# 208 vs 230?

I almost always work with pure 115V AC equipment, but now with the new
Cisco 6500 equipment I am getting, I am little confused about
something.
In a house, you have two 115V supply lines of the same phase. In your
breaker panel, you can install a breaker which grabs voltage from each
bus, and you wire a standard 230V device - like a dryer or AC unit,
etc.,.
Here is where I get confused. Because I have a triple phase UPS, I
only have two types of output power - 115V or 208V. I have three 115V
phases, and none of them are of the same phase. So its impossible for
me to wire the 230V equipment like I would at home. However, I have
the 208V power.
Is it safe to assume that any 230V appliance can run off 208V? Cisco's
power spec for the 6500 just says anything between 100V and 250V. Can
someone clarify this for me. I just want to be sure I am correct in
assuming that 208V and 230V are the same in when it comes to powering
a devices. Obviously the wiring is different. 230V is 4 wires (115V
supply, 115V supply, return, and ground), and 208V has 3 wires (208V
supply, return, and ground)....
thanks
john
You really have to read the name playe but most computer equipment will work fine on 208.
A house system is called the "Edison" system and consists of two phases exactly 180 degrees out (opposite phase) such that the voltage from each phase to neutral or ground is 120 volts. (formerly 115 volts) Voltage Between the phases is 230 or 240 volts.
So if you have an appliance such as stove or dryer the voltage that runs the high wattage heating elements is 230 and is hooked between the phases. Other items (lamps, timers etc.) are run off of one phase (115v) to neutral which produces standard house 115 voltage.
A three phase circuit has three wires plus a neutral (if star connected) and each phase is out 120 degrees. the voltage from any ONE phase to neutral is 115 volts but the voltage BETWEEN any two phases is 208 volts. Such power may or may not run a given appliance. It depends upon whether the high voltage part of the circuit will run on a reduced voltage of 208 volts. And just HOW the lover voltage 115 volt circuits are hooked up. (remember there is 208 volts between phases which can play havoc with certain circuits. It also depends upon whether or not the appliance in question needs THREE phases to operate or just uses a single phase or two phases of the three.
I STRONGLY urge you to seek expert electrical help from someone who can evaluate the power and the Cisco gear in question to determine proper power connections. As encouragement much gear is able to be powered from either the Edison hook up or two phases of a 208 three phase source. But CHECK THE MANUAL AND GET HELP FIRST!
Read the nameplate. A particular device may be rated at 240V only (they may have a number from 230-250V, most likely 240 or 250), 208 only or 208-240 (or for computer equipment with switching power supplies like your Cisco, 100-240V)
Heaters will work, but at 3/4 rated power, so it'll take longer to heat up or perhaps not get hot enough. Heavily loaded motors not rated for 208V probably won't like it and may overheat. Lightly loaded motors may be OK.
The wiring for 208V is actually similar to 240V single phase. Two hots with 120V to the neutral, ground, and the neutral is available but often not supplied. The difference is the voltage between the hots and the phase relationships of the hots to neutral.
In the US, 120/208V is common for multi-unit housing (especially condo buildings) that are served by one transformer individual or bank of three-phase transformers and where each unit has its own service (meter, CB box). The tranformer secondarys are wired in wye, the center tap serves as the netural and the voltages are 120V each leg to neutral and 208 V. across any two hot legs. Only two (out of a possible 3) hot legs are supplied to each dwelling unit.
I've lived in several buildings with 120/208V service and didn't like it for these reasons.
1. The standard electric dryer in North America has a heating element that is designed to run at 240V and will not heat up properly if plugged into 208V. The dryer runs a lot longer to dry the same load of clothes. There may be 208V. dryer heating elements available from some manufactuers but it is a hassle to deal with, especially if you move from place to place with different voltages.
2. Electric Ranges (ovens) are subject to the same limitation. In this case however, special 208V. heating elements are readily available, but not all builders put them in during construction and if your oven has not been modified, it will heat up slower.
