Edison Base Fuse, Voltage Drop and More

By Jim Dollard | Mar 15, 2024
Edison Base Fuse, Voltage Drop and More

Jim Dollard has an extensive background in codes and standards. Send questions about the National Electrical Code (NEC) to Jim at [email protected]. Answers are based on the 2023 NEC.

Jim Dollard has an extensive background in codes and standards. Send questions about the National Electrical Code (NEC) to Jim at [email protected]. Answers are based on the 2023 NEC.

Edison base fuse replacement

A client received direction from his insurance company to address an apartment complex that has load centers with Edison base fuses in each unit. Do we have to remove the load centers and install circuit breakers? That would be extremely problematic, as AFCI protection would be required.

Unfortunately, we cannot see the written direction from the insurance company. However, it is likely that they want Type S fuses installed. It is not likely that their intent is to replace each panelboard with circuit breakers. The owner could certainly choose to replace the fused panelboards completely, and if the replacement panelboards are in the same location, AFCI protection of branch circuits would not be required. Section 210.12(E) addresses AFCI protection of branch circuit extensions, modifications or replacements of branch circuits, which includes replacing a panelboard. 

The exception to 210.12(E) permits a replacement panelboard without adding AFCI protection where the extension of the existing branch circuit conductors (if necessary) is not more than 6 feet in length and does not include any additional outlets or devices, other than splicing devices (wire nuts). When making this measurement, it is from enclosure to enclosure; it does not include the conductors inside the panelboard cabinet, enclosure or junction box.

The most feasible solution in this case is to replace each Edison base fuse with Type S fuses and adapters. The NEC requires that Edison base fuse holders be made to accept Type S fuses by the use of adapters; see 240.52. Section 240.54 provides requirements relevant to the insurance company concerns, including the installation of Type S adapters in Edison base fuseholders to accept only the proper size Type S fuse. The issue here is that old Edison base fuseholders accept multiple fuse ratings, for example 15A, 20A and 30A, which increases the likelihood that an occupant will install a fuse sized in excess of the conductor ampacity. Type S adapters are installed in Edison base fuseholders and cannot be removed (240.54(C)). Once the correct Type S adapter is installed, only the proper size fuse will fit. For example, this eliminates the possibility of an occupant replacing a 15A fuse with a 20A one. Where Type S fuses and adapters are added to existing Edison base fuseholders, installers must remove panelboard covers, identify conductor sizes and ampacity and then install the proper Type S adapter and fuse.

Voltage drop conductor size

At a dwelling, we installed a very long outdoor branch circuit to supply only a security camera and other security-related sensors. The load was under 2A. We calculated a 5A load at 120V, which required a 4 AWG copper protected at 20A. The owner wants to add more equipment there. The new electrician claims we did not meet NEC requirements for voltage drop. Apparently, they plugged in a resistive electric heater and measured less than 90V when it was running. Did we need to size the conductors for a 16A load on a 20A circuit breaker?

No, the requirements for minimum branch circuit ampacity and size are in Section 210.19. The general requirements are met as the original installation, you stated, was sized to meet the continuous and maximum load for the security equipment after any adjustment or correction factors. Section 210.19(D) applies and simply requires branch circuit conductors have an ampacity sufficient for the loads served, and in no case can they be smaller than 14 AWG. There are no general voltage drop requirements such as 3% or 5% for branch circuits in the NEC.

See the informational note following the parent text in 210.19, which explains that a voltage drop on feeders and branch circuits to the farthest outlet that does not exceed 5% should provide reasonable efficiency of operation. Voltage drop is considered a design issue. In your case, the installation exceeded the load supplied as designed. It is important to note that the NEC contains minimum requirements, intended only to keep electrical installations free from hazard. Compliance with minimum requirements does not necessarily mean that expansion of installed conductors and equipment will be adequate for future loads. See Section 90.2(B).

Utilities and NEC requirements

NEC 230.2(D) states that an additional service shall be permitted for different voltages or phases for different use. We applied to our electric utility to get a new 480/277V service where a 208/120V service already exists. The utility company said they don’t do that anymore. I know it’s a stretch, but the NEC says that “shall” be permitted. Can we force them to do it?

No. The NEC applies only from the service point downstream to include all premises wiring, so the utility company is not subject to NEC requirements. The general rule in Section 230.2 is that a building or other structure can be supplied by only one service unless specifically permitted in 230.2(A) through (D). In each of the permissive requirements for additional services, the words “shall be permitted” exist to ensure that the electrical inspector will approve the additional service. Those words do not drive the electric utility. Multiple options exist, including, but not limited to, expanding the size (ampacity) of the 208/120V service and installing a transformer to step up to 480/277V to supply the new loads.

Listed as portable GFCI protection?

We installed temporary power and lighting at a casino renovation. During a safety audit, the owner’s consultant cited us as noncompliant with NEC Section 518.3 and the use of listed portable ground-fault circuit-interrupter protection. All temporary receptacles we installed are GFCI-protected. We don’t know what they are talking about. 

The section quoted (518.3) is correct as a casino is a place of assembly. However, Article 590 and Section 590.6 apply. A GFCI device listed as a portable GFCI provides open neutral protection. A standard GFCI-type receptacle does not. These listed portable GFCI devices are readily available and are intended to be used where an individual will plug into an existing (permanent) receptacle for use during construction renovation or remodeling. 

The auditor may have observed trades using permanent receptacles for power without using a device plugged into the permanent outlet listed as a portable GFCI. Their employers should deal with this issue. As stated, you installed temporary power with GFCI protected receptacles, which should be used by all trades where power is needed. All portable GFCI devices are not necessarily “listed as portable GFCI protective devices.” 

Look at the options the next time you are in a large home improvement retail store. There are small, very inexpensive portable GFCIs that are not “listed as portable GFCI protective devices.” Read the labeling and be sure to purchase the right device.

Circuit directory schedule in English?

Are panelboard schedules required to be written in English? During renovation of multiple strip stores, several have all circuit identifications in Spanish. Is that a violation and are the new occupants at a loss?

No, it is not a violation. Requirements for a circuit directory exist in Part I of Article 408 and apply to switchboards, switchgear and panelboards. Section 408.4(A) mandates that the circuit directory is not dependent on transient conditions of occupancy. The NEC requirement does not mandate a specific or multiple languages. Not being dependent on transient conditions of occupancy means we cannot identify circuits, for example, as “Theresa’s bedroom” or “Mr. Adams’ office.” The correct method is the “second-floor bedroom, street side” or “office 522.” / Morphart

About The Author

DOLLARD is retired safety coordinator for IBEW Local 98 in Philadelphia. He is a past member of the NEC Correlating Committee, CMP-10, CMP-13, CMP-15, NFPA 90A/B and NFPA 855. Jim continues to serve on NFPA 70E and as a UL Electrical Council member. Reach him at [email protected].






featured Video


New from Lutron: Lumaris tape light

Want an easier way to do tunable white tape light?


Related Articles