Heat Damage on Ceiling Side of Luminaire
This is what the underside of a ceiling-mounted luminaire looks like after years of operating with oversized wattage lamps. This luminaire is UL listed for use with no more than a 75W lamp. But when occupants need more light, they frequently install 100W or 150W lamps in these types of luminaires. Most kitchen luminaires have a decorative glass or plastic globe that covers the lamps. This traps much of the lamp heat within the enclosed canopy. As the heat rises upward, most of it is directed toward the luminaire wires and the building conductors in the outlet box. The excessive trapped heat (operating for many years) frequently damages the building conductor insulation in the ceiling outlet box. In many cases, the building conductors entering the outlet box must be replaced or cut back to sound insulation. However, they can only be cut back if there is enough excess conductor available in this area.
Heat Damage on Lampholder Side of Luminaire
NEC Sec. 410.74(A) requires that the luminaire manufacturer mark the maximum lamp wattage or electrical rating on the unit. As you can see in this photo, the paint on the canopy has turned to powder from the excessive heat produced by oversized lamps. Although the electrical industry developed plug-fuse adapters and newer, non-interchangeable plug-fuse types that prevented over-fusing in older fuse boxes, the same cannot be said for limiting the lamp wattage used in a luminaire. The proper lamp wattage size requires the installer to know the rated wattage limit and then not exceed it. After many years of use, the wattage label may fall off or be unreadable. Many users installed the maximum wattage lamp that would physically fit inside the globe to provide the most light. For every 10°C that the conductor insulation is operated above its rating, the insulation life is reduced by one-half. This applies to the high-temperature fixture wires and the building wires that supply power to the luminaire.
Replacement Lampholder Creates Shock Hazard
This lampholder is not the original one that came with this unit from the factory. The original lampholder was most likely replaced after being damaged by excessive heat from using oversized lamps. NEC Sec. 410.5 requires that luminaires have no live parts normally exposed to contact. This replacement lampholder has exposed terminals that can shock the person changing the lamp. In addition, the grounded or white wire is improperly connected to the brass colored screw, and the ungrounded conductor is improperly connected to the silver colored screw. This is a violation of Sec. 410.50, which states that the grounded white conductor shall be connected to the screw shell or silver colored screw. This is important to reduce the shock hazard when replacing a lamp. In this configuration, the lamp screw is energized the moment that it comes in contact with the screw shell of the lampholder. It is not uncommon for someone to hold the lampholder with one hand while turning the lamp in the socket with the other hand. Anyone simultaneously touching the lamp screw shell and a grounded surface will create a dangerous, hand-to-hand circuit path through the heart.
Heat Damage Visible in Fiberglass Insulation
This fiberglass insulation pad is needed to protect the building materials and wiring in the outlet box from excessive heat. As you can see in the photo, the dark areas on the pad are the result of overheating due to the use of oversized lamps. The fiberglass pad is part of the luminaire’s original design that is tested by UL. If this insulation pad is removed, the luminaire will most likely not be able to meet UL requirements for maximum temperature limits at the outlet box. NEC Sec. 410.74(A) states that a luminaire requiring supply wiring rated higher than 60°C shall be marked with the minimum supply wire temperature rating on the luminaire and the shipping carton or equivalent. By having this information on the product carton, the purchaser can determine before opening the carton if there is a temperature rating conflict with the building wiring.
Choose LED Lamps that are Suitable for Use in Enclosed Luminaires
This luminaire features two 60W equivalent LED lamps that are rated 9.5W each. Using lower wattage LED lamps in a luminaire designed for two 60W incandescent lamps is a great energy-saving idea. However, the LED lamps produce heat that must be transferred to the surrounding air though their aluminum heat sink. When the lamps are used in an enclosed, ceiling-mounted luminaire, the air around the heat sink gets trapped within the globe. This can damage an LED’s sensitive electronic components and severely reduce its life. This is why it’s important to use lamps that are rated “Suitable for Use in Enclosed Luminaires.” This rating is necessary to prevent the LED electronic driver within the lamp itself from overheating due to a lack of airflow across the lamp’s aluminum heat sink. It also reduces the heat available in the canopy, which can damage the luminaire’s internal wiring and potentially the building wires in the outlet box.
Overheated and Damaged Luminaire Wires
The porcelain lampholder in this photo is not original to this luminaire. It is clearly damaged beyond repair. In this case, the high temperature luminaire wire was overheated from the use of oversized lamps. The white grounded conductor is dark brown in color due to excessive heat. The wires passing through the threaded mounting bracket are exposed and ready to short or ground to the fixture canopy through the mounting bracket. Although someone used electrical tape as a quick fix here, it is not a suitable repair for the heat damaged wires on this lampholder. Lampholders are factory designed with high temperature wire pigtails and recessed, riveted connections at the screw shell and the center contact. Lampholders with riveted conductors assure that the white wire connects to the screw shell and the black wire connects to the center contact. Proper polarization of terminals helps prevent shock hazards to anyone replacing the lamps.
Overheated and Damaged Building Conductors
Heat from an incandescent lamp flows through the lampholder contacts and the copper luminaire wires to the building conductors. The copper building conductors act like a heat sink for the heat produced in the lamp. Section 410.21 of the NEC states that the conductors in the outlet box shall not be subjected to temperatures greater than that for which they are rated. If the luminaire is marked for 90°C building conductors, this can create a problem for pre-1980 buildings that could have been wired with 60°C branch circuit wiring. These heat damaged building conductors should have been replaced a long time ago. This makeshift repair using electrical tape did not withstand the excessive heat produced by oversized lamps. This type of insulation failure can energize the luminaire canopy or cause arcing on a loose grounding conductor return path. Although this type of deterioration is common in older installations, an arc fault circuit interrupter (AFCI) would certainly help in detecting and interrupting arcing faults on these conductors.
Don’t Forget About the Lampholder
Section 410.122 of the NEC states that lampholders of the screw shell type shall be made of porcelain or other suitable insulating materials. In this photo, the porcelain lampholder is the only material that can take the excessive amount of heat that occurred from the use of high wattage lamps. If this had been a plastic lampholder, the plastic lampholder would most likely be brittle and crumbling like the luminaire wires are in this case. This conductor insulation is extremely brittle. Moving these conductors will instantly crack the insulation. You can see the exposed copper conductor is annealed from operating at high temperatures. The conductor strands are broken on the grounded conductor due to excessive heat and corrosion. The reduced wire size further increases the electrical resistance and heat at the grounded lampholder termination.
When heat-damaged ceiling luminaires are encountered, there are several good replacement options available to a qualified electrician. Proper repair and parts replacement is one option. Replacing the entire luminaire with a new incandescent type lampholder luminaire is another option. These units can be used with newer LED screw-in type lamps that typically use just 9.5W instead of 60W. Finally, newer luminaires are available that do not have a standard lampholder socket. These luminaires are manufactured with an array of LEDs directly mounted to the unit’s interior, under the glass globe. When these luminaires fail, the entire unit is typically replaced. Depending on the degree of heat damage to the building wiring, additional repairs may be warranted on this front for fire and shock safety.
Follow Proper Grounding Requirements
Verify that the luminaire is properly grounded, according to the Art. 250 and Art. 410, Part V of the NEC — as well as any instructions supplied with the luminaire. This luminaire UL label references a wiring and grounding instruction sheet supplied with the unit. If the luminaire does not have a proper equipment grounding connection, the canopy or other metal components of the luminaire could remain energized if the lampholder wiring insulation is damaged and contacts the metal parts of the luminaire. Section 410.46 requires that luminaires with exposed metal parts must be provided with a means for connecting an equipment grounding conductor.