3. Residential air conditioners with external compressors are almost always designed for 240V. They will run at 208V, but some will run hot and become overloaded, and they may fail more frequently. Several electricians have complained about this in earlier posts to this newsgroup.
4. At one of these 120/208V buildings where I lived, we had an incident where one and only one of the 3-phase primary fuses blew at the pole due to a fault at the emergency fire pump. I came home to an apartment with half bright lights and measured something like 56V at my refrigerator outlet. This was not good (especially for some electronic devices) and would not have happened if I had the usual 120/240 V. service.
Beachcomber
Correction to above post - I said "center tap" when I really meant "common point of the wye secondary". Sorry about that!
Beachcomber
| I almost always work with pure 115V AC equipment, but now with the new | Cisco 6500 equipment I am getting, I am little confused about | something. | | In a house, you have two 115V supply lines of the same phase. In your | breaker panel, you can install a breaker which grabs voltage from each | bus, and you wire a standard 230V device - like a dryer or AC unit, | etc.,. | | Here is where I get confused. Because I have a triple phase UPS, I | only have two types of output power - 115V or 208V. I have three 115V | phases, and none of them are of the same phase. So its impossible for | me to wire the 230V equipment like I would at home. However, I have | the 208V power.
The three phase UPS will not operate correctly if supplied with single phase power. I hope you are not trying to do that.
| Is it safe to assume that any 230V appliance can run off 208V? Cisco's
No. I've seen motors burn up because they got 208 volts but were designed for 230 volts or so. Due to the low voltage, they pulled extra amps and may have even stalled due to reduced torque.
| power spec for the 6500 just says anything between 100V and 250V. Can | someone clarify this for me. I just want to be sure I am correct in | assuming that 208V and 230V are the same in when it comes to powering | a devices. Obviously the wiring is different. 230V is 4 wires (115V | supply, 115V supply, return, and ground), and 208V has 3 wires (208V | supply, return, and ground)....
Computer switching power supplies can easily be made to handle dual voltages in two ranges, or with just a bit more cost (usually offset by the savings of producing and stocking a single part instead of two) can handle the full range from 100 volts (as available in Japan) to 250 volts (as available in China). The PSU that handle just two separate ranges (they have a "115/230" switch) may have some trouble with 208 volts. The ones listed as "100-250" or "100-240" should be just fine on 208.
In the USA, the 240 volts connection involves two hot wires, each being 120 volts relative to ground or neutral. This may pose some risk to appliances expecting one of the power supply wires that provide power to be grounded.
Not all circuits have the neutral. You will see that in appliances that need to have both voltages, such as a stove with a 120 volt light bulb in the oven. The typical stove and clothes dryer circuits have the extra neutral wire for the extra voltage tap. Other uses don't need it, such as electric water heater, or air conditioners (central or window type).
A computer power supply designed for all countries will have to deal with that fact that in many countries, there is no specific polarization that defines which wire is grounded. This is the case with the classic Europlug and continues with the Schuko (larger round grounded version of Europlug). These can be reversed and are expected (and now required) to be equally as safe. That means neither wire is allowed to be touchable. Neither can be connected to a metal case. And in many countries such as Germany, it is not allowed to use the large screw in bulb bases on plug connected lamps (because the rim of the socket is touchable and could present a 230 volt shock if plugged in a certain way). The computer power supply must be safe in dealing with this reversable plug. Rather than have extra cost circuit to detect a reversed plug and shut down, it's cheaper to just support either wire being hot by keeping them both isolated. That works out to an advantage for the USA style 240 volt circuit. The rocker style power switch controls both wires (not just one). So it should be just as safe on USA 240 volt power as it is on German 230 volt power.
208 volts, if that is what you have due to a two wire tap on three phase, would just be a "slight brownout" to something expecting 230 volts. It would be nominal for something expecting 100 to 250 volts.
