Master Electrician Exam (NEC) flashcards

The point of connection between the facilities of the serving utility and the premises wiring system, marking the demarcation of responsibility between the utility and the building owner's electrical system.

• Demarcation point between utility and premises wiring.
• Defined in NEC Article 100.
• Important for determining service vs. feeder rules.

Memory trick: Service Point: 'Utility's Handshake' with 'Premises Wiring'!

Rules governing the placement of the service disconnecting means to ensure rapid and safe power cutoff during emergencies.

• Must be readily accessible (NEC 230.70(A)(1)).
• Located outside or inside nearest the point of entrance (NEC 230.70(A)(1)).
• Minimizes the length of unprotected service conductors inside a building.

Memory trick: The service disconnect is the 'emergency exit' for power; keep it close to the door.

The process of determining the minimum size of the main bonding jumper when service entrance conductors are installed in parallel, requiring the sum of their circular mil areas.

• Sized according to NEC Table 250.102(C)(1).
• Based on the equivalent circular mil area of the largest ungrounded service entrance conductors.
• Ensures effective ground-fault current path for large services.

Memory trick: Parallel service conductors need their 'total strength' calculated for the bonding jumper.

Branch-circuit conductors supplying continuous loads must have an ampacity rated for at least 125% of the continuous load current.

• A continuous load is defined as a load where the maximum current is expected to continue for 3 hours or more.
• NEC 210.19(A)(1) mandates the 125% factor for continuous loads.
• The conductor's ampacity, after any derating, must meet or exceed this calculated value.

Memory trick: Continuous load, continuous 125% for the wire.

The main bonding jumper (MBJ) is a conductor that connects the equipment grounding conductor(s) and the service-disconnect enclosure to the grounded conductor of the service.

• Sized based on the largest ungrounded service-entrance conductor.
• Refer to NEC Table 250.102(C)(1) for sizing.
• Ensures a low-impedance path for ground-fault current.

Memory trick: Bonding bridges the gap for safety.

Service drop conductors must maintain specific minimum vertical clearances from various surfaces to prevent accidental contact and ensure public safety.

• Clearances vary depending on the area below the conductors (e.g., pedestrian, vehicle, road).
• NEC 230.24(B) specifies these clearances.
• Public streets typically require the highest clearances due to truck traffic.

Memory trick: Clearance: higher for traffic, lower for feet.

This protection device protects the motor branch-circuit conductors, motor control apparatus, and the motor itself from short-circuits and ground-faults.

• Sized based on the motor's full-load current (FLC) from NEC Tables 430.247-430.250.
• Maximum ratings are specified in NEC Table 430.52.
• Inverse-time circuit breakers are typically allowed up to 250% of FLC.

Memory trick: Motor protection: FLC, then multiplication, then standard size.

Service entrance conductors supply power from the utility to the service equipment and must be sized to safely carry the connected load, including continuous loads.

• For continuous loads, conductors must be sized at 125% of the load.
• Applies to both branch circuits and feeders/services.
• Refer to NEC 230.42(A)(1) for service conductors.

Memory trick: Service conductors: 125% for continuous, 100% for non-continuous.

When service conductors are installed in parallel, the main bonding jumper must be sized based on the equivalent cross-sectional area of the largest ungrounded service conductor or set of conductors.

• Sum the kcmil of all parallel ungrounded service conductors.
• Use NEC Table 250.102(C)(1) with this equivalent area.
• The table provides the minimum size for copper or aluminum bonding jumpers.

Memory trick: Parallel conductors mean sum the kcmil for bonding.

A continuous load is one where the maximum current is expected to continue for 3 hours or more.

• Overcurrent devices and conductors must be rated for 125% of the continuous load.
• This means the continuous load cannot exceed 80% of the overcurrent device rating.
• Applies to branch circuits and feeders.

Memory trick: Continuous load means 80% capacity.

