any single phase (A, B, or C), but you will still measure 208V between A and B, B and C, and C and A. The 208V is used to power three-phase loads and the 120V is very handy if you need to power a 120V single-phase load, such as a toaster! In a wye system, the supply service line-to-line voltage is 1.73 times the voltage from any phase to neutral.

Delta power is used for motors, 3-phase heaters, anywhere you don't need a neutral.

The biggest use of delta is in power transmission. Way too expensive to run a fourth wire all those miles, especially since a 3-wire delta transmits the same amount of power. Look up at a transmission tower and you see three phases and a ground wire for lightning suppression. No neutral.

At the destination, (a distribution transformer outside the home or business), the primary of the transformer is wired delta and the secondary is wired wye. This creates the neutral that can be used to derive single-phase power where needed. The neutral is grounded at the service entrance. Wye systems must be used where you have single phase loads that you must feed.

Interestingly, if you hide the neutral, you really can't tell the difference between star and delta systems. The phase-to-phase voltage is exactly the same. Most of the time 3-phase motors (which are internally delta-connected and have no neutral) are fed from a wye-connected source, simply omitting the neutral.

The three phase windings in a generator /tranformer/motor can be interconnected in two ways. If the similar ends of the coils are connected together and the other ends are connected to the 3 incoming supply service lines, that is called "star connection". The internally-connected point is brought out as the neutral connection. The service line "line-to-line" voltage (between any 2 lines) is 1.732 times the voltage between any line and neutral. Thus we can get two voltages for distribution within a building or site to supply lighting and power. However the service line currents are the same as the phase winding currents.

If the dissimilar ends of each winding are labelled A and B and the three windings are then connected together B->A, B->A, B->A, and the 3 incomiing supply service lines are then connected to the junctions, it is called DELTA. Here the values of line voltage and phase voltage are the same while the service line currents are 1.732 times the phase winding currents.

When the windings of a 3-phase motor are connected in STAR:

• the voltage applied to each winding is reduced to only (1 /.'/'3) [1 divided by root three] of the voltage applied to the winding when it is connected directly across two incoming power service lines in DELTA.
• the current per winding is reduced to only (1 /.'/'3) [1 divided by root three] of the normal running current taken when it is connected in DELTA.
• so, because of the Power Law V [in volts] x I [in amps] = P [in watts],

  the total output power when the motor is connected in STAR is:

  PS = [VL x (1/.'/'3)] x [ID x (1/.'/'3)] = PD x (1/3) [one third of the power in DELTA]

  where:

  VL is the line-to-line voltage of the incoming 3-phase power service

  ID is the line current drawn in DELTA

  PS is the total power the motor can produce when running in STAR

  PD is the total power it can produce when running in DELTA.

• a further disadvantage when the motor is connected in STAR is that its total output torque is only 1/3 of the total torque it can produce when running in DELTA.

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For more information see the answers to the Related Questions shown below.

If a +/- 10% service voltage variation is allowed then the 380 volts RMS "nominal" voltage could in fact vary between 342 volts and 418 volts.

Whether or not it would be safe to run a 3-phase motor, which was designed to run continuously on a 380V service, on a 415V service will depend on how closely the actual voltage which is being supplied stays to 415V because, allowing for a 10% variation either way, the actual service voltage could vary between 373.5 volts and 456.5 volts.

The lower voltage would be ok but the higher voltage would be too high such that there could be a risk of the motor overheating and/or catching on fire if the circuit breakers don't trip to shut off the current.

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As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.

Before you do any work yourself,

on electrical circuits, equipment or appliances,

always use a test meter to ensure the circuit is, in fact, de-energized.

IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB

SAFELY AND COMPETENTLY

REFER THIS WORK TO QUALIFIED PROFESSIONALS.

Isolation amplifier are good to reduce common mode noise interference in measurement's, breaking earth loops, isolate signals fx. from sensor to computer, etc.

Isolation amplifiers have application in many fields like:

- R&D and other professional laboratory

- Education

- Field measurements

- ECG, EEG & EMG measurements

Example of a classic isolation amplifier : http://www.h-instruments.com/Isolation_Amplifier__ISO-10___01Hz_to_100KHz/p484050_1774436.aspx

A fuse's main purpose is to quickly disconnect a short circuit from the distribution system. A circuit breaker has a twofold function: it trips on a short circuit by utilizing a magnetic sensor device and it also trips on a thermal device which senses a current overload that is higher than its rated current. Both devices are housed inside the breaker case.

