[Sticky] BAV CORDAGE

Several questions on power cord philosophy.

Go here- https://www.iconoclastcable.com/techpapers/bavpoweranalysis.pdf

To summarize the paper, we use an EPDM dielectric that is simply awful for RF, it is attenuated out passively. You don't need the expensive shielding, and the current in the cord itself emits a MAGNETIC field, not an ELECTRIC field and the foil or copper braid shield won't attenuate magnetic interference out. Power cords used with VFD, Variable Frequency Drives, emit large amounts of RF and need shielded cords. We don't have that on our analog systems.

The second issue is how "fat" should the cord be? This is as simple as voltage dropped on the cord (loss) = current in the cord times the resistance of the cord. If we have a turntable with next to nil power draw (that little synchronous motor or digital drive) will drop next to no voltage across a 14 AWG power cord. A large amplifier will pull many, many amps and need that larger size power cord. Will it hurt to use a 10 AWG on  a DAC or T.Table? No, just maybe your wallet.

Our power cords are designed to optimize the analog performance at a reasonable price and use industry standard Rs (swept resistance) measurement techniques to evluate their performance across frequency.

Galen

A lot of power cords with the six pack…six more. But let’s talk power cords a second. We get a LOT of questions on power cords. Most of it is pure myth. And yes, we tested dozens of cords for actual properties before we selected the 600V Industrial cordage that we use to make BAV cord sets. For the nitty gritty, go here; https://iconoclastcable.com/techpapers/bavpoweranalysis.pdf

The biggest issue people have is shielded power cords are “better”. Well, no. How can all those unshielded power cords on the P20 be whisper quiet?

Basics, a shield has to overcome a problem that is worse than the shield superimposes into the mix. Yep, a shield has a negative performance contribution too. A shield adds reactance in capacitance and the closer it is to the inner wires, the worse it becomes. It also will rat out bad ground differentials in your wiring and give you a nice ground loop.

The purpose of a shield is to limit mostly EGRESS, stuff radiating OUT of the cord, not INGRESS, which is what we audiophiles always tend to think about. Don’t mess with my turf! Well, we can’t mess with other people’s turf, either!

The FCC has emissions limits devices needs to pass in order to be sold and if we use an open IEC socket that accepts any cord, UL will use the worst case cord during the test, and unshielded cord with the AWG based on the equipment specification current draw.

Why test this way? Because ANY cord can be used in the wild and the worst case prevents excessive emissions. The graph below is a FCC chart for emissions. The two lines are class A and B levels. The home class A limit is STRICTER than the INDUSTRIAL class B limit line. Yep, we consumers are big complainers when we use our stuff, and with far less knowledge than the pro’s that consider EMI/RFI far better than the average person at home.

Here is a UL test file showing the emissions limits for a device to be sold. The upper is CLASS B and the lower is CLASS A for home usage devices.

 

Why even have shielded power cords? Some devices with digital power supplies and VFD, variable Frequency Drive, devices are massive emitters of RFI, and require a shielded power cord for EGRESS. Here the negatives of the shields reactance is far, far less a problem than what is also mitigates. Everything is a balance and trade-off.

The next issue is what is called SPG, single point ground. NO, NO and NO on lifting the shield at EITHER END! A shield is not an antenna, and required both ends to be grounded to attenuate the RF on the shield. One end left open creates a resonance system that radiated RFI based on the shield resonance frequency determined by the length of the cable. You added yet another problem, not a solution. For those that want more tech on this, Email me for the entire paper to credit Larry West’s work.

All, of you that are using SPG are simply adding a problem that is just less of a problem than the “hum” or ground loop you removed. The proper solution is to figure out why your ground is lifted at some point in your chain and fix it. Saying I can’t find it, so a SPG “works” is STILL wrong! You are creating a radiating, and receiving, antenna that is doing the exact opposite of what a shield is supposed to do. The solution? Use an UNSHIELDED cord and fix the ground differential. The shield should be bonded to the chassis (green wire), or earth ground, not the neutral side. AND AT BOTH ENDS.

Industrial installations require an IEEE bonding specification (IEEE 3003.2-2014) be met for all ground points. This removes the grounding current to an acceptable level. ALL grounds have a “wire” between them with some DCR and voltage drop/current, yes. But proper bonding DCR differentials keeps issues below being problematic.

The next question is does a UTP cable even mitigate RFI? Yes, and no. Depends on the dielectric’s ability to move RF along the wires. We chose an EPDM insulation and it is AWFUL as a RF dielectric. It actually absorbs high frequency energy. Most UL approved equipment already has robust RF filters built-in to the power supply and pass the emissions and ingress testing as well. We don’t really need the suppression on the cord, but hey, we all want better so we chose better. Here is the RS against frequency and the impedance, or resistance, to RF energy down the cable. The EPDM 19105 is essentially equal to or worse at passing true RF. This attribute is probably not a benefit with good equipment more than a feel good thing. The durability of 600V (thicker insulation than 300V versions) EPDM cords is a big asset, though. Flexible, tough and relatively cheap in our world.

A quick primer on power cord testing for our usage shows we need high quality UTP power cords of suitable construction to be easy to use, durable and safe. I go with the data and so should you when it is available.

Best, Galen Gareis