Marshalling Box
External enclosure housing transformer control wiring, terminals, and auxiliary circuits for substation connection.
A marshalling box houses all control terminals, auxiliary circuits, and monitoring connections on the transformer tank. Interface between internal instruments and substation control.
Contains: tap changer control, temperature indicator contacts, Buchholz relay connections, oil level alarms, pressure relief contacts, cooling control, winding temperature connections.
Features: IP55 weatherproof, labeled terminals, DIN-rail blocks, internal lighting.
QDTB equips all power transformers with comprehensive marshalling boxes with premium terminal blocks.
Related Products
Related Terms
Buchholz Relay
A gas-actuated protective relay between transformer tank and conservator detecting internal faults by sensing gas accumulation.
Temperature Rise
The temperature increase of transformer components above ambient at rated load, a key design parameter.
Cooling Class (ONAN/ONAF/ODAF)
Standardized codes describing transformer cooling methods: O=Oil, N=Natural, A=Air, F=Forced, D=Directed flow.
More Terms Starting with “M”
Magnetic Core
The laminated silicon steel assembly providing a low-reluctance path for magnetic flux, backbone of transformer operation.
Magnetizing Current
The reactive component of no-load current establishing magnetic flux in the transformer core.
Moisture Content
The amount of water in transformer oil and solid insulation, critical for dielectric strength and insulation life.
Magnetic Flux
The total magnetic field passing through the transformer core cross-section, fundamental to electromagnetic energy transfer.
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.
Frequently Asked Questions
What is a marshalling box on a transformer?
A marshalling box is a weatherproof cabinet mounted on the transformer tank that collects the auxiliary and control circuits — tap changer, Buchholz relay, pressure relief, temperature sensors, current transformers and cooling fans — and terminates them on a single terminal strip. The substation then wires to one interface instead of to each device separately.
What is the difference between a marshalling box and a junction box?
A marshalling box is specific to power transformers and groups control, protection and monitoring circuits, usually with space for link terminals and test disconnects. A junction box is a general-purpose enclosure for cable branching, such as a cable branch box on a distribution network. Field terminology overlaps, but the role as the transformer's control interface is what defines a marshalling box.
What is normally wired inside a marshalling box?
Typical contents are tap changer control and position indication, Buchholz and pressure-relief alarm/trip contacts, winding and oil temperature sensors, current-transformer secondary circuits for protection and metering, cooling fan or pump control, and the box heater and thermostat. Wiring follows the project's protection scheme and is tested before dispatch.
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