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208y power, does it suck?
November 1, 2006 6:55 PM   Subscribe

What are the characteristics and drawbacks of 208Y power? Specifically will it run my industrial sewing machines that want 220v?

I am in the process of converting an old beer warehouse into a live/work space where the work I will be doing is clothes manufacturing. We were originally told that our power was to be 60 amps of three phase 220 power. It now seems that it is 60 amps of 208Y power. I have heard conflicting views on whether it's better or worse than 220, but what I'm worried about is whether it will run several industrial sewing machines and irons or not.

If the machines call for 220v will they run at 208? I have heard they will, but they will run slower, is this true/will it harm the motors?

I don't know the amperage draw for these machines, but I do know a 1700 watt iron pulls about 15. I'm trying to upgrade to at least 100 amps and preferably 125. Will this be enough?
posted by Jawn to Technology (10 answers total)
 
many 120v devices will operate fine over a voltage range of about 110v - 130v as long as the frequency is the same (usually 60 Hz in the US). IANAE but since the difference between 208 and 220 is about 5% I would guess it shouldnt be too dangerous.

How many horsepower to the motors on the machines draw? Are they 3-phase also? You can caculate the current draw with these two number, Ill dig up a chart for you.
posted by ernie at 7:11 PM on November 1, 2006


If a 1700 watt iron is drawing 15 amps, then it's operating at 110 volts. If you plug that into 220 (or 208) and get it wrong it's going to get very bright for a short time, and then all the magic smoke will be released.

You don't need advice from us. You need a competent electrician, and you will need to pay him. Otherwise you may end up with a fire that turns your entire warehouse into magic smoke.

As to how much power you are permitted to draw, only the power company knows that. Draw too much, and the nearest step-down transformer will release its magic smoke.

(All electrical devices work because they contain magic smoke. If the magic smoke gets released, they cease to work.)

Seriously: when it comes to high power, don't fool around. This is not a place to cut corners financially; get an electrician in and tell him what you want to do. He'll tell you if it's possible.

3-phase power:

"Another system commonly seen in North America is to have a delta connected secondary with a centre tap on one of the windings supplying the ground and neutral. This allows for 240 V three phase as well as three different single phase voltages (120 V between two of the phases and the neutral, 208 V between the third phase (known as a wild leg) and neutral and 240 V between any two phases) to be made available from the same supply."
posted by Steven C. Den Beste at 7:28 PM on November 1, 2006


208 Y 3 Phase power does not suck -- it's the commonly available work horse power in most factories in North America.

The Electrical Wiring FAQ puts it thusly:
"Subject: A word on voltages: 110/115/117/120/125/220/240

One thing where things might get a bit confusing is the
different numbers people bandy about for the voltage of
a circuit. One person might talk about 110V, another 117V
or another 120V. These are all, in fact, exactly the same
thing... In North America the utility companies are required
to supply a split-phase 240 volt (+-5%) feed to your house.
This works out as two 120V +- 5% legs. Additionally, since there
are resistive voltage drops in the house wiring, it's not
unreasonable to find 120V has dropped to 110V or 240V has dropped
to 220V by the time the power reaches a wall outlet. Especially
at the end of an extension cord or long circuit run. For a number
of reasons, some historical, some simple personal orneryness,
different people choose to call them by slightly different numbers.
This FAQ has chosen to be consistent with calling them "110V" and
"220V", except when actually saying what the measured voltage will
be. Confusing? A bit. Just ignore it.

One thing that might make this a little more understandable
is that the nameplates on equipment often show the lower (ie: 110V
instead of 120V) value. What this implies is that the device
is designed to operate properly when the voltage drops that
low.

208V is *not* the same as 240V. 208V is the voltage between
phases of a 3-phase "Y" circuit that is 120V from neutral to any
hot. 480V is the voltage between phases of a 3-phase "Y"
circuit that's 277V from hot to neutral.

In keeping with 110V versus 120V strangeness, motors intended
to run on 480V three phase are often labeled as 440V..."
Out on the pole that feeds your building are either 3 wires or 4 wires, depending on whether your distribution system delivers a neutral (many don't). A 4 wire system is often called a "Y" or "Wye" system, because that's how it's usually diagrammed [in this case, upside down], whereas a 3 Wire system is a "Delta" because the diagram for that kind of connection looks like the Greek letter delta. The "neutral" wire, if there is one in your distribution system, doesn't carry any current if the power being delivered by the 3 power phases is balanced, but if they are unbalanced, phantom voltage and current (reactive power components) will appear in the neutral leg. These "phantom" components are created by the service transformer at your location as it tries to balance the load you are creating. A Delta system doesn't try to balance the load, and will just have high (hot) or low phases if your loads are unbalanced. In both Y (Wye) and Delta systems, a ground leg is usually required, which should never carry current in normal operation, but provides an emergency path to ground stakes driven into the earth at the service entrance, should an insulation fault or other problem develop in a piece of electrical equipment. Many systems that deliver just the 3 phase legs to the pole transformer in a Delta distribution system will be connected on the secondary side for 4 wire Y distribution by electrically bonding the secondary neutral wires to grounding stakes driven into the earth near the service entrance, from wires taken out of the service transformer secondary winding, through the main disconnect switch. But a ground and neutral are not the same thing, and serve different purposes, although in normal conditions, neither may be carrying current, and both may be at the same electrical potential as the earth.

