Sizing Equipment Grounding Conductors Explained NEC 250.122
NEC 250.122 answers a super common contractor question:
“How big does my ground wire need to be?”
This “ground wire” is usually called the equipment grounding conductor (EGC). It’s the green or bare wire (or metal path) that helps breakers trip fast during a fault.
👉 If you want the basics first, read our Grounding and Bonding Overview.
👉 If you want to understand where grounding starts at the service, read NEC 250.24.
👉 If you want to understand bonding jumper sizing (different rule), read NEC 250.102(C).
What Is an Equipment Grounding Conductor (EGC)?
The EGC is NOT the same as the neutral.
The EGC is there for safety. It connects metal parts (like panels, conduit, and equipment) back to the source so:
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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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The equipment doesn’t stay “electric”
Simple way to think about it:
The EGC is the “emergency return road” that helps shut power off during a fault.
What NEC 250.122 Says (The Big Rule)
NEC 250.122 says the EGC size is based on:
✅ The size of the breaker or fuse protecting the circuit
(Not the wire size… not the motor size… the overcurrent device size.)
So:
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Bigger breaker → bigger EGC (usually)
Why It’s Based on the Breaker Size
If a fault happens, the breaker has to trip fast.
To trip fast, a lot of fault current must flow. A properly sized EGC helps fault current flow quickly so the breaker shuts off power.
If the EGC is too small:
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Fault current might be limited
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Breaker could trip slower
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Equipment could stay energized longer
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Arc flash risk can increase
Where Contractors Deal with NEC 250.122
You’ll use this rule all the time in commercial work:
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Feeder circuits to panels
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Conduit runs to HVAC units
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Motors and pumps
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Roof-top units (RTUs)
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Disconnects feeding equipment
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Branch circuits feeding machines
It applies everywhere you have equipment that needs grounding.
Important Detail: If You Up-Size the Hot Wires, You May Need to Up-Size the EGC Too
Sometimes you upsize conductors because of:
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voltage drop
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long runs
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temperature limits
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bundling / derating
When you do that, NEC says the EGC may also need to increase in size so it still works properly in a fault.
Simple idea:
If you make the hot wires bigger for a reason, the ground path may need to stay strong too.
Common Contractor Mistakes
❌ Using the same EGC size for every circuit (wrong)
❌ Thinking the neutral can be used as the EGC (dangerous and not allowed)
❌ Forgetting to upsize EGC when conductors are upsized
❌ Confusing EGC sizing with bonding jumpers (different code section)
❌ Poor ground terminations (loose lugs, paint, corrosion)
How This Connects to What We Already Covered
Here’s the simple map:
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NEC 250.24 = where neutral and ground bond at the service
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NEC 250.52 = what counts as grounding electrodes
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NEC 250.102(C) = sizing bonding jumpers (service/supply-side bonding)
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NEC 250.122 = sizing equipment grounding conductors (EGCs) based on breaker size
So 250.122 is one of the most “everyday” grounding rules contractors use.
👉 Related: NEC 250.102(C) and NEC 250.24
Why Labels Matter Here Too
When you have multiple feeders, panels, and circuits, clear labeling helps inspectors and maintenance teams quickly understand what’s connected to what.
✅ At Print Pro, we make NEC-compliant electrical labels that help keep panels, disconnects, and circuits clearly identified and inspection-ready.
Pro Tips for Contractors (Simple but Powerful)
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Size your EGC based on the breaker/fuse size, not the conductor size
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Use proper lugs and clean metal contact points for terminations
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If you upsize your hot wires for voltage drop, check if you need to upsize the EGC too
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Don’t mix neutral and ground bars in subpanels (that’s a 250.24 issue)
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Take pictures of grounding terminations before closeout—saves time later
