I am looking to interlock a new ERV to the existing air handler. The wiring diagram from the ERV manual is included below.

My question concerns how to splice together (is this the correct term for it?) the wires shown in the highlighted area. What I'm currently planning (for each of the wires, red and green):

  1. Cut a short wire "stub"
  2. Twist together the copper ends of the wires from the ERV, the thermostat and the stub wires and put a wire nut over the connection
  3. Run the stub wire to the air handler board

Is this the correct approach (located in the US)?

For reference the ERV is a Panasonic FV-10VEC2, the air handler is a Carrier 40MBAAQ24XA3 and the thermostat is an Ecobee 5.

Screenshot from ERV manual showing the wiring diagram


3 Answers 3


Your plan for how to connect the wires sounds fine. Wire nuts will work well.

You can also get good results from Wago 221 or Ideal In-Sure lever connectors. They are really fantastic for connecting mixed gauge wires, particularly small wires.


The only real issue is wire size. But looking at the Ideal catalog, there are plenty that are designed for as little as 2 x 22 AWG wires. You will have 3 wires in each wire nut, so as long as the wires are at least 22 AWG (for comparison, typical thermostat wire is 18 AWG and typical 120V mains wire is at least 14 AWG) you should be fine.

That is separate from the question of whether this is the right way to connect the ERV - i.e., where to splice it in the circuit. But if this is the right place, wire nuts should do the job.

  • 1
    Thanks @manassehkatz. If I understand you correctly, your main concern would have been that the wires might be too thin to be well held together by the wire nut. But since I have three wires that are not all that thin (~ 18 AWG), I should have no trouble finding an appropriate wire nut (such as 74B® Yellow from the catalog). Can I ask if you're concerned about the location of the splice in the circuit? Would you have interpreted that wiring diagram differently (where two wires meet at the same terminal)?
    – ErnChe
    Nov 29, 2022 at 1:02
  • I read through a bit more of the Panasonic ERV manual, and that all sounds correct. But keep in mind that the wires from the ERV to the HVAC/AHU are not included - you supply them, and they are supposed to be in conduit. Nov 29, 2022 at 1:16

It turns out that the simplest approach was simply to insert both the ERV and the thermostat conductors into the same terminal on the air handler board. I had not realized that there usually is enough room under the screw clamps for two small gauge wires.

  • 1
    As long as it is designed for that, it is fine. And it likely is designed for that because these are not only low voltage but also low current. The standard advice here is usually for 15A or larger, 120V or 240V, wires - where putting two in one screw is generally not allowed (exception: screw-to-clamp receptacle screws that allow one wire straight in on each side of the screw). Especially circuit breakers. Dec 16, 2022 at 15:39

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