# fuses blow



## soundop (Mar 19, 2006)

ok so in the middle of the show the fuses for your ligh board and sound board blow, and the audience starts to panic what would you do?


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## soundman (Mar 19, 2006)

Let house manigment deal with the audence, if the situation would not be able to be fixed in under a minute throw some house lights on if possible. First question would be why both went at the same time. The best anser I can think of is a electrical surge hit the building. If it is storming out that might be an explanation but then why wasn't the surge stopped at the surge protector ? To go about fixing the problem just pull out the spare fuses that should be kept some where around the theater.


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## soundop (Mar 19, 2006)

true, but surge projectors fail


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## Footer (Mar 19, 2006)

get to a safe place in the buidling because crap is hitting the fan


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## Chris15 (Mar 20, 2006)

soundop said:


> ok so in the middle of the show the fuses for your ligh board and sound board blow, and the audience starts to panic what would you do?



My guess is that if you simultaneously blow both fuses, then that is going to be the least of your problems. For something to cause that, its going to be rather strong. Something that strong is probably going to knock out other things in the theatre. I say hit the emergency lights and see about replacing the fuses, but remembering that fuses blow for a reason and really you should find what caused the fuse to blow and fix that before replacing the fuse.


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## soundop (Mar 20, 2006)

the reason i asked is because my middle school had wired the light and sound board to the same fuse and it blew


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## AVGuyAndy (Mar 20, 2006)

I really hope that there are no fuses, at all. It sounds like they are both on the same breaker on the panel. In that case, just flip the breaker on.

In our auditorium, if the power goes out then the panic lights automatically go on.


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## MircleWorker (Mar 20, 2006)

Fuses in the Building? I hope you mean breaker. Initially I would throw our lights up through an architectural control unit. If it is the main power coming into the building, then we have a generator that takes over, for emergency lights only. 
I've had a show were everything went out, it was one of the craziest things ever to happened to me. The ushers and I had to use flashlights to get about 500 people out of the auditorium.


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## CHScrew (Mar 20, 2006)

A few years ago, our light board and both of our spots went out during a show. Mainly because whoever wired our booth was STUPID. So, when we thought we wound be OK using an outlet on the opposite wall for the followspots, it turns out that the lightboard and both spots were all running of the same circut and it flipped the breaker in the middle of out performance of "Oliver". We just ran outside and turned on the emergency lights (the lightswitch to turn them on is in the middle of the auditorium), then went and fixed the breaker. Ever since then we haven't had that problem anymore.


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## RelativeMischief (Mar 20, 2006)

Good idea to shut off the power amps for your speakers before flipping any breakers back on.


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## Chris15 (Mar 21, 2006)

Is not the answer simple? Know what circuits are where and what they are rated for and don't overload them. And if there are serious problems, get it rewired by an electrician.


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## mbenonis (Mar 24, 2006)

In my opinion, if the lights remain out for more than a few seconds, then the stage manager (or designated crew member nearest the stage) should step out and ask the audience to please remain seated. In the mean time, the house crew should ensure that everyone is OK and assist any persons needing assistance.

Every theater should have a written emergency situation plan that covers things like this, and all crew members should know what to do in various situations.


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## ManOfLights (Mar 24, 2006)

Just what ever you do dont replace it with a .22 bullet... there pretty much the same size.. i say this because i have heard stories that if the surge happens again the bullet will shoot... probably causing injury


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## AVGuyAndy (Mar 24, 2006)

This was tested on Mythbusters and they only got them to fire with heavy gauge wire shorted to the car battery. You won't find fuses like that on a panel.


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## Mayhem (Mar 28, 2006)

Well I have seen jewellers screwdrivers and also 16AWG solid core wire used before. I actually thought of buying the guy that used the screwdriver a cheap set of them and grinding a flat section and engraving 250mA, 500mA, 1A etc on the different sizes. However, I never actually got around to doing that. Besides, I probably would have gotten confused as to whether Philips drive screwdrivers are fast blow or not.

