Calculating the feeder or service neutral load
NEC 220.61 The neutral load is the maximum unbalance between the neutral and one ungrounded conductor, with a 70% demand factor allowed only on range/dryer and over-200-amp portions — never on 3-wire wye or nonlinear loads.
Q1 NEC 220.61
Per 220.61(A), how is the feeder or service neutral load determined on a standard single-phase, 3-wire system?
- A The average of the two ungrounded conductor loads
- B The maximum net calculated load between the neutral conductor and any one ungrounded conductor
- C 125% of the largest ungrounded conductor load
- D The sum of all ungrounded conductor loads
Show answer & explanation
Correct: B — The maximum net calculated load between the neutral conductor and any one ungrounded conductor
220.61(A) defines the neutral load as the maximum unbalanced load — the maximum net calculated load between the neutral and any one ungrounded conductor. Summing all ungrounded loads or applying a continuous-load-style 125% factor confuses this with ampacity sizing rules elsewhere in the Code.
Optional dwelling calc: general loads + heating/AC selection
NEC 220.82 Under 220.82, add the 10 kVA/40% general load to whichever heating/AC selection is largest — never combine more than one heat/AC selection.
Q2 NEC 220.82
A dwelling unit is served by a single 120/240-volt, 3-wire feeder. What minimum feeder ampacity is required before the optional calculation method in 220.82 can be used instead of Part III?
- A 60 amperes
- B 400 amperes
- C 200 amperes
- D 100 amperes
Show answer & explanation
Correct: D — 100 amperes
220.82(A) requires the total connected load to be served by a single 120/240-volt or 208Y/120-volt, 3-wire set of conductors with an ampacity of 100 or greater before the optional method applies. 200 A and 400 A are common panel sizes but not the minimum threshold, and 60 A is below it entirely.
Household Range Demand Load (NEC 220.55)
NEC 220.55 Never just sum range nameplates. Use Table 220.55 Column C for the demand load of household ranges not over 12 kW; for equally-rated ranges over 12 kW, increase Column C by 5% for each kW over 12 (Note 1).
Q3 NEC 220.55
A dwelling has 3 household electric ranges, each rated not over 12 kW. What is the demand load on the service per NEC Table 220.55?
- A 14 kW
- B 24 kW
- C 17 kW
- D 36 kW
Show answer & explanation
Correct: A — 14 kW
Table 220.55 Column C gives the maximum demand for 3 ranges directly as 14 kW — you do not sum the nameplates. Distractors multiply a single range value or the 12 kW nameplate by 3.
Electric clothes dryer load calculation
NEC 220.54 Size each dwelling-unit dryer at 5000 W or its nameplate rating (whichever is bigger), then apply Table 220.54's demand factors when there's more than one.
Q4 NEC 220.54
A household electric clothes dryer has a nameplate rating of 4800 watts. What load value must be used for it in a dwelling unit feeder calculation under 220.54?
- A 5000 W, since the floor value exceeds the nameplate rating
- B 2400 W, half the nameplate rating
- C 4800 W, the actual nameplate value
- D 4800 W reduced by the Table 220.54 demand factor
Show answer & explanation
Correct: A — 5000 W, since the floor value exceeds the nameplate rating
220.54 requires using 5000 W or the nameplate rating, whichever is larger. Since 5000 W is larger than the 4800 W nameplate, 5000 W is the value used. Using the raw nameplate value ignores the 5000 W floor, and demand factors from Table 220.54 only apply once the base per-dryer value is established and multiple dryers are involved.
Demand factors for commercial kitchen equipment
NEC 220.56 Table 220.56 demand factors shrink the calculated load for commercial kitchen equipment, but the feeder or service load can never be set below the sum of the two largest kitchen equipment loads.
Q5 NEC 220.56
A restaurant's kitchen equipment load is calculated using Table 220.56 demand factors. After applying the table, the resulting sum is less than the two largest individual kitchen equipment loads combined. What load must be used for the feeder calculation?
