Take a look at this handy gadget. They only cost a buck or two, but can not only help improve your sound system, it can also help prevent an entire building's electrical system from burning up.
(http://howtosound.com/images/FerriteCore.jpg)
So what is it and what does it do? There's actually two correct answers (maybe three) but one of them is its most important function (IMHO).
I'll post the answer next Monday.
As far as preventing a building system from burning up ???? Not sure how RF energy put back on a AC line could do that.
I know this is true because it happened to me where I worked in the 70's. This was in a million square foot warehouse with a 100,000 square foot production floor. Took out the entire electrical system, and the plant was was down for days with hundreds of exploded bulbs, ballasts, and electrical controls.
Hmmmm..... How could this happen??? ;D
The little gadget shown above might have made a difference.
I'll give you all a hint: Triplen Harmonics.... ::)
Triplen harmonic frequencies are well below the RF range in 3 phase power systems, . I don't see any evidence that ferrite beads of a conventional nature are able to operate anywhere near there. And the most problematic harmonics are the lower frequency harmonics closest to the fundamental.
According to this: http://www.csgnetwork.com/harmonicscalc.html the 15th harmonic of 60Hz is only 960Hz. I find it hard to believe there's substantial power at harmonics much past the first few cycles.
That's true, but I have one report of an office building full of desktop computers with switching power supplies that burned up the neutral bus via Triplen harmonics. It's not just 3rd order harmonics, but also 5th, 7th, 9th, 11th, 15th, 19th, 21st etc... I don't think there's a top end to it.
Some of these harmonics are created primarily by variable speed motor controllers, some by Thyristor light dimmers, and some by inverter power supplies in computers. I've just begun to think about modern power amplifiers with switching supplies. All of these odd-order harmonics can be additive on the neutral of a 3-phase power system rather than subtractive and can cause trouble with neutral overheating.
Also, the triplen harmonics generated by switch mode supplies have rapid energy drop off as you go up in harmonic order/frequency. The following is a typical graph:
So even if you could get a ferrite bead that would get down into the upper end of the audible band, it's not going to do much good unless it can work down to a pretty low frequency.
Also, before a lot of non-linear loads were introduced, it was common practice to undersize the neutral wire in a 3-phase WYE circuit because the different phase currents were normally subtractive. So a 100-amp, 3-phase circuit might only have a 60-amp sized neutral simply because 3-phase motor loads would have no neutral currents at all. Fast forward to modern times and this same warehouse can now have dimmer lighting and all sorts of non-linear loads. That undersized neutral could be carrying way more than its 60 amp current rating, and that's when the real overheating problems start.
Sounds like we need a new type of circuit breaker that also measures current in the neutral, and when that current exceeds a safe value, disconnects the hot/live lines related to that neutral.
I worked in an 1890's theater once, and ALL the neutrals had fuses. Guess that's how it was done back in the day. Of course, we now know that's a bad idea. If you're ever working around K&T (Knob & Tube) wiring, watch out for neutral fuses.
So what is it and what does it do? There's actually two correct answers (maybe three) but one of them is its most important function (IMHO).
Sounds like we need a new type of circuit breaker that also measures current in the neutral, and when that current exceeds a safe value, disconnects the hot/live lines related to that neutral.
Triplen harmonic frequencies are well below the RF range in 3 phase power systems, . I don't see any evidence that ferrite beads of a conventional nature are able to operate anywhere near there. And the most problematic harmonics are the lower frequency harmonics closest to the fundamental.
If your filter design needs higher series impedance or has to operate at lower (power line) frequency, use a coil, along with all its fiddly trade-offs.
I've used these Neutrik EMC connectors with an integral ferrite bead and RF capacitors to knock out AM radio stations. See the full specs at http://www.neutrik.com/en/xlr/emc-series/nc3mxx-emc (http://www.neutrik.com/en/xlr/emc-series/nc3mxx-emc)
Yes. The Mackie VLZ radio station removal XLR.
Sounds like we need a new type of circuit breaker that also measures current in the neutral, and when that current exceeds a safe value, disconnects the hot/live lines related to that neutral.
... I have one report of an office building full of desktop computers with switching power supplies that burned up the neutral bus via Triplen harmonics. It's not just 3rd order harmonics, but also 5th, 7th, 9th, 11th, 15th, 19th, 21st etc... I don't think there's a top end to it. ...
That is a very interesting effect. Well explained.
As indicated in the equation above, higher order harmonics will generate as much heat as the 3rd, but at much lower amplitudes. For instance, according to the equation above 1 Amp of the 5th harmonic will generate as much heat as 1.7 Amps of the 3rd, and 1 Amp of the 9th harmonic will generate as much heat as 9 Amps of the 3rd. For this reason, the higher order triplen harmonics contribute as much to distribution equipment overheating as the lower frequency. For instance, it doesn’t take much 21st harmonic current to generate heat when, according to the equation above, the harmonic frequency (h) is squared for a multiplier of 441x (212) compared to the multiplier of 9x (32) for the 3rd harmonic.
Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com
For more on 3 phase AC power and harmonics see pages 6 & 7 of this Jim Brown paper:I just read through some of the EMI/RFI problems and trouble shooting.
"Power and Grounding For Audio and Audio/Video Systems -- A White Paper for the Real World"
http://www.audiosystemsgroup.com/SurgeXPowerGround.pdf
50 more Jim Brown papers:
http://www.audiosystemsgroup.com/publish.htm