Control/Dimming - Is this possible: Lamp failure breaks a dimmer?

[slimrocktwo]

I was geling lights for a Battle of the Bands that's coming up, and i noticed an ellipsoidal was burned out in the catwalk. I changed out the bulb, plugged it back in, and nothing. So i tried connecting it to a different circuit that was powered, and it fired right up. I tried a another light on the troubled circuit, and got nothing from it. Our system is double patched, so I tried the same method on the other plug and got nothing as well. I checked the dimming rack and found none of the dimmers had a tripped breaker.

Is it possible that when the bulb burned up that it took the dimmer with it? Prior to the bulb going out, both circuits of that dimmer worked fine.

Thanks in advance

[mrb]

what kind of dimmers? I have seem lamps develop a short circuit when they fail but it usually trips the breaker or burns itself out before damaging the dimmer.

[derekleffew]

Yes, it's possible, but rare.
First, are you sure all the breakers on the dimmers were un-tripped? On some, it's difficult to tell just by a visual inspection. On almost all, the handle must be switched fully to OFF then to ON, to reset the circuit breaker.
Second, are you absolutely certain the console was telling the circuit/dimmer to be on?
Third, IF you are qualified and IF you have modular dimmers, assuming this to be a DPC installation, swap the suspect dimmer with a known-good module. If the problem follows the module, it's likely a bad SSR--a relatively easy and inexpensive repair, depending on the make/model of the dimmer. If a "good" module doesn't work in the "bad" slot, and the "bad" dimmer works in another slot, it's a wiring or control issue. Very rare, but again, possible.

Here's the link for the User's Manual for your dimmer rack, in case you don't have it: EDI Mark VII DimmerBank.pdf. (via Google)

[slimrocktwo]

The dimming rack is a Mark VII Dimming Bank, made by Electronics Diversified Inc. It was installed in '96, when the High school/ Auditorium was built.

Yes, it's possible, but rare.
First, are you sure all the breakers on the dimmers were un-tripped?

I'm pretty sure i flipped it on & off, but i'll gve it another try tomorow.

Second, are you absolutely certain the console was telling the circuit/dimmer to be on?

Yes, because I after I moved the light to a working dimmer, I changed the channel from the troubled dimmer to the working dimmer.

Third, IF you are qualified and IF you have modular dimmers, assuming this to be a DPC installation, swap the suspect dimmer with a known-good module.

I'll try this tomorow as well.

Thanks

[gafftapegreenia]

And then there is always the chance the circuit itself has died.

[Clifford]

We have the same rack a similar problem with two circuits. Please post if you find the problem.

[icewolf08]

I like how people jump to the rack/dimmers as the problem. Have you opened up the female connector to make sure that the wiring is good inside? I would do that before I assumed that there was a dimming issue. This is especially pertinent if you don't have flush-mount female connectors (i.e. you have pigtails). One step at a time folks.

[photoatdv]

Yeah, the connectors are often the culprit. We have had SO MANY of those go recently. My favorite was the once that was getting so hot it melted both plugs together. By the time we got the plugs off they were in multiple pieces. And yes the breaker was off when we did this.

[slimrocktwo]

We have flush mount connectors in the catwalk, so I didn't test that. I don't think it's an connector issue though, because the troubled dimmer is double patched, and neither circuit/plug is working.

[gafftapegreenia]

How old is your venue? Sometimes wiring goes bad.

[slimrocktwo]

Our auditorium is about 12 years old.

While on the topic of wiring, how is a double patch system generally wired? Is the two sets of wires coming from each dimmer? Or is there one set that comes from the dimmer, and the second channel ties into it down the line?

Thanks for everybody's suggestions

[derekleffew]

I like how people jump to the rack/dimmers as the problem. Have you opened up the female connector to make sure that the wiring is good inside? I would do that before I assumed that there was a dimming issue. This is especially pertinent if you don't have flush-mount female connectors (i.e. you have pigtails). One step at a time folks.

Good point, Alex. However, in this case, the impetus was a lamp failure. And both outlets on the same circuit were non-functional. Also since, prior to opening a female connector, one must first http://www.controlbooth.com/forums/g...t-tag-out.html the dimmer rack, (NFPA 70E) I'd do the module swap first, (after checking the circuit breaker) because I had to go to the rack anyway. It's sort of a philosophical discussion, that I think I raised before: When trouble-shooting, do you go for the most likely, or the easiest to diagnose, symptom first?

...While on the topic of wiring, how is a double patch system generally wired? Are there two sets of wires coming from each dimmer? Or is there one set that comes from the dimmer, and the second channel ties into it down the line? ...

It could be either, but the more cost-effective method would be to run one set of wires from the dimmer to the connector strip, and then gang the outlets at the terminal block. I doubt your school would have paid for more labor and materials than necessary, to meet the minimum specifications.

[JChenault]

If by double patch you mean two female receptacles per dimmer - and both females are in the same wiring strip, then there is usually a single run from the dimmer to a terminator strip in the raceway. At the terminator strip, the circuit is split into two lines to the receptacles.

IE when plug strip is constructed, the manufacturer runs the females in the plug strip to a wiring block. If you have 6 circuits and 12 ( or 18 or 24) plugs, you will have 6 circuits running from the dimmers to the plug strip. Assuming three phase power, this usually means 8 wires in a permanent installation. ( you could have some spares in the run as well).

Copper is spendy. Electricians to run more wire than needed is spendy.

[derekleffew]

...Assuming three phase power, this usually means 8 wires in a permanent installation. ...