- A The full nameplate sum of all kitchen equipment with no demand factor applied
- B The Table 220.56 demand factor result, since it is the code-prescribed method
- C The average of the Table 220.56 result and the two largest loads
- D The sum of the two largest kitchen equipment loads
Show answer & explanation
Correct: D — The sum of the two largest kitchen equipment loads
220.56 sets a hard floor: the feeder or service calculated load shall never be less than the sum of the largest two kitchen equipment loads, even if Table 220.56 demand factors would otherwise produce a lower number. Using the table result alone, the full nameplate sum, or an averaged figure all ignore this floor requirement.
Electric range and cooking appliance load in dwellings
NEC 220.55 Table 220.55 lets you apply a demand factor to household cooking equipment over ¾ kW instead of adding up nameplate ratings.
Q6 NEC 220.55
An electrician is sizing a feeder for a dwelling unit with a single household electric range. Which method does 220.55 permit for calculating that range's load?
- A Using the small-appliance branch-circuit demand factors
- B Using 100% of the range's nameplate rating with no demand factor
- C Applying the demand factors in Table 220.56
- D Applying the demand factors in Table 220.55
Show answer & explanation
Correct: D — Applying the demand factors in Table 220.55
220.55 permits household electric ranges and similar cooking appliances rated over 3/4 kW to be calculated using Table 220.55. Table 220.56 is for commercial cooking equipment, not dwelling-unit household appliances, and 220.55 exists specifically because full nameplate totaling isn't required.
Minimum unit load for dwelling units
NEC 220.41 Dwellings use a single 3 VA/ft² blanket load that already covers general-use receptacles and lighting — no separate calc needed for those circuits.
Q7 NEC 220.41
Under 220.41, which receptacle outlets are already accounted for in a dwelling unit's minimum unit load?
- A Only receptacles rated over 20 amperes
- B All general-use receptacle outlets of 20-ampere rating or less
- C Only receptacles in habitable rooms, excluding bathrooms and garages
- D Only receptacles serving the kitchen small-appliance circuits
Show answer & explanation
Correct: B — All general-use receptacle outlets of 20-ampere rating or less
220.41(1) folds in all general-use receptacle outlets of 20-ampere rating or less, including those tied to the 210.11(C)(3) and (C)(4) circuits — not just kitchen small-appliance receptacles, and not limited by room type or excluding higher-rated outlets.
Optional feeder/service calc for multifamily dwellings
NEC 220.84 The Table 220.84(B) shortcut only works if every unit has its own feeder, electric cooking, and electric heat or AC — and house loads still get calculated the standard way and added on.
Q8 NEC 220.84
A 12-unit apartment building has electric ranges and heat pumps in every unit. Which additional condition must also be met to use the optional calculation in Table 220.84(B)?
- A No dwelling unit is supplied by more than one feeder
- B Every unit's Part III load must first be calculated and compared to the optional load
- C The service must be rated at least 400 amperes
- D The building must have at least 4 dwelling units
Show answer & explanation
Correct: A — No dwelling unit is supplied by more than one feeder
220.84(A) requires three conditions: no dwelling unit fed by more than one feeder, electric cooking equipment in every unit, and electric heat or air conditioning (or both) in every unit. The minimum unit count is three, not four, comparing loads against Part III is only relevant to the cooking exception in 220.84(A)(2), and there is no minimum service rating requirement.
Optional feeder/service calc for new restaurants
NEC 220.88 A new restaurant may size its service or feeder using Table 220.88's demand factors instead of Part III, but only if the feeder carries the entire calculated load.
Q9 NEC 220.88
A contractor wants to size a restaurant's service using the optional method in Table 220.88. Which condition must be satisfied?
- A The restaurant's connected load must be under 100 kW
- B The method may be used even if the feeder serves only part of the total load
- C The optional method applies only to additions to existing restaurants
- D The restaurant must be a new restaurant, and the feeder must serve the total calculated load
Show answer & explanation
Correct: D — The restaurant must be a new restaurant, and the feeder must serve the total calculated load
220.88 permits the optional calculation only for a new restaurant, and only where the feeder serves the total load. There's no connected-load ceiling in the rule itself, it does not apply to existing-restaurant additions, and a feeder serving only part of the load doesn't qualify.
