Control-circuit transformers

Q: Do the requirements of Article 450—Transformers and Transformer Vaults or Article 725—Class 1, Class 2 and Class 3 Remote-Control, Signaling, and Power-Limited Circuits apply to a control-circuit transformers in a 480-volt combination motor starter? The transformer reduces 480 volts to 120 volts for the remote- control start-stop push buttons.

A: Let’s look at the articles mentioned to find out if they apply. An exception in 450.1 indicates that the article does not apply to transformers that are a component of other electrical equipment.

The scope in Article 725 indicates that the transformer is not covered by this article if it is an integral part of a device. It states: “Scope. This article covers remote- control, signaling, and power-limited circuits that are not an integral part of a device or appliance.”

Since Articles 450 and 725 do not apply to a control transformer that is factory installed in a motor controller, the rules in 430.72 through 430.74 apply. Where the transformer is included in the motor controller, it must be connected to the load side of the disconnecting means in the combination motor controller. This is required by 430.74(B).

When a combination motor starter is listed by a recognized independent third-party testing laboratory, the control transformer will have primary overcurrent protection (if required by the NEC).

The installation instructions should also indicate the minimum control-circuit conductor size for push-button stations that are remote from the controller. If not, minimum control-circuit conductor sizes can be obtained from Column C of Table 430.72(B).

GFCI-protected receptacles

Q: A temporary electric service provides one 125-volt, 20-ampere duplex receptacle and one 50-ampere, 250-volt receptacle. Is GFCI protection required for the 20-ampere and 50-ampere receptacles?

A: Ground fault circuit interrupter (GFCI) protection is required for the 20-ampere, 125-volt duplex receptacle and may also be required for the 50- ampere 250-volt receptacle. Part of 590.6(A) states: “All 125-volt, single-phase, 15-, 20- and 30-ampere receptacle outlets that are not part of the permanent wiring of the building or structure and that are in use by personnel shall have ground-fault circuit interrupter protection for personnel.”

An exception permits elimination of GFCI protection in industrial establishments under very limited conditions. The 50-ampere, 250-volt receptacle must also be protected by a GFCI or be inspected and maintained under the Assured Equipment Grounding Conductor Program, which is explained in detail under 590.6(B)(2). Here is a summary of the tests that are required for the Assured Equipment Grounding Conductor Program:

1. A designated individual or individuals to ensure that equipment-grounding conductors are installed and maintained in accordance with various parts of the NEC

2. Equipment-grounding conductors must be tested for continuity and be electrically continuous

3. Each receptacle and attachment cap must be tested for proper attachment to the correct terminal.

These tests must be performed before first use on the construction site, where there is evidence of damage, before equipment is returned to service after any repairs, and at intervals not exceeding three months. All tests must be recorded and made available to the authority having jurisdiction (AHJ).

All of these tests and related costs can be avoided by providing GFCI protection for the 50-ampere, 250-volt receptacle.

Transformer secondary conductors

Q: What size main bonding conductor is required for the secondary conductors that consist of four 500 Kcmil copper conductors per phase? The secondary voltage is 208Y/120.

A: The term, “system bonding jumper,” is now used to separate the main bonding jumper at the service from the bonding jumper that is used to connect the grounded circuit conductor to the equipment-grounding conductors of a separately derived system.

Note 1 to Table 250.66 advises that the sum of the areas of all conductors connected to the same phase be taken to arrive at an equivalent cross section area.

Therefore, four 500 Kcmil conductors per phase results in 2,000 Kcmils. Multiplying this figure by 12.5 percent (2,000 x 0.125) results in a wire size of 250 Kcmil. The minimum size for the system bonding jumper is 250 Kcmil copper.

Stairway panelboard

Q: Is it permissible to install a panelboard on a stairway in a residence where the handrail for the stairs is 48 inches from the panelboard?

A: Sufficient working space must be provided around the panelboard if it is serviced and maintained while energized. For a panelboard that operates at 150 volts to ground or less, the minimum clear space in front is 3 feet. The minimum width of the working space is 30 inches or the width of the panelboard, whichever is greater.

Although not clearly stated in 110.26, the width and depth of the working space should extend to the surface of the floor or ground and be fairly level. In my opinion, the surface in front of the panelboard should be flat and have a minimum dimension of 3 feet by 30 inches to comply with 110.26.

Conductor color coding

Q: Does the National Electrical Code require color-coding of conductors for branch circuits and feeders where 208Y/120 and 480Y/277 volt systems are present in the same building? If so, are two-conductor Type AC and MC cables available with other than white and black conductors?

A: Yes, there are various places in the NEC that specify identification of conductors where different voltage systems exist in the same building. Circuit- grounded conductors must be white, gray or have three white stripes on other than green colored insulation (see 200.6 and 200.7).

Each ungrounded branch circuit conductor of each voltage system, where accessible, must be identified by color, marking type, tagging or other approved means and must be posted at each panelboard. These same requirements apply to feeder conductors. Some of the Code references for these requirements appear in 200.7, 210.5 and 215.12. Two-conductor types AC and MC cables are available with conductor colors other than black and white.

Fire-pump disconnect

Q: Must the disconnecting means for a fire pump be located within sight of the fire-pump motor? How is the ampere rating of the disconnecting means determined? Can the disconnecting means be an overcurrent device in a panelboard?

A: Where a disconnecting means is provided for the fire pump, it does not have to be within sight of the fire-pump motor or controller.

I must point out that Article 695—Fire Pumps and NFPA 20, Standard for the Installation of Stationary Pumps for Fire Protection—does not require a separate service-disconnecting means for a fire pump. Service-entrance conductors are permitted to be run directly to the fire-pump controller. However, the fire-pump controller must be marked “Suitable for Use as Service Equipment.”

Where a disconnecting means and overcurrent protection are installed ahead of the fire pump controller, the minimum ampere rating of the overcurrent protection is 600 percent of fire-pump motor full-load current.

The disconnect cannot be an overcurrent device in a panelboard. If a disconnect is provided, it must be supplied by a separate utility service or tap at the service ahead of, and not within the service-equipment enclosure.

Where a disconnecting means is provided ahead of the fire-pump controller, it must comply with all of the following:

1. Be identified as suitable for use as service equipment

2. Can be locked in the closed position

3.Not be located within equipment that feeds loads other than the fire pump. The disconnecting means shall be marked: “Fire Pump Disconnecting Means” with letters that are at least 1 inch high. At the fire-pump controller, a sign must be provided that states the location of the key if the disconnecting means is locked.

Finally, the disconnecting means must be supervised in the closed position by one of the following means:

1. Control station, proprietary or remote station signal device

2. Local signaling service that causes the sounding of an audible signal at a constantly attended point

3. Locking the disconnecting means in the closed position

4. Sealing the disconnecting means and approved weekly inspections

As can be seen from this list of requirements, it is better to eliminate the expense and procedures required for a disconnect ahead of a fire-pump branch circuit where service conductors can be run directly to the fire-pump controller.

Feeder for pool panelboard

Q: Does the NEC allow service-entrance cable with a bare equipment- grounding conductor to supply a swimming pool panelboard?

A: Requirements for feeders that supply panelboards that provide branch circuits for swimming pools are in 680.25. The wiring method used for the feeder must be one of the following: rigid metal conduit, intermediate metal conduit, liquid-tight flexible nonmetallic conduit and rigid nonmetallic conduit.

Electrical metallic tubing and electrical nonmetallic tubing are also permitted under restricted conditions. An exception allows the use of flexible metal conduit or a cable assembly with an equipment-grounding conductor within the outer sheath where the feeder is existing. EC

FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720