What happens above 480V.

[cvirgil467]

If equipment is rated for 480V, what happens if the voltage fluctuates above 480v due to the utility company? Is the actual rating of 480v equipment 600V or is there some "buffer "factor that the panel is rated for?

Thanks.
Carl

 

[bphgravity]

Equipment is rated in "nominal" voltages. State/federal regulations specify maximum voltage fluctuations that local utilities are permitted to distribute. In general, equipment can withstand voltage fluctuations +/- 5-10% of nominal voltage.

 

[kingpb]

Equipment is rated in "nominal" voltages. State/federal regulations specify maximum voltage fluctuations that local utilities are permitted to distribute. In general, equipment can withstand voltage fluctuations +/- 5-10% of nominal voltage.

This is not really correct.

The document that stipulates standard, maximum, and minimum voltages is ANSI Standard C84.1 - Electric Power Systems and Equipment-Voltage Ratings (60 Hertz). The standard provides the nominal system voltages as well as utliization voltages. Additionally, equipment rated voltages are specifcally found within other standards, of which are listed in C84.1, Appendix E. It is true that a utility company may be able to provide the upper and lower limits of their generation and transmission system, but the limits they use are based on operating within the guidelines of C84.1

 

[bcorbin]

Actually, I think he was correct. ANSI may create the standard, but the AHJ (i.e. the government) is the one who stipulates adherence to the standard.

 

[haskindm]

Also remember that 480-volt is the RMS voltage. The peak voltage during each cycle is higher, but I don't remember the formula off-hand.

 

[kingpb]

Actually, I think he was correct. ANSI may create the standard, but the AHJ (i.e. the government) is the one who stipulates adherence to the standard.

FERC and NERC certainly have beefed up there requirements for transmission systems, especially since the more recent blackouts. However, these entities do not provide oversight of the utility distribution systems, or the voltage variations in which the utility company establishes (based on C84.1) internally. Further, the voltage at the point of utilization is controlled at the substation level by using tap changers on the substation transformers. The taps are adjusted to maintain acceptable maximum and minimum steady state voltages for the customer, so the customer doesn't see the transmission system fluctuations anyway, or care for that matter. Certainly, you could have momentary fluctuations due to a large motor start, especially out on the end of a line, but the normal utilization steady state values will be kept within the standard values.

Please provide a reference, that can be corroborated, supporting your position that there are government agencies that provide distribution line voltage oversight for adherence to any specific standard.

 

[iwire]

This is not really correct.

The document that stipulates standard, maximum, and minimum voltages is ANSI Standard C84.1

:roll:

And what does C.84 tell us?

That in general equipment can operate safely within 10% of its rated voltage.

In addition a lot of equipment will operate safely far below that range.

My Dell PC is rated about 90 to 180 volts without changing any settings.

 

[iwire]

Please provide a reference, that can be corroborated, supporting your position that there are government agencies that provide distribution line voltage oversight for adherence to any specific standard.

King in general the each States utility commission sets the limits that the power companies must follow.

They can choose to use C84.1 but they do not have to.

 

[bphgravity]

Please provide a reference, that can be corroborated, supporting your position that there are government agencies that provide distribution line voltage oversight for adherence to any specific standard.

Contact or look into your state's Public Service Commission. The ususally are in charge of utility regulation...

 

[robbietan]

regulators here limit the distribution utilities voltages +/- 10% steady state rms. equipment then must be able to operate within that window, if not, no one can blame the utility for breakdowns.

peak voltage must be within the 1.414, otherwise the sine wave will be distorted.

 

[tallgirl]

Also remember that 480-volt is the RMS voltage. The peak voltage during each cycle is higher, but I don't remember the formula off-hand.

VPEAK = VRMS * sqrt (2)

The peak voltage for a 480v system would be 678v.