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Paying attention to certain details of bus dud projects will ensure trouble-free service.
bus duct system is an effective method of distributing power to your switchgear and various loads. Yet, bus duct problems lead to catastrophic damage and extensive downtime. Let's look at how you properly order and install your system. Ampacity. You may know the basic bus duct selection requirements already (see sidebar, on page 56). One of those requirements is ampacity. Rather than establish ampacity based on a standard chart's temperature assumptions; account for your actual operating environment. Bus typically occupies the high-temperature area near the ceiling.
Once you've determined that area's maximum ambient temperature, factor in the specified temperature rise from no load to full load. For example, it's common for industrial bus duct specifications to limit ampacity to 1000A per sq in. of copper conductor. However, many brands of bus duct have current ratings based on 1800A per sq in. of copper; thus the temperature rise (from no load to full load) increases. If your bus duct run is long and operates at 1800A per sq in., you must accommodate voltage drop within the bus duct. Location. Many bus ducts installed in industrial and commercial facilities are immediately downstream of the transformers, but upstream of the main overcurrent device. Thus, transformer protection devices often inadequately protect the bus duct zone from fault. So, consider the value of extra protection with service conductor bus ducts. The extra up-front cost is nothing compared to the savings in downtime.
Allow for the space requirements and weight of the bus duct. You may need to change other components or select a different style of bus duct for your installation. One place to pay particular attention is at the transformer. Since torque forces can easily induce transformer-- bushing seal leaks, you want to prevent vertical loading on transformer bushings. To do so, ensure proper support for the vertical sections of the bus bars within the bus duct enclosure. Also, the air terminal chamber at the transformer must be of adequate structural design to assume the weight of the vertical bus duct as it terminates at the transformer end. Otherwise, the weight of the bus duct may bend the air terminal...