Hello: I would like to ask a question pertaining to resistors and specifically WHY one would use a resistor.

I understand what resistors are used for in residential installations i.e. to offer resistance to the flow of electricity. But I would like to know why one would need a resistor. Why does there have to be a resistance to the flow of electricity in a commercial or residential setting?

I understand also that there are different kinds of resistors, but again, my question would not pertain to that specifically. Only to WHY resistors are installed to begin with.

Thanks very much in advance for your replys.

Also, if you are an Journeyman electrician, your answer would be much more appreciated over one who may only know only a little about electricity and electrical components. Again, thanks in advance for your reply. :)

OK, resistance in general is an undesirable property in power transmission, but it is an electronics component satisfying ohms law: R=V/I.

It is a Desirable property when you you want to make heat as in resistance heating as in Pd=V^2/R or power disapated is equal to the voltage aquared dived by the resistance.

Agreed. Everything that draws current (a load) will have resistance.

If you are referring to a resistor, as in electronics, they have no place in typical AC wiring.

What information is it you are looking for? Your query is a bit strange. One would not use a resistor (by this I mean electronics) in residential wiring.

Well, a lamp wouldn't work if it didn't have reistance, would it?

A typical purpose for resistors in everyday building wiring is in fire alarm systems. This may be where you ran into some.

A resistor is used at the End Of Line (AKA EOL) for various circuits, to allow a small amount of current to flow, to prove the circuit is working. Wiring for fire alarms are "supervised", or monitored, continuously to prove the circuit is always ready to operate when needed.

If there is a break in the wiring, or a connection comes loose anywhere in the circuit, the small amount of current drawn by the resistor stops flowing, the fire alarm control panel sees this as a problem, and issues a trouble alarm warning to get someone's attention the system needs repair.

Hello everyone. I will just take a quick moment to answer stanfortyman's question with respect to what it is that I'm looking for in concern to my query.

Its not that I'm looking for an answer to home electronics, though its interesting to read of, though not quite what I'm looking for. More so for receptacles, lights, etc, in residential settings, and WHY resistors are needed. WHY are resistors used in industrial applications {large scale industry}.

WHY are resistors needed?


again. I understand that resistors can displace a lot of heat and how one can measue their ohmic value as per their color coding and how one can tell of their size proportional to their wattage rating... those I all know.

basically, what I really don't understand is WHY resistors are used. Thanks in advance for your reply. :)


EDIT: I just read tkrussell's answer hand he mentioned "...to allow a small amount of current to flow, to prove the circuit is working..."

I think this might help me know WHY resistors are needed. Is this the reason , as it seems now logical to understand why.

basically, what I really don't understand is WHY resistors are used. They are NOT. That's my point.

They are NOT. That's my point.


I don't understand.

Firstly, home electronics is commonly referred to as TV's , radio's, computers, etc... yes?

I don't understand.Neither do I.

Resistors as you describe are NOT used in AC construction electrical wiring. They are used in electronics, such as an alarm panel.

Neither do I.

Resistors as you describe are NOT used in AC construction electrical wiring. They are used in electronics, such as an alarm panel.

Yes. That's the sort of answer to my query that I'm looking for. Not for home electronics. I.E. tv's, radio's, little gadgets, etc... more so geared to residential, commercail, and industrial wiring. But I think that someone in this thread did help me to understand WHY resistors are organized into electrical circuts. To prove that the circuit is working when the resistor is drawing a small amount or current from the load. If the resistor is not drawing a current from the load, then, in the case of fire alarms, the fire-alarm panel recognizes the fact that there is no current being drawn and sounds an alarm or message re: the fact that a part of the system is malfunctioning.

Is this correct?

Is this one of the reasons resistors exist?

Perhaps this will help you:

Resistor - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Resistor)

I think you are confusing yourself, AND me.

You are saying:
"Its not that I'm looking for an answer to home electronics, though its interesting to read of, though not quite what I'm looking for. More so for receptacles, lights, etc, in residential settings, and WHY resistors are needed. WHY are resistors used in industrial applications {large scale industry}."

You say you are not looking for information about resistors in electronic circuits.
You say you are interested how they are used in lighting and receptacle circuits.
Several times I tried saying they are NOT, at all, ever, used in those types of circuits.

