Applications include threading a pipe directly into a box (and in similar applications that call for grounding lugs) and installing connectors to a box that need a bushing with an insulating sleeve.
Steel Bushings are a cutting-edge product that combines two products into one and only needs one assembly step as opposed to two. There are no similar products on the market because of this distinctive feature.
Steel Bushings are installed primarily inside a box, and the box determines whether they are compliant for wet or dry locations.
Steel Bushings essentially combine a locknut and a bushing into one body, with the locknut’s small diameter and internal threads “stretched” to accommodate the insulating sleeve. There is no requirement for a separate bushing in applications where the connector or threaded pipe needs a bushing to be installed.
Steel Bushings have a steel main body and a 150 C-rated polyetherimide (PEI) insulating sleeve for durability and long life. They do away with the locknut and address the issue of not having enough thread remaining to engage the bushing after the locknut installation
Q. How are bushings to be installed on rigid metal conduit (RMC) to comply with NEC regulations?
Informational Note: Unless the design of the box, fitting, or enclosure provides equivalent protection, conductors 4 AWG and larger that enter an enclosure must be protected from abrasion, both during and after installation, by a fitting that provides a smooth, rounded, insulating surface, such as an insulating bushing. 300. 4(G).
These materials are provided to us by Mike Holt Enterprises in Leesburg, Fla. To view Code training materials offered by this company, visit www.mikeholt.com/code.
A. Regardless of the size of the conductor, a metal or plastic bushing must be installed on the conduit threads at terminations to protect conductors from abrasion unless the box, fitting, or enclosure is made to do so [Sec. 344. 46].
Where conductors pass through panelboard enclosures and tap box openings, conduit bushings are crucial in preventing damage to conductor insulation. The plastic bushing inserts have been frequently missing, moved, or damaged recently to the point where they no longer function to keep the conductors from coming into contact with the equipment’s sharp edges. The electricians were aware that the bushings at one location were broken, but they did not think the issue was critical enough to address. To safeguard the conductors, we insist that damaged bushings be replaced during inspections.
Although it may be difficult to imagine, a cheap plastic (or metal and plastic) component plays a crucial part in the safe and reliable operation of an electrical distribution system. Conduit bushings must be installed correctly in panelboards and tap boxes for your electrical equipment because they are crucial to the electrical system.
The next morning, a feeder was being monitored by a Hioki, and the Hioki at the main breaker noticed an arcing overcurrent condition, C-phase to ground. The fault was not long enough to trip any breakers, but the data showed that several thousand amps of current flowed twice for a fraction of a cycle.
We made site staff aware of the intermittent arcing condition and advised them to turn off the feeder breakers to this panel and thoroughly inspect the conductor route. A conductor was found to be fusing to the conduit when it entered a tap can during their inspection (see on the right). The conduit’s end lacked a protective bushing, and the sharp edges had pierced the insulation covering the conductor. Other conductors entering the same tap box were also damaged, even though this was the only feeder that had a fault. The feeder breaker was able to be closed after the ground fault trips happened because the pressure wave created by the fault was able to expel enough material from the point of contact to eliminate the electrical path between the phase conductor and ground.
The client is working to correct this condition. Where conductors are damaged, new conductors must be pulled, and the conduit ends must have bushings installed. On feeders that aren’t yet damaged and don’t need a re-pull, split ring bushings might be installed. This incident had a significant negative impact on the customer, but bushings could have prevented it.