NEC 620.21(A)(1)(c)

[erickench]

As I look at the above NEC section something about it troubles me. The statement:

"circuits operating at 30 volts rms or less or 42 volts DC or less"

Now let us suppose we have an AC sine wave at an amplitude of 42 volts. The rms value would be .707X42=30 Volts rms. Now these rms values are considered to be the same as a DC value even though it's an AC sine wave. I would think that it would be proper to say:

"30 volts DC or less or 42 volts peak or less".

Does anybody agree with me on this?

 

[Buck Parrish]

ummmm, No:wink:

 

[erickench]

Well is'nt an rms value an AC effective value? Just like the DC value is the effective value. It's the fact that these two numbers 30 and 42 are related by a factor of .707 that I see this as unique?!

 

[realolman]

Now let us suppose we have an AC sine wave at an amplitude of 42 volts. The rms value would be .707X42=30 Volts rms. Now these rms values are considered to be the same as a DC value even though it's an AC sine wave. I would think that it would be proper to say:

"30 volts DC or less or 42 volts peak or less".

Does anybody agree with me on this?

Strictly speaking on the subject of RMS, what you state is my understanding of it.

But,the article you cite is re: wiring\wiring methods\Elevator\ Hoistways\ flexible cords and cables 6 feet long or less.

Why the distinction... I don't know.