TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker or making a Paypal contribution here: paypal.me/SupportTMC

Is NEMA 14-50 a two-phase connection?

Discussion in 'Model S: Battery & Charging' started by HankLloydRight, Jul 8, 2014.

  1. HankLloydRight

    HankLloydRight Fluxing

    Joined:
    Jan 18, 2014
    Messages:
    5,769
    Location:
    Connecticut
  2. Cottonwood

    Cottonwood Roadster#433, Model S#S37

    Joined:
    Feb 27, 2009
    Messages:
    5,062
    Location:
    Colorado
    Although purists will call it Split-Phase, yes the 14-50 connected with 2-Phase service. The 4 pins are Ground, Line, Neutral, and Line.

    The only (slight) confusion is that in many commercial and RV Park systems, the 14-50 is connected to 2 of the 3 Phases available.
     
  3. tga

    tga Active Member

    Joined:
    Apr 8, 2014
    Messages:
    2,201
    Location:
    New Hampshire
    Short answer - You will want to install both CT's on each hot, and make sure the unit is set to 120V (looks like the default for #1 and #2).

    Long answer - The sensors are essentially clamp on transformer secondary coils. The varying magnetic field around the cable induces a current in the coil. The unit measures this induced current to calculate the current flow through the wire. Multiply that by the voltage carried in the line over time and you have kWh.

    These systems are intended to be installed at the main panel, with a CT on each incoming 120V line, and the voltage setting in the monitor set to 120V. It then measures each leg separately, since the 120V loads in your house are unbalanced.

    I scanned through the Efergy manual. It looks like you can set it to 240V, then use one CT on one hot of your 14-50. Assuming no ground fault, the current on the two legs will be equal. You could then use the second CT on some other 240V load, but it looks like the display will only show the combined usage of both, so I don't see much advantage in this setup. Plus, they'd have to be plugged into the same transmitter, so the two sensors need to be near each other.

    #1 looks to be settable to 240V, so I guess you could use 1 CT, but the ebay description is not clear (not a native English speaker)
    #2 can bet set to 240V, and has a link to a full manual (see page 20 - can run 120/240 split phase, up to 575 3-phase)
    #3 has no useful information in the description. But it does have an utterly useless CO2 (not CO) detector built in, according to the video. :rolleyes:
     
  4. HankLloydRight

    HankLloydRight Fluxing

    Joined:
    Jan 18, 2014
    Messages:
    5,769
    Location:
    Connecticut

    Thanks so much for your detailed answer! Do I need to be concerned about how close each CT is to each other when clamped around each hot line? Or do you think I'll get the same results using just one CT around one hot line set for 240v? IOW, do I really need two CTs if I'm just monitoring the energy consumption of one 14-50 outlet charging the Model S?
     
  5. Cottonwood

    Cottonwood Roadster#433, Model S#S37

    Joined:
    Feb 27, 2009
    Messages:
    5,062
    Location:
    Colorado
    You would need both CT's if you wanted accurate measurement of all power used for an RV plugged into the 14-50. If it is only the Tesla, it does not matter. The magnetic fields are all kept in the iron cores of the CT's, so location should not matter. If you put then immediately against each other, there might be a way to get some error, but I doubt it.

    What does matter is which way the wire goes through the CT. Most have a source and/or load direction arrow. This determines which way energy is flowing. Important for Solar PV, etc.
     
  6. tga

    tga Active Member

    Joined:
    Apr 8, 2014
    Messages:
    2,201
    Location:
    New Hampshire
    I didn't know that, but it makes sense. FWIW, the Efergy (#2) installation manual doesn't mention directionality of the CT's.

    If I were picking from one of these 3 ebay listings, I'd probably go with the Efergy. It's not the cheapest, but it the manual is available pre-purchase and it looks like it does what you want.

    Random aside - if both wires run through the CT, the opposite magnetic fields cancel out, and the CT sees 0 current (assuming all is well). If not, some current is taking a different path (back on the Neutral in a 120V circuit, through the ground wire, or through your body to ground). That's how the GFCI circuit in the OpenEVSE works - you'll see both wires passing through the CT. If the currents aren't equal, a current is induced in the coil and the GFCI trips.
     
  7. HankLloydRight

    HankLloydRight Fluxing

    Joined:
    Jan 18, 2014
    Messages:
    5,769
    Location:
    Connecticut
    Interesting, thank again!

    I've seen most of these type of monitors explicitly indicate the direction of power for the CTs.
     

Share This Page