Prime electric bill cost to operate

Discussion in 'Prime Plug-in Charging' started by PriusPrimeOwner, Jan 17, 2017.

  1. Old Bear

    Old Bear Senior Member

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    I is definitely not a project for the "clueless" because it requires a moderate amount of skill and involves working with electric wiring which always carries the risk of serious injury or even death. Improper electrical work can also pose a fire hazard and other risks.

    However, there really are only two parts of the project which require much effort. The first is cutting a rectangular hole in the cover plate so that the meter can be mounted. (I used an aluminum cover plate which I cut easily using a half-moon saw blade of an oscillating tool. The aluminum plate I used was very soft. A plastic plate would probably work just as well.)

    The other part of the project was to splice about 18-inches of wire to the sensing transformer so that it could reach to one of the 240-volt wires attached to the circuit breaker supplying the EVSE.

    The sensing transformer is a small ring through which one of the 240-volt wires supplying the EVSE is run. There is no electrical connection because it just detects the intensity of the magnetic field caused by current running though the wire. One has to disconnect one of the 240-volt wires from the circuit breaker, slip the sensing transformer over it, and reconnect it to the circuit breaker.

    kwh-meter-assy.jpg

    One also needs to run a pair of small gauge wires of similar length from the 240-volt breaker to the meter so that the meter can sense the voltage and also have power to operate.

    kwh-meter-hookup.jpg

    I am not comfortable trying to write step-by-step instructions for this as a D.I.Y. project for someone with no electrical knowledge or skills. But it is not rocket science either.

    You would be well advised to get assistance from someone with basic electrical knowledge and skills. And be aware that this may or may not conform to your local code standards.

    If you do attempt this, just be sure to completely turns of the power to the panel before doing any work.
     
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  2. Oniki

    Oniki Active Member

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    Thanks -- very informative post.

    My uncertainty relates to the snippet I quoted. Do you splice into the wires running into and out of the breaker ?
     
  3. Old Bear

    Old Bear Senior Member

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    The only "splicing" was to extend the thin red and black wires on the little sensing transformer donut ring so that they would be long enough to reach to where the meter is located. The transformer comes with about 8 inches of wire and I had to add about another foot or so.

    kwh-meter-assy.jpg

    sub-panel-with-meter.jpg mounted-watt-hour-meter.jpg

    In my installation, the 50-amp circuit breaker supplying the EVSE is located at the bottom right of the panel. (I guess I should have take a picture with the door open. Sorry.)

    Here is a view inside the panel:

    Current-Sensing-Transformer.jpg

    The 50-amp breaker (1) has two heavy wires (2) which go to the EVSE. One of those wires has to be disconnected from the breaker and threaded through the current sensing transformer (3). The heavy wire is then reconnected to the breaker. The current sensing transformer works by sensing the magnetic field which surrounds the wire supplying the EVSE. There is no splicing or electrical connection between the wire (2) and the transformer (3).

    (Note: It does not matter which wire the transformer is placed around. In the photo it is on the white wire (2) just because it was a little easier to get at. It would work the same around the black wire (2). Regardless of which wire you use, it is important that only one of the two wires pases through the transformer ring.)

    As noted above, the red and black wires on the transformer were not long enough to go to where the meter is located above the panel, so they are spliced (4) to extend them. I soldered the splice and used heat-shrink tubing to provide permanent insulation.

    The meter also requires an electrical connection to the circuit breaker so that it can know the voltage being measured. In this installation, this is done with a light 2-conductor "thermostat wire" cable (5) which has a red wire and a black wire. Each conductor is connected by loosening the terminal screws on the circuit breaker, inserting one wire into each terminal, and firmly re-tightening the screws to assure good contact both these wires and the heavy wires going to the EVSE.

    (Unfortunately, in the photo, this 2-conductor cable happens to have a white color outer jacket which makes it look like the heavy white wire from the circuit breaker to the EVSE. Do not be confused.)

    Just for neatness, there are blue tie-wraps bundling the wires running up to the meter. This is not necessary but helps keep them out of the way and routed neatly.

    It is important to wire the meter correctly. The meter has four terminals. Two are specifically for the sensing transformer and two are specifically for the voltage from the circuit breaker. If you do not wire these correctly as shown in the diagram below, the meter will be destroyed, possibly with great drama.

    kwh-meter-hookup.jpg

    To repeat what I said in my earlier post:

    This is not a D.I.Y. project for someone with no electrical knowledge or skills.

    Working with electric wiring always carries the risk of serious injury or even death! Improper electrical work also can create a fire hazard and place users at risk of shock or electrocution!

    You would be well advised to get assistance from someone with basic electrical knowledge and skills. And be aware that this may or may not conform to your local code standards in your location. It's always best to employ a qualified professional.

    If you do attempt this, be sure to completely turn off all power to the panel before doing any work.
     
    #143 Old Bear, Mar 22, 2018
    Last edited: Mar 22, 2018
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  4. Oniki

    Oniki Active Member

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  5. Old Bear

    Old Bear Senior Member

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    I should have mentioned that the meter does not have to be installed at the breaker panel. You could install it near the EVSE. All you need is to be able to put the sensing transformer ring around one of the wires running into the EVSE and to tie into to the 240-volt connection.

    Here is an example:

    meter-located-at-EVSE.jpg

    This might be preferable if the location is easier for you to read. You can discuss alternatives with your electrician.
     
  6. Oniki

    Oniki Active Member

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    Understood -- thanks.

    I've been 'educated' to assure excellent connection between the high voltage/high amp cables and their contacts, so it makes me a little uncomfortable to do anything that reduces surface area. I'd feel better about the install if the small wire gets embedded into the larger wire, so that they are both flush with the contactor surface.
     
  7. Old Bear

    Old Bear Senior Member

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    You are correct about the importance of having good, clean, and solid connections. You always want to minimize resistance at the point of connection to avoid heat, power loss, etc. You also want to minimize the chance of oxidation or corrosion which contributes to these problems.

    However, if your concern is the effect of adding the small wires needed to feed the 240 volts to the meter, it's not likely to be a problem. Using small gauge (#20 or #22) solid wire adds very little to the number of strands in the #6 or #8 power wiring:

    stranded-wire.jpg circuit-breaker.jpg

    It is the equivalent of adding one more strand which will be clamped down and compressed under the terminals of the circuit breaker.

    This is a place where there are few rules other than the experience and judgement of someone who works with this kind of hardware on a regular basis -- i.e., a professional electrician.
     
  8. Stever56

    Stever56 Junior Member

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    There are times when my cost per kwatt is 2 or less, can check with Com Ed's app

    Posted via the PriusChat mobile app.
     
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  9. MMBH

    MMBH Member

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    ? .... I think he was just trying to say that it might not be as accurate.... not that you had to ;)
     
  10. MMBH

    MMBH Member

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    I take the total paid and divide it by the number of Kw's to get a real-life overall monthly average paid.
     
  11. MMBH

    MMBH Member

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    This is why I didn't go into the physical science realm. I'll stick with the natural sciences and humanities; although I do find the whole physics field extremely fascinating, it just seems like my internal RAM & CPU gets maxed out on the depth of these conversations :)
     
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