Load calculations and Panel ratings

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  #1  
Old 08-06-07, 01:41 PM
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Load calculations and Panel ratings

A bit of Humor to start off.

A well pump was Installed Right before I bought the house. No tags on the visible end of things , and I need an amp rating for some calculations. Called the plumbing Co who installed the pump. He cant remember what he used, and doesnt have the paperwork, BUT... For 750$ he'll pull the pump and let me read the Markings on the case before he drops it in again........

Obviously I have since borrowed an "AMP CLAMP" , Which according to the instructions,I can only measure on one conductor at a time. This is a 220 v pump , two hots and a ground. In theory , I would measure the live wires individually and add them together??

#2.. As simple as possible.. A generator panel, Set up for "Backfed breakers"-
The "LINE" breaker is 60 amp, the GEN FEED breaker is 50amp. Provided the "PANEL" is rated at over 60 amps , and "Wire Gauged" accordingly, is there any limitation to using a larger line breaker? (Upgrading to 70a at max)
 
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Old 08-06-07, 02:06 PM
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You only need to measure one hot wire on a 240 volt line. Both lines, by definition, have the same current.
 
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Old 08-06-07, 05:42 PM
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Understood, However....
Is that the Total load of the pump , or do I double the reading?
 
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Old 08-06-07, 06:00 PM
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That tells you how many amps you have at 240 volts.
 
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Old 08-07-07, 05:14 PM
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Don't bother upsizing the genny panel feeder breaker.
A typical "portable" generator likely could not feed that much power. Just install the circuits you need.

If you want more emergency power, you will probably want a fixed generator with an ATS, which you can use a more traditional sub-panel for, ans can size larger.

You multiply the amps by the volts to see how many watts of power you need. Take into account the starting current though.
 
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Old 08-07-07, 05:41 PM
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actually the Genny Was an afterthought, and I wont be using all that power in emergencys, but the primary purpose was to add a new Dryer ckt to an already overloaded main panel. I needed to free up space in the main, and since all my "NECESSITIES" (Well Pump, hot water ,and heat) are all in the vicinity of my new sub, Those were the ones I would put in the sub. The gen would only power each individually as needed, and would be hooked thru manual transfer/I read the labels for all but my well pump, and It will be close to the 60 amp marker, so a little bit of a cushion was all I was interested in (Only on the LINE side)
Ive never used an amp clamp before, I do understand "OHMS LAW" but I Dont get how one conductor of a 240 ckt gets me TOTAL AMPERAGE.If thats the way it is , I'll take your word for it, but Im baffled.
 

Last edited by Unclediezel; 08-07-07 at 05:44 PM. Reason: misspell
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Old 08-07-07, 06:35 PM
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One line of the 240 gets you the amperage the same way that one line of 120 gets you the amperage.

With 120 volts you don't measure both the neutral and the hot wire, you only measure one. Why would you measure two for 240 volts?
 
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Old 08-07-07, 06:50 PM
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I could be way off base on this, But I figured if a 220 ckt is 2 120 volt circuits, Then each hot leg would be carrying its own current. I understand they would be carrying Identical amounts of current, but arent they 2 seperate 120v ckts and treated ---Seperately? Am I Overthinking this?
 

Last edited by Unclediezel; 08-07-07 at 06:52 PM. Reason: misspell
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Old 08-07-07, 07:09 PM
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240 volts in the US means 240 volts between the two wires. It could just as easily be 240 volts from ground. If it were 240 volts from ground would you still want to double the current?
 
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Old 08-07-07, 07:20 PM
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Thank You Racraft, I got it.Sometimes I need a Picture drawn for me.
 
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