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Old 07-25-2009, 07:44 AM   #1
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208V vs 240V 3 phase


I am looking at some electric items (it's an oven for what it's worth) for a "project" of mine. These are offered from the manufacturer in either 208 3phase and 240 3phase. I sort of always thought that 3phase indicated 208 volts and 1 phase was 240 volts.

Which one would I want in a normal commercial (USA of course) building? Most of them in the used market seem to be tagged 208v 3phase.

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Last edited by pcampbell; 07-25-2009 at 07:50 AM.
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Old 07-25-2009, 08:46 AM   #2
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208V vs 240V 3 phase


Chances are your commercial service is a 208v wye service, which is the most common 3 phase transformer configuration.

However there is such a thing as a 240v delta transformer configuration, which is not as common but I still run into them sometimes. These are usually in older manufacturing/industrial type buildings, but not always. Delta setups are generally in place so you can use only 2 transformers for a three phase system, where a wye setup would need 3 transformers. If you do have a delta system, you could have a "wild leg" which will have a higher voltage to ground than the other 2 phases (around 200v to ground vs. 120v to ground) so you would need to be careful dealing with this type of system.

This is probably way more info than you are looking for, but is still a very watered down version of delta systems. If you are unsure of what type of service you have your best bet would be to contact your power company (they should be able to tell you per their records what kind of service you have), or check with a meter what voltage you get phase to phase (208v or 240v).

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Old 07-25-2009, 11:20 AM   #3
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208V vs 240V 3 phase


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Originally Posted by pcampbell View Post

Which one would I want in a normal commercial (USA of course) building? Most of them in the used market seem to be tagged 208v 3phase.
it isn't a matter of what you want but rather what your service is and buying the correct unit based on that.
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Old 07-25-2009, 11:29 AM   #4
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208V vs 240V 3 phase


What type of service do you have? 3 Phase? Single Phase? Voltage? Your oven will work on either 208 or 240, provided you have a 3 phase service. It could even be configured to work on single phase.
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Old 07-25-2009, 02:01 PM   #5
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208V vs 240V 3 phase


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Which one would I want in a normal commercial (USA of course) building
Normal isn't appropriate here.

Older neighborhoods here in Phoenix use 120/240 Delta 3 phase systems. Two phases are 120V to ground. One phase is about 200 volts to ground. All phases are 240 between them.

Newer installations (post mid 60's) are the more common 120/208 Wye systems. All phases are 120V to ground and 208V between them.

You need to look at the service and in some cases measure voltage to determine what you have. A simple phone call to the power company would also do the trick.
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Old 07-25-2009, 11:12 PM   #6
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208V vs 240V 3 phase


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What type of service do you have? 3 Phase? Single Phase? Voltage? Your oven will work on either 208 or 240, provided you have a 3 phase service. It could even be configured to work on single phase.
stretching things a bit aren't we JV? How can you configure an oven that has a 3 phase motor to run on single phase?

as well, some equipment is not rated to run on either /or. If the spec is 240 volts, 208 volts is not adequate since anything under 216 volts would be beyond a 10% tolerance.

Of course, if we are just speaking about heating elements, your post may be workable but in many large ovens, there are motors and such that would not work on either/or voltages.
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Old 07-26-2009, 07:47 AM   #7
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208V vs 240V 3 phase


OK I will ask the people at the building. In terms of heating elements, I am guessing if it is 240 volts and I run it @ 208,I'm going to be losing heat (watts), right?
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Old 07-26-2009, 12:15 PM   #8
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208V vs 240V 3 phase


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stretching things a bit aren't we JV? How can you configure an oven that has a 3 phase motor to run on single phase?

as well, some equipment is not rated to run on either /or. If the spec is 240 volts, 208 volts is not adequate since anything under 216 volts would be beyond a 10% tolerance.

