Amps vs watts.

DeltaRed · Sep 21, 2022

How do you convert watts to amps? I have an appliance that is 1350 watts,and another at 1500. Dont want to overload a circut and pop a breaker. Thanks,Steve.

old · Sep 21, 2022

Been to many decades since I took this in school but if I remember right you divide voltage into watts to get the amps

Janicholson · Sep 21, 2022

Amps equal watts divided by Volts. 1350 divided by 120 equals 11.25 amps. 1500/120=12.5amps. No doing both at the same time on a 15 amp or 20 amp breaker/ Jim

Eric in IL · Sep 21, 2022

If you can remember this question it might help to remember the equation.

What is a volt amp?

Watts = volts times amps. Then transpose the equation to solve for whatever you are wanting to find.

old_bc · Sep 21, 2022

Here is a calculator to do it.
Calculator

MarkB_MI · Sep 22, 2022

For purely resistive loads, you divide the watts by the voltage. HOWEVER, you need to understand that the rated power (watts) ASSUMES a nominal voltage, typically 120 volts. If your voltage is higher or lower, the actual current will be higher or lower, respectively, than this calculated value.

Here's an example: A 1200 watt resistive device, rated at 120V, will draw 10 amps at its rated voltage. But what if your house voltage is 125 volts? The actual current draw will be 10.4 amps. (Ohm's law tells us the load resistance is 120 volts &div; 10 amps = 12 ohms; at 125 volts the current is 125 &div; 12 ohms = 10.4 amps.) Probably close enough for your purposes.

BUT, when you start dealing with inductive loads, particularly motors, it's a whole 'nother ball game. First, although motors are often rated by power (either in horsepower or watts), they draw VOLT-AMPS, aka apparent power. Without going too deep, just understand that a AC motor's volt-amps will be significantly higher than its power. For example, a 1200 watt motor might actually draw around 1700 volt-amps.

The other thing about motors is they tend to draw however many amps they need. This means that as their supplied voltage drops, they tend to draw MORE AMPS, unlike resistive loads which behave in the opposite way. That's why a motor that works just fine plugged into the wall will blow the circuit breaker when you put it on an extension cord.

I'm going to assume the appliances you're dealing with are purely resistive, but if they're not tell us what you have and we'll go from there.

gene bender · Sep 22, 2022

AMPS TIMES VOLTS = WATTS Example 10 AMPS times 120 VOLTS = 1200 WATTS

buickanddeere · Sep 22, 2022

Mark MI has the only correct answer .
Failure to understand reactive power is one of the reasons cheapskates who purchase minimum sized generators . Who then wonder why the generator trips the breaker when the "watts match " .

Tim PloughNman Daley RIP · Sep 22, 2022

OHMS LAW

V or E = VOLTAGE -measured in VOLTS (V)

I = CURRENT -measured in AMPERES (A)

R = RESISTANCE -measured in OHMS ()

P = POWER -measured in WATTS

FORMULAS:

I = V/R

E = IR

P = IE

I = P/E

I = E/R

R = E/I

P = IE

Tim Daley(MI)

Tim PloughNman Daley RIP · Sep 22, 2022

OHMS LAW

V or E = VOLTAGE -measured in VOLTS (V)

I = CURRENT -measured in AMPERES (A)

R = RESISTANCE -measured in OHMS ()

P = POWER -measured in WATTS

FORMULAS:

I = V/R

E = IR

P = IE

I = P/E

I = E/R

R = E/I

P = IE

BarnyardEngineering · Sep 22, 2022

(quoted from post at 02:52:40 09/22/22)
Mark MI has the only correct answer .
Failure to understand reactive power is one of the reasons cheapskates who purchase minimum sized generators . Who then wonder why the generator trips the breaker when the "watts match " .

True but it's more than most people care to know.

Watts = Volts x Amps puts you in the ballpark, ESPECIALLY when you're talking about appliances where the manufacturers make claims of XXXX Watts. ESPECIALLY ones with inductive loads, like your "5.1HP" vacuum cleaner that runs off 120VAC.

Geo-TH,In · Sep 22, 2022

Short answer, Most 120v circuits in a house are wired with 12g wire, 20 amps. 2400 watts. Typically you want to keep the watts around 80% of 2400w.
Add your 1350w and 1500w and you have exceeded 2400 watts. You will trip the circuit breaker..
When I wire a new kitchen, I like to have a dedicated circuit for the fridge only. One for the microwave. Two more circuits for other appliances on the countertops.. No GFCI for fridge.
The other 3 should have GFCI protection.

