I find tie wire far superior to even the best quality tie wraps
for supporting bx to chain. I use mostly aircraft cable
for hanging fixtures and tie wraps simply don't work as well for this
and they are combustible.
Regarding the stranded wire issue, cables such as cab tire
may not conform to building codes as far as being combustible etc so
they are only tolerated in very short lengths in non combustible buildings.
Does anyone know if there is a flexible cable that is approved for this
application. I notice that fluorescent fixtures meant to be cable hung come with a piece of white cable that looks far better than an ugly piece of bx.
I think that movement of a hanging fixture is rare so solid wire is suitable
and trying to find a code rule that prohibits it is counter productive in real
practise but reasonable for discussion.
I hope there are no inspectors who would actually reject this practise.
I regularly reject the use of Ty wire as you describe. It might hold the BX neatly but the use of Ty wire is completely at the discretion of the electrical inspector and my tolerance is limited to use inside of steel stud walls. Straps inside walls are more to prevent the accidental insertion of screws or pinching of the wire between board and studs. Also to provide some pull out protection at the connector.
Ty wire is ubiquitous and I have seen some jurisdictions that do not permit any use of Ty wire except in concrete.
Ty wraps are another matter. Unlike straps for bx or EMT they don't have an encompassing listing of the wires and cables for which they are approved. IE 1 to X #14-2 or cables with diameter of X.
Ty wraps are approved for load, and environment. They are general purpose straps for use on cables and wires.
The problem for most inspectors is almost all components of an electrical installation are approved for a specific purpose and Ty raps are approved for general purpose.
The other issue for an inspector is it is a lot easier to insist the contractor use a strap approved for strapping bx rather than a 1/4" Ty rap which might or might not be adequate for the load imposed upon it or the environment it is installed.
Ty wire also presents the same dilemma except the inspector has no data at all as to the load capability. There is no control over how tight it can be wound up. There is no control over bundle size, there is no ability for an inspector to see if the installer over tightened the wire and if it is nearly at the breaking point. there is no way to tell if the armour has been damaged or the internal wires compressed either.
Some of these things apply to Ty wraps but a Ty wrap does have a consistent length and even tightening limit. There is specific data as to yield strength and load capability etc.
As for the use of BX in pendant and chain hung applications?? I spoke to my supervisor as we have both leaned about 30-406 as a result of this discussion. Unless there is intentional movement between the building and the fixture I doubt we will ever reject an installation where the fixtures only move as a result of accidental contact or seismic event.