John Owen on the Sinai Covenant

Part III: Anthropology (Man) and Covenant Theology
Chapter 18 - John Owen on Sinai

Owen's view on this can't be categorized so easily.  He didn't see Sinai simply as another administration of the covenant of grace, or as a distinct law covenant subservient to it.

The old covenant spoken of in Hebrews 8 is not Adam's covenant of works, but the redeclaration of the moral commands from that, at Sinai.
The new covenant spoken of in Hebrews 8 only takes effect formally at the death of Christ, so is not synonymous with the covenant of grace administered from Genesis 3:15 onward.
The promises of the covenant of grace were in effect during Moses, but the Sinai covenant did not bring "reconciliation with God nor salvation" (299).  It is added for our sins (Gal 3:19-24), bringing up the futile promise of life and certain curse of death on our way because of them.  But this points us ahead to Christ's work.  So, even though it has some positive aspects (established worship, civil and church government, pictured heaven in Canaan), it is a negative overall compared with the new covenant.

Owen's main concern was exegetical - doing justice to 2 Corinthians 3:6-9; Galatians 4:24-26; Hebrews 7:22; 8:6; 9:15-20.  He could write that there are two covenants we are wrapped up in: Adam and Christ.  But also that the Sinai covenant wasn't synonymous with the covenant of works or the covenant of grace.  Neither was the new covenant (Christ's obedience and death) synonymous with the covenant of grace.  So there are at least 4 covenants/testaments to deal with, that overlap in complex ways.

Owen's view can't be easily dismissed, though it differs with the Westminster majority, given his careful exegetical motivation.