Outlet load for luminaires, heavy-duty lampholders, and sign lighting
NEC 220.14(D) Luminaire outlets use the fixture's actual max VA rating, but heavy-duty lampholders (600 VA) and signs (1200 VA per required circuit) have fixed minimums that ignore actual draw.
Q10 NEC 220.14(D)
Which statement correctly describes how to calculate the load for an outlet supplying a luminaire under 220.14(D)?
- A Use a flat 1200 VA minimum regardless of the luminaire's actual rating
- B Use a flat 600 VA minimum regardless of the luminaire's actual rating
- C Use the maximum volt-ampere rating of the luminaire's equipment and lamps
- D Use 80% of the luminaire's nameplate rating
Show answer & explanation
Correct: C — Use the maximum volt-ampere rating of the luminaire's equipment and lamps
220.14(D) calculates a luminaire outlet at the maximum VA rating of that luminaire's equipment and lamps — not a fixed minimum. The 600 VA figure is the separate minimum for heavy-duty lampholders under 220.14(E), and 1200 VA is the separate minimum for sign and outline lighting under 220.14(F). There's no 80% derating for luminaire outlets in this section.
Receptacle outlet load: general rule and office building calculation
NEC 220.14(I) Count 180 VA per receptacle yoke (90 VA each on 4+ gang strips), but office buildings must use whichever is larger — that count or 1 VA/ft².
Q11 NEC 220.14(I)
A single multi-outlet assembly has 6 receptacles mounted on it. Per 220.14(I), how is this load calculated?
- A 90 VA per receptacle, since it's a multiple receptacle of four or more on one assembly
- B 180 VA total for the whole assembly regardless of receptacle count
- C 1500 VA for the assembly, the same as a small-appliance circuit
- D 180 VA per receptacle, the same as any other receptacle outlet
Show answer & explanation
Correct: A — 90 VA per receptacle, since it's a multiple receptacle of four or more on one assembly
220.14(I) drops the rate to 90 volt-amperes per receptacle once a single assembly has four or more receptacles, instead of the standard 180 VA. The 1500 VA figure belongs to small-appliance/laundry circuits under 210.11(C)(1) and (C)(2), which this section explicitly excludes.
Optional feeder/service calc for schools
NEC 220.86 Schools with electric heat, A/C, or both can size feeders and services with Table 220.86 demand factors instead of the standard Part III method — except portable classrooms.
Q12 NEC 220.86
A school building has both electric space heating and air conditioning installed. Under the 220.86 optional calculation, how is this load folded into the connected load?
- A Only the larger of the air-conditioning or space-heating load
- B Both the air-conditioning and space-heating loads added together
- C Only the air-conditioning load, regardless of the heating load size
- D The average of the air-conditioning and space-heating loads
Show answer & explanation
Correct: A — Only the larger of the air-conditioning or space-heating load
220.86 states the connected load includes the larger of the air-conditioning load or the space-heating load, not both. Adding them together, always defaulting to A/C, or averaging them all misstate the rule.
Additional load for show windows and track lighting
NEC 220.46 Show windows add 200 VA per linear foot of base width, and track lighting outside dwellings adds 150 VA per 2 ft of track, unless a current-limiting device sets the load instead.
Q13 NEC 220.46
A retail store installs track lighting on a single circuit. Per 220.46(B), what additional load must be included?
- A No additional load if the track is on a single circuit
- B 150 VA for every 600 mm (2 ft) of track or fraction thereof
- C 200 VA for every 600 mm (2 ft) of track, matching the show-window rate
- D 150 VA for the entire track run regardless of length
Show answer & explanation
Correct: B — 150 VA for every 600 mm (2 ft) of track or fraction thereof
220.46(B) requires 150 VA for every 2 ft of track or fraction thereof, regardless of whether it's a single- or multicircuit installation. The 200 VA rate applies to show windows under 220.46(A), not track lighting, and a load is always required unless a current-limiting device is used.
Load calculations for additions to existing installations
NEC 220.16 Dwelling unit additions always calculate under 220.14; non-dwelling additions use 220.42 or 220.14, whichever fits the load.
Q14 NEC 220.16 Code lookup
A homeowner is finishing a previously unwired attic space above an existing dwelling unit, adding new lighting and receptacle circuits. Which section governs how to calculate the load for this newly wired portion?
