PLEASANTON -- Power to all but 49 customers was restored after an underground equipment failure left about 3,800 customers in the city without electricity Wednesday morning, a PG&E spokeswoman said.

Crews were still investigating what caused equipment to fail at 3:45 a.m., spokeswoman Tamar Sarkissian said. At its height, the outage affected 3,821 customers, according to PG&E's outage map.

All but 49 were back up and running as of noon, Sarkissian said.

It was not known how long it would take to restore power to those remaining customers, Sarkissian said.

The location of the equipment failure initially was thought to be near Delucchi Park at East Angela and First streets, but crews later determined that it was at Hearst Drive about 150 feet east of Brunell Avenue, Sarkissian said. The cause of the outage appears to be the failure of an electrical splice, which is where two wires conjoin.

Check back for more details.

Contact Rick Hurd at 925-945-4789 and follow him at Twitter.com/3rdERH.