OK, this is probably gonna be a dumb question. If a residential panel is rated at 100 amps that means that each hot leg in the panel provides 100 amps, and therefore the panel actually provides a total of 200 amps to the house, right? wrong? So many questions, so little time.

hmmmm, really it's not so dumb a Q, considering some of the threads going on in the "Electrical Theory" area.

each leg IS a #2, not a #8 or #6....

I realize that I may be considered the token "village idiot" in this forum, but this seems rather simple to me.

100 Amps requires #2 Aluminum wire. 277V, 240V, 208V, 120V, doesn't matter.

Each leg in a 120/240V 100A service provides 12,000 Volt-Amps of power. Both legs provide 24,000 Volt-Amps of power...either 100A @120V or 100A @240V. All of the "doubled" power comes from the voltage, not the current. The current remains 100A.

GE Panels (200A) use 4 100A single pole breakers, 2 100A paired in parrallel to get 200A, but still 200A per leg...

Make sense?

[This message has been edited by sparky66wv (edited 03-16-2001).]

hehe, I saw some of those theory posts. You gotsta put your beanie cap on before going in there.

ok, not to beat a horse to death, but I just want to make sure I'm clear on this ...

a 100 amp service drop means there will be 200 amps of capacity to use, a 200 amp drop means there will be 400 amps to use, etc.

Yes?

Hi Sparky66,
I was composing my post while you were posting yours. I'm still trying to digest yours. Burp!

Thanks for the responses guys. I'm still wet behind the ears, but getting drier day by day.

Use Volt-Amps in your service calculations and you won't get confused. Think about it in terms of volt-amps and it makes more sense.

Oh, and hey ... pass that village idiot cap over to me! I'll do right by it!

We've gotta stop posting like this. People are gonna start talking.

OK, Roger that! Makes sense.

Thanks again guys.

[This message has been edited by Boscodog (edited 03-16-2001).]

You guys are never going to take the Village Idiot Cap away from Me, so don't even try to!!
I also hold the title of "Anesteticly Induced Messages", which suppliments the Village Idiot Achievement Award.

Now on the serious side, '66 gave a good suggestion as to using Volt-Amps [or KVA] to figure a system's rating [or service's rating].

To answer Boscodog's original question in as few words possible [oh, how I've said that so many times before ]:

For a simple 100 amp, 120/240 volt 1 phase 3 wire service, the panel would be able to draw a maximum of 100 amperes per Ungrounded Conductor [hot].
That loosely translates into two [2] 100 amp hots at 120 volts [line to neutral], or a total of 100 amps at 240 volts [line to line].

It's more proper to say that the panel / service is rated at 100 amps, because that's the highest load that can be drawn on one "hot" conductor, or through one pole of the main breaker, at one time.

It will, as you asked, have a combined total of 200 amps when using Line to Neutral [120 volt] loads only - so it's not really totally incorrect to say that, just not completely and technically correct.

That alone must be a mountain of jibberish to understand

As Sparky mentioned in the first reply, the ampacity [size] of the wire will be the primary thing to determine maximum current.
This plus the main breaker's rating will determine the maximum amperage a panel can draw [continuously and without LCL], provided it's not more than the panel's designed for [like using a 150 amp breaker for the main on a 100 amp panel with 100 amp bus bars].

Can't really use the combined totals of the branch circuit breakers to do this.

Also, as '66 mentioned, the typical 120/240 VAC 1 phase 3 wire service will have a total Volt-Amp capacity of 12,000 VA [12.0 KVA] per Line to Neutral load [hot to neutral], for a combined total of 24,000 VA [24.0 KVA]. The 12.0 KVA is 120 volts times 100 amps.

Consequently, the total Volt-Amp capacity for the same panel, using Line to Line loads [240 volts, or both "hots"] is also 24,000 Volt-Amps [24.0 KVA].
Multiply 240 volts times 100 amps, which equals 24,000 VA [24.0 KVA].

Please pardon the vague and slang terms I have used in this message. I'm trying to make it easier to comprehend [any luck ?? ].

Other than "twilight Zone Stuff", what did you think of the topics and threads in the Theory discussion area?

Let us know!!

Scott SET

Thanks Scott and Sparkies. I think I'm finally totally clear on this now. As I mentioned in my very first post on this board a week or 2 ago I'm not a sparky myself, just a homeowner who has known how to do basic wiring for some time now, but now I want to know more than the basics. I actually think wiring is fun! I fantasize sometimes about scrapping this desk job of mine, becoming an apprentice, and roping some homes. Yeeee dawgy!! Pretty bizarre, huh?

Scott, as long as you've got the time and energy, keep posting the theory stuff. They work way better than my Sominex!

JUST KIDDING!!

Seriously, although I don't understand everything you write, I do pick out pieces here and there. I greatly appreciate the effort that you, and everyone else, puts into this board. It's a fun place to come to. (Can you tell I don't have a life? )

hmmmm...the utility rates their x-formers, 15,20,25 kva. sometimes, if one x-former is a feed for 3 or 4 residences , i think it's
larger....

so can this thread relate back to it???

Sparky,

You have to take Demand loading into account.
Does anyone know what percentage they may figure for typical residential housing? It's probably pretty low percentage-wise.

ok let me take over the dumb seat for a while the question was a 100 amp panel actually can serve 200 amps am i correct in that. now i never saw a clear cut answer to that question so now I am going to say yes 100amps or really 80 percent of 100 amps down each leg but in real terms you could only bring 80 percent of 50 amps down each leg because of the neutral conductor only being sized for a total of 100 amps now am i right

doc,
does the ol' sine wave apply to ampacity here? A & B side?
i can read 240 voltage, but cannot amprobe from A to B.
Taking the demand into account, there must be a defined amount of x-former va ???

Bill,

As you mentioned, the demand percentage for a typical residential application is rather low. The optional method (220.30) states the first 10 KVA at 100% plus 40% of remainder. The "remainder is listed at 220.30(b)

Frank (cinkerf)

doc,

In a 'typical' residential situation where there is no Harmonics (or other weird stuff) the Currents on the 2 legs would sort of cancel each other out and therefore very little would flow on the neutral. And anything at 240v would not be using the Neutral anyway. Until recent years the Neutral was even allowed to be downsized because of this.

So, in short, if you were using exactly 80 amps on each leg the Neutral would be carrying - 0 - It wouldn't matter what size it was.

So, it could be looked at as being able to use (if perfectly balanced on a 100a 240v service) 100 amps per leg at 120v for a total of 200A (@120v) or 80A continuous per for a total of 160A (@120v).

Like Scott said, this is not the conventional way of looking at things or proper terminology because your House is supplied with 240v Service which happens to be capable of being used at 120v only because of the Neutral tap.

These are my thoughts and may or may not be considered proper or correct. If anyone has anything to add to this or corrections to something feel free to Comment.

Bill

Bill,

You explained in a way that was taught to me early on. Easy to understand. I've always looked at the situation in that manner.

Frank (cinkerf)