- A 220.16(B)
- B 220.11
- C 220.16(A)
- D 220.41
Show answer & explanation
Correct: C — 220.16(A)
220.16(A) directs that loads for a previously unwired portion of an existing dwelling unit be calculated per 220.14, making it the section a student flips to for this scenario. 220.16(B) only applies to other-than-dwelling occupancies, so it doesn't fit a dwelling unit addition.
How to pick the right branch-circuit load calculation method
NEC 220.10 220.10 doesn't calculate anything — it routes you to the correct section based on occupancy: dwelling to 220.41, non-dwelling lighting to 220.42, hotels/motels to 220.44, additions to 220.16, everything else to 220.14.
Q15 NEC 220.10 Code lookup
You're sizing branch-circuit conductors for a single-family dwelling unit and need the minimum unit load requirements to begin the calculation. Which section applies?
- A 220.41
- B 220.42
- C 220.16
- D 220.14
Show answer & explanation
Correct: A — 220.41
220.41 covers the minimum unit load for dwelling units per the routing table in 220.10. 220.14 is for general 'other loads' across all occupancies, and 220.42 is specifically for lighting loads in non-dwelling occupancies — neither fits a dwelling unit's branch-circuit load.
Max branch-circuit load: ballasted/LED lighting and electric cooking demand factors
NEC 220.11(B) Ballasted/LED lighting loads are based on driver ampere ratings, not lamp watts; household cooking appliances over 1¾ kW can use Table 220.55 demand factors instead of full nameplate load.
Q16 NEC 220.11(B)
A branch circuit supplies fluorescent fixtures with ballasts. Per 220.11(B), how should the load be calculated?
- A Based on the total wattage of the lamps installed
- B Based on the fixture's nameplate voltage rating alone
- C Based on the total ampere rating of the ballasts
- D Based on 125% of the total lamp wattage
Show answer & explanation
Correct: C — Based on the total ampere rating of the ballasts
220.11(B) requires calculating the load from the ballast/transformer/driver's ampere rating, not the lamp wattage — the driver's actual draw is often higher than the lamp's stamped watts. Using lamp wattage, applying a 125% continuous-load multiplier to lamp wattage, or using voltage alone all substitute the wrong basis for the calculation.
Household Clothes-Dryer Demand (NEC 220.54)
NEC 220.54 Each household dryer counts as 5 kW (or nameplate if larger); the total connected load is then reduced by the Table 220.54 demand factor for the number of dryers.
Q17 NEC 220.54
A dwelling has 6 household electric clothes dryers, each rated 5 kW. What is the demand load per NEC 220.54?
- A 19.5 kW
- B 22.5 kW
- C 30 kW
- D 25.5 kW
Show answer & explanation
Correct: B — 22.5 kW
Each dryer is 5 kW, so the connected load is 6 × 5 = 30 kW. Table 220.54 applies a 75% demand factor for 6 dryers: 30 × 0.75 = 22.5 kW. Distractors skip the demand factor or use the factor for a different count.
Demand factor for fixed dwelling appliances
NEC 220.53 Four or more fastened-in-place appliances (≥1/4 hp or ≥500 W) on the same feeder can be demanded at 75%, but cooking equipment, dryers, space heat, AC, and EVSE never qualify.
Q18 NEC 220.53
A one-family dwelling feeder serves a fastened water heater, a built-in exhaust fan, a garbage disposal, and a dishwasher, each rated 500 watts or greater. What demand factor may be applied to these four appliances under 220.53?
- A 75% of the total nameplate rating
- B 65% of the total nameplate rating, matching the range demand factor
- C 100% of the total nameplate rating, since only cooking equipment can be demanded
- D 50% of the total nameplate rating
Show answer & explanation
Correct: A — 75% of the total nameplate rating
220.53 permits a 75% demand factor on four or more fastened-in-place appliances rated 1/4 hp or 500 W or greater served by the same feeder. None of these four loads fall on the exclusion list, so the factor applies. 50% and 65% are demand figures from other calculations (small-appliance and range demand tables), not this section.
