Main breaker needed for subpanel????

No.

hvacrmedic

Well, the panel has space for 8 20A breakers but only 6 are filled. So, sounds like I satisfy the rule, right?

That's a "service panel" that has to have 6 or less switches (and a 2 pole breaker with the handles tied counts as only 1.) I don't think there's any such requirement for a subpanel -- unless it is located in a separate building (in which case it's treated like a service panel)

Bob

The "6 handle rule" basicly says that no more than 6 hand motions shall be required to disconnect power to a building, or occupancy.

The 6 handles may be fused disconnects or circuit breakers rated at 30 amps or greater. Fire pump, and emergency lighting supplied as separate services are excluded from the 6 handle count.

Subpanels must be protected by overcurrent protection not greater than the rating of the subpanel.

Feeders must be protected by overcurrent protection not greater than the capacity of the feeder.

If the overcurrent protection on the feeder is less than or equal to the subpanel capacity, then no additional protection is required at the subpanel.

In the original example, the 200amp service disconnect would be sufficient for the 200amp feeder supplying the 200amp subpanel, and no additional breaker would be required at the 200amp subpanel.

The same would apply to the 100amp feeder to the 100amp subpanel, which would be protected by the 100amp breaker in the 200amp subpanel.

If the 200 amp feeder supplied 100amp subpanel(s), then 100amp breakers would be required to protect each subpanel.