How many amps per leg on a 220V circuit?

Question

If the nameplate on a piece of 240VAC equipment says 10.0 Amps, does that mean that the load is 10 amps per leg, or 10 amps total, therefore 5 per leg?

Answer 1

If you put a current meter one leg, it reads 10A; if you put it on the other leg, it also reads 10A. But that does NOT mean there is "20A" in the circuit. The current in the two wires is not additive. Current flows from one point to another through the CIRCUIT, and the circuit consists of those two wires.

Answer 2

The confusion is not the amperage. The confusion is how much power do you have. For the record a 10A 220V circuit will have a minimum 10A/2 pole Breaker.

In the USA a 110v, 10A circuit will pull 1100VA. A 220v 10A circuit will pull 2200VA, twice as much power as the 110v circuit. Technically on a 220v that is connected to 2 phases there is no return. That's as simple as I can make it for a DIY'er. Otherwise we need to get into a course on phase relationships.

Answer 3

10A in one hot, 10A out the other hot

A 240V-only piece of gear connects to two hot legs and a ground (no neutral), so if it pulls 10A, that 10A has to be going in one hot leg and out the other hot leg -- there's nowhere else for it to go! (In other words, it draws 10A, period -- the legs do not "add together".)

Answer 4

10A, you're confusing current (measured in Amperes) with Energy (measured in Watts):
10A@ 12V => 120W
10A@ 120V => 1200W
10A@ 240V => 2400W
So the same current (directly related with wire thickness) can carry more energy rising the voltage.

Breakers are there to protect against overcurrent, so a 10A will break at 10A being at 24V, 120V or 240V.

All the current coming from one "leg" is going out trough the other (if the neutral is involved the vector sum on legs and neutral should be 0) It means than one leg may carry 9A, the other 10A and the neutral 1A (I'd say -1A because it's "going back" to the transformer).

Answer 5

On a 240 volt circuit 10 amps is 10amps on each leg bot not calculated as 20 amps if you can slow it down the amps high pathetically when one leg reads 10 amps the other leg reads 0 alienating back and forth 10amps then 0

Answer 6

There are a lot of answers out there about this that don't get the idea across I think people are asking for. So adding to an old post that comes up a lot in search results for people getting frustrated with the same odd responses about 220v current measurement for non technical people. This is a long one but it's to cover a lot of the follow up questions and to get them to ask more detailed questions if they have them.

I am not an electrician, don't be dumb, it's your safety, correct me if I'm wrong, etc.

Three things to start out with:

All electrical current has to have a complete path, a full circle. Nothing happens if this path is broken, it's just waiting voltage but no current and no work getting done. You flip the light switch off and break the path, no current moving, but voltage waiting at the switch to start moving amps again when you reconnect. You flip the light on, current flows in and back out of the load (light in this case). Always needs two wires minimum.

AC means alternating current. That means that the positive and negative are reversing (about 60 times per second in the US). In this example, this is not ground potential moving around. This is each wire voltage potential moving above and below ground in opposite timing of the other. They swap places, alternating.

Measuring voltage is always in reference to something. For example: +12v in reference to ground. Usually when people talk about it, they automatically think it's in reference to ground or zero volts so they leave the "in reference to ground" part off. But it doesn't have to be in reference to ground, and in this case it isn't.

Here we go...

So a two wire 220v split phase (not real "two phase" or "three phase" which isn't common for people asking these question) system would have the positive and negative flipping back and forth. There are cases where you can imagine the amperage in this like a DC circuit and others where you can't. When there are any other active wires involved it needs to be measured and discussed like a split phase system. If there are only two wires and you aren't looking to understand any more about AC circuitry, you can imagine it like a DC circuit and shortcut the answer to just "X amps" for this half only.

Finding the amps from a 2 wire 220v AC system you measure the amps with a clamp meter on one wire of a pair. Done. That's your answer. Say you get 10 amps at 220v, which means that it draws 2200 watts. You can measure the other wire and it should be the same value of 10 amps. Great.

