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#126973 - 03/22/01 07:51 AM RMS question?  
old Appy  Offline
Joined: Mar 2001
Posts: 118
Auckland, New Zealand
Hi again,
we use 230 volts RMS or 325 volts p to p we use 0.707 to find 230 volts from 325 this i the equation to find 0.707 is R M S? how does this equate out longhand?

Tools for Electricians:

#126974 - 03/22/01 01:31 PM Re: RMS question?  
John-Tx  Offline
Junior Member
Joined: Mar 2001
Posts: 8
Austin, Texas
Hi everyone. I'm not an electrician; I'm an electronics tech in Austin, Tx. I hope nobody minds me posting here, even if I do work on the other side of the disconnect (I'm also a homeowner, but at least I know the difference between a codebook and a Sunset Book.)

Appy, RMS is the equivalent DC voltage for an AC supply. I think you're asking why RMS equals .707 peak voltage. This is because pure AC power is considered to be a sine wave. If you average the absolute voltage across one cycle, it will be the peak voltage multiplied by the sine of 45 degrees, which is .707. This makes sense as this is also the voltage at an instant halfway in time between zero volts and a peak.

It might be worth noting that RMS doesn't equal .707 peak for all AC signals. For example an AC square wave, where voltage jumps immediately between positive and negative peak voltage, would have an RMS voltage equal to the peak voltage. It's just that electric power is pretty much kept to a clean sine wave.

Here's a page that explains it pretty well (probably better than I could.) In any case, I hope I helped out with this.

#126975 - 03/22/01 02:10 PM Re: RMS question?  
Bill Addiss  Offline
Joined: Oct 2000
Posts: 3,875

One of the reasons for this separate Theory section was to promote more interaction between those involved in the 'Practical' Electrical applications (Electricians) and those involved in Theory and Electronics (such as yourself). So, to answer your question, you're not only Welcome, We've been kinda waiting for you! [Linked Image]

Feel Free to jump into something else or ask us something.

Do you know where all the 'lost' Electrons go? [Linked Image]


[This message has been edited by Bill Addiss (edited 03-22-2001).]

#126976 - 03/22/01 07:45 PM Re: RMS question?  
sparky  Offline
Joined: Oct 2000
Posts: 5,303
Hi John,
neat link, very interactive with those "wave sounds".

Welcome aboard!

[Linked Image]

[This message has been edited by sparky (edited 03-22-2001).]

#126977 - 03/23/01 01:34 AM Re: RMS question?  
old Appy  Offline
Joined: Mar 2001
Posts: 118
Auckland, New Zealand
Thanks John,
I appreciate your help and great link

#126978 - 03/26/01 03:09 PM Re: RMS question?  
John-Tx  Offline
Junior Member
Joined: Mar 2001
Posts: 8
Austin, Texas
Sorry for this being a late response. I work nights and didn't have a chance to reply until now. I'm glad that I could help, and I'll try to join in on the other theory secions.

Right, Sparky, all we're doing in an electrical circuit is pushing electrons around a loop. In an AC circuit, were pushing them back and forth. I think it takes a subatomic physicist to destroy them.

That said, can you tell me how to put the smoke back into shorted components? It would save us a lot of time at work. [Linked Image]

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