Normally, an industrial building will have at least 2 electrical services. One will be a "normal" single phase service, much like you have at home, for delivering power for normal lights and office equipment, and for 110 volt convenience outlets in your office suites and break rooms. The other will be a 3 phase service, used for powering industrial motors and other equipment requiring significant current. That's because 3 phase motors tend to be more efficient than single phase motors, and don't require starting capacitors or other control circuits to establish their proper rotation when they are turned on [there very nature as 3 phase devices does that]. You'll actually have 2 sets of transformers, 2 sets of circuit breaker boxes, and 2 separate wiring systems, all of which should be labeled appropriately. You may also have a 480/277 volt service system, with yet a third set of transformers, breaker boxes, and wiring system, for powering high intensity industrial lighting (mercury or sodium vapor ceiling lights in factories and warehouses).

Industrial sewing machine motors are generally fractional horsepower motor units, either DC electronic, or with mechanically or electronically operated clutch systems, and if electronically controlled, their electronics may also supply signals for additional machine functions like automatic thread trimmers or needle positioners. Nearly all are produced in Taiwan, China, Japan, Korea and Germany, for the international market. To minimize the complexity of the distribution requirements for sewing machine manufacturers all over the world, most motor manufacturers try to make their motor products workable for a wide range of voltages and powerline frequencies, by offering several "taps" for the motor windings, and various sized output pulleys to adapt the developed shaft speed of the motor for the machines it will drive. The only thing that is not "adjustable" is the basic design of the motor, as either a single phase motor, or a 3 phase motor. You can't use single phase motors on 3 phase electrical systems, nor can you use 3 phase motors on single phase power. But, by consulting the motor manufacturers connection diagrams, and changing the pulleys, you can often use the same 3 phase motor on 50 Hz 200 VAC 3 wire 3 phase systems in Japan or the UK, and on 60 HZ 208 VAC 3 phase, 4 wire systems in the U.S. just by changing wiring jumpers in the motor connection box and at tje same time, exchanging output shaft pulleys for appropriate diameter. The motor armatures have enough iron to work without overheating on 50 cycle power, yet, by changing taps, work at nearly 98% efficiency on 60 Hz power, too. So, if you have these "international" motors, their nameplate information should indicate several power/frequency ratings. If not, you'll need to deliver the rated power for your motors, by changing taps on the secondary side of your main distribution transformers.

For AC motors, the voltage you deliver will not directly affect their output speed, but the frequency you deliver will. An "international" motor will often be designed to turn 1725 RPM when connected to 60 Hz power, but only 1450 RPM when connected to 50 HZ. Different pulleys change the sewing machine to operate at the correct speed.

Most industrial sewing machine motors are rated 1/2 hp, 3/4 hp, or 1 hp. You will need to deliver more current to single phase motors at start, and under load, than to 3 phase motors. Your motor nameplates or service manuals should list the current demand for the motor, as it is to be connected. A typical 1/2 hp, 1725 rpm 3 phase clutch motor will pull about 400 Watts, or about 1.6 amps per phase, but its temporay inrush currents at start will be several times that amount.

You need to examine the motors to see what their power requiments are, and perhaps contact the motor manufacturer, or local distributor, for connection diagrams and information. With that information in hand, most electricians could make the appropriate connections, but you'd still need to measure the pulleys and determine the correct size for the application you have. The wrong size pulley will wear the motor clutch quickly, and make the sewing machine very slow, or very "jumpy" in operation. A pulley that is far too large in diameter can even overspeed the sewing machine, breaking parts in the sewing head. Most industrial sewing machine distributors are quite familiar with these motor products, and can guide you by phone, make arrangements for paid service calls to setup and service your machines, or direct you to online resources.
posted by paulsc at 9:29 PM on November 1, 2006 [1 favorite]


IAAEe (that's engineer with a small e). I mostly specialized in circuits and signal processing, but I did take a semester of power systems once (which is what we're talking about here). So don't take this as professional advice. Or even accurate advice. Hence, the small e.