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Imagine it like measuring a point on a circle of wire. One leg starts then it goes through your dryer or AC or whatever and then back in the other leg. Big circle. Single effective wire to measure. Or you can imagine it like a single hose carrying water, measure any part of it and you'll get the same value, the hose circle is just squished into a long oval and you are seeing two sections as they pass you with water flowing in through one and back through the other, (and also having them flip directions but it's ok to ignore that part for only two wire 220v systems and a simple amp question). If you measured the flow of both wires at the same time it would be zero since you would see 10 amps flowing through one part of the hose on direction and the same 10 amps flowing back down the hose in the opposite direction and your total flow at that point with both hoses would be zero. Even when they flip it still nets zero. That's why you have to measure a single wire on the circle. Usually you can access them split apart at the breaker panel, inside the outlet box, or inside the appliance. Or create an extension cord with only the outer insulation removed, and the inner wires spread apart but still insulated so you can clamp onto them individually for measurement.

If you were to look at the actual amps over time with some better equipment than you're likely to have, you would see one wire increasing up to your measurement while the other one drops to a negative value of the same amps as it swings in voltage at the same time. Then both would meet back at zero and then flip. The wire you started with would show negative amps and the other would show positive. That's why you can measure only one wire. The other wire is 180 degrees out of phase with the first so the load is being carried through both wires at any time and the circle of amps is only the single wire value you are reading. Now this is happening very quickly but it acts like a DC measuring result for those not familiar with AC phases or neutrals, or extra correct math. Just use the correct equipment like a good clamp meter to test one wire of a 2 wire 220v AC system and you're done. The difference in voltage between the two wires will go from zero to 220v and back to zero as they cross paths and back to 220v, but in the opposite polarity. Each phase going positive to negative opposite the other. Not in respect to ground, but to each other, we get our 220v. Each wire in respect to ground is only 110v away.

Now we come to the issue of neutral or ground current. So far we're only measuring the voltage with respect to each other. One wire against the other equals 220v. But each wire is only going positive or negative 110v and the difference between them is the 220v we use in large loads. Your dryer may not only use 220v as measured across two wires. It probably has a ground for protection but not meant to carry any real operating current. It also has a neutral. 220v AC in most places is what's commonly called split phase. Because it can be split off and just use one side and have the return line be the neutral instead of the opposing phase wire. This is avoiding a lot of better explanations on two phase which is only actually used in residential in Pennsylvania and parts of Connecticut in the US and most of Europe I believe uses a single wire that carries 220v rather than having two at 110 to deliver the 220v. But again we ignore this for those asking how to measure amps for 220v as the neutral check will be the same or the wire won't be there.

Take the example above of measuring a a two line system at each line with a good ammeter that shows direction of current. You check one wire and it shows 10 amps going through it while the other wire shows -10 amps coming back down the path. Nice circle of current doing the work in your load and needing to return back around. Electricity always needs a full path. But with this setup, we need more info if they're not balanced exactly by only using two wires in a single circle.

If there's a neutral wire involved you can now expect that some component in your dryer or whatever uses a 120v AC leg to do something since it doesn't need the full voltage difference between two opposite legs. It only needs the 120v difference between one leg and zero. That zero is ground reference, neutral, which are roughly the same in a three wire system for simple explanation sake. So now you have your two wires heading in opposite directions to each go 110v away from ground and creating a total difference of 220v between them. But you attach something to only one side and neutral. A wire kept at ground potential (0v)in this case. You can use that power and for most of the USA we use that setup for lights, outlets, etc. Only using the full difference of each leg of the 220v for large appliances like dryers, heaters, air conditioners, etc. But here's the part where you likely came to read:

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So like we said above. To measure something that uses the difference between two different phases of 110v that are 180 degrees apart, you can measure one wire since the other wire is just the return or source and will be carrying the current from or to the wire you're measuring. To measure a load that may be using a neutral to return current from one side or the other you need to measure three places to make sure you are taking into account all the amps. You could measure just two wires but we need to verify ourselves here.