Calculating Floor Area for Load Calculations
NEC 220.5(C) Floor area is measured from the building's outside dimensions, but for dwelling units you drop open porches and unfinished spaces that can't become habitable rooms.
Q19 NEC 220.5(C)
When calculating the floor area of a dwelling unit for a load calculation, from what should the measurement be taken?
- A The footprint of the foundation only, excluding any upper floors
- B The centerline of the exterior walls
- C The inside dimensions of each habitable room, summed together
- D The outside dimensions of the dwelling unit
Show answer & explanation
Correct: D — The outside dimensions of the dwelling unit
220.5(C) requires floor area to be calculated from the outside dimensions of the building, dwelling unit, or other area involved — not from interior room measurements or wall centerlines, and upper floors are each calculated the same way, not excluded.
Dwelling Optional Service Calculation (NEC 220.82)
NEC 220.82 The optional method (220.82) totals all general loads at nameplate, then applies 100% to the first 10 kVA and 40% to the remainder; the heating/AC load (220.82(C)) is added as the largest applicable option.
Q20 NEC 220.82
Using the optional method (NEC 220.82) at 240 V, size the service for a 1500 ft² dwelling with a 12 kW range, a 5.5 kW dryer, appliances totaling 5700 VA, 5000 VA of air conditioning and 9000 VA of central electric heat. What is the minimum service size?
- A 100 A
- B 125 A
- C 150 A
- D 175 A
Show answer & explanation
Correct: B — 125 A
General loads at nameplate get 100% of the first 10 kVA + 40% of the remainder = 18880 VA. Add the 220.82(C) heat/AC (5850 VA) → 24730 VA. ÷ 240 V = 103 A → a 125 A service. Distractors are adjacent standard service sizes.
Dwelling Service Load Calculation — Standard Method (NEC 220 Part III)
NEC 220.45 Build the dwelling service load as a ledger: general lighting + small-appliance + laundry (with the 220.45 demand factor), plus range (220.55), dryer (220.54), fixed appliances (220.53), and the larger of heat or A-C (220.60); divide by the voltage for the minimum service size.
Q21 NEC 220.45
A 1500 ft² dwelling has a 12 kW range, a 5.5 kW dryer, 3 fixed appliance(s) totaling 6600 VA, 10000 VA of electric heat and 5000 VA of air conditioning. Using the standard method (NEC 220 Part III) at 240 V, what is the minimum service size?
- A 175 A
- B 125 A
- C 150 A
- D 200 A
Show answer & explanation
Correct: C — 150 A
The demanded general load is 5100 VA; adding the range (8000 VA), dryer (5500 VA), appliances (6600 VA) and the larger of heat/AC (10000 VA) gives 35200 VA. ÷ 240 V = 147 A → a 150 A service. Distractors are adjacent standard service sizes.
Existing dwelling optional calc, adding new HVAC
NEC 220.83(B) When adding new air conditioning or electric heat to an existing dwelling under the optional method, count only the larger of the two loads — never both.
Q22 NEC 220.83(B)
An existing dwelling using the 220.83(B) optional method is having both a new central air conditioner and new electric baseboard heat installed. How should these two new loads be combined in the calculation?
- A Average the two connected loads
- B Add the full nameplate ratings of both the air conditioning and the heating together
- C Use only the heating load, since heating always takes priority over air conditioning
- D Use only the larger of the two connected loads
Show answer & explanation
Correct: D — Use only the larger of the two connected loads
220.83(B) directs that the larger connected load of air conditioning or space heating be used, but not both. There is no rule giving heating automatic priority, and the loads are never summed or averaged.
Using actual maximum demand data for existing loads
NEC 220.87 You can size added load on an existing feeder or service off metered demand data instead of a full recalculation, if the data, the 125% headroom, and the protection requirements all check out.
Q23 NEC 220.87
An electrician wants to add load to an existing service using actual maximum demand data under 220.87 instead of a full standard calculation. Which of the following is a condition that must be met?
