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I still run into these from time to time. This is a circa 1955 GE 720 cycle load management device. They were installed on water heaters back in the day, along with a reduced rate "water heater meter". This device would toggle the water heater on and off when the utility sent out the 720 cycle signal. These old one's have a HUGE blob of mercury inside, so disposal can sometimes be tricky. Pictures for your enjoyment:







 

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Wyome
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Never have seen one of those. We still run into some of the old dual meter systems, one meter being for water heat only. Also have never heard of the 720 pulse thing, but then we are in the sticks here. Interesting.
 

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R.I.P. 2014
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Beautiful pictures . . .

I miss Washington, DC where ole this stuff still lurks.
Can still be seen in the older parts of NY and NJ as well.
Hell I think some of Edisons original work is still working in upper NJ.
 

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R.I.P. 2014
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I'd seen them in the past and never was sure what they were used for. I deff. didn't know about the 720 cycle. Someone can probably explain better than me about the 720 cycle but, it's like the way fiber optic cable can send mutiple signals at the same time. It's using the wire at a different time than the normal 60 cycle.
 

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Thank you. I am familiar with superimposing signals, an info stream or data pulse "riding" on the 60 cycle line, I was asking what the purpose of the 720 signal was. Does the fact it's a multiple of 60 mean anything?
 

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flat rate water heater contolled by poco. 720 hertz imposed on line for 30sec = off 60sec = on. 720hertz is passed by capacitor 60 hertz is blocked.
 

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Going strictly from memory, the 720hz switching device was an extrapolation of the Bell Telephone selective frequency party line ringer. There had been a lengthy period of negotiation to determine if a tuned circuit to pull a relay coil in or a Wurlitzer Organ Company vibrating reed system would be chosen. Wurlitzer must have been more expensive on licensing.

The system was originally envisioned for a method line operators could employ to remote operate substations and believed to be more cost effective than leasing paths from the telco.

The idea of controlling water heaters remotely to absorb excess generating capacity was brilliant in that the heaters could be brought on or off line quickly when needed as opposed to allowing heater load only in pre determined time slots. There seems to be a movement to go back to utility control of customer owned load today to fill the same need.
 

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Ambassador of Amps
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flat rate water heater contolled by poco. 720 hertz imposed on line for 30sec = off 60sec = on. 720hertz is passed by capacitor 60 hertz is blocked.
You realize that this thread is 3+ years old?
 

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RIP 1959-2015
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Harry stop being such a troll.
Look who is talking you are the one that comes here to pick apart just about every post you read and recking the enjoyment of the forum for the other guys that post here ..

You are more then welcome to be here but why don't you tone down the jumping on peoples case crap..

Calling every one on here a hack because you somehow think you better does not cut it.

I don't mind jokes and a little rasinig but really you seem to enjoy posting crap that makes people look like fools when they have a question that derserves a valid answer..


You are an Electrician try to be a little more professional.
 
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