Quick Hits

EPISODE 7 — Main and System Bonding Jumpers (270.28)

Slide 1 — Hook "Quick but important — the jumper that ties it all together at the service or separately derived system."

Slide 2 — Material & attachment

• Main bonding jumpers and system bonding jumpers: copper, aluminum, copper-clad aluminum, or other corrosion-resistant material.

• Connected using any of the methods from 270.8 that are appropriate for the jumper/enclosure material.

Slide 3 — Sizing

• General sizing: per Table 270.102(C)(1) — sized off the largest ungrounded conductor.

• If a service has MORE than one disconnect enclosure: size each enclosure's main bonding jumper based on the largest ungrounded conductor feeding THAT enclosure.

• If a separately derived system feeds more than one enclosure: either size each enclosure's system bonding jumper individually, OR install a single system bonding jumper at the source sized for the equivalent combined conductor area.

Slide 4 — Quiz + CTA Q: "For a service with multiple disconnect enclosures, how is each enclosure's main bonding jumper sized?" A) All the same size, based on the total service size B) Based on the largest ungrounded conductor feeding that specific enclosure C) Always 3/0 AWG copper D) Based on the smallest ungrounded conductor in the building

✅ Answer: B — 270.28(C)(2): sized per enclosure, based on what actually feeds it.

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