Now you are saying:
"Thats the sort of answer to my query that I'm looking for. Not for home electronics. I.E. tv's, radio's, little gadgets, etc...more so geared to residential, commercail, and industrial wiring. But I think that someone in this thread did help me to understand WHY resistors are organized into electrical circuts. To prove that the circut is working when the resistor is drawing a small amount or current from the load. If the resistor is not drawing a current from the load, then, in the case of fire alarms, the fire-alarm panel recognizes the fact that there is no current being drawn and sounds an alarm or mesage re: the fact that a part of the system is malfunctioning."

As I said before, a fire alarm panel is an electronic circuit. VERY different from lighting and receptacles.


Is there something I am not seeing or reading right??

There is resistance in wire per foot, too long or too small of a wire, the resistance may be too great and will have an excessive voltage drop. Resistance is not desirable in electricity(usually).
They do use diodes in light bulb sockets, so it uses half of an ac cycle, saves electricity.

Great Question, my kind of question. Eveyone knows everything about them but not why they are needed. Here is what I was able to find online. Resistors are made for the express purpose of creating a precise quantity of resistance for insertion into a circuit. They are typically constructed of metal wire or carbon, and engineered to maintain a stable resistance value over a wide range of environmental conditions. Unlike lamps, they do not produce light, but they do produce heat as electric power is dissipated by them in a working circuit. Typically, though, the purpose of a resistor is not to produce usable heat, but simply to provide a precise quantity of electrical resistance.

Electronics has MANY Uses for Electronics, Timing, Filters, Amplifiers,
Many Many Uses.

I don't think the question has been answered yet. The definition has been offered, the description has been offered as well. But the question was... "why are they needed".

So... Why are they needed?

Why is anything Really needed?

Without them no electric heat, no electric water heaters etc.

No resistive sensors like gas pedal position.

The material property resistivity would vanish. No semiconductors for starters.

Can't the "alarm system" get the idea that a circuit is broken because it is not getting a return current from the source?
I don't think resistors are needed in that scenario. But I do know why resistors are used in things like cameras... because they build up power and then BANG. Releasing the stored voltage through a light bulb producing a flash for taking photos at night. That's one application of a resistor.

(Electronics) Resistors are inserted in circuit to create a Voltage drop (IR). The drop is used to power the next electronic device in the circuit.
Thumbnail description - High Level viewpoint.

In electricity, you do not really see the effects of a Resister. First of all a resister will not behave in well in an AC circuit. The sine wave has to be manipulated to take advantage of a resistors services.

What you see is a "Load" and within the Load is the resistance needed to create the necessary voltage and amperage's for the device to operate.

In the world of electronics you are more likely to see an AC power source rectified (converted to DC). The design used to call for what is called a Diode Bridge.

Once the source has been rectified, then the use of resistors and capacitors are much more straightforward.

MGM092692, The End of line resistors used in a Fire Panel, has a Known value, say 2200 ohms.
Detectors need 2 wires for power and a pair for supervision, In a alarm condition a detector in the circuit will close making it zero ohms, triggering an alarm, If the wire is cut, resistance will go high and show as line trouble.

Stan:

Beg to differ a tiny bit. See http://ecatalog.squared.com/pubs/Machine%20Control/0140CT9201.pdf

pdf page 69, document page 65 figure #1

A part-voltage motor starter CAN use resistors.

Shunts or low value resistors allow one to measure currents by looking at the voltage drop across the resistor. Typical values might be 50 mV drop at 100 AMPS.

Shunt ammeters.

Dynamic braking for motors can also use resistors.

These are the applications of pure resistors in an electrical AC environment I can think of.

Lets go back a ways in the old automobile ignition system consisting of points, condenser and a coil to generate a spark. The ignition switch would provide full voltage to the coil when starting. When running, the current would be limited by a resistor mounted on the firewall. This resistor extended the life of the points. I know, this isn't what you asked.

Now, triggering is replaced by a magnetic sensor and a computer. When I was 16ish, I converted my ignition system in my first car from points to an optical system.

Generally you will be considering resistive losses in a circuit. The wire size you pick, for instance must have less than a particular loss. Measuring the contact resistance when troubleshooting. Wire has resistance.

MGM, A capacitor is what you were describing.
However, the Resistor used as an end of line resistor is needed to show an intact circuit, without it, if you had a short across the pair, it would not be seen without the resistor. It MUST be within a couple of hundred ohms(more or less depending on Panel) or it will show as a fault.

Commercial fire alarm panels that I had to interface with used 4700 ohms for monitoring of a contact closure.

I used that plus a three wire system, so I also had an indicator. Off when tripped or turned off because we routinely disabled the panel during fire alarm testing.