- A The new load alone must not exceed 80% of the service rating
- B The existing maximum demand at 125% plus the new load must not exceed the service rating
- C The demand data must be recorded for at least 90 days if a full year isn't available
- D The service must have a renewable energy system to qualify for this method
Show answer & explanation
Correct: B — The existing maximum demand at 125% plus the new load must not exceed the service rating
220.87(2) requires that the maximum demand at 125% plus the new load not exceed the feeder ampacity or service rating. The minimum recording period is 30 days, not 90, and having a renewable energy system actually disqualifies the 30-day recording alternative rather than being required to use it.
Demand factors for farm buildings other than the dwelling
NEC 220.102(B) Once a non-dwelling farm building has two or more branch circuits, size its feeder or service load with the demand factors in Table 220.102(B) — not a straight sum.
Q24 NEC 220.102(B)
A farm workshop (not the dwelling) has two separate branch circuits — one for lighting, one for a welder receptacle. How must the feeder serving that shop be sized?
- A Count only the larger of the two branch circuits and ignore the other
- B Apply the demand factors from Table 220.102(B) to the connected load
- C Apply the dwelling-unit demand factors used for the farmhouse instead
- D Sum both circuits at 100% connected load with no demand factor
Show answer & explanation
Correct: B — Apply the demand factors from Table 220.102(B) to the connected load
Per 220.102(B), once a farm building other than the dwelling has two or more separate branch circuits, the feeder or service load must be calculated using demand factors not less than Table 220.102(B) — not a raw sum, not the dwelling-unit method, and not just the largest circuit.
Demand factors for general illumination load
NEC 220.45 Table 220.45 lets you shrink the calculated general lighting load on feeders and services, but only for the occupancy types it lists — everything else stays at 100%.
Q25 NEC 220.45
An electrician is sizing a feeder and wants to apply the demand factor from Table 220.45 to reduce the number of general lighting branch circuits in the panel. Is this correct?
- A Yes, but only for dwelling units where the demand factor is highest
- B No, Table 220.45 cannot be applied to general lighting loads at all
- C No, the demand factor applies only to the calculated load used for feeder and service sizing, not the branch-circuit count
- D Yes, the demand factor reduces both the calculated load and the required number of branch circuits
Show answer & explanation
Correct: C — No, the demand factor applies only to the calculated load used for feeder and service sizing, not the branch-circuit count
220.45 is explicit: the demand factors in Table 220.45 apply to the general illumination portion of the calculated load, but they 'shall not be applied in determining the number of branch circuits for general illumination.' The branch-circuit count is always based on the full connected load, regardless of occupancy type.
Demand Factors for Health Care Facility Receptacle Loads
NEC 220.110 Receptacle loads in patient care spaces can be derated using Table 220.110(1) or 220.110(2), but only for circuits at or under 150 volts to ground.
Q26 NEC 220.110
A designer wants to apply demand factors to receptacle loads in a Category 2 patient care space per 220.110. Which condition must the branch circuits meet?
- A Supplied only by circuits on the essential electrical system
- B Supplied by branch circuits not exceeding 120 volts to ground
- C Supplied by branch circuits not exceeding 300 volts to ground
- D Supplied by branch circuits not exceeding 150 volts to ground
Show answer & explanation
Correct: D — Supplied by branch circuits not exceeding 150 volts to ground
220.110 permits demand factors only for receptacle loads supplied by branch circuits not exceeding 150 volts to ground. 120 volts and 300 volts are plausible but incorrect voltage thresholds, and the rule makes no distinction based on essential electrical system status.
Calculating shore power receptacle load demand at marinas
NEC 220.120 Table 220.120 lets you apply demand factors to the feeder or service supplying marina shore power receptacles, but you can't also apply the 220.61(B) neutral demand factor.
Q27 NEC 220.120
A designer is sizing a feeder for a marina's shore power receptacles and applies the demand factors in Table 220.120. What else must be true about that calculation?
- A Table 220.120 replaces the need to calculate general lighting loads under Part III
- B The demand factor in 220.61(B) cannot also be applied
- C Table 220.120 can only be used for feeders under 100 amperes
- D The demand factor in 220.61(B) must also be applied for the neutral conductor
Show answer & explanation
Correct: B — The demand factor in 220.61(B) cannot also be applied
220.120 states that where the Table 220.120 demand factors are applied, the demand factor in 220.61(B) is not permitted. General lighting and other loads still must be calculated under Part III of Article 220, and 220.120 sets no such 100-ampere limit.