They do make single phase in, 3 phase out UPS's. We even had single phase 60hz UPS's that output 3p 400hz for the old water cooled CPUs
Reminds me of the office building where I worked. It is delivered 480v Y with 277 to the lighting. A couple transformers in the electric room provided single phase 120/240v. When power went out somewhere, it was never usually a total outage. 2/3 of the buliding would get reduced voltage from 1 leg of the phase being lost. some equipment with switching power supplies would be damaged at every outage. Newer equipment seemed to handle it well. We asked every one to shut down their computers and unplug them. Some computers and monitors would continue running fine on 60 volts, but I'm sure the PSU was straining. John
| Reminds me of the office building where I worked. It is delivered 480v Y | with 277 to the lighting. A couple transformers in the electric room | provided single phase 120/240v. When power went out somewhere, it was never | usually a total outage. 2/3 of the buliding would get reduced voltage from 1 | leg of the phase being lost. some equipment with switching power supplies | would be damaged at every outage. Newer equipment seemed to handle it well. | We asked every one to shut down their computers and unplug them. Some | computers and monitors would continue running fine on 60 volts, but I'm sure | the PSU was straining.
Get computers with autoranging (100-240 volts) power supplies and plug the computers into a 240 volt outlet.
| |>The three phase UPS will not operate correctly if supplied with single |>phase power. I hope you are not trying to do that. | | | They do make single phase in, 3 phase out UPS's. We even had single | phase 60hz UPS's that output 3p 400hz for the old water cooled CPUs
So where can I get one for 1600 to 2400 VA?
Liebert A 3090 600S pulled 105KVA @400hz There would be a bunch of these big Lieberts in the computer room and a huge battery room next door.
| |>|>| |>|>The three phase UPS will not operate correctly if supplied with single |>|>phase power. I hope you are not trying to do that. |>| |>| |>| They do make single phase in, 3 phase out UPS's. We even had single |>| phase 60hz UPS's that output 3p 400hz for the old water cooled CPUs |> |>So where can I get one for 1600 to 2400 VA? | | Liebert | A 3090 600S pulled 105KVA @400hz | There would be a bunch of these big Lieberts in the computer room and | a huge battery room next door.
But where can I get a _small_ one in the 1.6 to 2.4 kVA range?
Probably cheaper to just get an MG set (rotary converter)
| |>|>| |>|>|>|>| |>|>|>The three phase UPS will not operate correctly if supplied with single |>|>|>phase power. I hope you are not trying to do that. |>|>| |>|>| |>|>| They do make single phase in, 3 phase out UPS's. We even had single |>|>| phase 60hz UPS's that output 3p 400hz for the old water cooled CPUs |>|> |>|>So where can I get one for 1600 to 2400 VA? |>| |>| Liebert |>| A 3090 600S pulled 105KVA @400hz |>| There would be a bunch of these big Lieberts in the computer room and |>| a huge battery room next door. |> |>But where can I get a _small_ one in the 1.6 to 2.4 kVA range? | | | Probably cheaper to just get an MG set (rotary converter)
Probably. In the low power/VA range, it seems no one makes anything other than basic L-N UPSes at the conventional domestic voltage. I was just hoping maybe there was a ray of hope that something a bit unusual might be made. But I guess not, unless custom made in 500+ unit quantity.
Liebert used to make a GXT1800 UPS that specifically supported 208-240 volts L-L. But they don't make it anymore. I presume, like all other products tried by big corporations, they failed to market it properly (how many people here even knew about it), it didn't sell, and so they dropped it. Or maybe it did sell well. I've known big corporations to drop product lines because they sold too well, outstripping their capacity to manufacture.
If you are just trying to make 3 phase out of single phase, and don't need the backup, a VFD will work nicely. Toshiba is real good about that sort of configuration.
|> |>|>| They do make single phase in, 3 phase out UPS's. We even had single |> |>|>| phase 60hz UPS's that output 3p 400hz for the old water cooled CPUs |> |>|> |> |>|>So where can I get one for 1600 to 2400 VA? | | If you are just trying to make 3 phase out of single phase, and don't need | the backup, a VFD will work nicely. Toshiba is real good about that sort of | configuration.
Actually, I want the backup and at L-L voltage, not the three phase. If something for three phase would have done it for me, that's fine.

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