What's behind those explosion sounds near Sydney?

The explosive sounds around the Northside area of Cape Breton have been compared to claps of thunder, fireworks or the noise made when a dump truck tailgate comes crashing down.

But the loud bangs are actually related to the installation of a new transmission line that will meet the Maritime Link where it comes ashore in Point Aconi and transmit electricity 48 kilometres to the Woodbine substation southwest of Sydney.

Emera Inc., whose subsidiary NSP Maritime Link owns the Maritime Link, has been contacting people near the blasts to let them know it's only part of the building process, according to Phil Stevens, the director of operations for Emera Utility Services.

Detonation fuses wires

The transmission line construction involves connecting a series of 2.5-kilometre-long conductor wires, which are about as thick as a small pop bottle.

Two ends are joined by placing them in a 60-centimetre-long "implosive sleeve." But since it's not a perfect connection, a further step has to be taken.

"A small implosive charge is in the middle of the sleeve, and there'll be a detonator on it," Stevens said.

Once everyone has moved a safe distance back, the person in charge of controlling the site, known as a master blaster, takes over.

"We sound an air horn, three air horn blasts, then we wait approximately 60 seconds, and then we detonate the sleeve, the implosive charge, and that's what fuses the wires together," Stevens said.

After that, crews continue to reel out the wire to the next juncture where they will repeat the process, he said.

Detonations almost complete

Last week, workers began installing the Maritime Link itself, slowly unraveling 170 kilometres of subsea cable that will sit on the bottom of the Cabot Strait between Nova Scotia and Newfoundland. The cable will bring electricity from Labrador's Muskrat Falls hydroelectricity project to Nova Scotia.

Stevens said the construction of the transmission line on Cape Breton is quite far along.

"We did our first detonation in February. We're 80 percent complete."

He said Emera is continuing to notify people in a three-kilometre radius, including farmers whose animals may be spooked by the explosions, before the blasting is done.