wiring question

[archimedes]

I've been thinking of installing a solar water heater on my house.  Before doing that I wanted to determine exactly how much electricity I was using at my electric water heater,  to determine if it would be worth it,  and ultimately determine how much power I would be saving.. 

So,  I bought an hour meter   http://us.element-14.com/jsp/search/productdetail.jsp?SKU=78H0980&CMP=AFC-GBE14    to monitor my hot water heater electric usage. 

The meter has two wire terminals on it.  The wiring directions that came with it say to "connect one terminal to the power wire and the other terminal to the neutral wire".  Problem is,  that on a 240v water heater there is no neutral wire.

What do I do?

I realize that this is a little off topic but I figured someone here might know.

[Don_P]

That's an hour meter not an electric useage meter... it's just marking time. One hot and the neutral (ground) and it'll start working as a clock.

[MountainDon]

The water heater has a fixed wattage. If the meter could be wired to go on whenever the thermostat calls for heat one could calculate the amount of energy used.

[archimedes]

Yes mountaindon,  I'm planning on connecting the power supply to the heating element.  So that every time the heating element is energized the hour meter will run,  multiply the hours running by the 4500 watts it uses gives me the exact (almost) eletrical usage.

My only question was where to connect the neutral. 

If I'm understanding Don P's post,   he is saying to connect the neutral to the grounding terminal on the water heater (since there's no neutral).

Thanks

[bayview]

   I wonder what the multiplier would be?    Times two?

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[archimedes]

It's quite not as simple as I made it sound earlier.  There are two heating elements,  an upper and a lower.  Most of the time the lower element doesn't get used,  unless there is a large amount of hot water demand at one time. 

If I had two hour meters I would put one on each element and the calculate the total wattage used.  Since I only have one hour meter (I was too cheap to pay for two)  I will have to meter the upper element separately for a week and make an estimate of monthly usage by multiplying my reading by 4.  Then meter the lower element for a week and multiply my reading by 4.

The usage for the lower element will almost certainly be less than the upper. 

So,  total hours X 4500 watts (per element)

[bayview]

   On the lower element you will want to wire the hour meter between the thermostat and the element.
 
  Follow this url for a diagram . . .

http://www.askmehelpdesk.com/attachments/electrical-lighting/17023d1235701426-giant-water-heater-wiring-120v-0r-240v-heater-wiring-2.jpg

  In this diagram, I would wire the "upper" to the "yellow wire and ground.   And for the lower, I would wire to the "black" wire between the lower thermostat and the element and then ground.   In parallel, of course. . .    You wouldn't cut any wires.

  Ok guys!   Double-check me . . .

  The easy way would be two hour meters . . .

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[archimedes]

Bayview,  let me see if I've got this right.

The upper element is pretty straight forward.   Connect to either live wire and the ground.

But the lower element is more tricky.  If I was to the connect the meter to the "red" wire on the lower element (in your diagram),  then when the upper element came on,  the meter would be running even though the lower element wouldn not be energized. 

So when it comes to the lower element,  I have to be sure to connect to the wire (in this case back) that is coming from the lower thermostat.

Right?

[bayview]

   In the diagram, the red and blue wire appear to be "Hot" all the time . . .    When the upper thermostat is "On", it completes the circuit for the upper element and sends electricity through the black wire to the lower thermostat.

   In this diagram, the upper thermostat must be "On" before the lower thermostat is able to work.   They do not work independently of each other.   The lower can only turn "On" when the upper is "On".

   For your experiment, I would attach to the yellow wire for the upper, and the black wire between the thermostat and the element for the lower.

   Of course, your heater may be different.   I would check your heaters wiring with a volt meter.   See if one leg on each element is always "Hot".

   Its pretty common for a 220 volt circuit to have one leg always hot . . .      And to switch the other 110 volt leg.   Gas pumps for example.   Always check with a volt meter.

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[archimedes]

Thanks Bayview.  Coincidently,  my water heater is wired exactly the same as the diagram.  Thanks for pointing that out.  I guess I had a 50/50 shot of getting it right,  by accident,  but I would have been really scratching my head if the meter reading for the lower element had been higher than the upper element due to connecting it to the wrong place.  Now I know to make sure to connect the meter to the lower elements thermostat wire.  Thanks again!

Another question has come up though.

A friend said that since the meter is rated for 240v that I don't even need a neutral connection.  He said just connect both hot wires to the meter and call it done.

What do you think?

[MountainDon]

I was going to suggest that, but had no real idea if that was going to be right... 

[archimedes]

MtDon,  I think the reality is that it would work both ways. 

A concern that was raised about the ground as neutral option is that a ground wire is not designed to handle current on a regular basis.  So using it that way would not be a good idea. 

However,  I checked the ground wire on the water heater connection and it appears to be the same size as all my neutral wires,  so maybe that concern is unwarranted.

Would like to hear others opinions.

[archimedes]

Well,  I attached the meter as described above.  The meter did work.  But unfortunately,  it never shuts off.

I connected one terminal to the yellow (hot) wire and the other terminal to the ground.  Since it kept running even when the heating element wasn't on I tried switching to the blue (or other hot) wire.  And the same thing happened,  the meter never shuts off.