Fuse: When the current passing through a fuse exceeds its rated value it physically burns through a thin strip of metal and opens the circuit so current can no longer flow. You have to get a new fuse to restore operation.

Circuit breaker: When a circuit breaker trips it opens a mechanical switch to interrupt the flow of current. You just need to reset the breaker and you are ready to go again.

In both cases you must always be sure to remove the cause of the over-current situation because, if you don't do that, the effects of a blown fuse or a tripped breaker will continue!

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Fuses and circuit breakers were invented to protect electrical items from being damaged by taking too much current (amps), something which is also known as an over-current fault condition.

When an over-current fault condition occurs, which is the same as saying the current gets bigger than the fuse can carry, its internal "fuse wire" gets so hot that it melts and breaks apart, which cuts off the supply of current. When that happens the fuse is said to have "blown".

After whatever caused the over-current fault condition in the circuit has been repaired, a blown fuse must either be replaced with a new one or, if it is the type of fuse which can be rewired, it must be repaired using the correct size of special "fuse wire".

A new fuse should then remain in place un-blown until another over-current fault condition occurs in the circuit it is protecting, which would then cause the new fuse to blow.

What are the advantages and disadvantages of fuses?

To give the same over-current protection, fuses are generally cheaper to make and smaller in size than circuit breakers.

However an ordinary fuse cannot blow as quickly as a circuit breaker can "trip".

Some equipment may require special "quick-blow" fuses so that damage can be prevented when an over-current fault condition occurs. Quick-blow fuses cost much more to make than ordinary fuses but must sometimes be used where a circuit breaker would be too expensive and/or too large in size.

Further notes about fuses:

• Some fuses are rewireable, meaning they can be repaired if they blow. This must only be done using new fuse wire of the correct size. It is dangerous to use fuse wire which is thicker than the size marked on the rewireable fuse's body.
• Other fuses, known as "one-time" or "cartridge" fuses, cannot be repaired when they blow. If that happens they must be thrown away and replaced by a new fuse of the correct size.

  Some one-time fuses look like small cylinders with a metal cap at each end; others look like a small cylinder with a metal screw-cap on one end like a light bulb. One-time fuses for vehicles, known as "fuse-links", have small bodies made of plastic and two metal blades which push into fuse slots in the vehicle's fuse box.

  If a one-time fuse blows it should only be replaced by a new one of the correct size (Amps) for the circuit. The ones which screw in have different sized screw-caps for each size of fuse, with matching sockets to ensure that only a fuse which is the correct size can be screwed into the fuse holder. Similarly, fuse-links have different sized metal blades and matching slots to ensure that a given slot can only accept the correct size of fuse link.

When an over-current fault condition occurs, which is the same as saying the current gets bigger than the circuit breaker was designed to carry, it's mechanism causes its switch contacts to open, which cuts off the supply of current. When that happens the circuit breaker is said to "trip".

When whatever fault condition in the protected circuit has been repaired, the circuit breaker can be "Reset" by pressing a button to close its switch contacts. The contacts should then remain closed until another over-current fault condition occurs in the circuit it is protecting, which would cause the breaker to trip again.

What are the advantages and disadvantages of circuit breakers?

To give the same over-current protection, circuit breakers can be designed to trip much faster than an ordinary fuse but they are generally larger in size and cost more to make.

However circuit breakers are re-usable and can easily be reset after they have tripped - provided, of course, that the fault condition in the protected circuit has been repaired.

A fuse is a protective device that destructively opens when the current flow exceeds a preset value. It is usually designed as a low value resistor that heats up and melts at the specified current value. Once the fuse blows, it must be replaced.

A circuit breaker is a protective device than non-destructively opens when the current flow exceeds a preset value. It is usually designed as a tripping relay/switch that can be reset and reclosed when the fault is cleared.

In both cases, the design can provide for different preset values as a function of time. It depends on whether the intended load pulls a larger startup current than when it runs, such as a motor, which can easily pull four times their run current when they startup. The protective device is selected for the specific type of load, and for the rating of the conductors supplying it.