Exploding Lamp???

[dmxtothemax]

Unlikely to be a fault with the dimmers, unless someone has been messing around with the three phase supply, unlikely!

The most likely cause is a fault/failure of the lamp,

Remember these lamps run very hot, so any defect in the glass will cause a spectacular failure,

Its not common, but It does happen.

If you send the remains of the lamp to the manufacterer they might tell you the cause!

 

Hi a couple of days ago at school we turned one of the par cans on and the lamp exploded :) All of are lights are PAT Tested and the dimmers are checked every year by a service technician.

Could it be the lamp??? or a Power Surge???

We havnt used the dimmers since just in case it does it again and a service technician is coming next week to check them over so what could it have been??

[Maddison]

Unlikely to be a fault with the dimmers, unless someone has been messing around with the three phase supply, unlikely!

 

Setting aside, for a moment, the fact that the OP was over a year ago...

 

How do you figure that one out?

 

For all you know that's exactly what it was. A faulty MCB, for example, could have been a contributing factor. You really have no idea.

 

(Note I'm not saying it was caused by a faulty dimmer)

[Smiffy]

[grumpyoldman] Three pages for a blown lamp.... I am truly dumbstruck[/grumpyoldman]

[csg]

Unlikely to be a fault with the dimmers, unless someone has been messing around with the three phase supply, unlikely!

 

Setting aside, for a moment, the fact that the OP was over a year ago...

 

How do you figure that one out?

 

For all you know that's exactly what it was. A faulty MCB, for example, could have been a contributing factor. You really have no idea.

 

(Note I'm not saying it was caused by a faulty dimmer)

 

 

 

How exactly does a faulty MCB cause a lamp to fail badly?

 

Really, I think a decent dose of common sense is required here - lamps can and do fail badly sometimes. wasnt there a famous clip of Angela Ripon ( I think) reading the news when a 5K backlight bubble blew?

 

Now, when you have been in the vacinity of a 3Kw short arc xenon failing, everything else is tame. Heard one go once in the Albert hall when I was focusing up in the gods, sounded more like a grenade going off!

[Ynot]

Unlikely to be a fault with the dimmers, unless someone has been messing around with the three phase supply, unlikely!

A faulty MCB, for example, could have been a contributing factor.

How exactly does a faulty MCB cause a lamp to fail badly?

Er, yes - I'd be very interested in hearing the answer to that one...

Also how does 'someone messing with the 3-phase' at the dimmer end contribute to potential for blown lamps?

 

Honestly guys, if you're not really sure of what you're speaking of it's best to not comment on such topics.

[adam2]

To be pedantic, a defective MCB might cause a lamp to fail violently.

When a lamp fails, internal arcing can occur, resulting in substantial overcurrent. That is why fuses often blow/MCBs trip when a lamp fails.

If the MCB was defective or very oversized, then this overcurrent could persist for longer, and therefore be more likely to shatter the lamp.

 

I must stress however that this is a very unlikely eventuality, and I only note it in the interests of accuracy.

As I posted previously, by far the most likely reason is bad luck or a hidden manufacturing defect.

[Ynot]

To be pedantic, a defective MCB might cause a lamp to fail violently.

I think I may see (perhaps) where some confusion may have crept in - so to clarify...

 

A defective or oversized MCB cannot CAUSE a lamp to fail in any way at all.

 

It may contribute to the way that the lamp blows, I will concede, but it can't CAUSE that lamp to blow in the first place.

[paulears]

The times when I've had a lamp explode make me wonder if the real problem isn't the lamp on it's own, but a combination of the lamp and the fitting.

 

How many times do you try to spin a PAR lamp and find it won't quite turn the amount you want? You try to get the oval the correct angle, but it needs perhaps an extra 20 degrees of twist and it binds. You spin it back 180 or so and this gets you there. If there is insufficient clearance for the lamp to spin any way, is this a fitting that is slightly oval, rather than circular meeting perhaps a lamp with a bit of excess glass when moulded, and the two together prevent the lamp turning? When the lamp expands, and there is no space for expansion, this must put pressure on the glass. Repeated cooling and heating cycles could easily fracture the seal, I'd have thought. I don't think I've ever seen any mention of this binding issue anywhere - but it does seem to have potential for causing this style of lamp failure?

[Maddison]

Unlikely to be a fault with the dimmers, unless someone has been messing around with the three phase supply, unlikely!

A faulty MCB, for example, could have been a contributing factor.

How exactly does a faulty MCB cause a lamp to fail badly?

Er, yes - I'd be very interested in hearing the answer to that one...

 

Sigh. I didn't say that did I! You've even quoted what I said....

 

Even so...

 

Mostly this will be telling be people how to suck eggs, so sorry, but here we go. A filament gets thinner during its use until, at its thinnest point, it melts. This has all been covered above I think..

 

The resistance in the element melting will be, for a moment, very low. Ohms law shows us that this will cause a current surge.

 

In normal circumstances, a lamp with a large power draw, such as a 1kW PAR lamp, will pop the the MCB when it fails on account of this current draw.

 

However if the MCB doesn't respond correctly, and then arcing could occur across the filament gap. This could cause the temperature inside the lamp to rise sufficently to cuase the air inside in the lamp to expand sufficently to blow the join betwwen the front and the reflector (which is quite a weak bond).

 

I'd repeat that I'm not saying that this I the most likely, or even a likely, cause of the fault. Just simply that something relatively unlikely could have happened.

 

Honestly guys, if you're not really sure of what you're speaking of it's best to not comment on such topics.

