Article 110 Requirements for Electrical Installations
Article 230 Services
Article 240 Overcurrent Protection
Article 310 Conductors for General Wiring
Article 430 Motors, Motor Circuits, and Controllers
Article 450 Transformers and Transformer Vaults
Article 695 Fire Pumps
Warning signs for electrical equipment
Q: We are installing a 1,000-ampere switchboard as a replacement for a 600-ampere switchboard in an industrial plant. We also have to install and connect a larger motor control center. The electrical inspector told us that warning signs must be provided for this equipment. Where should the signs be placed and how should they read?
A: The electrical inspector is probably enforcing 110.16, which requires field marking of some types of electrical equipment that must be worked on by qualified persons while energized. The Second Fine Print Note to 110.16 provides information for the signs: ANSI Z535.4—1998 Product Safety Signs and Labels. Generally, the sign should use the word “WARNING,” state what the hazard is “ELECTRIC ARC FLASH,” what can result from exposure to the hazard, “SERIOUS BURNS, INJURY OR DEATH” and how to protect from the hazard, “USE PERSONAL PROTECTIVE EQUIPMENT,” or with the owner’s consent, “DEENERGIZE BEFORE SERVICING” instead of “USE PERSONAL PROTECTIVE EQUIPMENT.”
These words are an example of what I think the signs should indicate. However, before having the signs made, check with the inspector to make sure they meet with his approval for size, color, text, etc.
The signs should be placed in a conspicuous place on the switchboard and motor control center, preferably at eye level.
Remote service disconnecting means
Q: Is a remote control device acceptable as a service disconnecting means for a small commercial building? The main service disconnect is a 400-ampere shunt-trip circuit breaker installed about 55 feet inside of the building.
A: A remote switch, push button, or other device that opens the 400 ampere circuit breaker is not acceptable as a service disconnecting means. Remote control devices that are used to actuate the service disconnecting means are mentioned in item (3) of 230.70(A). Although these devices are allowed, they are not recognized as a service disconnecting means.
Because some enforcement agencies were accepting remote switching devices as service disconnects, a paragraph with the title Remote Control was added to 230.70. It reads like this: “Where a remote control device(s) is used to actuate the service disconnecting means, the service disconnecting means shall be located in accordance with 230.70(A)(1).” And this part (A)(1) requires that the disconnecting means be readily accessible outside the building or structure or inside at the nearest point of entrance of the service conductors.
Although remote control of the service disconnecting means is permitted, the requirements for accessibility and location of the disconnecting means are not changed because of the presence of a remote control device.
Fire pump control conductors
Q: What types of conductor insulation are suitable for “Fault Tolerant External Control Conductors” as described in 695.2 for fire pump controllers?
A: A new definition with the title “Fault Tolerant External Control Conductors” appears in Article 695, “Fire Pumps.” It indicates that the external control circuit must be designed so that broken, disconnected or shorted external control circuit conductors will not prevent the controller from starting the fire pump and may cause the controller to start the pump under these conditions.
I think the definition could be improved, and less likely to be misunderstood, by changing the title to “Fault Tolerant External Control Circuit” because the conductors are not fault tolerant, but the circuit is. Part of the definition indicates that the control circuit conductors may be broken, disconnected or shorted without preventing the operation of the fire pump.
Wiring methods for fire pump control circuits are mentioned in 695.14(E) and include rigid metal conduit, intermediate metal conduit, liquid-tight flexible metal conduit, liquid-tight flexible nonmetallic conduit Type B (LFNC-B) or Type MI cable.
Any of the conductor insulations listed in Table 310.13 that are suitable for the conditions may be used as external control circuit conductors for electric drive fire pumps, unless the fire pump controller manufacturer specifies a minimum conductor size and insulation type in the installation instructions.
Branch circuit conductors for part-winding start motors
Q: Do the power supply conductors from a part-winding start controller have to be sized at 125 percent of motor full-load current, or does this requirement only apply to the branch circuit conductors between the motor disconnecting means and the controller? We installed a standard part-winding start 100 horsepower, three-phase, 480-volt induction motor with a nameplate full-load current of 120 amperes using No. 2/0 Type THWN copper conductors from the switchboard to the motor controller. From the controller to the motor, we provided No. 4 Type THWN copper conductors in a single conduit. The electrical inspector says that the No. 4s are too small because the conductors must be sized for 125 percent of half of the motor full-load current. Is he correct?