The grounding electrode conductor (GEC) connects the service equipment or a separately derived system to the grounding electrode system.

• Sizing generally follows NEC Table 250.66 based on the largest ungrounded service or feeder conductor.
• For made electrodes like ground rods, a specific maximum size of 6 AWG copper applies.
• This 6 AWG limit applies regardless of the feeder or service conductor size.

Memory trick: Ground rod GEC: always a 6, copper, no bigger.

The grounding electrode conductor (GEC) connected to a metal underground water pipe electrode must be sized according to NEC Table 250.66 based on the largest ungrounded service-entrance conductor, without the size limitations applicable to rod, pipe, or plate electrodes.

• Sized using Table 250.66.
• Based on the size of the largest ungrounded service-entrance conductor.
• Not subject to the 6 AWG copper maximum for ground rods.
• Must be continuous or spliced per NEC 250.64(C).

Memory trick: Water pipe's GEC size is like a direct current, straight from the table.

The grounding electrode conductor (GEC) for a concrete-encased electrode (Ufer ground) has specific sizing limitations that differ from other types of electrodes.

• Not required to be larger than 4 AWG copper.
• This exception is found in NEC 250.66(B).
• Applies regardless of the size of the service-entrance conductors.

Memory trick: Ufer's Concrete Cap: Four AWG is the limit, no matter the flow.

Electric Vehicle Supply Equipment (EVSE) loads are always calculated at 100% of their nameplate rating for feeder and service calculations.

• Applies to all EVSE installations.
• No demand factors are permitted for EVSE loads.
• Calculated at 100% of the equipment's rated current or power.

Memory trick: EVSE: Electric Vehicle, Straight-up Exact.

The ratio of the maximum demand of a system, or part of a system, to the total connected load of the system or part of the system under consideration.

• Demand Factor = Maximum Demand / Total Connected Load.
• Always less than or equal to 1.
• Used to size feeders and services more accurately.

Memory trick: Demand is always 'down' from the total connected load.

The main bonding jumper (MBJ) connects the equipment grounding conductor(s) and the service-disconnect enclosure to the grounded conductor of the service, ensuring electrical continuity and fault current path.

• Sized based on the largest ungrounded service-entrance conductor or equivalent area for parallel conductors.
• Referenced in NEC Table 250.102(C)(1).
• Must be copper or aluminum.

Memory trick: Bonding Jumper: Connects the grounds, like a bridge for safety.

A load where the maximum current is expected to continue for 3 hours or more. NEC requires overcurrent devices for continuous loads to be sized at 125% of the continuous load.

• Load operates for 3 hours or more.
• Overcurrent device must be sized at 125% of the continuous load.
• Continuous load cannot exceed 80% of the overcurrent device rating.

Memory trick: Continuous loads are a '25% more' commitment for protection.

For farm services or feeders, demand factors from NEC Table 220.102 are applied to individual loads (excluding the dwelling, which is calculated separately) in descending order of size: 100% for the largest, 75% for the second largest, 65% for the third, and 50% for remaining loads.

• Applies to farm services and feeders.
• Dwelling load is calculated separately per Part III of Article 220.
• Demand factors from Table 220.102 apply to other farm loads (buildings, equipment).
• Factors are applied to individual loads in descending order of size.

Memory trick: Farm loads: Dwelling first, then big to small for the rest, percentages test.

For dwelling units, each 2-wire small-appliance branch circuit is assigned a minimum of 1500 VA for load calculation purposes, irrespective of the actual connected load.

• Minimum 1500 VA per circuit.
• Applies to dwelling units.
• Used for service/feeder calculations.

Memory trick: Small appliances get a fixed 'slice' in the load pie.

For feeder and branch-circuit calculations, continuous loads (expected to operate for 3 hours or more) must be multiplied by 125% to determine the minimum conductor ampacity, per NEC 215.2(A)(1) and 210.20(A).

