Electricians, a questions about volts.

[Kaiser Tang]

This a question for you electricians. I know the basics behind amps, watts, and volts. At home power comes out at 120 volts (about). Are volts constant? Meaning do all pieces of equipment consume power at the same voltage? Or do pieces of equipment draw power at 120 and others at 80 and others at 15 etc.? Does my question make sense?

[Kaiser Tang]

Since I'm here, I'll ask another electrical question. If I'm running a dual 400w ballast, am I using 800 watts of power or does the ballast decrease the power consumption?

[Crusty Old Shellback]

Volts should stay consistant but may vary slightly only because of the source, not the user. That varaition will be slight, less than 10% I beleive. Highly sensitive electronic devices will require more stable power, down to the 1% range. But you will usually only find that in some high end equipment. If the requirment for the equipment is that it needs a 1% stability within it, then it will have circuitry within to stabilize the input voltage since the source, power company, cannot supply it.

There are several ways of doing this. One is to use a higher frequencey of AC voltage, ie 400hz vice the 60hz that is common household frequency. The other is to convert the power to DC and then back to AC but at the higher freq, at 400hz. I work with several differnt high power radar systems that incorporiate both methods.

If you have 2 X 400 W bulbs running on a dual ballast, then yes you are using 800W.

[Kaiser Tang]

If a piece of equipment gives me a amperage and voltage rating such as 115V / 7.4 A does that mean that it draws 7.4 Amps at 115 Volts, meaning that the amperage would go up or down depending on the voltage.

[BlueCorn]

Originally posted by Kaiser Tang
If a piece of equipment gives me a amperage and voltage rating such as 115V / 7.4 A does that mean that it draws 7.4 Amps at 115 Volts, meaning that the amperage would go up or down depending on the voltage.

Yup. That's it exactly.

[israelnajar]

Don't forget a change in resistance can change voltage also.

[JOSEPHLB]

Originally posted by Kaiser Tang
If a piece of equipment gives me a amperage and voltage rating such as 115V / 7.4 A does that mean that it draws 7.4 Amps at 115 Volts, meaning that the amperage would go up or down depending on the voltage.

Also, alot of equipment will post the max amps or "100% load" amperage. Your real world amp usage may be lower than what is stated on the product.

[Kaiser Tang]

Originally posted by israelnajar
Don't forget a change in resistance can change voltage also.

What do you mean "change in resistance"?

[Crusty Old Shellback]

A change in resistance within the equipment will cause a change in curent draw as the voltage from the source is constant. The resistance can change for a number of reasons, age, heat, etc.

Also remember that when the components are made, ie resistors etc, they have a tollerence. Depending on the spec they are built to will determine the tollerence, + or - 5%, 10% or 15%. With that said, each individual piece of equipment will have a specific resistance due to the components within it. So each peice of equipment will draw a current based on that resistance. That is why you will have a difference between each peice of equipment of the same model number and manufacture. The manufactuer gives you anumber based on the original design and values of the components within the equipment. Unfortunatly we don't live in a perfect world.

[Kaiser Tang]

blown63chevy, my grandpa was in the Army and part of D-Day. I thank you!

[rsw686]

Like stated voltage is constant. You will have around 120v in your house. Equipment consumes voltage in terms of current which is expressed in amps.

Watts = Voltage X Amps

So if your equipment consumes X watts then you can calculate how many amps it will consume by dividing by 120 volts.

Likewise if your house voltage is 110V and your equipment is using 5 amps, at 120V it would be using 4.58 amps.

Household circuits are either 15A or 20A so the amount of equipment you have running should not exceed this value, if it does the circuit breaker should trip.

[alan214]

Originally posted by blown63chevy
Volts should stay consistant but may vary slightly only because of the source, not the user.

That's not entirely correct. When a piece of electrical equipment with a large voltage draw kicks in, it will drop the overall available voltage to that circuit (i.e. when the AC compressor turns on, my voltage drops from 120V to 196.7).

[BlueCorn]

Originally posted by rsw686

Watts = Voltage X Amps

That's actually only for DC.

for AC it's Watts = VOLTS x AMPS x PF (PF is Power factor)

[Kaiser Tang]

Now you guys are over my head. I'm basically just trying to make sure I don't overload a circuit. I calculated that on one breaker my equipment is 11.4 amps at 120 volts. If I have a 20 amp GFCI, should my breaker be above or equal to that.

[Crusty Old Shellback]

Originally posted by alan214
That's not entirely correct. When a piece of electrical equipment with a large voltage draw kicks in, it will drop the overall available voltage to that circuit (i.e. when the AC compressor turns on, my voltage drops from 120V to 196.7).

