NEC Questions and Answers Based on the 2008 NEC

January Part 2

 

Here is the follow up to yesterday’s newsletter. This includes all of the answers to the questions sent yesterday so you can see how you did.

 

By Mike Holt for EC&M Magazine

 

Q1. Is GFCI protection required for drinking water fountains in office buildings?

A1. Yes [422.52].

 

Q2. A 400Aservice is made up of two 200A main breaker panelboards that are nipple together. Can the service conductors pass through one of the cabinets to supply the other panelboard?

A2. Yes [230.7].

 

Q3. Section 680.51 of the NEC requires GFCI protection for fountain equipment. Is there a maximum fault current to ground requirement with this section that should be used when providing ground fault protection for fountain equipment?

A3. When the Code requires GFCI protection, it is a “Class A” type. A “Class A” ground-fault circuit interrupter opens the circuit when the current-to-ground has a value of 6 mA or higher and doesn’t trip when the current-to-ground is less than 4 mA [Art 100 Ground-Fault Circuit Interrupter FPN].

 

Q4. Is a receptacle required within 25 ft of a roof-top exhaust fan?

A4. No. A 15A or 20A, 125V receptacle outlet must be installed at an accessible location for the servicing of heating, air-conditioning, and refrigeration equipment [210.63]. An exhaust fan is not heating, air-conditioning or refrigeration, so a receptacle is not required.

 

Q5. What is the minimum burial depth for cable TV cables?

A5. There is no minimum cover requirement for coaxial cable.

 

Q6. What size conductors are required to supply a 75A load, if the device terminals are rated for 75°C?

A6. 4 AWG, rated 85A at 75°C [Table 310.16].

 

Q7. What is the ampacity of three 8 XHHW conductors installed in a wet location at an ambient temperature of 45°C?

A7. XHHW conductors are rated 75°C in a wet location [Table 310.13(A)].

Conductor Ampacity [75°C] = 50A

Correction Factor [Table 310.16] = 0.82

Corrected Ampacity = 50A x 0.82 = 41A

 

Q8. What is the separation distance of communication raceway on the same rack with raceways containing power and lighting conductors?

A8. None.

 

Q9. What are the Code requirements for bonding bushings on 277V or 480V circuits?

A9. Metal raceways or cables containing 277V and/or 480V circuits terminating at ringed knockouts must be bonded to the metal enclosure with a bonding jumper sized in accordance with 250.122, based on the rating of the circuit overcurrent device [250.102(D)]. A bonding jumper isn’t required where ringed knockouts aren’t encountered, totally punched out, or where the box is listed to provide a reliable bonding connection [250.97].

 

Q10. Is the lighting in a bathroom allowed to be fed from the load side of the bathroom GFCI receptacle, which means that the lights will go out when the GFCI trips?

A10. Yes, as long as the circuit to the bathroom receptacles only supplies that bathroom [210.11(C)(3) Exception], and no single load fastened in place is rated more than 10A [210.23(A)].

 

Q11. Is it a Code violation to install 15A rated duplex receptacles on the 20A circuit?

A11. No [210.23(B)(3)].

 

Q12. In a school science lab are 15A or 20A, 125V receptacle within 6 ft of the lab sink, required to be GFCI-protected?

A12. Yes, all 15A and 20A, 125V receptacles installed within 6 ft of the outside edge of a sink must be GFCI-protected [210.8(B)(5)].

 

Q13. What are the NEC requirements for the installation of smoke detectors in dwelling units?

A13. The NEC doesn’t specify the locations of smoke alarms in a dwelling unit. That information is best obtained in the locally adopted building code. The NEC does require smoke alarms located in dwelling units to be AFCI-protected [210.12(B)].

 

Q14. Does the Code require a paddle fan to be switch controlled, or can the paddle fan be wired directly without a switch?

A14. The Code doesn’t specify, so a direct wired fan would be fine.