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I am pulling the permit and installing the electrical wiring for my Waterfurnace 7 Series 4-ton Ground Source Heat Pump / Furnace. These are the components:

My questions:

  • Is it fair to say I need two separate circuits for this equipment? That seems clear to me, but I feel I should ask.
  • 6/2 wiring should suffice for both of these circuits in terms of amperage for the equipment in question, correct? The maximum amperage as I understand for 6 gauge wire is 55A. Per the documentation and screenshots below, the aux heater should draw a maximum of 40A at 240 V; and the furnace is requiring a 50A breaker, meaning the breaker will trip before it reaches the maximum of 55A for the wire gauge.

The unit is being installed in an unfinished basement, replacing a propane furnace. I will be running all wiring from the panel, to the unit. Wiring will be 6/2 romex from the top of the load center / breaker box, traveling along the sill and along the joists, stapled every 12"-16". While not fully required (because the panel is within direct eyesight of the furnace), but best practice, I am installing 60A physical disconnects on a plywood panel at eye level for each circuit. Where the wiring departs the joists and travels to the disconnects, I am using flexible non-metal 'liquid proof' conduit for ease of install over PVC or metal conduit.

My circuit plans are as followed:

  • A 50A breaker with 6/2 romex for the furnace
  • A 60A breaker with 6/2 romex for the auxiliary heater

Technical Details of Equipment:

Furnace: Furnace Electrical Ratings

Furnace Wiring Diagram: enter image description here

Auxiliary Heater: Auxiliary Heater Electrical Ratings

Auxiliary Heater Wiring Diagram:

Heater diagram

Please let me know if you have any questions or clarifications. I appreciate any tips, advice, critiques, or feedback. I'll be happy to answer any questions I haven't addressed. Thank you!

Davek804
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    **A)** Well asked! **B)** A phone screenshot is better than nothing, but a link to the Aux Heater installation instructions would be even better than that. **C)** Sch 40 conduit (the grey stuff, not white plumbing pipe) is pretty simple to install, much cheaper than Liquid Tight, and much, _much_ easier to pull wire through. – FreeMan Feb 16 '23 at 13:06
  • @FreeMan. Thanks! B) Added! C) Yeah, I kinda thought that. Regardless, I've already got the liquid tight :). Any thoughts on the primary questions around the wiring + circuit sizes? Thank you! I haven't been able to find an online copy of the install manual for the aux heater, btw. – Davek804 Feb 16 '23 at 14:32
  • Sorry, that's about all the help I'm able to provide at the moment. One of the electricians will be along shortly, I'm sure. A pic without the glare of the plastic sleeve would be a bit easier to read, though. ;) – FreeMan Feb 16 '23 at 15:52

1 Answers1

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The ampacity of a given cable depends on several factors (e.g. conductor, insulation, ambient temp, number of conductors within confined space), which are incompletely specified. However, you stipulate that your #6 is rated for 50A, a reasonable assumption. The breaker protecting that wiring should be rated the same or lower, thus <=50A, not 60A as you intend.
I didn't see your location, but for USA, I look to NEC 2023, Section 310.21, Table 310.16, Ampacities of Insulated Conductors with not more than three current-carrying conductors in Raceway, Cable, or Earth.

MadMonty
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