208 vs 220 single phase what's the diff. besides 12Volts? 1

[thomasks]

This may be an ignorant question, but what is the difference (if any) between 208 VAC single phase, and 220VAC single phase? (besides 12 VAC of potential) is there a diffenent connection or phase relationship?
I was told that 208VAC was noisier than the 220VAC.
Thanks

 

[davidbeach]

First off, 220V as a service voltage is like the Easter Bunny, it doesn't exist. If 208V is a service voltage option, then 240V is the other option. Both would be phase-phase voltages and the only discernible difference would the 32V difference. Neither is inherently noisier than the other.

 

[thomasks]

Thanks for the quick response.
So if my transformer says the secondary is 208VAC, then I should be able to get 240VAC from this transformer?

The reason I am asking is that my company makes equipment stating an operating voltage of 220 VAC single phase for the main power feeder. (the 24VDC power supplies have a switch that can be set for either 110VAC primary side, or 220VAC) We have some customers that are using 208 VAC single phase to the machines, and complaining of noise issues on the low votage side to the servos and analog sensors after the 24VDC power supplies etc. Does the main power feed being 208VAC have anything to do with this?

 

[magoo2]

If your transformer secondary is 208 V, then you will not be able to get 240 V from that same transformer. You need a different transformer to get 240 V.

Normally, 208 V is obtained from 3 single-phase transformers or 1 three-phase transformer connected in wye. You can get 208 V from phase to phase or 120 V from phase to neutral.

240 V can be obtained from a single phase transformer like you have serving a house. There is also a three phase transformer connection, floating wye primary and delta secondary. The delta scondary supplies 240 V from phase to phase.

As davidbeach says, there is no 220 V service voltage.

 

[Skogsgurra]

There is 220 V service voltage. Not in the US and not in EU any more (we have changed to 230 V). But there are still places where 220 V is the voltage you have in "the wall". It would help if you say what country you are from. I guess US for several reasons, but can't be sure.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[davidbeach]

Neither 110 nor 220 exist as service voltages anywhere that 208 might be a service voltage. The service voltages will be 240 or 208. 120 can be had from either. But, no, you can't get 240V from 208V without a boost transformer. If the DC power supply is expecting 240V (or even 220V) into its step down transformer and you only give it 208V, I can see why the DC might be a bit noisy.

 

[thomasks]

Yes, United States.

 

[rbulsara]

No, you cannot get 240V when the transformer nameplate says 208V. But you can get 120V, phase to neutral.

You may have some grounding issues. See thread248-278883. 208V is part (two hot wires) of a three phase grounded wye system. 110V or 220V operating voltage are typically meant for single phase system with a grounded neutral.

I would do the following:
1.In the USA, do not use 208V single phase. Instead use 110V switch on your P/S and use 120V from L-N of a 208V/120V system.
2. Do not use 220V switch in the USA. Leave it for European or Asian application where 220V or 230V single phase L-N is common.



Rafiq Bulsara

http://www.srengineersct.com

 

[stevenal]

What's the nature of the load? If it's for simple resistive heating, such as a water heater, 208 will work fine. I'll just run longer to produce the same amount of heat.

 

[thomasks]

24 VDC power supplies for control voltage, 240 VAC for servo power, 120 VAC for heaters and motor control.

 

[stevenal]

Servo might be a problem at 208.

I meant to say "It'll just run longer..." above. I only run when needed to avoid danger.

 

[waross]

Did you mean to say that the transformer PRIMARY was rated 208 volts? Where is the equipment made? In the US, 120 Volts is a standard supply voltage. 115 Volts and multiples thereof are standard utilization voltages for motors.
Another issue with 208 vs. 240 Volts is slightly higher line currents and line losses. When 120/208 Volts is used you must add higher neutral losses also.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

If your company's devices are rated 110V or 220V, that is likely a conscious decision so that they can be used +-10% in many areas. 220 - 10% = 192 which covers 208V input, even down to 200V (Japan) and 220 + 10% = 242V which covers 230 or 240V input. 110V is a similar compromise between 100V (japan) and 120V (North America). So just double check that your power supplies are rated +-10%, you should be fine.

Servos use DC so the amplifiers are just rectifying the AC to DC. The peak DC voltage you end up with is limited to 141% of the incoming supply, so at 208V you will have 5% less top end, but still 293V. But most Servo motors are rated under 200VDC and the amplifiers limit the available peak to what the motor actually needs, so that 5% loss is not likely a problem.

Noise issues are more likely a result of poor filtering design. If the normal use is residential / light commercial where one would find 120/240V single phase service, noise is generally not a problem. But if you go somewhere that has 208V 3 phase service, like a large commercial / light industrial installation, more likely there are other things nearby that generate noise. Sounds as though someone in your company failed to anticipate that possibility.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[cranky108]

If it's a large commercial / light industrial installation in the US, then most likely they will have 480 for motors, and 277 for lighting.

This must be a smaller installation, or some location with more 120v load, and less in motors.

However, having said that, in some locations here we do have 120/208 service to residential customers. This is because of there closeness to other larger customers that require three phase.

The 120/208 service has caused some problems to some solar installers for the residentual customers. But most 240 equipment works on 208.

 

[thomasks]

Our installations are to light industrial areas. There may be some 480 3 phase and 240 3 phase, along with 240 single and 120 single.

 

[VLFit]

think globally. 208V is a line to line voltage of a 208/120Y system. 220V is a line to ground voltage of a 380/220Y system. 240V is the line to ground of a 415/240Y system. The important dfference, othere than maybe having too high or low a voltage, is that one of the input leads is either ground referenced or both are hot.

 

[stevenal]

The problem with stating that 208 lies within +- 10% of 240 or 220, is that 208 is also a nominal voltage for something that is hardly ever 208. ANSI C84.1 minimum utilization voltages for a 208 service are 191 for schedule A with infrequent brief excursions to the schedule B minimum of 184.

 

[jraef]

stevenal,
You know that, and I know that, but often OEMs know that the average user DOESN'T know that. What they are after is not having to make and sell several versions of the product because of the different service voltages around the world.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[davidbeach]

Auto-ranging power supplies that work from about 85VAC to 600VAC should about cover everything in NEC land. The 690VAC systems seen around wind turbine installations wouldn't work but they'd also require a whole new class of over 600V components.