Greg HN is Hall Node. The TAC 50-04 and TAC 32 hydro both use individual hall nodes for each hall station. This was an upgrade from the TAC 50 and TAC 20 line which used LON and had a single LN card for up to 8 floors. When the LN card went out, you lost a whole riser, when an HN goes haywire, you lose a single floor.
Let me know how that worked for ya, and if there is anything else you need bud.