BarnyardEngineering · Sep 22, 2022

MOST household circuits are 15A, wired with 14ga or even 16ga wire.

Only people who wire their own houses and are fans of overkill would put in all 20A circuits.

dr sportster · Sep 22, 2022

The reason for no fridge GFI is because it will ruin the floor to keep pulling out the fridge to reset the GFI.

Blackhole49 · Sep 22, 2022

If wiring from scratch and have unlimited breaker space, more is better. That being said, I've been in our house 37 years. Our kitchen is on 1 20 amp breaker with #12 wire. I can guarantee you that, at various times, the coffee pot , microwave, toaster and frig have been on at the same time. I have never tripped a kitchen breaker.

miangus · Sep 22, 2022

Great answer!

Goose · Sep 22, 2022

Those are the formulae we always used in Avionics in the Marine Corps.

But on the last one, don't you mean P/IE?

E(Volts) = Power in watts divided by Current in amps.

Current in amps = Power divided by volts.

Did I get this right? It's been years.

miangus · Sep 22, 2022

That would be me. Built my home in 1976, 200 amp 40 breaker box, all non 240 circuits have 20 amp breakers. All number 12 wire. GFI in the box on required circuits, added ARC fault later. All Square D QO. MY wife's contractor uncle thought I was crazy. My wife's other uncle ran a whole sale electric business and got us everything at his cost. If GFIs are installed in the circuits a location map should be taped to the breaker box. For a few dollars you can get the really nice magnetic labels to label the circuits.

DoubleO7 · Sep 22, 2022

(quoted from post at 10:53:24 09/22/22) The reason for no fridge GFI is because it will ruin the floor to keep pulling out the fridge to reset the GFI.

You could have two outlets on one circuit, the accessible outlet being a GFI upstream of fridge.

DoubleO7 · Sep 22, 2022

(quoted from post at 10:51:10 09/22/22) MOST household circuits are 15A, wired with 14ga or even 16ga wire.

Only people who wire their own houses and are fans of overkill would put in all 20A circuits.

Yep, everywhere but in Terra Haute, IN.
Per local code, per George last week.

BarnyardEngineering · Sep 22, 2022

(quoted from post at 08:29:10 09/22/22) That would be me. Built my home in 1976, 200 amp 40 breaker box, all non 240 circuits have 20 amp breakers. All number 12 wire. GFI in the box on required circuits, added ARC fault later. All Square D QO. MY wife's contractor uncle thought I was crazy. My wife's other uncle ran a whole sale electric business and got us everything at his cost. If GFIs are installed in the circuits a location map should be taped to the breaker box. For a few dollars you can get the really nice magnetic labels to label the circuits.

Yeah, if you're paying someone to do it and/or retail for the wire, it's a lot more to go with all 12ga and 20A circuits. Generally it's not necessary unless you are planning on putting a refrigerator in every room...

Tim PloughNman Daley RIP · Sep 22, 2022

HiYa Goose-

DEFINITION:

P = IE

POWER (WATTS) equals I (AMPS) times E (VOLTS)

EXAMPLE:

5 Amps x 240 Volts = 1200 Watts

Geo-TH,In · Sep 22, 2022

No not all refrigerators and motors get along with GFCI.
I HAVE a refrigerator that trips the GFCI EVERY TIME it goes through the defrost cycle.
Works fine without GFCI.
3 wire cord and no one can get shocked.
Rarely my vent fan in bathroom trips GFCI when I turn the fan off.

Johnhof · Sep 22, 2022

Divide watts by volts you have amps

Goose · Sep 22, 2022

True, but you get Amps by dividing Power by Volts, and you get Volts by dividing Power by Amps.

buickanddeere · Sep 22, 2022

There is a possibility that the breaker is welded closed .

buickanddeere · Sep 22, 2022

(quoted from post at 16:01:53 09/22/22) Divide watts by volts you have amps

What is your answer if the load on the circuit has a lagging power factor of 0.8 ?

buickanddeere · Sep 22, 2022

What kind of electrical load ?
Most people here are unaware of or are ignoring reactive , inductive and apparent power .

Amps vs watts.

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