Bonding Jumpers NEC 250.102(C)
NEC 250.102(C) answers a very practical question:
“How big does the bonding jumper need to be?”
A bonding jumper is a wire (or metal path) that connects metal parts together so electricity has a safe path during a fault. NEC 250.102(C) tells you how to size that bonding jumper correctly.
👉 If you want the basics first, read our Grounding and Bonding Overview.
👉 If you want to understand where bonding starts in the system, read NEC 250.24.
👉 If you want to understand what the grounding system connects to, read NEC 250.52.
What Is a Bonding Jumper?
A bonding jumper is used to make sure metal parts are connected together so that:
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If a hot wire touches metal, fault current has a path
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The breaker trips fast
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Metal parts don’t stay energized
Simple way to think about it:
Bonding jumpers help prevent “electric metal” by giving electricity a clear path back to the source.
What NEC 250.102(C) Is Really About
This section focuses on bonding jumpers on the supply side of the service equipment, like:
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Bonding jumpers for service raceways
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Bonding jumpers for service enclosures
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Bonding jumpers used around meters, CT cabinets, or service disconnect gear
These are serious areas because service conductors can carry very high fault current.
The Big Rule
NEC 250.102(C) says the bonding jumper size depends on:
✅ The size of the largest ungrounded service conductor
(That means the biggest “hot” conductor feeding the service.)
So, bigger service conductors = bigger bonding jumper.
Where Contractors Usually See This
You’ll most often deal with NEC 250.102(C) in commercial jobs with:
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Meter sections / meter mains
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CT cabinets
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Service switchboards
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Parallel service conductors
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Large service conduits and raceways
Inspectors check this because improper bonding can make fault clearing slow and dangerous.
Why This Matters (Simple Explanation)
If bonding jumper is too small:
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Fault current can’t flow well
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Breakers may trip slower (or not correctly)
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The system becomes more dangerous
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Arc flash risk increases
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Equipment damage risk goes up
If it’s sized correctly:
✅ Strong fault path
✅ Faster clearing
✅ Safer system
Common Contractor Mistakes
❌ Using a bonding jumper that’s too small “because it’s just bonding”
❌ Forgetting bonding jumpers when there are concentric/eccentric knockouts
❌ Assuming the conduit alone is always enough
❌ Not following manufacturer requirements for bonding bushings / fittings
❌ Confusing this with the equipment grounding conductor size (different rule!)
How This Connects to What We Already Covered
Here’s how it ties into the rest of your grounding and bonding setup:
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NEC 250.24 = where neutral and ground bond at the service
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NEC 250.52 = what grounding electrodes are allowed
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NEC 250.102(C) = how to size key bonding jumpers so metal parts stay safe
These three sections work together as the core of commercial grounding/bonding.
👉 Related: NEC 250.24 and NEC 250.52
Why Labels Matter Here Too
Bonding points, service gear, and grounding systems can be confusing in commercial installs—especially for inspectors and future maintenance.
✅ At Print Pro, we make NEC-compliant electrical labels that help keep service equipment, grounding points, and bonding locations clearly identified and inspection-ready.
Pro Tips for Contractors (Simple but Powerful)
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Size bonding jumpers based on the largest service conductor
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In big services, always double check bonding around:
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Meter sockets
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CT cabinets
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Service raceways
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Conduit fittings and bushings
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Don’t confuse bonding jumper sizing with EGC sizing (that’s NEC 250.122)
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If you see eccentric knockouts, plan for bonding bushings or jumpers early
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Take photos before closing gear—helps with inspections and future troubleshooting
