No-one was injured but the building was left with substantial damage.
Two fire engines from Lisnaskea arrived on the scene at 6.49pm and had dealt with the "well developed" fire by 8.46pm.
Station Commander Tim Richmond told UTV their efforts were made more difficult by the high level of electricity and the mountainous surroundings.
"We were unable to fight the fire initially because of the level of electricity in the area, as this carries 33,000 volts," he said.
Specialists isolated the cabinet and Northern Ireland Electricity turned off the power so that the fire fighting could begin.
Tim Richmond, NIFRS
"It was very difficult to tackle because of the location, because the substation is based on the side of a mountain and it was very windy, giving rise to letting the fire accelerate faster than normal, and also the amount of electricity involved."
Police believe the fire was started deliberately at some time between 6pm and 7pm.
It appears to come as the latest in a series of attacks targeting the Quinn Group since former billionaire businessman Sean Quinn was removed from the business.
Anyone with information on the incident has been asked to come forward.
The Quinn businesses once employed 7,000 people on both sides of the border, but earlier this year Mr Quinn, his son Sean Quinn Jr and nephew Peter Darragh Quinn were found in contempt of court for hiding millions of Euros in assets from the former Anglo Irish Bank.
Sean Quinn, who is 66 years old, was jailed for nine weeks in Dublin's High Court.
Workers at Quinn Group factories in Northern Ireland and the Republic staged a one-day walk out on Monday in support of their former boss.
Protesters used tractors and other agricultural vehicles to block the entrances of the cement and glass plants in the Derrylin and Ballyconnell areas of Co Fermanagh and Co Cavan.
They want immediate mediation between the former Anglo Irish Bank and the Quinn family over the long running debt row which resulted in the imprisonment of the fallen tycoon - and are also demanding his release of Quinn, while the talks take place.