• A continuous load operates for 3 hours or more.
• Feeder conductors must be sized to carry 125% of the continuous load.
• This factor accounts for heat generated during prolonged operation.
• Applies to calculated load for sizing, not to actual connected load.

Memory trick: Continuous loads: Three hours or more, one point two-five for sure!

When using the optional calculation method (NEC 220.82), the demand load for fixed electric space heating and air-conditioning equipment is generally determined by using only the larger of the two connected loads.

• NEC 220.82 is the optional calculation method.
• The principle of using the larger of heating or A/C load applies.
• This avoids overestimating the demand since both systems are not typically used simultaneously.

Memory trick: Optional calculation, but still pick the biggest climate control.

Under the optional method (NEC 220.82) for single-family dwellings, the full nameplate rating of an electric clothes dryer is typically used as its calculated load.

• Applies to single-family dwellings.
• Optional method per NEC 220.82.
• Dryers are not granted specific demand factors under 220.82(B) or (C) as individual units.

Memory trick: Optional method: if it's not special, it's full force!

For the optional method (NEC 220.82), fixed appliance loads (excluding ranges, clothes dryers, space heating, or AC if already accounted for) are summed at their nameplate ratings before applying the overall demand factors.

• NEC 220.82 is the optional method for dwelling unit load calculations.
• Specific fixed appliances (dryer, water heater, furnace) are summed at full nameplate rating initially.
• The optional method then applies a demand factor to the total calculated load.

Memory trick: Just add up the appliance 'powers' first, like adding prices in a shopping cart before applying a coupon.

The equipment grounding conductor (EGC) provides a low-impedance path for ground-fault current from equipment and enclosures to the service disconnecting means, ensuring overcurrent devices operate properly.

• Sized based on the rating of the overcurrent protective device in the circuit.
• Referenced in NEC Table 250.122.
• Must be copper, aluminum, or copper-clad aluminum.

Memory trick: EGC: Grounding conductor, sized by the breaker's bite.

For dwelling units or groups of dwelling units, only the larger of the air-conditioning or space heating load is included in the feeder or service load calculation, per NEC 220.60.

• Applies to dwelling units and groups of dwelling units.
• Only one of the two loads (A/C or heating) is selected.
• The larger of the two loads is always chosen.
• This rule prevents over-sizing due to non-simultaneous operation.

Memory trick: HVAC: Hot or Cold, pick the bigger story told.

The calculation of the minimum ampacity required for feeder conductors supplying a single motor, based on its full-load current and duty cycle, as per NEC Article 430.22(A).

• For continuous duty motors, conductors must be sized at 125% of the motor's FLA.
• NEC Article 430 covers motors, motor circuits, and controllers.
• Different multipliers apply for noncontinuous or intermittent duty motors.

Memory trick: Motor Feeder: Continuous Current needs 125% safe Amps.

A continuous load is a load where the maximum current is expected to continue for 3 hours or more. Overcurrent devices and conductors serving continuous loads must be sized at 125% of the continuous load.

• Continuous loads operate for 3+ hours.
• Overcurrent devices and conductors must be sized at 125% for continuous loads.
• NEC Article 210.20(A) and 215.2(A)(1) specify this requirement.

Memory trick: Continuous loads need 25% extra 'oomph' for safety, like charging a phone for a long trip.

For four or more fixed appliances (excluding ranges, clothes dryers, space heating, and A/C), a 75% demand factor can be applied to their total nameplate rating in a standard load calculation.

• Applies to four or more fixed appliances.
• Excludes ranges, clothes dryers, space heating, and A/C.
• Demand factor is 75% of the sum of the nameplate ratings.

Memory trick: Fixed appliances need a 'fixed' rule: sum the big ones, then demand-factor the rest.

The minimum VA assigned to each general-purpose receptacle outlet for load calculation purposes in commercial and industrial occupancies, as per NEC 220.14(I).

• Each single or duplex receptacle is considered 180 VA.
• This value is used before applying any demand factors from Table 220.42.
• Applies to general-use receptacles, not specific appliance outlets.

