200V vs. 208V grids, 3 phase

I understand that some metro areas have 208 V networks and others have 200 V networks. Further, I heard that NYC has multiple grids, some 200
V some 208 V. Motors rated (and nameplated) for 200 208 volt motors are suitable for either voltage but the calcs for sizing short circuit protection would be different, depending on the actual voltage. What is the history of, or what accounts for, the nominal ratings of 200 V and 208 V. metro grids? When in doubt, size the short circuit protection (CB/MCP) for 200 V?
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I don't know of any 200 volt networks in the US. All I have dealt with are 120/208volt. Perhaps someone is mistakenly referring to a 208V system as "200V"; much like some people will still call a 120V service "110V".
Charles Perry P.E.
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wrote:
| |>I understand that some metro areas have 208 V networks and others have |> 200 V networks. Further, I heard that NYC has multiple grids, some 200 |> V some 208 V. |> Motors rated (and nameplated) for 200 208 volt motors are suitable for |> either voltage but the calcs for sizing short circuit protection would |> be different, depending on the actual voltage. |> What is the history of, or what accounts for, the nominal ratings of |> 200 V and 208 V. metro grids? When in doubt, size the short circuit |> protection (CB/MCP) for 200 V? |> | | I don't know of any 200 volt networks in the US. All I have dealt with are | 120/208volt. Perhaps someone is mistakenly referring to a 208V system as | "200V"; much like some people will still call a 120V service "110V".
At one time it was 110 volts. Then for a while it was 115 volts. Now it is 120 volts. Some places have 127 volts.
Three phase WYE/star systems have a L-L voltage that is related to the L-N voltage by the square root of 3. The L-L voltage for a 110 volt system is 190 volts. For a 115 volt system it is 199 volts. For a 120 volt system it is 208 volts. For a 127 volt system it is 220 volts. Sound familiar?
I believe the reference to 200 volts is actually the 115 volt system. It may be actually 115 volts, unchanged since that was the standard, or it may be 120 volts and still labeled as 115. Instead of 199, the L-L voltage was "simplified" as 200 volts. Or perhaps it could be the reverse, dividing 200 by the square root of 3 to get 115.47 volts and rounded to 115. Whichever way, I do see references to "200/115" three phase systems.
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On 9/15/06 1:41 PM, in article snipped-for-privacy@p79g2000cwp.googlegroups.com, "Bill.N"

My guess is that any installation requiring significant three phase power has it own transformer bank to provide customized voltage and grounding. These transformers can then be connected to the power grid as it exists. For example, if the load is primarily lighting, the voltage would be 208/120.
Bill -- Fermez le Bush
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