LX bars could mean a number of things to me at least. Could mean the pipe that fixtures are hung on, or a lamp bar that has fixtures permanently mounted to it and wired to it, and that bar gets wired often to a
multi-cable fitting so as to
power up all individually.
Both often have a similar concept in what’s a grounded
fixture is a grounded pipe. Not such a good concept by way of loose bolts, paint
blocking conductance and other stuff - path of least resistance could be you.
In the past and of un-grounded systems, one might find these very questionable load rated isolator rigging balls rigged in the fly
system somewhere between the pipe and cables supporting it. Such isolator balls had no other purpose than isolating the
wire rope of the fly
system from any shorts now applied and welding it together in an un-safe way. You won’t find such things on the market these days - defiant doubtful load
rating by way of how often they need replacement much less what their actual load
rating was. Anyone else seen such things on a fly
system - sort of like a swivel with a 3" ball of material between eyelets?
Anyway, these days, on a fly
system at least, it’s code and or good practice that the electrical
drop box or gutter is mechanically by way of the box if not the pipe also grounded - this as with on a static
grid and or pipe that it’s also grounded supplemental to any
fixture grounding practice.
In a lamp bar, that’s a different thing. This concept of a pipe with fixtures semi-permanently mounted to it only requires one
safety cable given it’s now one
unit - often of four or six fixtures, which are assumed not in concept of
safety in ability to come loose due to improper mounting. One
safety cable per lamp bar is sufficient.
Lamp bars are fraught with design issues - both the code compliant ones and those more home made. Defiantly not something to be having students make without direct supervision. All realistically if they have conductors or splices within, should be properly grounded and not rely upon fixtures mounted to them to do so. Imagine if one will you have a six
circuit lamp bar and a pig-tail attached to it. Pig-tail meaning
fan-in or series of plugs attached to say a multi-pin
plug which the bar accepts. In any case of the six circuits, you have only #1 plugged in and with lamp working, #6 is also plugged in but it’s lamp is not and somewhere in the cable feeding #6, there is a short. It’s a question of resistance to
ground if you in touching the bar are a better path to
ground than what bolting method #1 has to the
yoke, than
yoke to
ground screw and
wire. Lots of ways one can find a un-grounded or high resistance short within a lamp bar. Best to
ground the lamp bar itself given this.
Ground everything in fact.
Get the idea here of wee problems in grounding a lamp bar proper? This beyond it being against code to have a
fixture supporting bar that also has
current carrying cable running
thru it. Against code in reality to do a pipe that both bolts fixtures to the bar and has those bolts passing by the conductors feeding the fixtures. Gee, all it takes is one
conductor nicked by a
bolt... makes sense. TMB to the best of my knowledge is the only company that has a compartmentalized lamp bar and they use a
Unistrut system which is also not so good by way of how them bolts secure in a permanent = not able to come loose sort of way. This short of threaded stud
Unistrut nuts and side lock nuts as a theory but not much of a ½ twist to be loose and falling concept. The TMB bar complies as most don’t with the
NEC in separate pathway for conductors than support of
fixture, but doesn’t by way of each individual
fixture being a part of the bar and unique. Were it my choice, each
fixture on such a bar would require a
safety cable. Given it is my choice... this might become the case.
None the less, conductors feeding the bar - bad thing when
thru bolting the bar to a more safely rigged
fixture yoke. This given good
crimping and splicing.
Leko department normally takes care of all them bars that in the past or in the field had someone using an other than
insulation displacement
crimp tool on the crimps of a lamp bar. Smashing the
crimp only holds conductors as long as they maintain their original shape while being smashed into conducting. Vibration and heat tend to make
wire move about and or move under expansion thus
settle. This causes resistance thus melting and or wires coming loose from a
crimp especially if the
fixture cable were twisted about a
yoke and attempering to make that
yoke twist just a
bit more, made the
fixture whip pull free from it’s
crimp. Ah’ good crimps, both a question of proper
crimp pressure and
insulation displacement tool as opposed to
insulation crushing tool.
None the less, all lamp bars if proper
fixture in one unit should be grounded but it’s a grey area. I
ground my lamp bars - but only those I re-wire in having insulated the bolts from the conductors. It’s a concept in terminating all circuits of
fixture ground to the pipe, than taking that in common
ground of the pipe to the cable or
plug that feeds that pipe so all lights are in common grounded and the pipe is also specifically grounded to all circuits.
Finally on the subject of “black” black oxide coated bolts don’t conduct well. If relying upon a black oxide coated
bolt such as on a
C-Clamp, try not to there is resistance to factor in.