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I’m installing this 100 amp square D QO subpanel. I’m running 2 gauge stranded wire from a 100 amp feeder breaker to the sub panel main lugs. There is no opening large enough on the neutral bar for the 2 gauge in the main panel. There is an empty lug between the incoming red and black cables just left of the silver wire which I assume is the ground.

There is also a square hole where it looks like a lug could be installed. On the ground bar there’s a big enough hole for a ground but it might be hard to get into. Where do I connect the neutral and ground wire in the main panel?

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    There is an empty lug between the incoming red and black cables just left of the silver wire which i assume is the ground. Please check your panel installation instructions. Normally that would be the neutral lug, and if not a service panel an accessory ground bar kit indicated on panel cover needs to be obtained. Feb 20 at 17:57

3 Answers 3

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QO Auxiliary Neutral Lug Kit - the "legs" go in the holes on the bar,

Auxiliary lug

Image Source no endorsement

Others bolt to the bar.

Bolt on lug for 100A panel

Image Source no endorsement

Follow the instructions of the one you get, particularly with regard to torque. I believe the latter type is correct for your panel size, but you can check when buying.

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    If you bring a picture of the labeling of your panel to an electrical supply house (not a big-box store), they'll make 100% certain you get the right one, and they'll probably also tell you the torque spec if you ask nicely.
    – FreeMan
    Feb 20 at 13:24
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2 AWG stranded aluminum is too small for 100A. It is limited to 90A, and that is a standard breaker size, so you'll need a 90A breaker there. There is folk "knowledge" that #2 aluminum is 100A wire, but those people are reading the wrong table. You need table 310.16, and you are in the 75C column because of 110.14(B).

2 AWG copper, which novices often mistakenly buy after hearing aforementioned folk knowledge but not picking up the "aluminum" part, is 120A wire.

Your description of panel terminals fills me with concern. The supply neutral should be attached to that third lug, I would think. Neutral and ground bars are not interchangeable. (In a main panel, grounds are allowed as a guest on the neutral bar). It would really help if you could add photos of the panel to the question. StackExchange's cookie-based accounts can be confusing, so make sure to either use the same device/browser to add the pic, or register your account to log on from different devices.

Note that any subpanel loads (looking at you, EV charging) must be fully accounted for in the main panel's NEC 220.82 Load Calculation, unless EVEMS or other EMS is used.

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It's essential to ensure proper grounding and neutral connections when installing a subpanel. Here's what you should do:

  1. Neutral Connection: Since there's no opening large enough on the neutral bar for the 2 gauge wire, you can use the empty lug between the incoming red and black cables. This lug should be suitable for connecting the neutral wire. Make sure the lug is rated for the wire size you're using and securely tighten it to ensure a good connection.

  2. Ground Connection: If there's a square hole where it looks like a lug could be installed, that's likely a suitable location for connecting the ground wire. Again, ensure that the lug is properly rated for the wire size and securely tighten it to the panel.

  3. Verify Ground Bar: You mentioned a ground bar with a hole that might be suitable for the ground wire. If this bar is intended for grounding purposes, you can use it as an alternative location for connecting the ground wire. Ensure it's securely tightened to the panel and that there's no paint or other coatings obstructing the connection.

  4. Double-Check Connections: Before powering up the subpanel, double-check all connections to ensure they are tight and secure. Loose connections can lead to overheating and potentially hazardous conditions.

  5. Consult a Professional: If you're unsure about any aspect of the installation, it's always best to consult with a licensed electrician. They can provide guidance specific to your setup and ensure that everything is installed correctly and safely.

By following these steps and ensuring proper connections for the neutral and ground wires, you can safely install your subpanel and ensure it functions as intended.

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    This feels very AI generated.
    – FreeMan
    Apr 3 at 16:21

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