Vegyes vezetékméretek egy dobozban: 14, 12 és 10 AWG

A 14, 12 és 10 AWG vezetékeket tartalmazó dobozt nem szabad egyetlen becsléssel számolni. A NEC 314.16 értékei 2,00, 2,25 és 2,50 köbhüvelyk.

Miért okoznak hibát a vegyes méretek

In renovations, garages, kitchens, workshops, and long branch-circuit runs, different conductor sizes often meet in one junction box. The safe method is to count each insulated conductor by its own size, then count clamps, grounding conductors, support fittings, and device yokes under the specific NEC 314.16 paragraph that applies.

A practical mixed box may include 14 AWG lighting conductors, 12 AWG receptacle conductors, and 10 AWG appliance or voltage-drop conductors. The calculation changes because 14 AWG is 2.00 cu. in., 12 AWG is 2.25 cu. in., and 10 AWG is 2.50 cu. in. under NEC Table 314.16(B). IEC 60364 projects do not use the same cubic-inch formula, but the same design habit applies: more copper and more terminations need more enclosure space.

"Mixed-size boxes are where lazy arithmetic gets expensive. A 10 AWG splice costs 2.50 cubic inches per conductor, but a device yoke only uses 10 AWG volume if 10 AWG actually terminates on that yoke."

Szabályok a megfelelő méret kiválasztásához

• NEC 314.16(B)(1): count each insulated conductor entering and splicing or terminating in the box at its own size.
• NEC 314.16(B)(2): internal clamps count once at the largest conductor present.
• NEC 314.16(B)(4): each device yoke counts as two allowances based on the largest conductor connected to that device.
• NEC 314.16(B)(5): all equipment grounding conductors together count once at the largest equipment grounding conductor.
• NEC 300.14: keep at least 6 inches of free conductor for splicing and termination.

Comparison Table

Gyakorlati példák számokkal

Example 1: A garage box with one 12/2 feed, one 12/2 receptacle load, and one 14/2 lighting tap has 9.00 cu. in. for the four 12 AWG conductors, 4.00 cu. in. for the two 14 AWG conductors, 2.25 cu. in. for grounds, and 2.25 cu. in. for an internal clamp. Total: 17.50 cu. in.; a 21 cu. in. square box passes.

Example 2: A kitchen GFCI on 12 AWG with a separate 10 AWG appliance splice needs 9.00 cu. in. for 12 AWG conductors, 5.00 cu. in. for 10 AWG conductors, 4.50 cu. in. for the GFCI yoke, 2.50 cu. in. for grounds, and 2.50 cu. in. for the clamp. Total: 23.00 cu. in.

"Device fill follows the largest conductor connected to that device. Ground and clamp fill follow the largest conductor present. Mixing those two ideas is the reason many box-fill counts are off by 2.25 or 2.50 cubic inches."

Example 3: A long-run voltage-drop splice with six 10 AWG insulated conductors requires 15.00 cu. in. before grounds and clamps. Add 2.50 cu. in. for grounds and 2.50 cu. in. for the internal clamp. Total: 20.00 cu. in.; a 30.3 cu. in. square box gives better working room than a box that barely passes.

"In a mixed 12 and 14 AWG junction, the 14 AWG conductors still count at 2.00 cubic inches each. The clamp and grounding bundle may still be 2.25 cubic inches if 12 AWG is the largest conductor present."

Authority References

• National Electrical Code
• American wire gauge
• IEC 60364

Internal Resources

• Box Fill Calculator
• Wire Gauge Chart
• NEC Code Reference
• Upsizing Wire for Voltage Drop
• Electrical Box Reference

Gyakori kérdések

Do I use the largest conductor size for everything?

No. Insulated conductors count at their own sizes. Clamps and grounds use the largest applicable conductor, and each device yoke uses the largest conductor connected to that device.

How much volume does 10 AWG require?

NEC Table 314.16(B) assigns 2.50 cu. in. per 10 AWG conductor. Six 10 AWG conductors require 15.00 cu. in. before other allowances.

Does a 10 AWG splice make a 12 AWG GFCI yoke count as 10 AWG?

No. If the GFCI yoke connects only to 12 AWG, the yoke is 2 x 2.25 = 4.50 cu. in. The 10 AWG splice still counts separately.

Do all grounds count separately?

No. NEC 314.16(B)(5) counts all equipment grounding conductors together as one allowance based on the largest equipment grounding conductor.

Can 14 AWG and 12 AWG share a box?

Yes, if the circuits, overcurrent protection, ampacity, and identification are correct. For box fill, count 14 AWG at 2.00 cu. in. and 12 AWG at 2.25 cu. in.

How should IEC users apply this?

Use the article as a design checklist, not as an IEC legal formula. IEC 60364 work still needs enough enclosure space for larger conductors and safe termination.