Master Electrician Practice study guide with diagrams.
Utilization & General Use Equipment — Arkansas Master Electrician Exam (AR-MST)
Learning Objectives
By the end of this chapter, you will be able to:
4.Distinguish between "utilization equipment" and "general-use equipment" and apply the correct Code sections to each.
5.Size branch circuits, feeders, and overcurrent protection for electric space-heating equipment, including continuous-load factors.
6.Apply the special rules for fixed electric space-heating equipment, central heating plants, and resistance-type boilers.
7.Select and protect motors, motor controllers, and motor feeders using the correct tables and multiplier percentages.
8.Calculate load for commercial kitchen equipment, including hoods and ventilation, with proper demand factors.
9.Identify the requirements for electric vehicle supply equipment (EVSE) and other emerging utilization loads.
10.Navigate the NEC efficiently to find the exact article, section, or table governing a given installation.
1.1 Scope and Definitions: Utilization vs. General-Use Equipment
The NEC draws a critical line between utilization equipment (Article 100) — equipment that utilizes electric energy for its mechanical, chemical, heating, lighting, or similar purpose — and general-use equipment (Article 100), which is equipment intended for general use and not designed for a specific load. While the distinction seems academic, it drives which Article governs.
Utilization equipment is covered broadly in Article 422 (Appliances) and Article 424 (Fixed Electric Space Heating), among others.
General-use equipment includes items like general-purpose snap switches, receptacles, and cord connectors, governed by Article 404 (Switches) and Article 406 (Receptacles).
A master electrician must instantly classify equipment on a plan review. For example, a water heater is utilization equipment (Article 422), but a baseboard heater is fixed electric space-heating equipment (Article 424). The distinction changes branch-circuit sizing, overcurrent protection, and disconnect requirements.
1.2 Branch Circuits for Utilization Equipment — Article 210
Article 210 is the backbone for all branch circuits. For a master, the key provisions are:
210.19(A)(1) — Branch circuits supplying continuous loads (loads where the maximum current is expected to continue for 3 hours or more) must be sized at 125% of the continuous load, plus 100% of the noncontinuous load. This is the single most common calculation error on exams.
210.20(A) — Overcurrent protection for branch circuits must be rated to carry the continuous load at 125%, plus the noncontinuous load. If the calculated value does not match a standard fuse or breaker size, you may round up to the next standard size per 240.6(A).
210.21(B)(2) — For a branch circuit supplying two or more outlets, the receptacle rating must not exceed the branch-circuit rating. Exception: a 20 A receptacle is permitted on a 15 A individual branch circuit only if it is a single receptacle (210.21(B)(1)).
Master-level trap: When a branch circuit supplies a single continuous load, the 125% factor applies to both conductor sizing (210.19) and overcurrent protection (210.20). However, if the branch circuit supplies multiple outlets, the overcurrent device is sized to the circuit rating, not the sum of the loads — the loads are calculated separately.
1.3 Fixed Electric Space Heating — Article 424
Article 424 is a dense, high-yield article for the master exam. It covers resistance-type heating elements, heat pumps (with resistance backup), and central heating plants.
1.3.1 Branch-Circuit Sizing — 424.3(B)
Branch circuits for fixed electric space heating must be sized at 125% of the total connected load (heating elements plus motors, such as blowers). This is a continuous load by definition — no exception for intermittent operation.
Example: A 10 kW baseboard heater at 240 V draws 41.7 A. The branch circuit must be sized at 41.7 A × 1.25 = 52.1 A. You would use a 60 A circuit with conductors rated at least 52.1 A (typically 6 AWG copper at 75°C).
1.3.2 Overcurrent Protection — 424.3(B) and 424.22
Overcurrent protection must be rated at 125% of the load. If the calculated value falls between standard sizes, you may round up to the next standard size (240.6).
424.22(B) — For fixed electric space-heating equipment with multiple resistance elements, each element must have its own overcurrent protection rated at 125% of the element rating, unless the elements are factory-installed and the assembly is listed as a unit.
1.3.3 Disconnecting Means — 424.19
Every fixed electric space-heating unit must have a disconnecting means that:
Is within sight of the equipment (visible and not more than 15 m (50 ft) away), or is capable of being locked in the open position (424.19(A)).
For heating equipment with motors over 1/8 hp, the disconnect must also satisfy Article 430 requirements for motor disconnects.
Supervision point: On a job site, verify that the disconnect for a rooftop heating unit is within sight. If it is not, the disconnect must be lockable — and the lock must be removable only with a key or tool.
1.3.4 Central Heating Plants and Boilers — 424.60–424.72
Resistance-type boilers (over 1 kW) have special requirements:
424.65 — Each boiler must have a disconnecting means that opens all ungrounded conductors.