Feeder / Service Neutral Load (NEC 220.61)
NEC 220.61 The neutral carries the maximum unbalanced load (220.61(A)). For the portion of that load over 200 A, a 70% demand factor is permitted (220.61(B)(2)).
Q28 NEC 220.61
A feeder has a maximum unbalanced load of 250 amperes. What is the minimum neutral load per NEC 220.61?
- A 175 A
- B 235 A
- C 35 A
- D 250 A
Show answer & explanation
Correct: B — 235 A
220.61: the first 200 A is at 100%, and the portion over 200 A (250 − 200 = 50 A) gets a 70% demand factor: 200 + 0.70 × 50 = 235 A. Distractors skip the reduction, apply 70% to the whole load, or forget the 200 A base.
Combining noncoincident loads in a single calculation
NEC 220.60 When two loads will never run at the same time, size the feeder or service to the largest one — not the sum of both.
Q29 NEC 220.60
A dwelling has electric resistance heat and a central air conditioner that are known to never operate at the same time. Per 220.60, how should these be handled in the feeder calculation?
- A Use only the larger of the two loads
- B Use only the smaller of the two loads
- C Add both loads together at full value
- D Average the two loads together
Show answer & explanation
Correct: A — Use only the larger of the two loads
220.60 permits using only the largest of two or more noncoincident loads when it's unlikely they'll be used simultaneously. Adding both at full value ignores the noncoincident allowance, and using the smaller load or an average would undersize the feeder.
General lighting load for non-dwelling occupancies
NEC 220.42 Multiply floor area by the Table 220.42(A) unit load for the occupancy type, unless an adopted energy code with power monitoring lets you use its lower values instead.
Q30 NEC 220.42
Under 220.42(A), which factor is multiplied by the floor area to determine the minimum general lighting load for a non-dwelling building?
- A The service disconnect rating
- B The connected appliance load in 220.53
- C The demand factor from Table 220.45
- D The unit load specified in Table 220.42(A) for that occupancy
Show answer & explanation
Correct: D — The unit load specified in Table 220.42(A) for that occupancy
220.42(A) requires using the unit load from Table 220.42(A) for the occupancy times the floor area per 220.5(C). Table 220.45 demand factors apply to a different calculation step, and connected appliance load and service disconnect rating aren't part of this general lighting load formula.
When optional feeder/service calculations apply
NEC 220.80 Part IV's optional calculations are a permitted alternative to the standard Part III method — never mandatory, and only when Part IV's own conditions are met.
Q31 NEC 220.80 Code lookup
You're calculating the feeder load for a single dwelling unit with an existing 100-ampere service, using the optional method rather than the standard calculation. Which section covers the optional feeder and service load calculation specifically for a single dwelling unit?
- A 220.85
- B 220.84
- C 220.82
- D 220.83
Show answer & explanation
Correct: C — 220.82
220.82 is the optional calculation section for a single dwelling unit's feeder/service load. 220.83 applies only to existing dwelling units evaluating added AC or heating load, and 220.84 applies to multifamily dwellings, so neither fits a single-unit new load calculation.
Dryers and cooking appliances skip the general branch-circuit load rule
NEC 220.14(B) 220.14(B) pulls electric dryers and electric cooking appliances in dwellings out of the general branch-circuit load rule — dryers go to 220.54, ranges and other cooking appliances go to 220.55.
Q32 NEC 220.14(B) Code lookup
A dwelling unit's electric range and clothes dryer are being included in a service load calculation. Which section directs the calculator to the specific dryer and range demand-load procedures rather than treating them as generic appliance loads?
- A 220.16(A)
- B 220.14(K)
- C 220.14(A)
- D 220.14(B)
Show answer & explanation
Correct: D — 220.14(B)
220.14(B) is the specific carve-out that sends dwelling dryer and cooking-appliance loads to the dedicated demand-factor methods in 220.54/220.55, rather than the general 'specific appliance' unit-load rule in 220.14(A) or the catch-all 220.14(K).