a. Where do you get that idea ?
b. Why would it matter ?
c. Why is your
distro close enough to your board to
plug into the
convenience outlet ?
d. How do you know what
phase the
convenience outlet is on without opening the
distro ? Are you licensed to do that ?
e. If your moving lights are 220v <typically they are> that means there are two phases per
fixture. Which
phase do you choose to
plug into ?
f. If you are using more than 3 moving lights how do you adequately balance the load on the panel between all 3 phases and get your board on the same
phase as all your moving fixtures.
g. Your'e not just guessing are you ?
This area is pretty interesting, and there are a variety of practices.
Because of how three
phase power works, and how the
distro in connected in and what service the building has it can be a
bit complex.
On the audio side of things it usually IS recommended to keep things all on the same
phase, so the hot
neutral and
ground are all the same for the equipment. It probably has more to do with equipment that has possible problems, for instance consumer gear that is only two wired, double insulated, and old tube guitar amps
etc, but while it is not a hard and fast rule, it DOES in a number of instances reduce
ground loop noise.
IN general, and this is an over simplification, I have found that having equipment that is either audio, or digital signaling (like
DMX) works best if they all share the same
GROUND. So the argument re knowing the same
phase is valid, but most of the problems can come if your board is on one
system say an
outlet in the
house, and your lights, dimmers and moving L are on another
system with a different path to
ground. The reason is that some buildings use the
conduit as the
ground, don't have a continuous independant
wire etc, and all of this can cause variations on the
ground. In addition sometimes the
xlr connectors are incorrectly wired where the
shield is connected to the case of the
connector, the
connector comes in contact with something that creates another
ground. Basically grounds work best if there is ONLY one
point in the
system where there is an actual
ground, vs multiple partial grounds.
This is also why in most concert setups, you will find that good practice is to run
power from the
distro back to
FOH or lighting positon.
Most
distro's should have the outlets color coded to determine the
phase they are on, In the US it is black red and blue, and different countries it is different colors.
Another potential area of problems is the whole issue of 220/240/208 volts here in the US
If you are connected to a three
phase wye service, than if you connect an
instrument using two of the hot legs from two of the phases, you will only get 208 volts. If your
instrument was rated at 220, you will probably not get the same
level of output. If your
system was wired up Delta, then you CAN get the full 220, but it is trickier to have a
distro connected in. (this is why most large houses have a pre wired disconnnect wired in to the
system to avoid problems and work with the design. The problems tend to arise when you show up with your own
distro, and the electrician connects it into the nearest panel for you. IF everything is running on your
distro, fine, but if part of the
system is already installed, and your
system needs to interface is where things can get a
bit more difficult
Sharyn