line voltage tolerances

[bob95678]

Can someone tell me where to find a standard on the standard deviation of line voltage in North American systems. Is there a given tolerance for the utility that they must meet when they supply each different voltage. For instance, if the line voltage is 277/480 volt how low can the 277 be and how high can it be. Question #2 would be is this the responsibility of the electrical engineer when doing the design? Question #3 would be is there a standard for that.
Thanks.

 

[Manindemand]

Answer to question 1...

http://utilities.dteenergy.com/infoZone/programsInfo/voltageLevels.html

 

[imok2]

Speaking from an operations point of view, we don't like to see a deviation of more then plus /minus 10%

 

[busbar]

A default answer is ANSI Std C84.1-1995, American National Standard for Electric Power Systems and Equipment – Voltage Ratings (60 Hertz). Resolution is often spelled out in utilities’-commission agreements, or the product of contractual verbiage in a purchase order. The lower limit for 277V systems is usually 254 volts, but C84.1 contains a number of qualifying conditions.

 

[mvcjr]

Personally, responsibility for voltage balancing does not rest on the utility engineers alone. The customers should also try to maintain a balanced load. Unbalanced loads can result to unbalanced voltage drops in the line thus resulting to voltage unbalance.

The standards require the customers to maintain a certain degree of load balance on their systems.

God bless!

 

[alehman]

If the utility voltage is low at the point of service, that is probably the responsibility of the utility, not the design engineer. If there is excessive voltage drop downstream from the point of service that is the responsibility of the owner, his engineer or contractor.

The NEC recommends for best efficiency that voltage drop of branch circuits not exceed 3% and there should be no more than 5% total drop from the point of service to the loads. This is a reasonable guideline.

 

[jbartos]

Suggestion: Even though the ANSI Std C84.1-1995, American National Standard for Electric Power Systems and Equipment – Voltage Ratings (60 Hertz) states -5% +5% voltage deviations from the rated voltage, the Utilities do often have the higher voltage deviations within the power distribution system in various areas due to unusual or unexpected load, that may eventually lead to a blackout.
However, the Utility is probably used to complaints about voltage drops approximately -10% to +10%; more often -10%.

 

[bob95678]

Thank you all very much for the information. It was just what I was looking for.

This is a great site and I will keep in touch in case I can answer a question for someone in the future.

Thanks again!