About 20,000 Maui Electric Co. customers lost power today when two generating units at the Maalaea Power Plant tripped offline at 1:37 p.m., the utility said.

The outage affected Pukalani, Makawao, Kula, Waiehu, Spreckelsville, Napili, Mahinahina, parts of Kahului, and Haiku as far as Hana town.

About 80 percent of the customers had power restored by 3:45 p.m., the company said. Parts of Haiku, Makawao, Kula and Mahinahina remained without power.

When the generating units went offline, the sudden loss of power triggered a “load shed” which is a safety measure that protects the electrical system and prevents a longer, more widespread outage, the company said.

Muai Electric said it was in the process of bringing up additional generating capacity at the power plant so it could restore power to the remaining areas.