As already pointed out, a fuse blows for a reason and whist it is possible that it failed due to a mechanical fault it is most likely that it did its job and protected your expensive equipment from major damage.

A fuse should only be replaced with one of two things. Another fuse of the correct rating (remember, that someone may have placed a lower rated fuse in – and I have actually purchased equipment that has specified a 3.15A fuse only to have 2A fuse in it), or a breaker of the same rating.


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## koncept (Mar 28, 2006)

i just read this, i though fuses/breakers only blow when too much current is drawn? can they be blown if too much is available/applied such as in a surge?

second, if the equipment can operate correctly on a lower amp fuse wouldn't it be smarter to keep the lower fuse in there so that it blows sooner in that kind of event?


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## soundman (Mar 28, 2006)

MircleWorker said:


> Fuses in the Building? I hope you mean breaker. Initially I would throw our lights up through an architectural control unit. If it is the main power coming into the building, then we have a generator that takes over, for emergency lights only.
> I've had a show were everything went out, it was one of the craziest things ever to happened to me. The ushers and I had to use flashlights to get about 500 people out of the auditorium.




I was talking about keeping a set of backups somewhere in the theater.


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## Chris15 (Mar 29, 2006)

koncept said:


> i just read this, i though fuses/breakers only blow when too much current is drawn? can they be blown if too much is available/applied such as in a surge?
> 
> second, if the equipment can operate correctly on a lower amp fuse wouldn't it be smarter to keep the lower fuse in there so that it blows sooner in that kind of event?



A fuse blows when too much current passes through it. It is irrelevant whether or not this current is caused by a surge or whatever.

The problem I see with a lower rated fuse is that it would be prone to premature tripping. This could mean that it trips mid show because you pull the full load and the fuse cannot handle it. Having said that though, if you must put a different value fuse in, a lower value would be safer.


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## Mayhem (Mar 29, 2006)

koncept said:


> i just read this, i though fuses/breakers only blow when too much current is drawn? can they be blown if too much is available/applied such as in a surge?
> 
> second, if the equipment can operate correctly on a lower amp fuse wouldn't it be smarter to keep the lower fuse in there so that it blows sooner in that kind of event?



Chris is right – the fuse doesn’t care what current it has available to it, it only cares what passes across it. Think of the Chauvet Insignia light that was mentioned in another post. This particular light (I still had the pdf open!) has a 6.3A fast blow mains fuse in it. 

You can plug that light into a 20A outlet and the fuse doesn’t blow. The fuse will blow however if a fault occurs in the light that causes a power draw of greater than 6.3A.

Say for example that the unit got wet and shorted the power supply – the current draw would rise dramatically, and the fuse would blow, protecting the unit from damage. 

Now surge protectors are an interesting topic and one that I am not going to go into in any depth – I’ll leave that for someone else to research. What I will say however, is that your fuse will generally not protect you. The hint that I will give you is that when we discuss electricity, we commonly discuss two variables. 
Consider these questions:

1.	What does a fuse/breaker protect against? 
2.	What is a “surge” or “spike” in electricity?
3.	How does a surge protector work?

Again – using a lower rated fuse could result in the fuse blowing whilst the equipment is working under normal conditions. However, using a lower rated fuse in a pinch may get you through a show (although there is no guarantee). However, do not put a larger rated fuse in as you really do risk further damage to your equipment and will certainly void your warranty.

Whilst on the topic of fuses, I will also add in these questions:

1.	What are ceramic fuses and why are they used?
2.	If a ceramic fuse blows and you have no more ceramic fuses, but do have a standard fuse of the same rating, should you use the standard fuse?


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## Chris15 (Mar 29, 2006)

Mayhem said:


> Chris is right – the fuse doesn’t care what current it has available to it, it only cares what passes across it. Think of the Chauvet Insignia light that was mentioned in another post. This particular light (I still had the pdf open!) has a 6.3A fast blow mains fuse in it.
> 
> You can plug that light into a 20A outlet and the fuse doesn’t blow. The fuse will blow however if a fault occurs in the light that causes a power draw of greater than 6.3A.
> 
> ...



