Hello all

I have three 3 feet long florescent light fixtures in a recessed cavity
in the kitchen ceiling. The cavity is 3 feet by 3 feet by 10 inch deep
made from drywall. The cavity is covered by thin plastic florescent
light covers made for T-bar ceilings. Above the cavity is the attic
with about 10 inch blown in insulation. These fixtures are regular Home
Depot fixtures and are paralel to each other about 10 inches apart.
They are all supplied from the same junction box also in the cavity.

Problem is that they get so hot that the thermal safety in the fixtures
trips and shuts off the fixtures. This happens after a year of constant
daily use. First time it happened, I replaced all three fixtures
because the ballast were leaking out. It is starting to happen again.
This time, the ballast are intact, but the lights still shut off if left
on too long.

Is this to be expected given the way they are installed? The one weird
thing that has me concerned is that the junction box supplying all the
fixtures have an unused red wire. The lights are connected to the white
and black wires. This was the way I found it when I first replaced the
original leaking ballast fixtures. Is there an electrical problem?

What are the possible solutions? Venting the heat into the attic is not
an option since that would bring other problems in the winter.

Any and all input most welcome. Thanks.

nn

The red wire is just a spare. You'd be better off not getting home depot
fixtures and get T8 fixtures with electronic ballasts, they don't heat up
like magnetic ballasts
"Nick Nicholas" wrote in message
...
Hello all

I have three 3 feet long florescent light fixtures in a recessed cavity
in the kitchen ceiling. The cavity is 3 feet by 3 feet by 10 inch deep
made from drywall. The cavity is covered by thin plastic florescent
light covers made for T-bar ceilings. Above the cavity is the attic
with about 10 inch blown in insulation. These fixtures are regular Home
Depot fixtures and are paralel to each other about 10 inches apart.
They are all supplied from the same junction box also in the cavity.

Problem is that they get so hot that the thermal safety in the fixtures
trips and shuts off the fixtures. This happens after a year of constant
daily use. First time it happened, I replaced all three fixtures
because the ballast were leaking out. It is starting to happen again.
This time, the ballast are intact, but the lights still shut off if left
on too long.

Is this to be expected given the way they are installed? The one weird
thing that has me concerned is that the junction box supplying all the
fixtures have an unused red wire. The lights are connected to the white
and black wires. This was the way I found it when I first replaced the
original leaking ballast fixtures. Is there an electrical problem?

What are the possible solutions? Venting the heat into the attic is not
an option since that would bring other problems in the winter.

Any and all input most welcome. Thanks.

nn

"Nick Nicholas" wrote in message
...
Hello all

I have three 3 feet long florescent light fixtures in a recessed cavity
in the kitchen ceiling. The cavity is 3 feet by 3 feet by 10 inch deep
made from drywall. The cavity is covered by thin plastic florescent
light covers made for T-bar ceilings. Above the cavity is the attic
with about 10 inch blown in insulation. These fixtures are regular Home
Depot fixtures and are paralel to each other about 10 inches apart.
They are all supplied from the same junction box also in the cavity.

Sounds unsafe; despite the lower heat dissipation of fluorescents than
incandescent bulbs I understand there are codes for not putting unvented
light fixtures into areas surrounded by insulation.
As the OP says there is heat build-up and potential for fire!
Probably a 'good' thing that the heat cut-outs worked as they did!
Coincidentally; fire in ceiling of a small commercial building here, today.
May have started in the 'office' area. Some plastic stock then caught fire
and local schools and some office buildings were evacuated because of toxic
smoke!
Fortunately no deaths. Several events scheduled in that area tonight were
moved to other locations.

"Nick Nicholas" wrote:

I have three 3 feet long florescent light fixtures in a recessed cavity
in the kitchen ceiling. The cavity is 3 feet by 3 feet by 10 inch deep
made from drywall. The cavity is covered by thin plastic florescent
light covers made for T-bar ceilings. Above the cavity is the attic
with about 10 inch blown in insulation...

And it gets too hot and the ballasts burn out. If you don't want to make
any holes in the top, you might open some knockouts in the fixtures near
the ballasts and add a small fan. If the fixtures make 1000 Btu/h of heat,
Grainger's 11 watt 36 dBa $37 3LE76 78 cfm fan will limit the box temp to
about 83 F in a 70 F room.

Nick

Sure nick pay for fans, hardware, installation, and electricity to run
them, and he still has junk ballasts that are not up to the job. Now
wouldn't it really be better if he got quality ballasts made for the job
! I mean this is standard stuff, enclosed fixtures, or didn`t you know
that.

m Ransley wrote:

Sure nick pay for fans, hardware, installation, and electricity to run
them, and he still has junk ballasts that are not up to the job. Now
wouldn't it really be better if he got quality ballasts made for the job...

You know little of heatflow, m. It sounds like the OP has about 3x80 = 240 W
ie 820 Btu/h in a 3'x3'x10" box with 10" of insulation above it and glazing
below it, and for all we know, the sides of the box may be insulated as well.
If it only loses heat by radiation, 0.1741x10^-8((460+T)^4-(460+70)^4) = 820
would make T = 401 F. What kind of ballast would survive that?

Nick

Nick you know nothing about lights, that is the issue.

m Ransley wrote:

Nick you know nothing about lights...

Would you have any evidence for this article of faith?

Nick

"Terry" wrote in message
. ..

"Nick Nicholas" wrote in message
...
Hello all

I have three 3 feet long florescent light fixtures in a recessed cavity
in the kitchen ceiling. The cavity is 3 feet by 3 feet by 10 inch deep
made from drywall. The cavity is covered by thin plastic florescent
light covers made for T-bar ceilings. Above the cavity is the attic
with about 10 inch blown in insulation. These fixtures are regular Home
Depot fixtures and are paralel to each other about 10 inches apart.
They are all supplied from the same junction box also in the cavity.

Sounds unsafe; despite the lower heat dissipation of fluorescents than
incandescent bulbs I understand there are codes for not putting unvented
light fixtures into areas surrounded by insulation.
As the OP says there is heat build-up and potential for fire!
Probably a 'good' thing that the heat cut-outs worked as they did!
Coincidentally; fire in ceiling of a small commercial building here,
today. May have started in the 'office' area. Some plastic stock then
caught fire and local schools and some office buildings were evacuated
because of toxic smoke!
Fortunately no deaths. Several events scheduled in that area tonight were
moved to other locations.

Two suggestions:

1. Replace the solid plastic panel with the open "cube louver" type. Get
the half by half by half (1/2 in. in all cube dimensions) for best glare
control. There will be plenty of natural air flow to keep the cavity cool.
The louver is not expensive and you'll like the improved lighting effect.
When the time comes, you can wash the louver by sloshing it in the bath tub
with dish detergent.

2. If/when the ballasts fail, replace them with commercial units. Check to
make sure they are UL and "Class P" labeled. HD carries such replacements.
I prefer "instant start" to "rapid start" types for home use since the light
comes on, well, instantly.

TKM

TKM wrote:

1. Replace the solid plastic panel with the open "cube louver" type. Get
the half by half by half (1/2 in. in all cube dimensions) for best glare
control. There will be plenty of natural air flow to keep the cavity cool.

Because warm air falls? :-)

Nick

No Nick it is called air circulation and the release of radiant heat.
And your 401f internal temp just shows you need some hands on
experience, that calculator of yours is no replacement for logic and
knowledge.

m Ransley wrote:

...it is called air circulation and the release of radiant heat.

Warm air rises, and the OP said there was 10" of insulation over
the box, with no holes. The 401 F was from a radiant heat calc.

How does air circulate in this case? Where are your numbers?

Nick