Fluorescent Light Fixture Installation and Repair Q&A
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My question is on wiring a florescent light fixture. I purchased six
florescent shop lights which I intended to install in a new workshop I recently
built. When I opened the shop lights I discovered that they had standard three
prong plugs. Since I wanted to direct-wire these lights to come on with a wall
switch I decided to cut the plug off. After cutting the plug off I discovered
that there was no way to determine which wire is which except that the ground
wire was green.
Does it matter which of the other two wires goes to the hot wire or can
they be wired either way?
Yes, it does matter. By switching the ground, hot, and
neutral wires you may inadvertently produce an electrocution hazard in the metal
frame of the fluorescent fixture. You will have to remove the cover on the
fixture that hides the ballast and determine which wire in the cord is hot.
Generally, the hot wire on the ballast is black, and the neutral is white. The
other colors are the wires that connect the ballast to the fluorescent tube
holders and to each other.
There is another issue, though. These non-commercial fixtures are generally not UL-approved for hard wiring
unless there is a manufacturer's fact sheet that says it's OK. So if there is no
indication that hard wiring is approved, you will have to install new
replacement three-prong plugs at the now cut ends of the power cords. These
plugs are available at any hardware store.
To solve the ON-OFF problem, simply install an outlet box(es) near the
fixtures, and wire the boxes so that it is controlled by a single wall
I have a couple of questions concerning fluorescent fixtures. First, how
can you tell with a flickering or slow starting florescent light fixture whether
to replace the lamp, replace the starter, or simply get a ladder and twist the
tube? If the lamp has no starter but both tubes are misbehaving the same, is the
problem both bulbs, the ballast (ouch!) or something else?
EN from Washington, D.C.
Generally speaking, a flickering fluorescent bulb means that one of the pair
of bulbs in the fixture has bought the farm. My philosophy of sensible repair is
to always replace both tubes. Fluorescent tubes have such a long life and are so
inexpensive that it makes sense. Not that it's the most economical solution...
it is just a practical viewpoint from someone who has been paid to do this type
of work for others. To receive a second call in a month because the other of the
two bulbs has gone bad is neither desirable from the customer's point of view
($$) or mine (pride in a job done right).
Fluorescent tubes can be tested with a multimeter by performing a continuity
test across the pins on either end. However, this is not a completely
reliable test, since a loss of gas can also cause fluorescent failure. So for the handyperson, the
best way to test the tubes is to install them
in another fixture that you know functions. If you have a 4-tube fluorescent
fixture, this is easy... remove one of the still-working pair of fluorescent
tubes and replace it with each of the questionable tubes, one at a time. 99% of
the time it will be one of the tubes that is the culprit.
However, if both tubes are functional, the problem is with the ballast or
starter. The starter is replaced first, and if that does not solve the problem,
the ballast should be replaced.
And a special note for the uninitiated... don't spend all day looking for a
starter in your fixture! Most modern fluorescent fixtures do not have starters,
so if it is not "in your face" (it looks like a small gray cylinder)
your fixture don't have one. They are never hidden, though they may be concealed
slightly by the tubes.
If you want some good technical information of testing ballasts, the most
complete source I have found on-line is The Lighting Center, at http://www.thelightingcenter.com/lcenter/technica.htm.
CONCERNING NOISY FLUORESCENT FIXTURES...
Last newsletter, MR from Pittston, PA wrote about a problem he
was having with a noisy fluorescent fixture. Some of our readers
offered suggestions that are worth noting... and passing on...
GB suggested replacing the inexpensive magnetic ballast with an
electronic ballast. However, he was wise to note that the
replacement ballast might cost more than the fixture!! (In my
research I found that electronic ballasts, besides being more
expensive, are also more sensitive to heat than magnetic ballasts.
Since some fixtures have the ballasts located right next to the
bulbs, this heat MAY be an issue.)
KG offered two suggestions concerning possible problems with
the wiring. First, if the fixture was as the end of a long run of
wire, there might be a voltage drop that could cause a
"dimming effect". Fluorescent fixtures are generally not
dimmable... trying to do so can either cause them to go off OR
produce some vibration in the ballast. KG also wondered if the
installer properly grounded the fluorescent fixture. Old
incandescent fixtures were typically not grounded, and lack of a
ground could cause a ballast to become noisy!
CF and SR suggested checking that the ballast was securely
mounted. Many ballasts vibrate to some degree, but a loose ballast
will be even louder! CF suggested checking the entire fixture, not
just the ballast. SR went a step further to suggest using a
heat-resistant silicone caulk if tightening was futile.
There was wide consensus, though, that the cheaper the fixture,
the noisier it will probably be! Thanks to all!
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