1] A fuse/ breaker engages when too much current is pulled through it. It protects against overloading.

2] A Surge / spike occurs when the voltage is higher than normal, usually for only a very brief period of time. Now this spike is often in the order of a few thousand volts, quite a bit higher than standard mains voltages, no matter which part of the world. This voltage has a habit of zapping sensitive circuitry, which is why the use of a "surge protector" is useful. Interesting fact: it is a spike if the voltage increases lasts only one or two nanoseconds and a surge if the increase occurs for three or more nanoseconds. A power increase can cause wiring to heat up and melt or burn. That is not a good thing. I imagine that this would be more observable or heavily loaded cabling more than lightly laden wiring.

If no one else offers insight into the workings of a surge protector and ceramic fuses, I'll do some research, but I'm sure someone out there knows more than me about it. The correct name for a "surge protector", a surge diverter, may offer some insight into its workings.


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## Mayhem (Mar 29, 2006)

Chris15 said:


> 1] A fuse/ breaker engages when too much current is pulled through it. It protects against overloading.
> 
> 2] A Surge / spike occurs when the voltage is higher than normal, usually for only a very brief period of time. Now this spike is often in the order of a few thousand volts, quite a bit higher than standard mains voltages, no matter which part of the world. This voltage has a habit of zapping sensitive circuitry, which is why the use of a "surge protector" is useful. Interesting fact: it is a spike if the voltage increases lasts only one or two nanoseconds and a surge if the increase occurs for three or more nanoseconds. A power increase can cause wiring to heat up and melt or burn. That is not a good thing. I imagine that this would be more observable or heavily loaded cabling more than lightly laden wiring.
> 
> If no one else offers insight into the workings of a surge protector and ceramic fuses, I'll do some research, but I'm sure someone out there knows more than me about it. The correct name for a "surge protector", a surge diverter, may offer some insight into its workings.



Well that is a good start – now, given that you have stated that a fuse/breaker senses current load, will a fuse protect against a surge/spike? In an earlier post, you said:


Chris15 said:


> A fuse blows when too much current passes through it. It is irrelevant whether or not this current is caused by a surge or whatever.”



– so, does the surge cause an increase in current or voltage or both?


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## Chris15 (Mar 29, 2006)

Mayhem said:


> Well that is a good start – now, given that you have stated that a fuse/breaker senses current load, will a fuse protect against a surge/spike? In an earlier post, you said:
> 
> 
> 
> – so, does the surge cause an increase in current or voltage or both?




Chris15 said:


> A Surge / spike occurs when the voltage is higher than normal



Did I not say that a surge is a voltage increase? Whether the current increases will depend on the nature of the load. With a purely resistive load, the current should increase proportionally to the voltage increase. With a prolonged surge, you would expect to see fuses blowing or breakers tripping however the key here is time. A fuse does not blow instantly, it takes some time for it to heat up enough to blow. A circuit breaker is the same. If overloaded by say 10% the breaker may continue to allow current flow for as long as a few minutes whereas at say 100% overload, it will trip within seconds. I suspect that if a circuit is already overloaded, then the surge could cause tripping more easily.

Theoretically a fuse/ breaker will trip in response to a surge but in practice, because of the nature of the devices, it is unlikely that this will be the case. In fact, fuses and breakers are designed to handle such things so that they do not trip upon startup of things like motors, discharge lamps and even resistive lamps.


