@garyvp I can tell you from first hand experience it's . . . . . . . "interesting / relieving / richly rewarding when you eventually hunt it down to within a junction box above a very expensively finished ceiling."Agree with Bill C . - You brought up the local switch in connection with a fixture that can be turned on and off normally but fed by two circuits. The whole two-circuit cause has to be before the switch, in this case the dimmer. It seems highly improbable in an SCR dimmer cabinet (as stated NSI Architectural dimmer from 20 years ago) that the dimmer feed and branch breakers could be off and still being fed by two circuits; and since it does dim normally it can't be fed by a secondcircuit after the dimmer.
And Ron - if you remove the front cover from a live breaker panel and meter the actual output terminals of the breakers themselves, you may expect to find voltage while a given breaker is switched on and you MAY expect to see the voltage fall to zero upon switching off the breaker. Some people will suspect a fault within thebreaker if the voltage remains present when the breaker is switched off when what they MAY in actuality be measuring is a combination of the voltage being supplied by the breaker coupled with voltage being back-fed to thebreaker's output terminal while it's switched on and the voltage being back-fed remaining on the output terminalwhen the breaker's switched off. This strongly points to an an inadvertent cross connection between load circuits from the same leg / phase amongst the circuits.
Wow....a good one. I would love to be there with my testers and hunt this one down.
Can't wait to hear what the problem really is.
Here's another puzzler for you:
There was / is a fairly spendy Crestron installation in the heart of downtown Toronto installed by one of the larger [All things to all people] factory authorized Crestron contractors.
I'll skip over the uglier legal aspects of "somebody else's problem" and proceed directly to my point.
A friend of many years became a then comparatively recently factory authorized Crestron dealer.
While making an exploratory site visit prior to bidding a new project within a building, he was asked would he mind looking at an existing installation elsewhere within the same building. The system's owners rep' led us to a small room containing a quite large collection of various Crestron modules, invited us to sniff the air then pointed to two modules which were the 'outcasts' from two previous visits by their then under contract maintenance company. Apparently a specific module had smoked and charred itself to death and was systematically, and symptomatically, replaced only to be found charred and in need of a third replacement. One factory original module next to its two replacements in two weeks with a third replacement / fourth module presently charred and dead within the rack enclosure. Crestron's anything but an upstart inexperienced company building to a low price point.
Quite the opposite. They've been charging top dollar for top tier gear for quite some years and definitely have a handle on what they're doing.
At some point, you'd think someone would've stepped back and figured they were treating the symptoms but not the actual root problem at hand. Here's the crux of the problem and it most emphatically wasn't Crestron's modules but careless installation of load circuit wiring external to the rack. When I tracked down the problem I felt honor bound to report it to Crestron but as the owners were contemplating legal action against their installation and maintenance contractors, my immediate supervisor suggested I keep my mouth shut and bask in the glory of having analysed the root problem. A few months later, I cold-called Crestron attempting to report my discovery and suggest they might keep their eyes open for a less than obvious loop-hole which could prove problematic in some cases of faulty mis-installations. If you've ever cold-called a company like Crestron and tried to suggest there's the tiniest of 'flies in their ointment' AND you're just some bozo they don't know calling from Canada . . . well . . . frankly they don't want to hear from you, they're so sure of themselves and their rigorously tested and approved products, it's beyond their comprehension that any bozo from the boonies could possibly have discovered any flaws. The fellow tersely explained ALL service was to be carried out EXCLUSIVELY by factory authorized technicians, which I personally clearly wasn't, and was about to hang up when I said: "Sorry! I thought you may want to learn of a potential fire hazard with one of your modules that a factory authorized tech' has routinely replaced twice in two weeks." Suddenly he was interested in hearing from me and noted my discovery.
Here's the bottom line:
In this series of dimmer modules, they offered the following amongst a great many others:
Modules that supply 120 VAC loads with 10 VDC contol.
Modules that supply 120 VAC loads with 120 VAC control.
208 VAC / proprietary control
Incandescent loads
Fluorescent loads
LED loads
You've got the notion, the range ran the gamut.
If you're supplying 120 VAC fluorescent loads with old fashioned dimmable magnetic ballasts employing 120 VAC control
AND an IBEW brother inadvertently confuses a black wire with a brown wire within a dimly illuminated junction box above a dimly lit ceiling during the 'rough-in' stage long before the Crestron rack arrives on site let alone before the installation's commissioning, you can end up with one poor little TRIAC suitably over-rated at perhaps an amp and anticipating being called upon to control perhaps 500 mill's, finding itself being called upon to control perhaps 5 of its 6 ballasts AND the full load current for its 6th fixture.
The clues to tracking it down:
The module was protected by let's say a 10 amp breaker supplying its input.
A higher rated TRIAC was employed to switch the steady-state mains power ON or OFF.
The lower rated TRIAC was only intended to provide the 120 VAC dimmed voltage for the ballasts' control winding.
When you supply both TRIAC's via the same 10 amp breaker, do not include lower on-board protection for the lesser rated TRIAC AND an installing "brother" inadvertently miss-identifies a black jacketed wire with a brown, you can keep right on smoking and charring poor little smoldering TRIAC's to death essentially as quickly as you're able to order and replace them.
To their credit: Crestron's boards were of excellent quality showing little damage considering the abuse they'd been suffering.
Have we communicated @garyvp? I suspect so and possibly you might explain this to the majority of our other posters.
It took some creative sleuthing to determine which fixture's dimmable ballast was cross-connected and the visible clue lay in which fixture would snap on vs. which would ramp up as if being supplied from a dimmer rather than what was essentially a non-dim.
Toodleoo!
Ron Hebbard.
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