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LAN & WAN Basics

4. Watch Out For AFCI Breakers

During previous HomePlug AV testing, I discovered an important source of powerline network signal attenuation. In the U.S., the National Electrical Code (NEC) has mandated the use of AFCI (Arc Fault Circuit Interrupter) circuit breakers to protect bedroom outlets for new residential construction as of January 1, 2002.

Figure 6 shows that AFCI breakers are easy to identify in your home's circuit breaker panel.

Regular and AFCI circuit breakers

Figure 6: Regular and AFCI circuit breakers

Putting a powerline networking adapter on a circuit protected by an AFCI breaker can easily knock throughput down by 50% or more. Figure 7 shows a quick experiment with an IxChariot throughput test running between two Cisco Linksys PLK300 kit HomePlug AV adapters.

The plot starts with one adapter connected to the outlet just outside my office, which is protected by a normal circuit breaker, and the other adapter connected to an outlet less than 6 feet away inside my office, which is behind an AFCI breaker. I then moved the adapter outside my office to the same outlet where the other adpater was plugged in (inside my office), then back to the hallway outlet again.

AFCI throughput reduction
Click to enlarge image

Figure 7: AFCI throughput reduction

Eyeballing the plot shows throughput went from around 15 Mbps up to ~ 50 Mbps and back again, which is ~70% change!

Fortunately, I found out from an Atheros contact (formerly from Intellon, which was acquired by Atheros) that all AFCI breakers are not the same. Here's what he said:

AFCI circuit breakers can harm HomePlug signals depending on the design of the breaker. If the design has an inductor in front of the power supply bridge, there is little if any impact on HomePlug signals.

Square D and Eaton AFCIs have this arrangement and are very HomePlug-friendly; it is fortunate that these brands have a large market share. Some other manufacturers (such as Siemens) have a capacitor in front and this is detrimental to HomePlug signals.

You can include Murray AFCIs, which are in my home, in the "bad AFCI" list, too. I priced Square D replacements at around $50 each, so I haven't yet swapped out the Murrays! But all of my HomePlug test locations are no longer behind any AFCI outlets.

NOTE!Note: The 2008 NEC expanded the mandated use of AFCI breakers to include hallways, family rooms, closets and many other areas. This isn't effective in all states, yet, but it is coming.

5. Find and Filter Noise sources

Electrical noise on the powerline has always had the potential to reduce powerline network performance. But it can be difficult to track down and its effect varies. But, once again, when noise does have an effect, it can be significant.

Noise that can knock down your powerline network throughput can come from things that may not be obvious. And some obvious sources sometimes don't have much of a negative effect.

In my tests, motor noise from hair dryers and power tools didn't seem to have much detrimental effect on powerline network throughput. On the other hand, I have found that light dimmers connected to halogen lamps can have an effect.

An innocent looking cellphone charger sitting in a kitchen outlet turned out to be the culprit that was affecting throughput testing in one of my test locations. I also found that my plasma TV sourced enough noise to prevent effective HD streaming via powerline to it.

The only way to find the sources that can be affecting your powerline network is to carefully look for them and then run throughput experiments using a tool like LAN Speed Test, or better NetStress. [see How Fast Is Your Network? Five Ways To Measure Network Speed].

Make sure you run a long enough test so that you get a good throughput average in each case. Some throughput loss can be intermittent and hard to find using a short test.

Once you find the offending noise source, you'll need to filter it. Fortunately, powerline adapter manufacturers are starting to address this by building filtered outlets right into the adapters.

I haven't yet tested NETGEAR's XAVB2501 AV+ 200 kit, which has filtered outlets. But I have found that Plaster Networks IX2 Isolator (Figure 8) was very effective in preventing my tiny little cellphone adapter from reducing powerline throughput.

Plaster Networks IX2 Isolator

Figure 8: Plaster Networks IX2 Isolator

It's a tad expensive at $25 and its form factor isn't ideal in some cases. But Corinex also makes a powerline noise filter (CXZCXPPWR) that's cheaper, too. If you know of more, please let me know.

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