This makes no sense since both wires can't be hot when the element isn't on.  

I'm stumped

[MountainDon]

Do you have a test meter? There must be some pair in what you have that goes live when heat is needed and dead when no more heat is needed.     Run some water so at least one element is on. Check for all the hot combinations. Let the tank sit and get hot, maybe even turn down the thermostat  at that point and look for what's now dead.   

[bayview]

   It appears that there is 110 volt "bleeding" through the element, causing the meter to never shut off . . .   See what happens when the meter is wired as a 220 volt with one lead to the yellow wire and the other to the blue.   Basically, running parallel to the heating element . . .    One side of the meter is now always "Hot" and the other side will switch when the thermostat turns on.  

  BTW:   Disclaimer . . .     Make sure you turn off the breaker.   Check for voltage with a volt meter and most importantly . . .   Don't hold me responsible for any damages. . .

 220 volt water heaters have no need for a neutral because the current both feeds and returns by way of the two hot wires as the current polarity alternates.   The ground wire serves only as a safety feature and never carries any current under normal circumstances.

  Basically, you have two separate appliances on the same 220 volt circuit.   (The upper element/thermostat and the lower element/thermostat)  

  It seems to me that you would still need two hour meters, even if 220 volt, to accurately meter when the elements are "ON"

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[archimedes]

Ok,  you're not gonna believe this but both wires (yellow and blue) are always hot.

I dug out my volt meter to do a test.  With the power on but the element not energized I connected yellow to ground, reading 120volts.  Then I connected blue to ground,  reading 120volts.  Then I connected yellow to blue NO volts.

Turned the temp on the W/H up so element would energize and connected yellow to blue reading 240 volts.

So then I connected one terminal of the meter to yellow and the other terminal of the meter to blue and the meter runs.  Turned down the temp to shut off the heating element and the meter stops.   

I never would have predicted that outcome.  Still don't understand how both the yellow and blue wires could be constantly hot and the element still remain off.   

Even now I can't believe it.  I'm gonna go double check.

[bayview]

Ok,  you're not gonna believe this but both wires (yellow and blue) are always hot.

I dug out my volt meter to do a test.  With the power on but the element not energized I connected yellow to ground, reading 120volts.  Then I connected blue to ground,  reading 120volts.  Then I connected yellow to blue NO volts.

Turned the temp on the W/H up so element would energize and connected yellow to blue reading 240 volts.

  Right . . .   The blue wire is always "Hot" and bleeding through the element.   You have confirmed to me that the thermostat is working when testing the yellow to blue.

  Again, try connecting one side of the hour meter to the yellow and the other to the blue.   Hopefully, the hour meter will only run when the heater element is "ON".

  Opps, was typing when I should have been reading . . .    Seems you have it figured out..


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[bayview]

   BTW:

  Checking the yellow to ground and the blue to ground was measuring the same voltage.   120volts and 120volts on the same leg will always be 120volts.   You received 240 volts across the yellow and blue because you were measuring both voltage legs.

  I'm guessing that there is not resistance across the element, allowing voltage to bleed through.

  If we follow the diagram . . .    To check the lower element/thermostat, you would follow the wires from the element.   The red wire (that is always "Hot"), and the black wire that goes from the element to the thermostat.

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[archimedes]

First,  thanks MtDon and Bayview

Connecting yellow to meter and blue to meter works.  When heating element is on,  meter is on.  When heating element is off,  meter is off.

I'm still surprised that the yellow and blue are always hot.  I would have thought that the thermostat would have kept and power from getting to the element.  But it seems that the thermostat just completes the circuit,  when hot water is called for,  but the power is already at the element all the time.  Counter-intuitive to my way of thinking.   But it is what it is.

One thing that is also surprising (and I need to confirm this tomorrow,  it's too late/dark now) is that when I connected the meter to the yellow,  or blue, and to the ground not only did the meter run but the element came on.  It's seems like by doing this I was bypassing the thermostat completely and getting a false reading because neither the element or the meter ever went off.    

[bayview]

I'm still surprised that the yellow and blue are always hot.  I would have thought that the thermostat would have kept and power from getting to the element.  But it seems that the thermostat just completes the circuit,  when hot water is called for,  but the power is already at the element all the time.  Counter-intuitive to my way of thinking.   But it is what it is.

   Again, the blue wire is bleeding through the element.   You are measuring the same voltage on both sides of the element (120 volts) - Until the thermostat engages.   You are then alternating voltage from the blue to the yellow through the element and then back again (240 volts).

   Remembering 120 plus 120 volts on the same leg is not 240 volts.   You must have both legs from the service panel for 240 volts.

   That's why you received 240 volts when measuring across the yellow and blue terminals (with the thermostat "ON").   And only 120 volts when measuring yellow to ground and blue to ground.   

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[bayview]

   This web site may be of interest . . .   

http://www.nojolt.com/Understanding_240_volt_circuits.shtml

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[archimedes]

Actually that helped a lot.  Thanks.

Some interesting results from my test so far. 

Using very little electricity at the water heater top elementso far.  There could be two probable reasons.  1) I'm just not using a lot of hot water.  2)  the lower element actually uses more power than I thought.   

We'll see soon enough.

[MountainDon]

That's a great web page bayview. Thanks a lot.