First, your irons. They're simple resistive loads, so a lower voltage would mean they don't get as hot. How much difference? Power output is governed by P = IV = RI^2 = V^2/R. In your case, it's the difference between 48400/R and 43264/R, or ~11%. So your irons will be about 11% cooler (no idea if this is bad, I don't iron much).

Second, your motors. This is more difficult. Notation clarification, a 208Y (or wye) is still three-phase. Transformers have a secondary winding (your side) of either a Y or Δ configuration, depending on your geometry. That is, three-phase has three wires, let's say A, B, and C. If A connects to B, B connects to C, and C connects to A then you have a Δ configuration (A,B,C on the vertices). If there's a fourth wire, called the neutral, and each phase connects to it, then you have a Y configuration (A,B,C on the points, N in the middle).

Now, I'm trying to think hard, but I can't come up with a reason why a three-phase motor would spin slower at a lower voltage. In your house with a DC motor or a single-phase motor this is obviously the case. How fast a motor spins depends on the strength of the electric field acting on a fixed magnet in the center, or perhaps another set of windings &pi/2 out of phase.

But with a three-phase inductor motor (common, what you probably have), the center is essentially nothing but some carefully arranged conducting bars. It rotates because the magnetic fields of the outside windings induces a current in the bars, which creates a magnetic field. The outside windings cycle through the phases (A,B,C,A,B,C,... etc) which also causes the motor to spin in a single direction (following the procession of the phases).

So how fast the motor spins depends not on the voltage, but on the frequency. One website I found gave the formula as proportional to frequency/poles.

What does this mean to you? Your three-phase motors should spin just as fast on 208 as they do on 220. However, nothing is free in electrical engineering. Since voltage is different, speed is the same, and power output (will try) to be the same, then current will necessarily increase. Increased current means increased heat, which means possibly letting the magic smoke out of your motors.

Long lesson short, you should hire an electrician. I would, and I've taken classes in this stuff. At the very least, you should call the manufacturers of the equipment and ask them the same question you've asked us.
posted by sbutler at 10:09 PM on November 1, 2006 [1 favorite]


Or your could just listen to paulsc :)
posted by sbutler at 10:13 PM on November 1, 2006


You should be able to get a transformer to convert your wye feed into delta, if that's what your machinery wants (and if you can't trivially adapt the machinery, like paulsc suggests).
posted by hattifattener at 12:03 AM on November 2, 2006


I would tend to think that a 3-phase motor running on insufficient voltage would have lower output mechanical power, and would freeze or back-step more easily. I can't see it drawing more current.

In fact, it ought to draw less current, since the resistance of the winding is constant and the voltage is lower. Also the inductance of the winding is constant and the voltage is lower. So you should get a less intense magnetic field, and therefore less ability to push.

I don't think it would smoke the motor; I think it's more likely that the device would simply refuse to work because the motor would be unable to make it go.
posted by Steven C. Den Beste at 12:27 AM on November 2, 2006


"...Also the inductance of the winding is constant and the voltage is lower. .."

You forgot to take into account back EMF, which in a properly designed AC electric motor, is the main factor limiting current through the motor. If the motor's excitation is lower due to lower voltage, the back EMF is far lower, and the operating current therefore increases at lower voltage, to keep the available torque up. Otherwise, AC motors would easily slip synchronous operation when loaded near maximum, and exposed to voltage variation. That would be very bad, mechanically, for the loads they are driving (vibration, noise, etc.) and bad for the electrical distribution equipment, too, which would see all kinds of transients.

So, actually, by design, the effective inductance of an AC motor is far from constant, at varying voltages.
posted by paulsc at 12:39 AM on November 2, 2006


Or your could just listen to paulsc :)

Would that we all took that advice! I think I will start getting "What paulsc will say" in early, it should improve my best answer count.

If the motor's excitation is lower due to lower voltage, the back EMF is far lower, and the operating current therefore increases at lower voltage,

The back EMF would be proportionately lower, I think, there has to be a flux balance. I really don't know how that comes out in the wash, but I'll guess that the current will be at most equal.
posted by Chuckles at 2:14 AM on November 2, 2006


Thanks for the great answers everyone. I now have a much clearer understanding of the situation. I wasn't planning on actually doing the wiring myself, there's an electrician for that, I just wanted to know if 208 power would suit my needs and it seems that it will. Since I don't actually have any industrial machines at the moment, it seems easy enough to make sure when buying them that they're set up for 208. And I know that my irons are 110 devices and wouldn't have dreamed up hooking them up to 208, just throwing that out as an example of what kind of amperage my stuff draws.

Planning on asking for 125 amps and hopefully can get at least 100, with gas powered major appliances I think that will be plenty.
posted by Jawn at 4:17 PM on November 2, 2006


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