What is Marshalling Box in Transformer and why it used.

Marshalling Box

A sheet, steel weatherproof marshalling box of IP-55 construction shall be provided. The box shall contain all auxiliary devices except those which must be located directly on the transformer. All terminal blocks for external cable connections shall be located in this box.

The marshalling box shall have the following but not limited to them:

a)         Load disconnect switch for incoming power supply for auxiliaries.

b)         AUTO-MANUAL selector switch and Local/Remote switch for OLTC

c)         Wiring and termination individually of the following alarm contacts for remote trip and alarm.

-        Buchholz relay alarm for main tank (For conservator type).

-        Buchholz/oil surge relay alarm for OLTC.

-        Winding temperature high alarm.

-        Oil temperature high alarm.

-        Tank oil level low alarm.

-        OLTC oil level low alarm.

-        Tap change incomplete alarm.

d)         Wiring and termination individually of the following trip contact for remote trip and trip alarm.

-        Winding temperature high trip.

-        Oil temperature high trip.

-        Buchholz relay trip or sudden gas and sudden oil pressure relay trip.

-        Pressure relief device.

Cubicle illumination lamp with door switch and space heater with thermostat and ON-OFF switch shall be provided.


    Marshaling box shall conform to all requirements as given in technical specification for LT Switchgear & DB. The    wiring diagram for the interconnection of three phase instrument transformer shall be pasted inside the box in such a manner so that it is visible and it does not deteriorate with time. Terminal blocks in the marshaling box shall have facility for star/delta formation, short circuiting and grounding of secondary terminals. The box shall have enough terminals to wire all control circuits plus 20 spare terminals.

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