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Old 06-18-2010, 04:11 AM   #1
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Default Exploding Metal Halide Fixture

What would cause a Metal Halide fixture to explode? Customer had a few of these 100w fixtures in an office space: http://www.hubbelloutdoor.com/produc..._883087_883091

The tenant says the light bulb exploded and shattered the Refractor, there was shattered glass all over the place, lucky no one was standing underneath yada yada etc.

The next day they said they heard buzzing then the lights dimmed and went out, they shut the switch off and the next day it was fine.

What I found: Ballast in the exploding fixture was burnt. In one fixture over I found a twisted neutral connection which if I wanted it to be the problem may have been lose but not really. Then I opened the switches, pulled out one of two switches and notice right away that the load side screw is not tight! the line side was loose as well so I thought I am done till I realized it was the wrong switch leg! I pulled the second switch and sure enough it is lose as well. I opened all the rest of the fixtures (8 total) and all the J-boxes with no major problems.

The buzzing and dimming can be attributed to the loose switch connections the question is, would that also cause the fixture to explode?

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Old 06-18-2010, 04:57 AM   #2
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http://en.wikipedia.org/wiki/Metal_h...lamp_explosion

Replace lens to acrylic type

Plastic will melt and get pit marks instead of shattering.

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Old 06-18-2010, 05:32 AM   #3
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Originally Posted by Geoff C View Post
http://en.wikipedia.org/wiki/Metal_h...lamp_explosion

Replace lens to acrylic type

Plastic will melt and get pit marks instead of shattering.

These have Acrylic Refractors!
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Old 06-18-2010, 05:44 AM   #4
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I dont know if this is relevant to your situation or not.

We had a similar canopy type light fixture such as that installed in a parking garage. The manufacturer sent out a hole saw along with some small vents for us to install in the center of the lens.
I dont remember the brand but there were quite a few fixtures.
The hole saw had a stop ring installed about 1/2" from the teeth so that we wouldnt drill through the lens and hit the lamp.
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Old 06-18-2010, 09:01 AM   #5
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A shorted capacitor will overdrive the lamp, causing it to melt or explode. It'll also overload the ballast.

Rob
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Old 06-18-2010, 10:29 AM   #6
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I never saw one explode I thought you were asking about a smoke show. Sometimes the ballast wires get pinched in the case and it looks like a cloud , big beautiful smelly cloud.
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Old 06-18-2010, 12:27 PM   #7
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Originally Posted by micromind View Post
A shorted capacitor will overdrive the lamp, causing it to melt or explode. It'll also overload the ballast.

Rob
These fixtures have been running for 3-4 years, the insulation on the wires in the fixtures were not melted and although I didn't specifically look at the capacitor I didn't notice anything unusual.
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Old 06-18-2010, 12:33 PM   #8
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It happens a lot, try to use quality lamps, there's a lot of junk out there.
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Old 06-18-2010, 12:59 PM   #9
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It happens a lot, try to use quality lamps, there's a lot of junk out there.

Is that the answer I give the customer? Should they wear helmets and protective gear when working in that office?
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Old 06-18-2010, 01:03 PM   #10
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perhaps they need fixtures that are the enclosed lens type
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Old 06-18-2010, 01:03 PM   #11
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Quote:
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These have Acrylic Refractors!
Oh. When you said there was shattered glass all over the place I assumed you meant from the lens.
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Old 06-18-2010, 01:11 PM   #12
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Open Fixture Rated MP and MPI lamps contain protective quartz shrouds which helps contain hot particles in the lamp within the event of an arc tube rupture. Open fixture rated metal halide lamps offer significant advantages for end-users, including: Do not require a luminaire lens, delivering more light; Recommended by the insurance industry; Continuous operation - 24/7/365 - No shut-off required.
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Old 06-18-2010, 01:26 PM   #13
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Quote:
Originally Posted by wildleg View Post
perhaps they need fixtures that are the enclosed lens type

This is the fixture

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Old 06-18-2010, 01:33 PM   #14
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Is that the answer I give the customer?
No, you should tell the customer that HID fixtures for office lighting is very unusual and a serious waste of energy. There are so many alternatives, I would suggest replacing them with 2XFO32/25W/841/XP/SS/ECO3 strips or better yet my personal favorite fixture: RELUME LED LOW BAY FIXTURES, PS Series Up to 15-years of LED lamp life, versus 3 years for metal halide, means far fewer re-lampings. In fact, maintenance savings alone make Relume LED fixtures less expensive on a lifecycle basis than conventional fixtures. 50% ENERGY SAVINGS Drawing just 80w to 136w of power depending on the model, Relume’s Low Bay LED fixtures provide energy savings of up to 50% over conventional HID lighting sources.
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Last edited by The Lightman; 06-18-2010 at 01:35 PM.
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Old 06-18-2010, 05:41 PM   #15
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I assume when you mean explode you mean the bulbs literally shattered. I have had this happen in an incandescent fixture.

The problem was that the porcelain socket extended too far out and when the buld was tightened it would actually score the bulb near the base. After awhile the bulb top would just fall out of the fixture right at the base where the score was.

Just something to think about. Were the bulbs the proper bulbs for the fixture?? Not sure that would make them explode but I thought I'd throw that out.
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Old 06-18-2010, 08:19 PM   #16
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i had this happen once a long time ago when i miswired the multitap ballast
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Old 06-18-2010, 08:56 PM   #17
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I'm tempted to say that the burnt ballast and the exploding lamp are coincidental.

We have a ton of MH wall packs that literally never get turned off. They run 24/7. I've gone to re-lamp a number of dark fixtures and found the lamp blown apart.