How does it DROP from 120 to 196.7?

Any load added to a circuit will cause a initial voltage spike. You can usually see this with a O'Scope. Most multimeters measure RMS voltage, not peak voltage. You need a special meter for that.

With that, you can see the flucations in the peak voltage. AC voltage is a Alternating Current, that means it goes both positive and negative. Each swing thru 0 Volts will only be half of the voltage. On a 120 V circuit, 60 Volts will be positive at peak, 60 volts will be neagitive at peak.

Voltage on a household circuit is actually 220Volts. It come sinto your power pannel on two "hot" legs and one netural. Inside the power pannel, it is split and you get one "hot" leg and one netural leg to produce your 110 Volts. As for teh current draw, the circuit is protecetd with a circuit breaker based on the size of teh wire run for that circuit. Just beacuse you have a 20 amp breaker on that circuit, it does not mean that you will have 20 amps on teh circuit anytime you turn something on plugged into that circuit. The equipment plugged into that circuit will only draw a current based on Ohms law (as stated by beergut )which takes into account the source Voltage and the resistance of the equipment. Once you have enough equipment running on that circuit to exceede teh 20 amps, then you will trip the breaker. Also remember that these breakers are "rated" at 20 amps and can trip at that value + or - a certin percent. This value will also change with rpeated use and age as it trips based on heat which is generated by current going thru resistance.

[Crusty Old Shellback]

OK to actually answer your concern, some stated in teh previous post. You can run put to a max of 20 amps continous on teh circuit if you have a 20 amp breaker. However, it is advisable to run something a bit less than the max for reasons stated above.

[clutch]

WOW power factor,amps,volts,ohms,watts,resistance,Alternating current, direct current,lets get some more confusing stuff like farads,capacitance,paralel circuit, lol

[Icefire]

blown63chevy not true, 120v ac have a 167v peak, both +/-. There is no such 60v.

Only thing you need to know is your breaker capacity in Amp, and the current from the lights/pump.

20A breaker can feed 16A of continious load (80%)
15A is 12A.

[Frick-n-Frags]

heh crazy thread......

some pretty loose theory flying around here, pretty entertaining

carry on.........

[amike5]

Originally posted by Frick-n-Frags
some pretty loose theory flying around here

Actually for the most part, most of the info here is factual.

[PrivateJoker64]

I've never seen 220 v except on a 50hz circuit (Europe). We have either 208 or 240 volts 60hz in the U.S.A. Let me qualify that by saying I have seen 277v on mining equipment and in a few lighting circuits in hospitals, and 480v on industrial equipment.
I have also seen (very rarely and dangerous) a grounded leg. That is, if you read from the grounded leg to an earth ground, you read zero volts. Read from the grounded leg to a "hot", 120v leg, and you read 240. That grounded leg is live, and dangerous if you don't know it's there. No one has ever explained that one to me.
"edit" - There is also what we call a "stinger" or "hot" leg. That leg carries 240v to ground. We always make very sure to use it as only on 3 phase equipment, and only on L3.

[alan214]

Originally posted by blown63chevy
How does it DROP from 120 to 196.7?

I'm no electician so I'm not sure why it drops from 120 to 196.7 but I definitely can see it when I connect a DVM to an outlet when the central air kicks in.

I'm not sure what all that other technical discussion of yours has to do with the fact that as a "user" of electricity, you indeed can affect the voltage on a circuit if a piece of equipment in your home can generate a large enough voltage draw.

[Icefire]

Originally posted by alan214
I'm no electician so I'm not sure why it drops from 120 to 196.7 but I definitely can see it when I connect a DVM to an outlet when the central air kicks in.

I'm not sure what all that other technical discussion of yours has to do with the fact that as a "user" of electricity, you indeed can affect the voltage on a circuit if a piece of equipment in your home can generate a large enough voltage draw.

It's a surge..

[PrivateJoker64]

Originally posted by alan214
I'm no electician so I'm not sure why it drops from 120 to 196.7 but I definitely can see it when I connect a DVM to an outlet when the central air kicks in.

I'm not sure what all that other technical discussion of yours has to do with the fact that as a "user" of electricity, you indeed can affect the voltage on a circuit if a piece of equipment in your home can generate a large enough voltage draw.

I'm sure that was originally supposed to be "96.7" not "196.7".
Inrush current on a large motor sure drops the voltage, although only briefly.

[JOSEPHLB]

Originally posted by clutch
WOW power factor,amps,volts,ohms,watts,resistance,Alternating current, direct current,lets get some more confusing stuff like farads,capacitance,paralel circuit, lol

aah.. lets throw some transistor theory in the thread also..