Do Canceling Meter Legs Work? (Was Re: ratcheting cyclometers) [RE-wrenches]

Christopher Freitas --- OutBack Power cfreitas at outbackpower.com
Tue Jan 20 12:58:07 PST 2004


This trick of using a 240 VAC meter for a 120 VAC system with the input 
and output flowing through the two legs in opposite directions does work 
- I did it years ago on some of the first grid-tie SW systems - but I 
remember using the type of meters which included a neutral tap - which 
must have been the "5 jaw" type. I think there might be a way to wire 
into the little 120/240 jumper on the back of the regular 4 wire type 
meters - but I am not sure... 

You also can do this trick with a current sense transformer as well by 
passing both input and output conductors through the same "hole" in 
opposite directions.  So using a meter with a seperate CT would be 
another option.  

Basically - a mechanical kwh meter is an analog multiplier. Think of it 
as having a tiny motor which spins based on voltage applied and the 
amount of current flowing through the meter.  There is actually a slight 
error when spinning the meter backwards as the drag of the bearing is 
calibrated out in the normal direction - so the KWH meters read slightly 
low when selling power back to the utility - figures!   

Christopher Freitas
OutBack Power Systems, Inc.
cfreitas @ outbackpower.com  
www.outbackpower.com
Arlington WA USA
Tel 360 435 6030  

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