Recently an electric utility asked us, the manufacturer, to investigate a possible "blast" wherein an event occured inside an electrical motor drive/enclosure. The event "blast" hurled the enclosure's hinged door approximately 20 meters and the inner, twin, doors about half that distance. The enclosure measures approximately 100cm high, X 60cm wide X 30cm deep. All sides of the enclosure were visibly deformed, but intact. Note, the enclosure is extremely robust, manufactured from cast aluminium alloy and designed for 40+ years service. This enclosure in subject to the maximum fault current available in an electric utility substation with only several feet of wire between the transformer secondary and the enclosure's circuitry. Applied voltage is 240VAC. There are no batteries located in or near the enclosure. To the best of our knowledge, there are no sources inside the enclosure that could generate explosive gasses.

The utility reports that the device was energized, but, not in service at the time of the event. There were no personel near the device immediately prior nor during the event.

What is unique is that there is no evidence of arcing nor even a component failure in, or outside the enclosure. There is no carbon residue inside nor near the enclosure.

Do any of the forum members have suggestions as to what could have caused this type of event?

Sounds suspect to me. Isn't blast pressure from either metal vaporizing and/or superheated air? I know you thought there were no gasses internally generated but was this a classified area and some gasses entered the enclosure via conduit or other means?

External Gasses



I have looked at the customer supplied photos once again - there is a single conduit that makes a "U" from the bottom of the enclosure and terminating at an adjacent, parallel, control-cabinet. There are no other orifices to the enclosure. The adjacent control-cabinet details are not visible in any of the photographs; however, I am able to see the conduit entrance to the Control-cabinet. There is not visible stress to that conduit connector.

Yes, this is a typical "classified" location with limited restricted access. It is a typical outdoor electric utility substation. The enclosure's door was not pad-locked closed.

Classified as in Class I Division 2 or Class II Division 1?
What was the classification (which could help identify the gas, if it's a gas)?

Classified Location



My mistake - I was looking at access restrictions. This is NOT a hazardous location, "...where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, combustible dust, or ignitable fibers or flyings."

This is a simple large power, high voltage substation. The enclosure is located outside "in the yard" and NOT near the substation control house. It is mounted well away from the station battery-bank.

Poltergeist - the only explanation.

If this is what I think you may be referring too, while likely an extreme stretch... is there a possibility of CT wiring nearby?