I can personally tell you of such an experience when doing something stupid, in having to with great effort
release the
conduit and copper now melting into my palms while the
stage lights in another room brown out all about breakers not
tripping.... Not fun.
Back to the concept of the 14ga
twofer... I remember sufficiently this being a taught technique at one
point - don't remember if passed on technique or
book learned. As stated, safe enough for most applications when supervised of a splitted load equalling less than 2.4Kw or in this case 2,000 Watts which is where this thing came from. By todays standards in having learned better, such a
twofer does not sufficiently idiot proof the
system as is the case in most systems having problems and what
current standards reflect. The 14ga
twofer assumes one is not say putting anything over 1,800 Watts such as 2Kw on one
leg and even nothing to up to 600w on the other
circuit in the
breaker (assuming it is in good condition) safely handling the load. On the other
hand the
wire feeding the
twofer in not being able to handle the
current would be the weak link and might or might not even cause the
breaker to trip before having a situation like what is presented in the Q' of the Day with the
panel mount that melted down. Possibly in that case also a bad
circuit breaker to look at in addition to what the problem at the
panel mount is.
None the less, one could say put 2Kw on one
leg of a
twofer, and 400w on the other
leg of it and not expect a
breaker to trip. Given that, the cable would melt down without any protection. Thus the concept of very supervised use or better yet removing from your inventory.
Is it possible that three of the above four lamps were tapped off one
leg of the
twofer? You note the
twofer(s) are in excellent condition that leads one to believe this is not the case, but on the other
hand given
voltage drop and longer twofers, weaker connections in the
system and smaller
gauge wire in use, such a thing could add up to a
circuit breaker tripping also - as a theory. One
leg at 1,500w, smaller
gauge cable, loose connections (any number of reasons) and long cable and even
conduit runs. That means
voltage drop and while it should be appairent at the
twofer, if the
breaker really is good it could mean the
breaker is doing its job before something in the
system melted down.
This much less the concept of hot patching - plugging lamps into live circuits could defeat the warm up/high
inrush current dismissal.
Lots of things, and something for someone highly trained and on site to reproduce and check out in finding the cause before there is other problems.
You might also just have a fussy
breaker! These things are not magic, they have a range to their tolerance, and sometime
shift way out of range after a few years.
Thermal breakers also can trip due to heat caused by oxidation of the contacts inside them. A three second
fade up rules out inrush. I have autopsied many old
circuit breakers, and believe me, it leaves you with an insecure feeling after seeing what's inside them! Remember Federal
Pacific? Many places burned down due to the fact that their breakers had a habit of jamming in the on position, quite literally allowing the full pole
current to travel to the load. (If you don't remember, just google the words: federal
pacific fire) Most times, luckily, breakers are likely to false trip at a low load.