Lighting Forum QOTW (11/6/09)

[icewolf08]

You have a chandelier that came internally wired with 18/2 lamp cord. There are two 120v candelabra base lamps on each of 10 "arms" of the chandelier. The bases on each arm are wired together (in parallel) and then all of the arms are are paralleled together at the hub to a single piece of 18/2 lamp cord that runs up the center hub of the chandelier to a non-polarized edison connector. Using a properly wired edison to stage pin adapter, why when plugged in one way, the chandelier lights fine, but when you reverse the polarity of the connection it trips the dimmer?

[fredthe]

Can we presume the chandelier is mounted on something that's grounded?

-Fred

[icewolf08]

The chandelier is hung from a standard batten connected to a grounded dimmed circuit.

[ship]

Originally Posted by icewolf08

The chandelier is hung from a standard batten connected to a grounded dimmed circuit.

could it be a short to ground on the neutrial wire? path of least resistance on the load side following the lamps most likely will not trip the breaker. thus hot incoming to center contact of the lamp sockets as it should be so you dont get shocked while changing lamps works fine or with a higher resistance voltage leak but with the resistance of the lamps preventing too much current flow in tripping the breaker. seems to work fine but still could be some or even all voltage going thru ground dependant on what neutral or ground or what % of each is less resistant. reverse this as incorrectly wired in feeding the screw part of the base anyway and you now have your hot line in to path of least resistance short to ground which is less resistant to current flow than current in going thru the lamps.

on the other hand, it could be a short on the hot also in situation the same but reversed in working while feeding the neutral part of the sockets the hot line and the center contact having a short but one that is higher resistance than the normal neutral return path pe above.

esy enough to troubleshoot and wire properly once the problem is solved. touch one probe to frame, the other to screw shell of base. get a beep, it means a short, if not frame to center contact would most likely have the short. while there with the multi-meter, meter center contact to the wire feeding it. there is no reversing plugs on screw based lamps, one way is correct, the other dangerous when changing lamps if power on. a hint also is that by code, the neutral wire is ribbed which normally leaves the hot to be the one with writing on it.

(forgive my typing - one hand in a cast.)

[rmarston]

Since the chandelier operates OK when plugged one way and trips a 20A CB when the plug is reversed, there is a path from line to neutral when the plug is reversed. From the setup description it appears that the chandelier frame is connected to building ground through the batten it is hung from.
So - somewhere in the chandelier wiring there is a short from one side of the parallel lamp wiring to the candelier frame. This would create a line to neutral short through the building or safety ground wiring when plugged one way. When the plug is reversed the fault connection is still there - it's just connected neutral to building ground which will operate OK.
It's a safety issue, obviously since the building or safety ground circuit is now carrying neutral current.

[derekleffew]

I believe rmarston's explanation is precisely why non-polarized plugs are only permitted today on double-insulated devices (such as my Apple laptop's power supply, without AC cord; and most wall-warts).

Those in the event decor industry should remember this thread when using Add-A-Taps.

[n1ist]

Depending on the type of sockets, you may be missing the fish paper that insulates the shell from the housing. Alternatively, there's a short on the neutral somewhere; I'd guess either a burr on one of the arms has nicked the insulation, or there's a single strand sticking out of a wire nut or splice.
/mike

[JChenault]

Of course this thread points out why hemp houses were far superior to those newfangled counterweight systems. In a hemp house your chandelier would not be grounded and, as long as you don't have another fixture on the pipe with a similar problem, you would never have an issue.

Perhaps we should start a movement to get rid of all of those computer controlled lighting systems and just go back to salt water dimmers. The old stuff never had an issue with fans getting clogged with dust.