I visited with a contractor friend’s engineer and electrician who were assigned to inspect a number of existing manholes on the property of a large industrial site. I was informed that they had the responsibility to verify if the load-side installation of the manholes complied with the procedures of the National Electrical Code (NEC) and, if they did, which sections of the NEC applied. Also, they had to determine if the manholes had been properly maintained and then refer to the standard that regulated such frequent checks. With the coordination of the utility, they also had to make an evaluation of the manholes on the supply side.
Application of the NEC
The following sections of the NEC outline the minimum requirements for constructing manholes on the load side. Note that electricians use Part V of Article 110 for installing wiring methods and equipment in manhole spaces. Therefore, that part should be used for evaluation purposes.
Section 110.70 explains the general requirements for enclosures used for personnel entry.
Sufficient working space must be provided for safety of employees who are maintaining conductors and equipment that has exposed energized conductors and circuit parts. Such space must also provide enough room for installation or withdrawal of conductors without damaging the insulation. Qualified engineers must design the means of access to manholes as well as to ensure their ability to withstand the loads that might be imposed on the structures.
The cabling workspace section incorporates the requirements for the appropriate space to maintain the cables. Listed are the proper vertical and horizontal distances necessary to maintain the cables safely.
Equipment installed in manholes that requires live parts to be examined, adjusted, serviced or maintained while energized must comply with 110.26 for 600 volts or less or 110.34 for systems over 600 volts.
Appropriate bending space must be provided for conductors routed through manholes. Such space is based on the voltage and determined by the provisions listed in 314.28 for systems of 600 volts or less and 314.71(A) and (B) for systems rated over 600 volts. Outlined is cable racking and safe-access requirements for personnel entering to make an installation or to perform maintenance.
Section 110.75 is used to size the dimensions necessary for rectangular and round openings to allow personnel access into the manhole space. Obstructions must be free of protrusions that can injure or prevent ready access. Location of equipment located below access openings is prohibited unless means of a preventive barrier or fixed ladder is provided. Covers for openings must weigh more than 100 pounds, and special tools must be provided for removal. Manhole covers must be equipped with markings or logos to indicate their specific function.
Application of the NESC
The National Electrical Safety Code (NESC) covers the requirements that must be applied when manholes are constructed and used for supply-side conductors and equipment. Rule 323 contains the necessary requirements that utilities apply when manholes are used to enclose wiring methods and related equipment. Note that these requirements should be used as guidelines for compliance of existing manholes.
Since the requirements for the load side and the supply side are similar, the following are the title heads of the rules as they appear in the NESC:
Rule 323. A. Strength
Rule 323. B. Dimensions
Rule 323. C. Manhole access
Rule 323. D. Covers
Rule 323. E. Vault and utility tunnel access
Rule 323. F. Ladder requirements
Rule 323. G. Drainage
Rule 323. H. Ventilation
Rule 323. I. Mechanical protection
Rule 323. J. Identification
Application of NFPA 70B
NFPA 70B, Recommended Practice for Electrical Equipment Maintenance, is used to develop a frequency check schedule, perform preventive maintenance and make visual inspections on conductors and cables installed in manholes.
Preventive maintenance is the best way to ensure continued reliable service from electrical cable installations. Visual inspection and electrical testing of the insulation are the major maintenance procedures. However, it should be stressed that no amount of maintenance can correct improper application or physical damage during installation as required per the NEC or NESC. Because of limited space, here are the section heads that should be reviewed in detail before an electrical contracting firm attempts to send personnel to inspect and evaluate the conditions of existing manholes:
Section 11.2. Visual Inspection
11.2.1. De-energizing cables
11.2.2. Condition of cables
11.2.3. Inspection of drainage, spalling, and deterioration, etc.
11.2.4. Inspection of cable termination
11.2.6. Intervals of inspection
Section 11.3. Aerial Installation
Section 11.4. Raceway Installation
Section 11.5 Testing
Employees can use the above requirements to inspect and evaluate the conditions of the existing manholes.
STALLCUP is the CEO of Grayboy Inc., which develops and authors publications for the electrical industry and specializes in classroom training on the National Electrical Code and other standards, including those from OSHA. Contact him at 817.581.2206.