This is a pretty well known phenomenon: Apparently it has to do with the high pressure inside the MH arc tube. Manufacturers recommend that a fixture gets turned off regularly. This allows the quartz arc tube to cool and it actually anneals it, making it stronger and reducing the risk of the lamp exploding when it reaches end-of-life.

So, it's always a little bit of a risk, and the risk goes up if the light is never shut off. My $0.02 says that's what you've got here.

A little side note: I recently learned what a "Type O" metal halide lamp was when I ordered some low bays that came with pink mogul base sockets. That pink socket is designed to only accept a type "O" fixture, which is designed for "Open" use without any sort of fixture lense. This lamp has an additional glass bulb which will (hopefully) contain contain the fragments if the arc tube explodes.

-John

Last edited by Big John; 06-18-2010 at 09:02 PM.
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Old 06-18-2010, 09:05 PM   #18
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Quote:
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I'm tempted to say that the burnt ballast and the exploding lamp are coincidental.

We have a ton of MH wall packs that literally never get turned off. They run 24/7. I've gone to re-lamp a number of dark fixtures and found the lamp blown apart.

This is a pretty well known phenomenon: Apparently it has to do with the high pressure inside the MH arc tube. Manufacturers recommend that a fixture gets turned off regularly. This allows the arc tube to cool and it actually anneals it, making it stronger and reducing the risk of the lamp exploding when it reaches end-of-life.

So, it's always a little bit of a risk, and the risk goes up if the light is never shut off. My $0.02 says that's what you've got here.

-John
These lights are in an office suite and I am assuming get shut off every night. I found the following on eHow ( http://www.ehow.com/way_5916056_oper...d-fixture.html ) :

"All HIDs have the same function. They regulate power flow in the HID so that the light does not flicker or abruptly change. A HID without a ballast is likely to overheat and potentially explode. This is partially due to the slow rate with which HIDs warm-up. If a HID is connected to a power source without an intermediary ballast, any sudden fluctuations in current will force the electrode arc to distort. Therefore, it is vitally important to purchase the appropriate ballast for your system so that your HID will operate properly"

I don't know how reliable it is but I would think it makes sense, the loose connections on the switch caused the voltage to fluctuate and adversly effected this lamp. Why didn't more lamps burn is another question I guess. Does this theory work?

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Old 06-18-2010, 10:49 PM   #19
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The other thing with metal halide bulbs you have to be aware some of them are very senstive to the burning postion due some bulbs are only rated for horzontal and some are vertical postion only so check it out.

I have see few exploded like that espcally if used wrong bulb format { like use the horzotal bulbs in vertical bulb luminaires or vice verisa }

Shorted capaitors can overdrive the MH bulbs and cause to expolde { some will do that way and some MH luminarie with shorted capaitors it will stay dim so it will varies a bit depending on ballast connection format }

Merci,Marc
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Old 05-02-2011, 07:11 PM   #20
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Quote:
Originally Posted by Wireless View Post
What would cause a Metal Halide fixture to explode? Customer had a few of these 100w fixtures in an office space: http://www.hubbelloutdoor.com/produc..._883087_883091

The tenant says the light bulb exploded and shattered the Refractor, there was shattered glass all over the place, lucky no one was standing underneath yada yada etc.

The next day they said they heard buzzing then the lights dimmed and went out, they shut the switch off and the next day it was fine.

What I found: Ballast in the exploding fixture was burnt. In one fixture over I found a twisted neutral connection which if I wanted it to be the problem may have been lose but not really. Then I opened the switches, pulled out one of two switches and notice right away that the load side screw is not tight! the line side was loose as well so I thought I am done till I realized it was the wrong switch leg! I pulled the second switch and sure enough it is lose as well. I opened all the rest of the fixtures (8 total) and all the J-boxes with no major problems.

The buzzing and dimming can be attributed to the loose switch connections the question is, would that also cause the fixture to explode?


Like most HID lamps, mercury vapor high pressure sodium , metal halide lamps operate under high pressure and temperature,
Common operating conditions inside the arc tube are 5-50 atm or more[1] (70–700 psi

t the end of life, metal halide lamps exhibit a phenomenon known as cycling.
All HID arc tubes deteriorate in strength over their lifetime because of various factors, such as chemical attack, thermal stress and mechanical vibration.

Since a metal halide lamp contains gases at a significant high pressure, failure of the arc tube is inevitably a violent event. Fragments of arc tube are launched, at high velocity, in all directions, striking the outer bulb of the lamp with enough force to cause it to break. If the fixture has no secondary containment (e.g. a lens, bowl or shield) then the extremely hot pieces of debris will fall down onto people and property below the light, likely resulting in serious injury, damage, and possibly causing a major building fire if flammable material is present.
· For continuously operating lamps, allowing a 15 minute shutdown for every 7 days of continuous operation.
· Relamp fixtures as a group. Spot relamping is not recommended.
there are measures that can be taken to reduce the damage caused should a lamp fail violently:
  • Ensuring that the fixture includes a piece of strengthened glass or polymeric materials between the lamp and the area it is illuminating. This could be incorporated into the bowl or lens assembly of the fixture.
Using lamps that have a reinforced glass shield around the arc tube to absorb the impact of flying arc tube debris, preventing it from shattering the outer bulb. Such lamps are safe to use in 'open' fixtures. These lamps carry an "O" designation on the packaging reflective of American National Lamp manufacturers have tackled
this problem by enclosing the arc tube with a protective
glass shroud. These lamps carry an "O" designation (for
  • Open fixtures)

Another lamp rating, the "S" lamp, does not include any
protective shroud, but is technically allowable for use in
open fixtures if operated according to certain parameters
(mounted base up, turned off for at least 15 minutes each
week, and group relamped at 70 percent of rated lifetime).

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