Interruptible Service for Hot Water

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Old 12-28-13, 08:53 AM
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Interruptible Service for Hot Water

Does anyone know where I can find a 2 source in, 2 load out, electrical box? My father has interruptible service on one element, regular service on the other, of his hot water heater. He has such a box in his house and it's ancient. I want to replace/relocate, but can't find such a box anywhere. I would like to mount it outside the house. Basically, it has two 240v power sources running into it. One off the main meter, and one off the interruptible meter. These sources then go thru their own breaker, and then back out of the box to the hot water heater. It says "property of Detroit Edison" on it, but they claim it's not their box.
 
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Old 12-28-13, 09:15 AM
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Welcome to the forums.

My father has interruptible service on one element, regular service on the other, of his hot water heater
I'm familiar with a second meter for a water heater. The premise was that there were two rates associated with it. A day rate that was much higher than the standard residential rate and a night rate that was much lower so that the customer would have a timer setup to only heat the water at night.

There was a second type of meter that had an actual timeclock built into it. It would turn off the electric to the water heater during the day and turn it back on at night.

However..... I've never seen a water heater fed with two completely separate services. Are you sure that is the way it's connected ?

I'm not aware of any panel that will handle two separate services thru it. You may have to use two independent panels now.

At one time..... the power companies offered meter pans and specialty switching boxes. Those days are over.
 
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Old 12-28-13, 05:39 PM
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It's probably been 45 to 50 years here since there were 2nd meters for electric water heating rates. They did away with those meters long ago and used to just show a credit on the monthly bill for electric water heating or electric space heating. I doubt that today they offer credits on either.

Does anyone know where I can find a 2 source in, 2 load out, electrical box?
I've never seen or even heard of such a thing and am pretty sure no one makes anything like that today. You'll probably need a small 2nd panel with 2 spaces in it, enough for a 2 pole 30A breaker.
 
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Old 12-29-13, 07:24 AM
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Thanks for the input, Yes, I think this was done quite a few years back, and it's definitely two sources, one for each heater element. It's an old farm house. The interruptible "meter" on the outside of the house may very well be a timer. I haven't opened it. My father claims he gets a discount for having it.

I think I'll end up using two individual 30 amp boxes outside the house. Are there regulations as to how hi/how close to the meter these boxes should be? I've uploaded a diagram of how it's wired.
 
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Old 12-29-13, 01:01 PM
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I think I'll end up using two individual 30 amp boxes outside the house. Are there regulations as to how hi/how close to the meter these boxes should be? I've uploaded a diagram of how it's wired.
The specs on installation dimensions should be provided by the power company although there are some coops that just don't care what the customer does. Better to call them and ask for their service rules.

The diagram you posted shows that ALL power comes through the first meter. The second meter may be nothing more than a timer or it could provide a reading that is deducted from the other meter's reading in calculating the monthly bill.
 
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Old 12-29-13, 01:50 PM
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I'm more inclined to think the second "meter" is indeed a timer that simply disconnects the lower element during peak power periods. Maybe a picture of this meter would help.

While there are some utilities that offer "time of day" services that have a lower rate during periods of low system utilization most people (not all by any means) that have tried them have gone back to the standard rates If you are capable of shifting all, or most, of your activities that consume large amounts of power to the off peak hours you could save a considerable amount of money. Unfortunately, all it takes is one roasted turkey dinner (electric oven on for six hours during high peak times) to negate ALL the savings during the billing period.

I would contact the utility and see if they have any kind of special rate for electric water heaters that have a timer preventing usage during peak periods. If they do not have such a rate structure then I would re-connect the water heater for non-simultaneous operation of the elements and connect directly to the circuit breaker panel and then remove (or have the utility remove) the extraneous equipment.
 
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Old 12-29-13, 03:25 PM
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Is this a standard water heater or one specially manufactured for this dual meter setup?

I don't know what that dual meter setup accomplished for the electric company. With each heater element connected to a different meter you could leave the high rate meter's breaker off all the time and the low rate interruptible meter's breaker on all the time and still get hot water all of the time although the tank would not heat up as fast.

More modern setups have two inputs (meter feeds) and just one output (continuing circuit to the water heater). They're simply transfer switches of the kind you use with generators. If you need hot water during the interrupted time period, you manually switched the (standard) water heater over to the higher rate regular meter using an ordinary 30 amp circuit from your main panel.

Even simpler modern setups have the water heater connected only to the lower rate interruptible meter.
 
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Old 12-30-13, 12:10 AM
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Because of the way the heater elements are wired I am all but sure that the second "meter" is a time clock. Since the majority of the water used is heated by the lower element alone it means that in the rare occasion that the majority of the hot water was used while the time clock was in the "off" position the upper element could always be used (at the standard metered rate) to provide a limited amount of hot water. Two meters were not necessary as the rate schedule assigned to the primary meter had a fudge factor to allow for the water heater not operating during peak periods. That fudge factor was probably something like 500 kWh per month or so (maybe less) and when it went over that amount a second tier price schedule went into effect.

With today's "smart" meters it is possible to change the rate schedule of cost versus kWh almost instantaneously. That means that complicated wiring devices like time clocks and dual input water heaters are no longer necessary to give the customer a break by using less power at certain times of the day.
 
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Old 12-30-13, 01:28 PM
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Ok, I went to my Father's home and took some more photos, I also noticed only one leg of the 220v runs thru the interruptible meter/timer, not both. Serves same purpose.

I then reviewed my father's electric bill and called the utility for an explanation. They don't show him on interruptible service, nor are they giving him any discounts. They simply show him as having "RESIDENTIAL ELECTRIC WITH WATER HEATING".

The panel in the house is a Square D Water Heater Control.
 
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Old 12-30-13, 01:35 PM
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The inside of the box. You can see the 4 cables coming in on the left, and the 4 conductor cable going out to the water heater in the bottom middle. I misspoke earlier. The UPPER element is the one on the special service.
 
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Old 12-30-13, 05:10 PM
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They don't show him on interruptible service, nor are they giving him any discounts. They simply show him as having "RESIDENTIAL ELECTRIC WITH WATER HEATING".
Then you can do away with the wiring through the timer and the second box and just run it all through the main panel, which may need to be replaced.
 
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