Feeder & service load

NEC 215.2 / Article 220 — minimum ampacity, 125% continuous, conductor lookup

Build a load schedule, mark continuous loads, and compare calculated amps to standard breakers and 75°C conductor tables used in the tool.

Calculate feeder and service entrance conductor sizing per NEC 215.2 and Article 220. Enter your connected loads, apply demand factors, and get the minimum feeder ampacity, conductor size, and required overcurrent protection — with full step-by-step math so you can show your work at inspection.

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NEC Table 220.42 — General Lighting Demand Factors

Portion of Load	Demand Factor	Application
First 3,000 VA	100%	All occupancies
Next 3,001 to 120,000 VA	35%	Dwelling units
Remainder over 120,000 VA	25%	Dwelling units

NEC 215.2 — Feeder Sizing Rules Summary

Rule	NEC Section	Requirement
Minimum ampacity	215.2(A)(1)	Not less than non-continuous load + 125% of continuous load
Minimum overcurrent protection	215.2(A)(1)	Not less than non-continuous + 125% continuous
Demand factors permitted	220.42, 220.53, 220.54	Apply per applicable NEC section
Minimum feeder — dwelling	215.2(A)(1) Ex.	100A for a single dwelling

Aluminum Service Conductor Sizes — Common Sizing

Load (Amps)	Aluminum Conductor	Copper Equivalent	Typical Application
60A	4 AWG Al	6 AWG Cu	Sub-panel, small loads
100A	1/0 AWG Al	4 AWG Cu	Small home service
125A	2/0 AWG Al	2 AWG Cu	Average home service
150A	3/0 AWG Al	1 AWG Cu	Medium home service
200A	4/0 AWG Al	2/0 AWG Cu	Standard 200A service

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Tools for feeder & service work

Clamp meters, distribution gear, and conductors electricians use when sizing feeders.

Clamp

Ideal 61-757 600A Clamp Meter

True RMS AC/DC to 600A
Large jaw for service and feeder conductors
Backlit display for panel work

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Panel

Square D QO140L200PG 200A Load Center

40-space layout for subfeeders and branch breakers
QO series common in service upgrades
Matches 200A feeder and service planning

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Meter

Fluke 117 Electricians True RMS Multimeter

Dead-front checks before energizing panels
Non-contact voltage detection
CAT III 600V for distribution work

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Find breakers

Klein Tools ET310 Circuit Breaker Finder

Map existing circuits before feeder changes
Built-in GFCI tester
Saves time during panel surveys

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Insulated

Klein 1000V Insulated Screwdriver Set

IEC 60900 insulation for energized-adjacent work
Useful for lugs, breakers, and panel terminations
Multiple profiles in one service kit

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NEC 215.2 — Feeder conductor sizing rules

NEC 215.2(A)(1) sets the minimum ampacity for feeder conductors: they must carry the non-continuous load at 100%, plus the continuous load at 125%. A feeder serving 60A of continuous load and 40A of non-continuous load needs a minimum ampacity of (60 × 1.25) + 40 = 115A — not simply 100A. That is the value you compare to conductor ampacity tables.

The overcurrent device protecting the feeder follows the same sizing basis. The OCPD must be rated at not less than the non-continuous load plus 125% of continuous load, then you select the next standard device per NEC 240.6(A).

Demand factors — when and how to apply them

NEC Article 220 allows demand factors on specific load types because not everything runs at full load simultaneously. Common references include:

NEC Table 220.42 — general lighting: First 3,000 VA at 100%, next 3,001–120,000 VA at 35%, remainder at 25% (dwelling units).
NEC 220.53 — fixed appliances: With four or more fixed appliances (excluding dryer, range, A/C, and heat), 75% may apply to the total.
NEC 220.54 — electric dryers: 5,000W or nameplate, whichever is larger, with additional rules for multiple dryers.
NEC 220.55 — cooking equipment: Demand tables for ranges and cooktops by quantity and rating.

Residential vs. commercial feeder calculations

Residential (NEC 220.82 optional method): For dwelling units, the optional method in NEC 220.82 groups general lighting (3 VA per sq ft), small-appliance and laundry circuits, and fixed loads, then applies set demand factors. Use our residential load calculator (NEC 220.82) for that path.

Commercial (standard method): Commercial feeders typically follow the standard method — sum loads, apply Article 220 demand factors where permitted, and separate continuous vs. non-continuous classification for the 125% rule.

Pro tip Aluminum is common for large feeders and services. Size from the aluminum column of NEC Table 310.16 (or engineering supervision where required), use connectors listed for aluminum, and follow manufacturer torque and antioxidant requirements.

Frequently asked questions

What is the minimum feeder size for a residential service?

For a single dwelling unit, the feeder must be sized for the calculated load but not less than 100A per NEC 230.79(C). Many new homes are built with 200A service to allow for EV and electrification.

What is the difference between a feeder and a branch circuit?

A feeder runs between service equipment (or another supply point) and the final branch-circuit overcurrent device. A branch circuit is downstream of the last OCPD before the load. Feeders fall under NEC Article 215; branch circuits under Article 210.

Do I need to apply the 125% rule to feeder conductors?

Yes. NEC 215.2(A)(1) requires feeder conductor ampacity not less than the non-continuous load plus 125% of the continuous load for loads operated as continuous (typically 3 hours or more).

Can I use aluminum conductors for feeders?

Yes, when permitted by the design. Size per NEC Table 310.16, use listed lugs and connectors, and follow termination preparation practices for aluminum conductors.

Feeder & service load