250 volts rating

[mbrooke]

How is the 250 volt rating derived on switches, receptacles, capacitors and other equipment?

Is 250 volts the absolute maximum voltage, or does it take into account plus 5% meaning 262 volts or 110% meaning 275 volts maximum voltage?

 

[gar]

100915-2337 EDT

Experience, testing, historical information, environment, and expected life. Generally specs are well below a sharp threshold point.

Mylar has a high dielectric strength, but it is both temperature and thickness dependent. You would not make a product, capacitor for example, with a stress level anywhere close to the said breakdown level. And the criteria will also be dependent upon expected life, ambient pressure, and other factors. AC or DC should also make a difference.

On switches and other similar devices over the surface breakdown may become a major factor along with altitude.

.

 

[LarryFine]

That would normally be the maximum voltage, period.

Maybe we can give you a better answer if you tell us why you're asking.

 

[mbrooke]

That would normally be the maximum voltage, period.

Maybe we can give you a better answer if you tell us why you're asking.

That would mean it would be a violation to use on a 240 volt system. 105% of 240 is 253.

 

[LarryFine]

Violation, no. The concern would be the cap's longevity on 240v.

f it pops, replace it one with with a higher voltage rating, like 450v.

 

[mbrooke]

Violation, no. The concern would be the cap's longevity on 240v.

f it pops, replace it one with with a higher voltage rating, like 450v.

Is this for all equipment?

The thing is I see equipment listed 240 volts and 250 volts- yet there is no 250 volt system in existence.

 

[kwired]

Most things can take well over what they are marked at least for short time, if not they would be destroyed every time a transient voltage occurs or even during meg testing.

And remember that 240 AC is RMS volts, peak volts is about 339.

 

[retirede]

Capacitor voltage ratings are maximum working voltages. AC ratings are rms ratings. 250 VAC capacitors are used on 240 systems depending on the application. A motor starting capacitor normally does not see full line voltage, for example.

 

[mbrooke]

Most things can take well over what they are marked at least for short time, if not they would be destroyed every time a transient voltage occurs or even during meg testing.

And remember that 240 AC is RMS volts, peak volts is about 339.

True, but you still have a peak in terms of dielectric breakdown and RMS in terms of energy dissipated from say a heating element.