Another great discussion
I think that there is a lot of misunderstanding re fusing in devices, how much the device actually draws and the protection on the
circuit it is attached to.
Lighting is totally different from audio, when you
plug in a 1000
watt light to an
outlet it takes 1000 watts, and infact even if it is dimmed, it takes more than the dimmed percentage, so for instance in a large concert it is easy for the lighting to take up a full 400 amp or higher three
phase connection and it is a resistive load
Audio is totally different, and it is interesting to see just how little actually is drawn. First of all you typically don't run the amps
flat out, but more important the draw in not continuous, it is inductive, and takes far far less in typical running mode. Where you get in to problems and blow speakers, and fuses is not from running a super powerful amp but rather a lower powered amp that is being over driven to the
point of
clipping. This is why for instance most audio folks will typically say that you should have an amp that is twice the
rating of the speakers. Most people don't understand it but for instance if you take a
speaker rated at for sake of argument 100 watts, and you feed it from a 100
watt amp, and you drive the amp to the full 100 watts and it clips, you will blow the
speaker. IF on the other
hand you take a 200
watt amp, drive it to 100 watts and it does not clip you will not. To give you an example in a large Metallica concert we were involved with, they had a 80,000
watt pa
system, it all ran off a 200 amp three
phase connection, measuring the
current showed using less than 30 percent of the
rating (about 70 amps a
leg). Rarely do you need more than 200 amps three
phase for audio. If you have access to a clamp on
meter and you look at the
current draw on the audio side of things you will be amazed at just how little it is drawing. In addition on large setups to avoid the
inrush current draw you have
power on sequencing as a side issue.
So for instance if you look at audio stuff and read the amp requirements on each item and add them up, you typically are way off. Again totally different for lighting.
So being able to run all the audio from a single 15 amp strip is probably not a s crazy as it seems. If you really crank up the subs and the amp starts to distort then you will pop the
breaker but other wise it is probably going to blow the
breaker. More of an issue especially in schools which typically have poor electrical systems from an audio standpoint, you wind up where all the outlets in the room are on the same
breaker so it really does not matter if you
plug them into different outlets, OR they are on differnet breakers but on different phases and therefore have different
ground connections back to the panel. It is at this
point especially with unbalanced connections that you start to get hum problems. For instance are the inputs to the amps
trs/
xlr connectors or
rca or 1/4 inch ts connectors. If it is all balanced in all the connections then probably no problem but say you add a cd player or something that does not have a balanced connection to the
mixer, then your problems start if all the equipment is not on the same
phase and the same
ground.
There are all sorts of
plenum rated cables
etc etc, but in general audio is put into the low
voltage side of things and has different requirements and they are more concerned with fire hazard from burning
insulation that the
gauge of the
wire. Ironically no one says for a 1000
watt amp you need to run 14
awg wire.
I noticed the other guy was from florida, and it is amazing the stupid things contracters will do when they install for audio. There are all sorts of
NEC
regulations for electricity and all the electricians are up to speed on that stuff, but on low
voltage audio stuff they are on their own based on how well things were speced out.
A lot of times what happens is that the designer originally is thinking of having the speakers and the amps together down on the
stage. So they are going to run a
line level connection from the
mixer. Then someone decided to put the amps back at the
mixer, and they then want to run the speakers. You saw this in the other post re a new setup for a pa at a school. So someone decides to spec a
snake running the
speaker lines, or they should run special cable. I guess it really comes down to if the cable is actually shielded, then it probably is mic cable which I AGREE is stupid. It could be double insulated or what ever, but I was assuming the poster was familar with shielded cable.
anyway all good stuff
Sharyn