fuses blow

[Mayhem]

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:

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?

 

[Chris15]

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?

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.

 

[Mayhem]

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.

 

[Chris15]

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.

 

[saxman0317]

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

 

[Chris15]

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.

 

[Chris15]

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?

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?

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

 

[GeneralDoom]

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.