Memory trick: Every Commercial Plug is One-Eighty.

For four or more fixed appliances (excluding ranges, dryers, space heating, and A/C), a 75% demand factor is applied to their total nameplate rating in a standard load calculation.

• Applies to 'fixed appliances' as defined by NEC 220.53.
• Excludes ranges, dryers, space heating, and air conditioning.
• Requires four or more such appliances to apply the 75% demand factor.

Memory trick: Four fixed friends get a 75% discount.

Service entrance conductors supplying continuous loads (expected to operate for 3 hours or more) must have an ampacity of not less than the noncontinuous load plus 125% of the continuous load, as per NEC 215.2(A)(1) and 230.42(A)(1).

• Continuous load is 3 hours or more of operation.
• Conductor ampacity must be at least 125% of the continuous load.
• Applies to service and feeder conductors, and their overcurrent protection.

Memory trick: Size the service for the long haul, especially continuous current.

The process of combining various demand-factored loads (e.g., lighting, receptacles, motors) in a commercial building to determine the total service or feeder current for a three-phase system.

• Continuous loads (e.g., general lighting) require a 125% factor.
• Receptacle loads have demand factors (NEC 220.44).
• Three-phase current calculation uses I = VA / (V_LL * √3).

Memory trick: Loads combined, continuous boosted, then divide by root-three-voltage.

For commercial general-purpose receptacle loads, the first 10 kVA is calculated at 100% demand, and any load exceeding 10 kVA is calculated at 50% demand, as per NEC 220.44.

• First 10 kVA @ 100%.
• Remainder over 10 kVA @ 50%.
• Applies to non-dwelling occupancies.

Memory trick: First ten, then half.

The reduced load calculated for multiple electric cooking appliances in commercial kitchens, based on demand factors provided in NEC Table 220.56, reflecting the unlikelihood of all units operating at full power simultaneously.

• Applies to commercial cooking equipment, not dwelling units.
• Table 220.56 provides demand factors based on the number of units and total connected load.
• Demand factors reduce the total connected load for feeder and service sizing.

Memory trick: Commercial Cookers: Count and Check Table 220.56.

Conductor impedance, a key factor in short-circuit calculations, is primarily determined by its resistance and reactance, which vary with conductor material, size, and length.

• Impedance (Z) = √(R² + X²), where R is resistance and X is reactance.
• Resistance (R) varies with conductor material, size, temperature, and length.
• Reactance (X) varies with conductor size, spacing, and frequency.
• For short runs, resistance often dominates impedance, especially in lower voltage systems.

Memory trick: Fault current needs to 'Z'ee the path, where 'Z' is impedance.

The demand load for fixed electric space heating and air-conditioning systems, where only the larger of the two connected loads is required to be included in the service or feeder calculation.

• NEC 220.60 governs these calculations.
• Only the larger of the heating or A/C load is counted.
• This accounts for the fact that both systems are not typically used simultaneously at their maximum capacity.

Memory trick: Heating OR Cooling, never both full blast.

The demand load for the largest motor-operated appliance or combination of motor loads is calculated at 125% of the full-load current rating of the largest motor or the sum of the full-load current ratings of the motors in the group, as per NEC 220.60.

• Applies to motors, not resistance heaters.
• Calculated at 125% of the largest motor's rating.
• Ensures adequate circuit capacity for motor starting and continuous operation.

Memory trick: Motor Magic: Multiply for More Power!

For farm buildings (excluding the dwelling), demand factors from NEC Table 220.102 are applied to the calculated loads, with the largest loads having higher demand factors.

• Largest two loads at 100%.
• Next largest at 75%.
• Remaining loads at 25%.
• Motor loads must first be calculated with 125% factor per 220.60 before applying 220.102 demand factors.

Memory trick: Big loads first, then smaller ones get less.