424.70 — Overcurrent protection for boilers must be sized per the manufacturer's instructions, but not less than 125% of the total load.
424.72 — Boilers must have a means to disconnect the control circuit (if over 150 V to ground) and a separate control circuit overcurrent device.
Master-level note: For boilers with multiple stages, the controller must prevent simultaneous energization of all stages if the total load exceeds the service capacity. This is a design responsibility — the master must verify the load calculation includes all stages at full rating.
1.4 Motors and Motor Circuits — Article 430
Article 430 is the most calculation-heavy article in the Code. A master must be fluent in the following:
1.4.1 Motor Full-Load Current (FLC) — Tables 430.247–430.250
Do not use the nameplate current for branch-circuit and feeder sizing. Use the FLC from the tables based on motor type and voltage.
Table 430.250 covers three-phase AC motors (the most common in commercial/industrial work). For a 10 hp, 230 V, three-phase motor, the FLC is 28 A — regardless of the actual nameplate current.
1.4.2 Branch-Circuit Conductor Sizing — 430.22
Branch-circuit conductors must be sized at 125% of the motor FLC (430.22(A)).
For a motor with a duty cycle (intermittent, periodic, etc.), use Table 430.22(E) for the percentage of FLC — e.g., 85% for a 15-minute duty cycle.
1.4.3 Overload Protection — 430.32
Overload devices (heaters in a starter) must be sized at 115% to 125% of the motor nameplate current (not FLC).
430.32(A)(1) — For motors with a service factor of 1.15 or greater, or a temperature rise of 40°C or less, the overload device must be sized at 125% of the nameplate current.
430.32(A)(2) — For all other motors, size at 115%.
If the calculated value does not correspond to a standard heater size, you may use the next higher size, but it must not exceed the motor's locked-rotor current (430.32(C)).
Exam trap: Overload protection is based on nameplate current; branch-circuit conductors and short-circuit protection are based on FLC from tables. Mixing these up is a guaranteed wrong answer.
1.4.4 Short-Circuit and Ground-Fault Protection — 430.52
The branch-circuit short-circuit and ground-fault protective device (fuse or breaker) is sized as a percentage of FLC per Table 430.52.
For a three-phase squirrel-cage motor: non-time-delay fuse = 300%, inverse-time breaker = 250%, time-delay fuse = 175%.
430.52(C)(1) Exception 1 — If the calculated value does not correspond to a standard size, you may round up to the next standard size. However, if the motor will not start on that size, you may increase further, but not beyond 400% for non-time-delay fuses or 225% for inverse-time breakers (430.52(C)(1) Exception 2).
1.4.5 Motor Feeder Sizing — 430.24
A feeder supplying multiple motors must be sized at 125% of the largest motor FLC plus 100% of the FLC of all other motors on the feeder.
Additionally, the feeder must be sized to supply the largest connected load per 220.61 (neutral) and 220.60 (noncoincident loads).
1.4.6 Motor Controllers and Disconnects — 430.102–430.111
A disconnecting means must be located within sight of the motor and the driven machinery (430.102(B)).
The disconnect must open all ungrounded conductors and be rated at least 115% of the motor FLC (430.109).
A controller must be rated for the motor type and horsepower — Table 430.151(A) provides the maximum horsepower rating for controllers at various voltages.
Supervision point: On a commercial rooftop, verify that each condensing unit has a lockable disconnect within sight. If the disconnect is on the ground and the unit is on the roof, it must be a "disconnecting means capable of being locked in the open position" — and the lock must be a keyed or combination lock, not a simple hasp.
1.5 Electric Vehicle Supply Equipment (EVSE) — Article 625
EVSE is a growing area. Key requirements:
625.40 — EVSE is a continuous load. Branch circuits must be sized at 125% of the rated current.
625.41 — The rating of the EVSE must be used for load calculations, not the vehicle's actual draw.
625.42 — For multiple EVSE units, a demand factor of 100% applies unless the units are controlled by a load management system (625.42(B)).
625.54 — All EVSE must have GFCI protection for personnel (for 240 V systems).
625.50 — EVSE must be connected by a dedicated branch circuit.
Master-level note: For a commercial parking garage with 20 EVSE units at 32 A each, the feeder load is 20 × 32 A × 1.25 = 800 A. Without load management, this is a massive load. With a UL-listed load management system, you can apply the demand factors from the manufacturer's instructions — but you must verify the system is listed for that purpose.
1.6 Commercial Kitchen Equipment — Article 210 and 220
210.19(A)(1) — Each piece of cooking equipment (ranges, ovens, fryers) is a continuous load if it is thermostatically controlled and rated over 16 A. Branch circuits must be sized at 125%.