See this document [edit: also attached] regarding the use of shared neutrals. As per 2008 NEC Section 210.4(B) the minimum number of wires required for six branch circuits in a dimming system would be thirteen.

Years ago, I worked with a dimmer installation that was commissioned, and then warranty-repair denied, by another manufacturer, due to the use of common neutrals. (Sidenote: Expressions aren't happy about 120V coming in through the DMX line, but it rebooted just fine. I think we had to reload the show from disk, however.)

[church]

yes a lamp failure can result in a TRIAC failure - this is usually a "feature" of the lower cost dimmers. As already mentioned when a lamp fails it often produces a large current transient dIcom/dt. If the rate of change of the commutating current exceeds the TRIAC capability then TRIAC failure results.

This is usually limited by including an inductor in series with the TRIAC. Dimmers that include an inductor for noise filtering purposes are ahead of the game here. Unfortunately inductors that can handle the currents found in dimmers without saturating are usually found on large torroidal cores or large E cores similar to a transformer. These are of course large, heavy and expensive. Note another cause of this problem is a motor load, the voltage and current waveforms are out of phase which can cause large values of dIcom/dt.

Do not confuse this with the snubber circuit which is used with non-snubberless TRIACs, this is used to limit the rate of change of OFF state voltage dVD/dt. A HIGH COM TRIAC can also be used to avoid this problem.

All of these are design choices made by the design engineer.

[slimrocktwo]

Alright, so when I had a free moment, I tried flipping the breaker on and off a few times, but that didn't help. I tried swapping the dimming module, and it didn't work at first. I tried flipping the breaker a few times, and it started working. I put the module back into its original place, and every thing is working smoothly now. Thanks for everyone’s help!

[gafftaper]

Um... That's weird. Is the rack full of dust bunnies and needs a good cleaning?

[mrtrudeau23]

also, you might try opening the male plug end of the instrument itself. one of the wires may be loose...

[slimrocktwo]

Is the rack full of dust bunnies and needs a good cleaning?

The rack is about due for it's annual cleaning

[gordonmcleod]

Sounds like it was possibly the connector on the module was corroded and most likely it was the low voltage control connector that had an issue
On the issue of triacs over the years I have found that shorts still kill them even with large torroid or E and H style chokes that are rate to prevent saturation
On thought that an engineer at Teccor told me was that the inductor was the culprit when the fuse or the breaker tripped the collapsing magnetic field in the inductor produced a high voltage spike that even the snubber could not absorb
So I tried a very high voltage rated triac with a set of GMovs across it and it didn't fail after 3 dead shorts being applied but the losses in the choke also prevented the dimmer from reaching line output and the snubbing caused it to missfire

[gordonmcleod]

[QUOTE=derekleffew;121101]See this document regarding the use of shared neutrals. As per 2008 NEC Section 210.4(B) the minimum number of wires required for six branch circuits in a dimming system would be thirteen.

That document comes up as a blank page at least on my machine

[ship]

Yes its possible your lamp caused the breaker to fail. Think of that broken filament while for that micro second in breaking flopping about and causing an arc between supply and return as if an arc lamp - now given an arc gap with high resistance for that moment but also for that moment limited to zero resistance to current flow. Or the other way around.

Broken filaments can arc in that last instance while it breaks and trip a breaker.

[dramatech]

I have had cases of lamp failure killing the Solid State Relay (SSR) in dimmer modules. Over the years, I have had it in Strand CD 80, EDI series 7, Teatronics and an LMI rack. The one thing that is common in all of these situations, is that the SSRs were crydon. I mention that just because it happened, but The fact that Crydon makes most all of the SSRs that are used in dimmer racks, the odds are that they would be the ones to fail. The real problem as I see it is that some times the lamp arcing across when it burns out, is so fast that the breaker doesn't always react quick enough. In every case of SSR failure that I can remember, the breaker also tripped. Read into it what you like, I'm not presenting a conclusion, just stating some experiences.
By the way the dual 40 amp Crydon SSR, that is used in so many dimmer modules, has many different prices depending on the purchase location. I have found them for $100 from the dimmer manufactures, and for around $55 at some electronic suppliers and the lowest was $35 at digikey. That was quite some time ago, so it may be priced higher by now.

[church]

see my explanation on page two of what can cause a TRIAC failure when a lamp fails. The problem is that a breaker you will find installedn a dimmer cannot protect against this type of problem because a standard breaker works on a thermal effect. This requires many cycles of the voltage waveform for it to react whereas the TRIAC or SSR as you refer to it has failed within one half cycle. Other types of breakers are available that can provide protection within a half cycle but they will not fit into your dimmer rack and the cost of such a dimmer pack would be prohibitive.

Unfortunately this type of issue is one of the factors you consider during the design of the dimmer or relay pack if you have not taken the appropriate steps in the design to limit the rate of change of voltage or current then you will experience TRIAC failures - not necessarily every time but it does happen. Note also that even when this is taken into account that a soft component failure of a capacitor or even high levels of dirt on inductor can change the performance of these components enough to give problems. this is why when snubber circuits and output filter circuits are included in a dimmer and TRIAC failures are being experienced you also need to check out these components

[gordonmcleod]

Fully magnetic circuit breakers will not protect a triac and often not even a SSR block
Gordos was also a major player in providing SCR modules to several dimmer manufacturers as well
Often one needs to be carefull in that many SSR modules have a zero crossing detector built into them since they are as their name implies a Solid State Relay (SSR) and as such is designed to switch only at the zero crossing point to prevent switching noise from the rise time
Strand was I believe the first to use them and the Cyrdon one they used was originally special ordered without the zero crossing in it