The Briton started last year's race on pole position, but McLaren have been off the pace this season and are currently third overall behind Mercedes and Ferrari.
Norris said: "We know it's better to take the penalty here than in Hungary or Zandvoort. I hope it's not the end of my weekend before it starts. I'm still confident we can have a good weekend.
"It won't be made easier by the grid penalty. We have been unlucky so far in losing different bits, the engine, the power unit or the controls.
"And I'm on the backfoot in terms of a spare parts point of view (for the rest of the season) but that is out of my hands. That's life, and you've got to take it on the chin."
Drivers are allowed three power electronics units per season and the change exceeds the limit, triggering the mandatory penalty.
McLaren said the first unit suffered a terminal failure in China in March, leaving Norris unable to start that race.
His teammate, Australian Oscar Piastri, also suffered engine problems and didn't start in Shanghai.
The second unit was fitted for the Japanese Grand Prix, also in March, but had to be withdrawn for remedial work after issues in free practice.
It was repaired but then suffered a terminal issue in Monaco practice in June.
"While the power electronics unit we installed in Japan, and have used in every session since Miami, has worked reliably, Mercedes-AMG High Performance Powertrains has since introduced a series of reliability fixes," the team said in the lead-up to Sunday's Belgian GP.
"However, in order to take advantage of these improvements, we must incur a 10-place grid penalty on Lando's car in order to take a new unit.
"We have chosen to do this in Belgium, a circuit where overtaking is relatively more prevalent, as opposed to the following two events in Hungary and Zandvoort (Netherlands).''
McLaren said they planned to use this fourth unit for the rest of the season.
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