Junction Box (Electrical)
An enclosure providing accessible entry points for electrical cables, enabling circuit branching and connections within power systems.
A junction box is a protective enclosure—metallic or non-metallic—housing electrical cable connections and providing terminals for circuit branching. In transformer and switchgear installations, junction boxes route control wiring, monitoring signals, and auxiliary power.
For oil-immersed transformers, junction boxes mount on the tank wall for marshalling connections including tap changer motor drives, temperature sensors, and Buchholz relay circuits. They must maintain the enclosure IP rating against dust and water ingress.
Materials: painted carbon steel, stainless steel (coastal/corrosive), or GRP. Rated IP55/IP65 for outdoor use.
QDTB supplies purpose-designed junction boxes on all transformer and prefabricated substation products, pre-wired per project requirements. Contact us for custom configurations.
Related Terms
Marshalling Box
External enclosure housing transformer control wiring, terminals, and auxiliary circuits for substation connection.
Bushing
An insulated device allowing a conductor to pass through a grounded barrier while maintaining insulation integrity.
Current Transformer
An instrument transformer producing secondary current proportional to primary current, for measurement and protection.
More Terms Starting with “J”
Joule Heating (I²R Loss)
Heat generated in electrical conductors proportional to current squared times resistance, the dominant source of transformer load loss.
Joint Box (Transformer)
A sealed enclosure on transformer tanks providing access to internal winding connections and tap changer linkages.
IEEE C57.12.38
IEEE standard specifying requirements for pad-mounted, self-protected distribution transformers for North American markets.
More in “Components & Accessories”
Bushing
An insulated device allowing a conductor to pass through a grounded barrier while maintaining insulation integrity.
Busbar
A metallic strip conducting electricity within switchgear, transformers, and distribution equipment.
HV/LV Bushing
High-voltage and low-voltage insulated conduits for transformer winding connections through the grounded tank.
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