ISSUE: DCA09-DEC-269. Petitioner seeks a Declaratory
Statement on an interpretation of Section 13-413.AB.1.1 of the
Petitioner in DCA09-DEC-269 seeks clarification of the following questions:
1. Is the voltage drop of 2 percent as stated in 13-413.1.ABC.1.1 intended as such or is it a scriverners error?
2. Why is the FBC so restrictive for the feeder conductor voltage drop at 2 percent and why is it not in agreement with the NEC?
Mr.
Thomas H. Ford of Bhamani, Ford & Associates, Inc. is designing parking lot
lighting for a large shopping center.
Background:
1. Section 13-413.AB.1.1, Feeders and customer owned service conductors, states as follows: “Feeder and customer owned service conductors shall be sized for a maximum voltage drop of 2 percent at design load.”
2. Section 13-412.AB.1.2, Branch circuits, states as follows: “Branch circuit conductors shall be sized for a maximum voltage drop of 3 percent at design load.”
3. Proponent quotes the National Electrical Code (NEC) 2005 Handbook, FPN No. 2: “Conductors for feeders as defined in Article 100, sized to prevent a voltage drop exceeding 3 percent at the farthest outlet of power, heating, and lighting loads, or combinations of such loads, and where the maximum total voltage drop on both feeders and branch circuits to the farthest outlet does not exceed 5 percent, will provide reasonable efficiency of operation.” FPN No. 4, conductors for branch circuits, says basically the same thing.
4. Section 90.5 (C) of the NEC, NFPA 70, 2005, Explanatory Material, states: “Explanatory material, such as references to other standards, references to related sections of this Code, or information related to a Code rule, is included in this Code in the form of fine print notes (FPNs). Fine print notes are informational only and are not enforceable as requirements of this Code.”
5. Section 102.4 of the Florida Building Code, Referenced codes and standards, states: “The codes and standards referenced in this code shall be considered part of the requirements of this code to the prescribed extent of each such reference. Where differences occur between provisions of this code and referenced codes and standards, the provisions of this code shall apply.”
6. The ASHRAE 90.1 User’s Manual, explains this requirement (Section 8.4.1 of ASHRAE 90.1-2004) as follows: “The Standard allows a maximum voltage drop of 2% for feeder conductors and 3% for branch circuit conductors. In practice, these voltage drop limitations result in selecting conductors and conduits based on the practice described in Table 9 of the 2002 National Electrical Code Handbook, which is repeated [in the Standard] as Table 8-A. In this table, the voltage drop is dependent on the following:
§ Circuit type (single-phase or three-phase);
§ Number and size of conductors per phase;
§ Conduit types (magnetic or non-magnetic);
§ Power factor of the load;
§ Circuit length;
§ Load current.”
The ASHRAE 90.1 User’s Manual further states: “…The voltage drop requirements in the Standard (ASHRAE 90.1) are presently only a recommendation within the NEC.
There are two types of problems caused by significant voltage drop. First, in most electrical circuits the current increases as voltage at the load drops because the load requires a certain amount of power. When the current increases, there is an increase in the power loss within the conductor that varies as the square of the current. Therefore, the voltage drop is an energy efficiency issue. Second, the voltage drop in the conductors, if excessive, may result in equipment operation problems or equipment failure.”
7. BOAF Informal Interpretation 5947 asks the Question, “Is it the intent of the voltage drop requirement, 13-413.1.ABC.1 that the loads specified in the plans panel schedules may be used for “design load” as identified in the requirement?” The question relates to loads of receptacle outlets. In the NEC, for feeder and branch circuit sizing calculation purposes, receptacles that are not intended for cord and plug connection to a specific load are sized at 180W. Would this also be valid in the context of Chapter 13? BOAF Answers: “Yes. The use of 180 VA per receptacle for the loading in the voltage drop calculation is acceptable. It would be valid for 13-413 purposes.” BOAF commentary further clarifies the issue as follows: “The panel loads normally are the “design loads,” which means that the 180W assumption would apply, unless additional calculations are indicated to support allowable diversity reductions. The calculations could include diversities for general receptacle circuits in offices or other locations. This could bring the “design load” below the 180W per duplex outlet with diversity of use and loading.” The commentary further quotes the ASHRAE 90.1 User’s Manual as described in No. 4 above.
8. BOAF Informal Interpretation 6078 asks the Question, “Is it the intent of Section 13-413.1.ABC.1.2 to use the rating of the branch circuit (80% of the overcurrent protective device) as the “design load” to determine the voltage drop at the farthest general purpose (non-dedicated) receptacle?” This would be a worst-case condition for branch circuit loading and, although possible, probably does not reflect actual usage. The problem is defining “design load” for nondedicated receptacles in branch circuits for the purpose of determining compliance with the voltage drop criteria of Chapter 13 of the FBC. BOAF Answers: “No. The rating of the branch circuit is the maximum permitted rating or setting of the overcurrent device protecti[ng] the circuit in accordance with 210.3 of the NEC.” The commentary furthers states: “The design load would be that as calculated by one of the approved methods in Article 220 of the NEC.”
Staff Recommendations: Based on the
above facts and circumstances, staff provides the following recommendations as
answers to proponent’s questions:
Question 1:
To the question, Is the voltage drop of 2 percent as stated in 13-413.1.ABC.1.1 intended
as such or is it a scriverners error?, the answer is Yes, Section 13-413.AB.1.1
of the Florida
Building Code, Building,
intended to limit the voltage drop for feeders and
customer-owned service conductors to 2 percent at design load. It is not a scribing error.
Question 2:
To the question, Why is the FBC so restrictive for the feeder conductor voltage drop at 2 percent and why is it not in agreement with the NEC?, the answer is that according to Section 102.4 of the code, specific energy conservation requirements in the FBC-B take precedence over the informational language in the NEC. There is no conflict between the two.