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## Mayhem (Mar 29, 2006)

Chris15 said:


> Did I not say that a surge is a voltage increase? Whether the current increases will depend on the nature of the load. With a purely resistive load, the current should increase proportionally to the voltage increase. With a prolonged surge, you would expect to see fuses blowing or breakers tripping however the key here is time. A fuse does not blow instantly, it takes some time for it to heat up enough to blow. A circuit breaker is the same. If overloaded by say 10% the breaker may continue to allow current flow for as long as a few minutes whereas at say 100% overload, it will trip within seconds. I suspect that if a circuit is already overloaded, then the surge could cause tripping more easily.
> 
> Theoretically a fuse/ breaker will trip in response to a surge but in practice, because of the nature of the devices, it is unlikely that this will be the case. In fact, fuses and breakers are designed to handle such things so that they do not trip upon startup of things like motors, discharge lamps and even resistive lamps.



Yes you did. My question was whether or not you thought that the surge caused the fuses to blow because of the increase in voltage or that a surge also caused an increase in current? This was not overly clear in the earlier post from which I referenced. Although I think that you know that fuses are current sensitive devices. It may have been a bit pedantic but I think that you are on the right track with most of what you have written here thus far. At this point however, I am going to stay quiet and invite others to debate such questions.

Keep in mind that current draw and available current are two different things and also remember that there are both fast and quick blow fuses available. Breakers, as you have pointed out will happily allow a steady increase of up to 27% (I think – can someone verify this?) over its rating.


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## Chris15 (Mar 29, 2006)

Mayhem said:


> Yes you did. My question was whether or not you thought that the surge caused the fuses to blow because of the increase in voltage or that a surge also caused an increase in current? This was not overly clear in the earlier post from which I referenced. Although I think that you know that fuses are current sensitive devices. It may have been a bit pedantic but I think that you are on the right track with most of what you have written here thus far. At this point however, I am going to stay quiet and invite others to debate such questions.
> 
> Keep in mind that current draw and available current are two different things and also remember that there are both fast and quick blow fuses available. Breakers, as you have pointed out will happily allow a steady increase of up to 27% (I think – can someone verify this?) over its rating.



I too am giving others an opportunity to contribute. I know that there are fast / quick blow fuses and there are slow blow fuses but really, when a surge is only a few nanoseconds long the fuse is unlikely to heat up quick enough to blow. We cannot escape ohm's law and as voltage increases, assuming that the resistance remains relatively constant, current will increase and so this extra current flow could cause a fuse to blow.


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## saxman0317 (Apr 3, 2006)

First....find closest rookie since our headsets are out without power. Then, send him to rigging with our sound and light fuses that are convently kept in the mic drawer next to the AA and 9V batteries. Then, make riggiing risk life and limb to chage the fuse and get the show going again. Afterwards, take out your frustrations by yelling at closest rookie or actor that pissed you off last rehersal


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## Chris15 (Apr 4, 2006)

saxman0317 said:


> First....find closest rookie since our headsets are out without power. Then, send him to rigging with our sound and light fuses that are convently kept in the mic drawer next to the AA and 9V batteries. Then, make riggiing risk life and limb to chage the fuse and get the show going again. Afterwards, take out your frustrations by yelling at closest rookie or actor that pissed you off last rehersal



Now why would you need to be going to the rigging to fix the fuses. Surely under OH&S type guidelines, anything that would need to be serviced, would need to be accessible. That is also plain common sense, you don't want to have to try to clean an air filter up in the air. And why take it out on some poor kid. Unless of course they caused it by allowing say a hot water urn to be plugged into the circuit, in which case, well they should know better. All that yelling at someone without due cause will do is make them think that you have problems.


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## Chris15 (Apr 23, 2006)

Mayhem said:


> Consider these questions:
> 
> 1.	What does a fuse/breaker protect against?
> 2.	What is a “surge” or “spike” in electricity?
> ...



Anyone else care to take a stab at Mayhem's questions?


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## GeneralDoom (Apr 24, 2006)

Every theater should have a written emergency situation plan that covers things like this, and all crew members should know what to do in various situations.[/QUOTE]

That's a very good idea. I was working a show once when heavy rains washed out a tree, and it took down the power lines; the onlything on a generator was the sound system, so our SM called the show off. I got a great learning experiance and the rest of the day off.


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