Measure the amps in one wire of the 220v system. Measure the amps in the other wire of the 220v system. Measure the Neutral of that system.

Here's a likely set of results from those tests at a circuit breaker feeding a dryer, readings taken at a theoretical dryer that wouldn't use this ratio but is easy to visualize:

L1 = 10a

L2 = 13a

N = 3a

So what we have here is a load that is tapping into the large difference between the two wires at their maximum voltage difference of 220v and using 10 amps of current. But that is also using another 3 amps from the L2 wire to power some smaller motor or circuitry and feeding that current back through the neutral wire. So you would think of this as: This circuit draws 10 amps at 220v and 3 amps at 110v for a total of: (2200 watts plus 330 watts =) 2500 watts.

This is not the same as saying "13 amps" or even "13 amps at 220v" which would have been 2860 watts. Since we have a neutral we need to be specific about what amps we're talking about or describe the system as the total watts used.

You have to note the voltage and amps, or the total in a unit that takes this into account. You can't say that it "uses 13 amps" since that's not true at 220v or 110v. It's like having two hoses with different pressure and diameter, you can't total them without taking into account the subtotal of each to get your actual total. But since watts is the work done while taking into account the voltage and the amps, we can use that to get our actual total for the circuit. So we have amps at 220v and amps at 110v and total wattage for both.

For 220v circuit breakers that touch the L1 and L2 wires you need them to be able to pass that 13 amps since inbound or outbound could trip the breaker connecting that wire. If L1 sees 10 amps but L2 sees 13 and the breaker can only handle 10, it would trip because that wire is carrying 13 amps. Doesn't matter that only 10 are returning through the L1 wire. Most of the time in residential, they are just two 110v breakers with a bridging plastic piece to make sure they trip or get reset in tandem. They are measuring the amps through the L1 and L2 wires but don't care which way the current is going, just that it doesn't exceed the speed limit. We care since it's all just a big circle and not two hoses heading in the same direction feeding amps out at the same time.

From our example above with a large circle of hose this one adds a smaller hose to the mix in the form of he neutral wire. One is a big circle that carries 10 gallons per second or water, measure it along any point and it's carrying 10 amps. Until the load taps on to only one side and connects it to neutral. Now there's a part of the large hose that's carrying that additional water but it gets diverted to the neutral wire and doesn't show as flow in the rest of the large hose.

So you have one wire (L1) carrying up to 10 amps at any given moment and can measure that amperage.

Then you have another wire (L2) that's carrying up to 13 amps at any given moment, 10 of which came through the other wire already.

With the missing 3 amps heading from L2 and through the neutral wire to make our math all add up.

So remember you have to have all the elements to reference when talking about amps and volts in a split phase system if there's a neutral. If it's just two wires and they are the same 10 amps of current you're ok to say it's 220v at 10 amps since it's flowing in a big circle.

If you have a neutral you have to measure three points to make sure you've got all your paths accounted for. If they show L1 and L2 are equal at 10 amps and no current through neutral then you're done there. 220v at 10 amps.

But if you have different readings (10 amps and 13 amps) on L1 and L2 and the difference (3 amps) is on the neutral. You have to say it then as: 220v at 10 amps and 110v at 3 amps. The highest of which is seen on the 220v breaker. L2 in this case at 13 amps.

If you don't match this all up you could have ground leakage current which is outside this answer and you should talk to an electrician.

Answer 7

It means 10 Amps in parallel.

That is both legs pull 10 Amps, but because they're in parallel they never exceed 10 Amps. The meter would read both legs when measuring kW

Edit: I made a drawing to help visualize. (using 20A load instead of 10A)