220.56 — For feeders supplying commercial kitchen equipment, a demand factor of 90% applies to the first two units and 80% to all additional units, provided the equipment is thermostatically controlled and the total load exceeds the demand factor.
Exam trap: The demand factor in 220.56 applies only to feeders, not branch circuits. Each individual piece of equipment still requires a branch circuit sized at 125%.
A master must understand the hierarchy of overcurrent protection:
240.4 — Conductors must be protected per their ampacity, with exceptions for motor circuits (430.52), transformer secondary conductors (240.21(C)), and tap conductors (240.21(B)).
240.21(C) — Transformer secondary conductors must be protected within 10 ft (3.0 m) of the transformer, with specific ampacity requirements.
Coordination for selective operation (240.12) is required for life-safety systems (elevators, fire pumps). For a master, this means the feeder overcurrent device must not open before the branch-circuit device. This is achieved by ensuring the feeder device has a higher time-current curve than the branch device.
1.8 Separately Derived Systems — Article 250.30
Transformers and generators that create a separately derived system (SDS) require:
250.30(A) — The system must have a bonding jumper between the neutral and the equipment grounding conductor at the first disconnecting means or at the source.
250.30(A)(2) — The grounding electrode conductor must connect the SDS to a grounding electrode (building steel, ground ring, etc.).
250.30(A)(4) — The size of the bonding jumper and grounding electrode conductor is based on the largest ungrounded conductor of the SDS, per Table 250.102(C)(1) and Table 250.66.
Master-level note: For a 480 V to 208Y/120 V transformer feeding a panelboard, the neutral must be bonded to the panelboard enclosure and a grounding electrode conductor must be run to the nearest grounding electrode. The neutral must not be bonded at the transformer if the bonding is done at the panelboard — this is a common inspection failure.
1.9 Code Navigation — Where to Find It
Concept
NEC Location
Branch circuits — general
Article 210
Branch-circuit continuous load
210.19(A)(1), 210.20(A)
Fixed electric space heating
Article 424
Heating branch-circuit sizing
424.3(B)
Heating disconnecting means
424.19
Resistance boilers
424.60–424.72
Motors — general
Article 430
Motor FLC tables
Tables 430.247–430.250
Motor branch-circuit conductors
430.22(A)
Motor overload protection
430.32
Motor short-circuit protection
430.52, Table 430.52
Motor feeder sizing
430.24
Motor disconnects
430.102–430.111
EVSE
Article 625
Commercial kitchen demand
220.56
Overcurrent protection — general
Article 240
Standard fuse/breaker sizes
240.6(A)
Separately derived systems
250.30
Grounding electrode conductor sizing
Table 250.66
Bonding jumper sizing
Table 250.102(C)(1)
1.10 Inspection and Supervision Points
When you are the master on a job, verify these items before signing off:
109.Continuous-load sizing — Check that every branch circuit for a continuous load (heating, EVSE, commercial cooking) is sized at 125%. Look for 80% rated breakers that are not permitted for continuous loads.
110.Motor nameplate vs. table — Confirm the electrician used Table 430.250 for FLC, not the nameplate. Overloads must match the nameplate; conductors must match the table.
111.Disconnect within sight — Walk the job site. If a motor or heating unit is not within sight of its disconnect, the disconnect must be lockable.
112.SDS bonding — At every transformer, verify the neutral-to-case bond is at the correct location (first disconnecting means or source) and that a grounding electrode conductor is present.
113.Overcurrent coordination — For life-safety loads, verify selective coordination per 240.12.
1.11 Common Exam Traps
Trap 1: Using the nameplate current for motor branch-circuit conductors. Always use the table FLC.
Trap 2: Forgetting the 125% factor on continuous loads when the load is already calculated at 100%. The 125% is applied to the load, not the breaker rating.
Trap 3: Rounding down on overcurrent protection for continuous loads. You may round up only if the calculated value falls between standard sizes (240.6).
Trap 4: Applying the 220.56 kitchen demand factor to branch circuits. It applies only to feeders.
Trap 5: Bonding the neutral at both the transformer and the first panelboard of an SDS. This creates a parallel neutral path and is a violation.
Trap 6: Sizing the grounding electrode conductor for an SDS based on the transformer kVA. It is based on the largest ungrounded conductor, per Table 250.66.
Summary
The master electrician's role is to ensure that every installation is safe, code-compliant, and properly supervised. This chapter covered the critical articles for utilization and general-use equipment: branch circuits (210), space heating (424), motors (430), EVSE (625), overcurrent protection (240), and separately derived systems (250.30). Master the calculations, memorize the tables, and navigate the Code with precision — the Arkansas Master exam rewards those who know where to look and what to apply.
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