A: According to 430.6, the Table value of full-load current must be used for selection of motor branch circuit conductor ampacity. The Table value of full-load current for this motor is 124 amperes; therefore, minimum branch circuit conductor ampacity is (1.25 x 124) 155, and the 2/0 AWG conductors are adequate.
Conductors between the controller and motor must have an ampacity of at least 77.5 after applying adjustment factors. Because there are more than three current-carrying conductors in a single raceway, they must be derated to 80 percent of the ampacity given in Table 310.16. This derating is required by 310.15(B)(2)(a) and by the accompanying Table. Applying an 80 percent factor to the No. 4s results in an adjusted ampacity of 68. To solve this problem, an additional raceway must be provided for half of the conductors or the conductor size must be increased to No. 3 Type THWN copper.
Circuit breakers for switching HID lighting
Q: Can molded-case circuit breakers with “SWD” markings be used to switch high-intensity discharge (metal halide) lighting fixtures?
A: A change in the 2002 edition of the NEC prohibits the use of circuit breakers marked SWD for switching high intensity discharge luminaires (lighting fixtures). Circuit breakers with the HID marking are listed and readily available from manufacturers. Circuit breakers bearing the HID marking are also suitable for switching fluorescent lighting loads; however, SWD circuit breakers can be used only to switch fluorescent lighting loads. This requirement appears in 240.83(D).
Sunlight-resistant service-entrance cable
Q:Can a No. 2/0 aluminum service-entrance cable be used outdoors for a 150-ampere, 120/240 volt, single-phase overhead service for a one-family dwelling? Does the cable jacket have to be marked “Sunlight Resistant” to comply with 310.8(D)?
A: According to Table 310.15(B)(6), which allows increased ampacities for 120/240-volt, three-wire, single-phase dwelling services, 2/0 AWG aluminum conductors have an ampere rating of 150 amperes; therefore, the overcurrent device rating is code compliant.
The language in 310.8(D) was changed. It now reads: “Locations Exposed to Direct Sunlight. Insulated conductors and cables used where exposed to direct rays of the sun shall be of a type list for sunlight resistance or listed and marked ‘sunlight resistant.’”
The General Information for Electrical Equipment Directory (White Book), published by Underwriters Laboratories Inc., contains this sentence under Service Entrance Cable (TYLZ): “Type SE-cable for aboveground installation. Both the individual insulated conductors and the outer jacket or finish of Type SE are suitable for use where exposed to sun.” Since all listed Type SE cable is sunlight resistant, it is not necessary that it be marked “sunlight resistant.” Also, according to information in the UL White Book, Types USE and USE-2 are suitable for use where exposed to the sun.
Liquid containment for insulating fluid in transformers
Q: I understand there was a proposal to eliminate the requirement for liquid containment for transformers filled with less-flammable liquid. Was this proposal accepted by the Code Panel, and if not, why?
A: Code Making Panel members gave various reasons for rejecting this proposal. Here are some of them: “fall and slip hazards from oil spills; cross contamination of water mixing with coolant and entering the waste water system; many building codes require confinement of any liquid. Transformers are not always installed in equipment rooms or vaults and may even be installed in a ceiling area or mezzanines. Additionally, transformers may also be installed in accessible areas of public buildings such as hospitals or schools. In any of the above installations, a liquid containment area is needed for the practical safeguarding of persons and property.”
The supporting comment for the proposal indicated that fluid pool fires have not occurred since the introduction of less-flammable liquid insulated transformers.
The requirement for a liquid confinement area is in 450.23(A)(1)(c).
Motor disconnecting means
Q: We have been advised that additional “in sight” disconnecting means are required at motors we recently installed in an office building. Lockable disconnects are provided at, and ahead of each motor controller. Has the Code changed on motor disconnects?
A: Yes, it has. The change appears in 430.102(B) Exception. A disconnecting means is not required within sight of the motor where the location of the disconnecting means would introduce additional or increased hazards to persons or property, or in industrial installations with written safety procedures where maintenance and supervision ensure that qualified persons will service the equipment. Under all other conditions disconnecting means must be provided at the motor location.
Fine Print Note No. 1 provides information on what constitutes increased or additional hazards. In the absence of increased or additional hazards, in-sight motor disconnects must be provided for the motors installed in an office building. EC
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.254.2132.