Of course, if we are just speaking about heating elements, your post may be workable but in many large ovens, there are motors and such that would not work on either/or voltages.
Maybe I am. I am talking about elements only not motors. But in each case 208 should operate a 240 volt oven. 240 volt motors are run on 208 all the time. Although I agree a motor name plated for 240 should not be run on 208 unless the nameplate says 120/208/240. So your point is well taken nap.
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Old 07-26-2009, 01:41 PM   #9
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208V vs 240V 3 phase


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Originally Posted by J. V. View Post
What type of service do you have? 3 Phase? Single Phase? Voltage? Your oven will work on either 208 or 240, provided you have a 3 phase service. It could even be configured to work on single phase.
In a commercial building, most likely the Service would be 3-phase. The oven could be made to run on either single phase or 3-phase. The ideal voltage to run it, however, is that on the nameplate. In general, any appliance, particularly one with heating elements, which is designed to run on 240V. will not run at peak performance if running at 208v. There are two ways in which that could be fixed. Either with a Delta/Delta connection in the Transformer (from the assumed 600v. service in commercial buildings.) Or through a Buck/Boost Transformer (Auto transformer) connected between the Branch circuit and the appliance! (No matter what)Don't Drink and Drive!!!
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Old 07-26-2009, 02:40 PM   #10
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208V vs 240V 3 phase


A 240 volt heating element operated on 208 volts will consume 25% less watts, and thus produce 25% less heat. It'll draw 14% less current.

Very few motors are marked 240 volts. 230 is more common. 230 volts minus 10% is 207. A 230 volt motor will produce its nameplate HP on 208 volts, but the service factor (overload capacity) will be lower. If the motor is marked 240 volts, it may or may not work on 208. Depends on the type of motor and actual HP vs. nameplate HP.

Most (but not all) 3 phase ovens can be re-connected for single phase provided the motor is single phase. If the nameplate states 240 volts, and it's operated on 208, the maximum temperature will be lower, and it'll take a bit longer to heat up. Unless you're running it at close to its capacity, it'll work on 208.

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Old 07-26-2009, 08:45 PM   #11
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208V vs 240V 3 phase


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Originally Posted by spark plug View Post
In a commercial building, most likely the Service would be 3-phase. The oven could be made to run on either single phase or 3-phase. The ideal voltage to run it, however, is that on the nameplate. In general, any appliance, particularly one with heating elements, which is designed to run on 240V. will not run at peak performance if running at 208v. There are two ways in which that could be fixed. Either with a Delta/Delta connection in the Transformer (from the assumed 600v. service in commercial buildings.) Or through a Buck/Boost Transformer (Auto transformer) connected between the Branch circuit and the appliance! (No matter what)Don't Drink and Drive!!!
One way to accommodate a secondary (voltage) Delta connection is to get Three Single Phase transformers and connect them in a Wye/Delta configuration!
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Old 07-26-2009, 09:36 PM   #12
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208V vs 240V 3 phase


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One way to accommodate a secondary (voltage) Delta connection is to get Three Single Phase transformers and connect them in a Wye/Delta configuration!
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Old 07-27-2009, 05:12 PM   #13
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208V vs 240V 3 phase


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Very few motors are marked 240 volts. 230 is more common. 230 volts minus 10% is 207. A 230 volt motor will produce its nameplate HP on 208 volts, but the service factor (overload capacity) will be lower.
I'll accept that. The reason I posted what I did was simply because JV's was to definite

Quote:
.If the motor is marked 240 volts, it may or may not work on 208. Depends on the type of motor and actual HP vs. nameplate HP.
it will most likely work but since the minimum voltage the motor should see would be 216, no promises of life expectancy. It would be best to not do this unless the owner does not mind the possibility of a new motor a bit sooner than it should be.

Since the OP has not purchased anything yet, it would make the most sense to buy the machine that fits his service unless he gets a steal of a deal on a different voltage rated unit and even after considering the risks or costs to adapt, it is still financially beneficial.
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Old 07-27-2009, 07:51 PM   #14
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208V vs 240V 3 phase


I have to agree. Find out what the voltage actually is, then buy the equipment to match.

Pretty much guaranteed to work this way!

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Old 07-28-2009, 12:12 PM   #15
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208V vs 240V 3 phase


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Since the OP has not purchased anything yet, it would make the most sense to buy the machine that fits his service unless he gets a steal of a deal on a different voltage rated unit and even after considering the risks or costs to adapt, it is still financially beneficial.
I totally agree.

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