A backup generator arrives at Fisher Plaza.

Engineers will be performing maintenance at Fisher Plaza East in Seattle this weekend to resolve an unspecified "issue" with the interim generators that have been powering the big Internet hub since it was hit by a fire and electrical outage that took dozens of websites offline for hours earlier this month.

According to an email distributed by Adhost Internet LLC, one of the colocation providers at Fisher Plaza, the early morning operation will result in "reduced cooling capacity for two intervals during the window, up to 30 minutes each." This weekend is expected to be one of the hottest of the year in Seattle, but Adhost says the process isn't expected to interrupt power or impact the performance of servers.

Here's an excerpt from the Wednesday email sent by Adhost's chief technical officer, Michael Smith, to tenants of the facility.

Fisher Engineers will be performing maintenance on the power systems supporting the Adhost East Data Center.  This maintenance is addressing an issue we are having with the redundant generator set powering the Fisher East building.  During this window, the three central electrical risers will, one at a time, be powered off and re-engergized a short time later.

We do not anticipate that there will be any interruption to the electrical service to the Adhost East Data Center during this window. Adhost and its vendors have reviewed the potential impact to our operations of this procedure. The electrical systems that service the Adhost East Data Center technical loads will be able to transfer from one riser to the other in an uninterrupted fashion. 

Because our mechanical systems (AC) are tied into the risers differently, we will have reduced cooling capacity for two intervals during the window, up to 30 minutes each.  We anticipate that there may be brief periods where temperatures in the data center may increase, but we do not expect to reach temperature levels that will impact server performance. We will be fully staffed during this window to monitor all environmental systems and respond to any issues that may arise.

The email invites tenants to be on site during the process, and notes that Adhost has "been working with Fisher Engineering to develop a plan for restoring redundant, city-fed power to Plaza East." Earlier messages from Internap Network Services indicated that it could be months before that permanent solution is in place.

We've left a message for Smith seeking details on the issues affecting the generator set, and we'll update this post if we hear back.

Previous coverage: Photos: Inside the Fisher fire