OTTAWA -- OC Transpo says the inclement weather over the weekend may be related to the trains losing power Saturday.

At least two trains, one at Tunney’s Pasture and one at uOttawa stalled and were out of service Saturday afternoon.

"The vehicles appear to be more prone to these failures during wet or inclement weather," OC Transpo General Manager John Manconi said in a memo.

“The trains have internal safety systems that monitor the flow of electricity and will automatically cut power using a rooftop high speed circuit breaker if required. When this happens, power to the vehicle is cut, and the train may come to a stop. This operates like a circuit breaker in your house.”

Late Monday, OC Transpo says the Tuesday commute is expected to have nine trains running for the morning and afternoon commutes. 13 trains would be full service at this point.

Supplemental bus service will also continue Tuesday. In the morning, dedicated buses will run downtown from Tunney's Pasture, Hurdman and Blair stations. The buses will run non-stop in the opposite direction for the afternoon rush. Similar to Monday, up to 50 trips will be cancelled during the morning peak, with 75 trips affected during the afternoon commute.

Rideau Transit Maintenance told CTV’s Christina Succi Saturday that one of the trains had an ‘electrical arcing issue’ which causes circuit breakers on the trains to trip.

The root cause of the issue is still not known.

“While the root cause of this issue is still under investigation by RTM, these incidents are the result of the train’s safety systems operating as designed,” said Manconi in his memo.

“When loss of power to the motors occurs, power for systems such as lighting and other onboard systems are still available.”

In a video posted to Twitter, sparks and a hazy substance that appeared to be smoke could be seen coming out of the roof of the train. Manconi said there was no safety hazard to passengers.

“Customers may hear a bang or see sparks where the train contacts the overhead power wires,” said Manconi.

“This may be startling but does not pose a risk to the safety of passengers in the train or on the platform. “

R1 replacement bus service was deployed Saturday between Parliament and St. Laurent stations, with full service restored later in the night.

Arcing is also to blame for the massive breakdown on New Year’s Eve.