Fluorescent lighting circuits, especially if equipped with the older
magnetic ballasts, are designed such that there isn't much room for wiring
errors, dirty lamps, low line voltage, poor connections or low temperatures.
What happens is that the ballasts can't supply enough voltage to start the
lamps under less than design conditions.

What isn't usually understood is that the metal of the lighting fixture is
part of the starting circuit. On such systems (known as rapid start
circuits), the lamp must be within a half inch or so of a piece of grounded
metal of certain minimum dimensions. It's called a "ground plane".
Usually, the metal of the lighting fixture handles the requirement; but if
the fixture isn't grounded or if the black and white wires feeding the
ballast are reversed somewhere in the circuit, the starting system doesn't
work as intended, the gas inside the lamp doesn't ionize and so the lamp
stays dark.

You can sometimes test to see if this is the problem simply by touching the
lamp. If it starts, the lamp is either dirty or there is a problem with the
starting circuit.

TKM



"Michael Muderick" wrote in message
news:k8D5h.1213$ZN1.362@trndny03...
SDB brings u p an interesting point. I was repairing a fixture in a
hallway with two identical circline fluorescent fixtures wired in
parallel. Couldn't get it to work. I reversed the black and white wire and
it works fine. Anyone know why?
mm


"sylvan butler" wrote in
message rnal...
On 16 Oct 2006 21:43:04 -0700, edgekaos wrote:
I"m trying to wire two dual 40w fluorescent light fixture in parallel
in a signal circuit and without success. Each fixture has two 40w tubes
and an electrical ballast. If I wire each one separatly then it'll
work. I gather the reason might be interference between the two
ballasts but I want to hear some expert opinon.

Odd.

What do you mean "without success" ?

So each ballast has a black wire and a white wire, and you hook the two
blacks together with the black supply, and the two whites together with
the white supply and one or both fixtures does not light? Or they
flicker?

Did you make certain to wire the ground securely?

Are both fixtures the same brand and style of ballast? If not, you
might risk reversing the leads from one of them, but really it should
not matter.

sdb

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