Keeping Power Separate

[headcrab]

I hear a lot that you shouldn't run nonlinear loads on the same breaker as a more sensitive load due to the harmonics. How does it help to put the nonlinear load on a different circuit? If you trace backwards through the breakers, it goes to the same bus bar.

[fredthe]

In an ideal world, the non-linear loads would be on a different transformer...

It's true that when mixing loads on the same panel, some of the harmonics will get to the other loads. But, they will be at a much lower level compared to being at the end of the same wire with the non-linear load.

-Fred

[Cashwalker]

I think it's more practical that at least the different types of loads be on different phases, even if the neutrals all end up on the same buss bar.

When I run a Battle of the Bands, I go as far as running the lights from one panel, the mixing equipment from another, and the band equipment from a third panel.

[TimmyP1955]

Originally Posted by Cashwalker

I think it's more practical that at least the different types of loads be on different phases, even if the neutrals all end up on the same buss bar.

When I run a Battle of the Bands, I go as far as running the lights from one panel, the mixing equipment from another, and the band equipment from a third panel.

That can cause some nasty "mic bites" owing to voltage differences between the PA ground and the backline ground. Of course if either the PA or the backline are not grounded properly this won't happen, but you then have bigger potential problems on your hands.

[headcrab]

What's so special about the breakers that they attenuate harmonics?

[Dionysus]

Nothing. Breakers do not attenuate harmonics.

The best solution is to run non-linear loads off of a separate transformer. In a lot of larger installs there is a separate transformer for Audio, and a separate transformer for lighting. These go to individual panels that distrubute to their loads.
The Audio panel often has receptacles all over the venue, and because of such they must be clearly labelled.

It is commonplace to run audio all off of a common phase in temporary situations. This minimizes the effect of the harmonics since the audio gear is all "common".

[fredthe]

Originally Posted by headcrab

What's so special about the breakers that they attenuate harmonics?

Nothing. But, long pieces of wire will. So, getting as much wire between the the noise source and the sensitive load is what is desired. (If you can't be on different transformers, or at least different phases.)

-Fred