How to use: Cut out each card, fold along the center line, and read the term on one
side and the definition on the other — or just fold the answer under while you quiz yourself off the sheet.
Q
Optional load calculation for a dwelling
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A
General loads (lighting, small appliance, dryer, etc.) are summed, the first 10kVA is taken at 100%, and everything above that is taken at 40% -- then added to 100% of the largest 4 (or all, per code year) HVAC loads.
NEC 220.82
Q
Selective coordination
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A
Arranging overcurrent devices so that only the OCPD closest to a fault opens, while all upstream devices stay closed -- required for emergency systems, legally required standby, and elevator circuits with more than one disconnect.
NEC 700.32, 701.27, 620.62
Q
Available fault current
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A
The maximum current that can flow at a given point in a system during a bolted fault -- every piece of equipment must have an interrupting/withstand rating equal to or greater than it.
NEC 110.9, 110.10
Q
Series rating vs. fully rated system
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A
A series rating relies on a tested combination of an upstream and downstream device to interrupt a fault jointly, at lower cost than fully rating every device for the full available fault current -- but it isn't permitted where motor contribution could exceed 1% of the downstream device's interrupting rating.
NEC 240.86
Q
Emergency system vs. legally required standby system
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A
Emergency systems (Art. 700) supply loads essential for life safety and must restore power within 10 seconds. Legally required standby (Art. 701) supplies loads required by code for safety but with a longer allowable restoration time (up to 60 seconds).
NEC 700, 701
Q
Transformer overcurrent protection -- primary only, over 9A
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A
Primary protection generally can't exceed 125% of primary FLC (250% for primaries under 9A) when no secondary protection is provided; a combined primary+secondary scheme allows different, often more flexible, ratios.
NEC 450.3
Q
Motor branch-circuit short-circuit and ground-fault protection sizing
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A
Based on a percentage of motor FLC from Table 430.52 (varies by protective device type -- e.g. up to 250% for an inverse-time breaker on a general motor), not the motor nameplate FLA.
NEC 430.52, Table 430.52
Q
Motor overload protection sizing
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A
Generally 115-125% of motor nameplate FLA, depending on the motor's service factor and temperature rise rating.
NEC 430.32
Q
Feeder tap rules -- 10-ft tap
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A
A tap conductor up to 10 ft long can be smaller than the feeder if it has an ampacity not less than the load, terminates in a single OCPD sized no greater than the tap's ampacity, and (with exceptions) doesn't extend beyond the equipment it supplies.
NEC 240.21(B)(1)
Q
Feeder tap rules -- 25-ft tap
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A
A tap up to 25 ft long is permitted with an ampacity at least 1/3 of the feeder OCPD rating, enclosed in a raceway, and terminating in a single OCPD sized to the tap's ampacity.
NEC 240.21(B)(2)
Q
Ground-fault protection of equipment (GFPE)
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A
Required on service disconnects rated 1000A or more on solidly grounded wye systems over 150V to ground but not exceeding 600V phase-to-phase -- protects equipment, not personnel (unlike a GFCI).
NEC 230.95
Q
Parallel conductors
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A
Conductors 1/0 AWG and larger may be run in parallel per phase/neutral if all sets have the same length, material, size, insulation, and termination -- to increase ampacity beyond what one conductor could safely carry.
NEC 310.10(H)
Q
Fire pump supply conductors
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A
Must be sized so there's no more than a 5% voltage drop at the pump controller with the motor running at 115% of full-load current -- and the supply must be as independent as practical from other loads.
NEC 695.6, 695.7
Q
Health care facility essential electrical system branches
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A
Life Safety Branch, Critical Branch, and Equipment System -- each with different restoration-time and load requirements to keep patient-care areas powered.
NEC 517.30
Q
Surge protective device (SPD) requirement on dwelling services
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A
An SPD is required for services supplying dwelling units.
NEC 230.67
Q
Neutral sizing on a service with electric range/dryer loads
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A
The neutral load for household ranges and dryers can be calculated at a reduced demand factor from Table 250.102(C)(1)/220.61, since these loads are not fully balanced across all phases at once.
NEC 220.61
Q
Generator system bonding -- separately derived vs. not
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A
A generator with a transfer switch that does NOT switch the neutral is not separately derived and must not be re-grounded/rebonded downstream; one whose transfer switch DOES switch the neutral is separately derived and needs its own grounding electrode connection and bonding jumper.
NEC 250.30
Q
Voltage drop -- code requirement vs. recommendation
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A
The NEC does not mandate a maximum voltage drop for general branch circuits/feeders -- the commonly cited 3%/5% figures are informational notes (FPNs), not enforceable rules, except where a specific article does make it mandatory (e.g. sensitive electronic equipment, some fire pump/health care rules).
NEC 210.19 Informational Note, 215.2 Informational Note