Initial thoughts - were talking about
DMM’s but have not mentioned true
RMS DMM’’s that should correct for this misleading
voltage thing possibly due to the lamp warming
current of the dimmers at least in part - though a good analogue
meter also has its uses in addition to a True
RMS meter.
That said... stop using the light and stop testing. If someone was shocked even by way of a high resistance or low
voltage shock as described, it is still a lighting
fixture that should not be used due to a short which could become worse due to use or heat in resistance due to that short breaking down what is left of the
insulation. Someone changing a lamp while at full
voltage could kill or lead to huge liability issues after reported. You don't want to continue using this light or testing it.
That or on an un-polorized
plug, if plugged in the wrong way, your hot is now the
screw shell of the lamp and its possible it is contacting the
reflector for the short - beyond internal wiring or
cord grip breakdowns. Also in making live the
screw shell to the lamp/lamp
base, if someone were to touch that screw or
base while screwing in a lamp they would get shocked beyond should the
socket be un-insulated or broken and it were touching the
reflector. They are also getting electrocuted in this way as a possible how this was reported.
The lamp warming
voltage given off on a
dimmer is enough to feel this "short" how ever it was caused and luckily not enough to harm someone if the
trim voltage is correct. Or it could be a high resistance short in touching the frame and being a better
ground than the lighting
grid. Literally your fly
system/lighting
grid is now the
neutral/
ground most likely in at least part for this lighting
instrument and it's not good for the
wire rope or any part of the
grid.
That plus the
asbestos.
In metering, I note you are doing frame to a
ground of some type of
ground found and also to the ladder in theory you are standing on... Aluminum ladders shouldn’’t be used for lighting, wood
deck/rubber feet if of a certain moisture contact can conduct a path to
ground etc. Stop metering it in the air at least because should while meterring it out you slip and both grab shorted light and another pipe in the
grid that would be a better path to
ground... That short just traveled between your arms by way of your heart and you can die! Again stop testing this,
power off and
drop the
fixture until replaced or safe to use.
Might have been as simple as a reversed un-polarized
plug that someone touched the hot
screw shell to while in lamp warmer mode, could be
screw shell touching
reflector or any number of things. No way to tell in the air safely and given there is a problem detected, the
fixture isn’’t serviceable or safe -
drop it and have it repaired or replace it. Start with that one and the rest should also get a proper look at.
Yes there is ways to test what’’s up further while still in the air, I don’’t think I would be up on an aluminum ladder trying to troubleshoot them short of
breaker off and even there enough has been described to pull the
fixture anyway.
Side but related story..
I now own a c.1911 Chicago Cinema Equipment 4.5" PC floodlight
fixture that was once the pin-rail spot for lighting it badly at a theater I worked at. Wasn’t the original crows’s
foot (Not normal
Edison)
porcelain sort of straight blade
plug found elsewhere but instead was a Mini un-polorized
twist lock plug that’s non-Nema in even the ML 1 series.
Plugged it in backwards at one
point I suppose in moving it over some I suppose (didn’t re-wire it yet.) Went to
bend a piece of ½" Sch. 40 for drape weight to
bend around the end some and I got sparks on my fly
rail once I touched one part of it to another. Don’t think I got shocked, instead the pipe protector for the
grid to the
grid now linked by way of this pipe being bent was a better path of least resistance somehow.
The hot was now the
neutral apparently for polarization of the lamp
socket and something was shorted there. All was fine as long as the hot were plugged in correctly at the
plug in path of least resistance, reverse the
plug and that wiring problem became a problem in electrifying basically the pipe the light was mounted on as per a higher resistance short to
ground than that of the
neutral. Or I could be reversed of this in concept. Protector for the pin
rail this pipe assembly was not connected to the pin-rail assembly. Once you linked the two together, they would spark if plugged in backwards on a wood floor
etc...
Old timer was fine with all of this - that was how it was done in the non-grounded and un-polarized days, just reverse the
plug and move on. I did install a properly wired
index light over the pin
rail before I left it. This
fixture went into their bone yard that I years later bought and added to the museum in making safe.
Strip lights are not nice or fun lights to work on in having worked on lots of them over the years. Lots of types out there in the un-polorized type... re-porcelaining 1928 era reflectors is really messy amongst other types and problems with getting certain lamps for them. Total service
call of the
fixture is necessary and probably cheaper to replace it with something more modern. That an no museums are looking for strip lights for their collections I think at this
point.
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