Installing a 100A subpanel in the same house 20 feet from the main panel.

Do NOT bond the neutral bar in the subpanel.

In a subpanel, the neutral and ground bars must be isolated from each other and from the enclosure. This is required by NEC 250.142(B) and 250.32(B)(1).

Why:

• The main panel is the only point where neutral and ground should be bonded (NEC 250.24(C)).
• If you bond them again in the subpanel, it creates a parallel path for neutral current on the grounding conductors and enclosure, which can cause:
• Overheating
• Electric shock risk
• Improper operation of breakers

What to do:

1. Remove the bonding strap or screw connecting the neutral bar to the enclosure in the subpanel.
2. Ensure the neutral bar is mounted on insulated standoffs (not touching the metal box).
3. Run a separate equipment grounding conductor (EGC) with your feeder cables (NEC 250.32(B)(1)).
4. Use a 4-wire feeder: two hots, one neutral, one ground (NEC 250.32).

Exception: If you're using a metal raceway (like EMT) that's properly bonded, it can serve as the EGC, but you still must not bond neutral to the subpanel enclosure.

Since this is in the same building and under 20 feet, you don't need a separate disconnect at the subpanel unless local code requires it.

Bottom line: No neutral-to-enclosure bonding in the subpanel. Keep neutral and ground separate.

No, do not bond the neutral bar in the subpanel.

NEC 250.24(A)(5) & 408.3(E): The grounded (neutral) conductor must be isolated from the enclosure and equipment grounding conductors at all subpanels. The main bonding jumper (or green screw/strap connecting the neutral bar to the case) must be removed or not installed.

Required Connections:

1. Four-wire feed: Run two hots, one neutral, one equipment grounding conductor (EGC) from the main panel to the subpanel (NEC 250.32(B)(1)).
2. Main Panel: Land the feeder neutral on the main neutral bar (bonded to case). Land the feeder EGC on the main ground bar.
3. Subpanel: Install an isolated neutral bar (or remove bonding screw/strap from factory bar). Land feeder neutral on isolated neutral bar. Land feeder EGC and all branch-circuit EGCs on a ground bar bonded to the subpanel enclosure. Neutrals and grounds must not mix on the same bar in the subpanel.

Why: Bonding neutral to ground at the subpanel creates parallel paths for neutral current on the EGC and metal raceways/enclosures (objectionable current, NEC 250.6). This is a shock hazard and violates code.

Exception: Only if the subpanel is in a separate structure (detached garage) and you run a 3-wire feed (no EGC) and meet all conditions of NEC 250.32(B)(2) (no metallic paths, GFPE, etc.). This does not apply to your same-house installation. Run 4 wires. Keep neutral isolated.