 

Well, thats rather what I was trying to say in the first place... If that didn't come across, mea culpa.

 

[Edit - thred seems to have covered most of these points since I clicked on the page. Most of my points have now been made...]

[cedd]

To be fair, it wasn't dmxtothemax who re-opened this one. If you look further up the page, TB1979 asks a question a few days ago about if he should be buying lanterns without safety grilles, it's just the way he's replied that has hidden it within the list - he replied to the very first post, rather than the whole thread. To save searching, he says this;

Not sure whether the done thing on this forum is to re-use old relevant threads or start new ones if they're ancient. So sorry if I'm committing a faux pas by replying to this one!

 

I have read with interest various threads on here about exploding PAR lamps. Some PAR lanterns are supplied with safety mesh - it seems, inevitably, to be the much more expensive ones. However, these seem to be in the minority, and most PAR lanterns I have seen on sale at cheaper prices seem to have no mesh.

 

Many people's accounts of PAR explosions include glass flying out, even where mesh is installed. Should I be concerned at buying a PAR lantern with no mesh, or are they not that much use anyway? I'd be interested in any pointers that people can give me on this one.

[dmxtothemax]

Incorrecttly wired three phase has the potentail to put 440v where only 240 should be!

Do you see now how it could cause a lamp to blow?

And I did say this was unlikely, but it is possible.

How do you know that I dont know what I am talking about?

I am qualified and experienced in electrical power and stage lighting.

Any way my main point was that the most likely cause was lamp failure,

As I have seen it happen,

But the original question was could power surges be responsible,

Its possible but remotely.

I still think lamp failure is the main cause,

And it seems many others agree.

 

Unlikely to be a fault with the dimmers, unless someone has been messing around with the three phase supply, unlikely!

A faulty MCB, for example, could have been a contributing factor.

How exactly does a faulty MCB cause a lamp to fail badly?

Er, yes - I'd be very interested in hearing the answer to that one...

Also how does 'someone messing with the 3-phase' at the dimmer end contribute to potential for blown lamps?

 

Honestly guys, if you're not really sure of what you're speaking of it's best to not comment on such topics.

 

A concurrent post has been automatically merged from this point on.

 

Most par 64s I have seen dont have the mesh still in place,

It seems to burn off quite quickly!

The heat in front of a par 64 lamp is tremendous,

Does any one have par 64s with the mesh still intact?

Mine certainly dont, perhaps the gells will stop most of the glass?

 

 

To be fair, it wasn't dmxtothemax who re-opened this one. If you look further up the page, TB1979 asks a question a few days ago about if he should be buying lanterns without safety grilles, it's just the way he's replied that has hidden it within the list - he replied to the very first post, rather than the whole thread. To save searching, he says this;

Not sure whether the done thing on this forum is to re-use old relevant threads or start new ones if they're ancient. So sorry if I'm committing a faux pas by replying to this one!

 

I have read with interest various threads on here about exploding PAR lamps. Some PAR lanterns are supplied with safety mesh - it seems, inevitably, to be the much more expensive ones. However, these seem to be in the minority, and most PAR lanterns I have seen on sale at cheaper prices seem to have no mesh.

 

Many people's accounts of PAR explosions include glass flying out, even where mesh is installed. Should I be concerned at buying a PAR lantern with no mesh, or are they not that much use anyway? I'd be interested in any pointers that people can give me on this one.

[JonM]

I have some cheap short nose PAR56's and they have no mesh, however they come with a filterframe which has holes no bigger than 20x20mm (I think that was the magic number) which apparently makes them ok. Link to similar frame

[tb1979]

To be fair, it wasn't dmxtothemax who re-opened this one. If you look further up the page, TB1979 asks a question a few days ago about if he should be buying lanterns without safety grilles

 

Yes, sorry - I had no idea I would create such a monster!

 

In amongst the slightly odd digression about very unlikely causes of exploding bulbs, I have reassured myself that the vast majority of PAR cans have either an internal mesh or, as JonM relates, a gel frame that is mesh-like in its design (I have those PAR56s as well, so know exactly what you mean).

 

My confusion came about because the internal mesh was not always visible in product photos, but I've since had a good look at several lanterns around the place and satisfied myself that they do all have some method of catching at least the bigger bits of glass should a bulb fail violently.

 

Apologies to anyone if I would have been better starting a new topic rather than bringing this one back from the grave!

[adam2]

To be pedantic, a defective MCB might cause a lamp to fail violently.

I think I may see (perhaps) where some confusion may have crept in - so to clarify...

 

A defective or oversized MCB cannot CAUSE a lamp to fail in any way at all.

 

It may contribute to the way that the lamp blows, I will concede, but it can't CAUSE that lamp to blow in the first place.

 

Agree entirely, a defective or oversized MCB cant make the lamp fail, but could turn a passive death into an explosion.

Not very likely in practice, but it certainly COULD happen.

[Ynot]

Incorrecttly wired three phase has the potentail to put 440v where only 240 should be!

Well, to be blunt, if 3-ph was mis-wired in any way, I really think that a blown lamp is probably going to be the least of your worries, and suspect that you'd 'find' that fault well before a lamp gets even close to being powered.

Do you see now how it could cause a lamp to blow?

I can't disagree that 440 across a 230v lamp would indeed blow it big time, but I seriously doubt that (as above) it's a likely scenario.

It's certainly HIGHLY unlikely in a fixed installation with a show under way.

How do you know that I dont know what I am talking about?

I don't of course. But all we can go on in this forum is what people post unless their profile states accredited qualifications.