The National Electrical Code (NEC) restricts the maximum overcurrent protective device (OCPD) rating for 14 AWG copper conductors to 15 amperes for most general-purpose applications, despite their higher ampacity ratings in temperature tables.

• NEC 240.4(D) specifies conductor protection limits.
• 14 AWG copper is generally limited to 15A OCPD.
• This is a common exception to the general ampacity rules.

Memory trick: Conductor Protection: 'Always Watch Limits'

The calculated demand load for electric ranges in multi-family dwellings, determined by applying demand factors from NEC Table 220.55 based on the number and rating of ranges.

• NEC Table 220.55 is used for electric range demand calculations.
• The table provides demand factors for various numbers of ranges and their ratings.
• Demand factors reduce the total connected load to account for diversity of use.

Memory trick: Many kitchens, one table. Find the row, get the power.

A simplified method for calculating the service or feeder load for a dwelling unit, often resulting in a smaller service size, by applying specific demand factors to the total connected load as outlined in NEC Article 220.84.

• Used for single-family or individual dwelling units.
• Requires summing all connected loads (general lighting, appliances, HVAC).
• Table 220.84 applies demand factors: first 10 kVA at 100%, remainder at 40% or 25%.

Memory trick: Optional Dwelling Load: Sum Everything, then Demand Factors.

The service grounded conductor (neutral) must be sized to carry the maximum unbalanced current and provide a low-impedance path for ground-fault current, not smaller than the sizes specified in NEC 250.24(C)(1) and Table 250.102(C)(1).

• Sized based on the largest ungrounded service-entrance conductor or equivalent area for parallel conductors.
• Must not be smaller than the sizes in NEC Table 250.102(C)(1).
• Must be capable of carrying the maximum unbalanced load (NEC 220.61).

Memory trick: Neutral is the balancing act, keeping current safe and sound.

The minimum demand load for electric cooking appliances in multi-family dwellings is determined using NEC Table 220.55, which applies demand factors based on the number and rating of ranges.

• NEC Table 220.55 is used for dwelling unit electric range demand loads.
• Demand factors reduce the calculated load based on the number of ranges.
• Different columns in the table apply based on the range's nameplate rating.

Memory trick: Remember, many ranges mean less individual demand, so check the table for the right 'group' discount!

The process of determining the maximum current expected on the neutral conductor of a service or feeder, often involving demand factors and specific reductions for certain loads like electric ranges.

• NEC Article 220 provides guidelines for calculating neutral loads.
• Demand factors reduce the total connected load to a more realistic expected load.
• Electric ranges and dryers have specific demand factors and neutral reduction rules.

Memory trick: Neutral Needs Careful Calculation: Range, Dryer, Lights.

The equipment grounding conductor (EGC) for a branch circuit provides a low-impedance path for ground-fault current from the appliance or equipment to the branch-circuit overcurrent device, ensuring rapid clearing of faults.

• Sized based on the branch-circuit overcurrent protective device rating.
• Referenced in NEC Table 250.122.
• Must be copper, aluminum, or copper-clad aluminum.

Memory trick: Branch EGC: The safety wire, matching the breaker's power.

To find the current in a balanced three-phase system, divide the total apparent power (VA) by the product of the line-to-line voltage and the square root of 3 (approximately 1.732).

• Formula: I = VA / (V_LL * √3)
• V_LL is the line-to-line voltage (e.g., 208V, 480V).
• √3 is approximately 1.732.

Memory trick: Three phases need Root 3 to find the amperes.

In a purely capacitive AC circuit, the current leads the voltage by 90 electrical degrees due to the capacitor's ability to store charge.

• Capacitors oppose changes in voltage.
• Current leads voltage by 90 degrees.
• Capacitive reactance (Xc) is inversely proportional to frequency and capacitance.

Memory trick: ELI the ICE man: Voltage (E) leads Current (I) in Inductors (L); Current (I) leads Voltage (E) in Capacitors (C).