14.2 Signs, Fire Pumps & Welders

14.2 Signs, Fire Pumps & Welders

ICC 703's Special Occupancies, Equipment, and Conditions area (11% of the exam) and Prov's Special Equipment area (4 questions) both draw on Chapter 6 articles. Signs, fire pumps, and welders are common choices because each has a short, testable set of numbers: a sign outlet load, fire pump voltage-drop limits, and welder duty-cycle multipliers.

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1. Electric Signs and Outline Lighting (Article 600)

Required sign outlet (600.5(A))

Each commercial building and each commercial occupancy accessible to pedestrians must have at least one outlet in an accessible location at each entrance to each tenant space for sign or outline lighting use. The outlet must be supplied by a branch circuit rated at least 20 amperes that supplies no other load. Service hallways and corridors are not considered accessible to pedestrians. For load calculations, each required sign branch circuit counts as at least 1,200 volt-amperes (220.14(F)).

Branch-circuit ratings (600.5(B))

Branch circuits that supply signs are treated as continuous loads in calculations. Circuits supplying signs with incandescent, fluorescent, or high-intensity discharge illumination may not be rated more than 20 amperes. Circuits supplying only neon tubing installations may not be rated more than 30 amperes.

Worked example: A strip center has six tenant spaces with one public entrance each. It needs six sign outlets on six 20-ampere branch circuits, and the service calculation includes $6 \times 1{,}200 = 7{,}200$ VA of sign load. Because sign circuits are continuous loads, feeder and service conductors and overcurrent devices are sized at 125% of that load: $7{,}200 \times 1.25 = 9{,}000$ VA.

Disconnecting means (600.6)

• Each sign and outline lighting system, and each circuit supplying one, must be controlled by an externally operable switch or circuit breaker that opens all ungrounded conductors and controls no other load. On multiwire branch circuits, all ungrounded conductors must open simultaneously.
• The disconnect is located where the supply circuit enters the sign enclosure or pole, or within sight of the sign. Where it is out of the line of sight from any section that can be energized, it must be lockable open in accordance with 110.25.
• Signs operated by external electronic or electromechanical controllers may have the disconnect within sight of the controller, under the conditions in 600.6(A).

Other sign rules

• Listing (600.3): Signs and outline lighting systems must be listed and installed according to their installation instructions.
• Clearance from vehicles (600.9(A)): Sign equipment must be at least 14 feet above areas accessible to vehicles unless it is protected from physical damage.
• Grounding and bonding (600.7): Metal sign parts must be connected to an equipment grounding conductor of the type in 250.118 and bonded together.

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2. Fire Pumps (Article 695)

A fire pump must keep running during a fire, even at the expense of the motor. Many Article 695 rules are the opposite of normal motor rules: protection is set to avoid tripping, not to protect the motor.

Power source and connection (695.3 and 695.4)

The power source must be reliable, such as a separate service or a tap ahead of the service disconnecting means (230.82(5)), or an on-site power production facility. Supply conductors connect the source directly to a listed fire pump controller (or listed combination controller and transfer switch). Where a disconnecting means and overcurrent device are installed between the source and the controller (695.4(B)):

• The overcurrent device must be selected or set to carry indefinitely the sum of the locked-rotor current of the largest fire pump motor and the pressure maintenance pump motors, plus the full-load current of the associated accessory equipment.
• The disconnecting means must be identified as suitable for service equipment, lockable in the closed position (110.25), not located in equipment that feeds other loads, and far enough from other disconnects that it is unlikely to be operated by mistake at the same time.
• It must be marked "FIRE PUMP DISCONNECTING MEANS" in letters at least 1 inch high, visible without opening enclosure doors or covers. A placard next to the fire pump controller states where the disconnect is and where the key is if it is locked.
• It must be supervised in the closed position by a central station or local signaling service, by locking it closed, or, in certain owner-controlled locations, by sealing it with recorded weekly inspections.

Conductors and protection (695.6)

• Conductor size: Conductors supplying the fire pump motor, pressure maintenance pump motors, and accessory equipment must be rated at least 125% of the sum of the fire pump and pressure maintenance motor full-load currents, plus 100% of the accessory equipment load.
• Protection from fire: Supply conductors routed inside the building must be protected, for example by encasement in at least 2 inches of concrete or a listed electrical circuit protective system or fire-rated assembly with a 2-hour rating, unless an exception in 695.6 applies.
• No GFPE: Ground-fault protection of equipment is not permitted in any fire pump power circuit, and 230.95 does not apply to a fire pump service disconnect.

Transformers (695.5)

A transformer dedicated to a fire pump installation must be rated at least 125% of the sum of the fire pump motor and pressure maintenance pump motor loads, plus 100% of the associated accessory equipment it supplies. Its primary overcurrent device follows the same locked-rotor rule as the supply, and secondary overcurrent protection is not permitted.

Voltage drop (695.7)

• Starting: The voltage at the controller's line terminals may not drop more than 15% below normal (the controller's rated voltage) while the motor starts.
• Running: The voltage at the motor terminals may not drop more than 5% below the motor's voltage rating while the motor runs at 115% of its full-load current rating.

Worked example: A 460-volt, 3-phase installation has a 50-hp fire pump (65 A from Table 430.250), a 1-hp pressure maintenance pump (2.1 A), and 2 amperes of controller accessories. Minimum conductor ampacity is $1.25 \times (65 + 2.1) + 2 = 83.9 + 2 = 85.9$ amperes. Controllers must be located as close as practicable to the motors they control and within sight of them (695.12(A)).

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3. Electric Welders (Article 630)

Welders draw heavy current for part of each work cycle, so Article 630 sizes conductors on an effective (heating) current instead of the full nameplate current.

Individual welder (630.11(A))

The supply conductor ampacity must be at least the I1eff value on the rating plate. If I1eff is not given, multiply the rated primary current by the multiplier from Table 630.11(A) for the welder's duty cycle:

For transformer-type (nonmotor-generator) welders, the multiplier is close to the square root of the duty cycle: $\sqrt{0.50} \approx 0.71$.

Group of welders (630.11(B))

For a feeder supplying several welders, start with each welder's individual current from 630.11(A), then add 100% of the two largest, 85% of the third largest, 70% of the fourth largest, and 60% of all the rest.

Worked example: Four welders have individual currents of 40, 36, 30, and 24 amperes. The feeder ampacity is $40 + 36 + (0.85 \times 30) + (0.70 \times 24) = 40 + 36 + 25.5 + 16.8 = 118.3$ amperes.

Overcurrent protection and disconnect (630.12 and 630.13)

• Welder protection (630.12(A)): Each welder must have overcurrent protection rated or set at not more than 200% of I1max, or of the rated primary current if I1max is not given. A separate device at the welder is not needed if the supply conductors' overcurrent device meets this limit.
• Conductor protection (630.12(B)): Conductors supplying one or more welders must be protected by an overcurrent device rated or set at not more than 200% of the conductor ampacity.
• If these values do not correspond to a standard size, or they cause unnecessary tripping, the next higher standard rating is permitted.
• Disconnect (630.13): Each arc welder without an integral disconnect needs a switch or circuit breaker in its supply circuit, marked as to its purpose (110.22(A)).

Worked example: A transformer arc welder has a rated primary current of 50 amperes and a 60% duty cycle, with no I1eff marked. Conductor ampacity is $50 \times 0.78 = 39$ amperes, so 8 AWG copper (40 A in the 60°C column) is enough. The welder limit is $2 \times 50 = 100$ amperes, but the conductor limit is $2 \times 40 = 80$ amperes, so the breaker may be no larger than 80 amperes.