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NEC Article 310.12 & Table 310.12Worked ExampleElectrical

200-Ampere Single-Family Residential Service Feeder Sizing

Calculate minimum service conductor ampacity for a 200A 120/240V dwelling service using NEC Table 310.12.

Direct Answer
166 A Ampacity Required (2/0 AWG Copper or 4/0 AWG Aluminum)

Calculated strictly in accordance with NEC Article 310.12 & Table 310.12.

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Given Scenario Parameters

wattage48000
voltage240
continuousNon-continuous

Interactive Calculator (Pre-filled)

Adjust inputs to evaluate variations of this NEC code scenario.

Interactive Electric Load Calculator

Pre-loaded with NEC 220.51 & 424.3(B) parameters

Nameplate wattage of the heating unit or load

Line-to-line or line-to-neutral

NEC 424.3(B) mandates that fixed electric space heating equipment branch circuits must be sized at 125% of the total load current.

Calculated OutputLive Recalculation
Base Running Current200 A48000W ÷ 240V
Required Ampacity (125%)200 A200A × 1
Minimum Circuit Breaker:200 Ampere
Recommended Conductor (75°C Cu):1 AWG Copper
Overcurrent Protection Rule:NEC 240.4 & 424.3(B)
Adjust wattage or voltage on the left to recalculate continuous service loads instantly.

Step-by-Step Solution

Formal engineering derivation citing applicable National Electrical Code articles.

Governing Code Equation
Feeder Ampacity = Service Rating * 0.83
Citing NEC Article 310.12 & Table 310.12
1

Per NEC 310.12, dwelling unit service and feeder conductors are permitted to be sized at 83% of the service rating.

2

Calculate 83% of 200 Amperes: 200 A * 0.83 = 166 Amperes minimum ampacity.

3

Select conductor from NEC Table 310.12: 2/0 AWG Copper or 4/0 AWG Aluminum rated at 75°C satisfies the 200A dwelling service requirement.

Conclusion: 166 A Ampacity Required (2/0 AWG Copper or 4/0 AWG Aluminum)
NEC Article 310.12 & Table 310.12