Mix Interview: Arthur Kelm

Jun 1, 2009 12:00 PM, By George Petersen

A WELL-GROUNDED APPROACH TO AC POWER PROBLEMS

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Some techs feel power and grounding is a lot of black magic that doesn't make sense, but to me it's not that complicated, especially with only three, four or six wires. I was recently working on a few home installations where they had problems. I found sump pumps, washer/dryers and air-conditioning units on the same panel board as their sensitive electronics and computer gear!

In studios, I've seen just about every type of home-brew solution, like people driving ground rods under consoles. Then I hear comments like, “The system works, but some days it buzzes and other days it doesn't.” It comes down to trying to use the audio chain to compensate for something that wasn't done properly in the electrical chain. For years, I didn't look at the electrical side when trying to solve hum and buzz problems; I only looked at my world. I'd use a whole box of Band-Aids, gum and baling wire — lifting a ground here or inserting fiber washers under the rack screws to isolate a piece of gear somewhere else — to get problems to stop.

Eventually, I decided to reverse-engineer the process. Once I read more and talked to people in telecommunications about power and grounding, I got a good understanding of it. I bought my first Fluke 43 [power-quality analyzer] for $4,500, worked with it and a light went on inside me. Testing and test equipment actually works with power systems, and if you do it right and follow the NEC [National Electric Code] book, it ends up quiet and clean.

What's your approach to studio grounding?

I use a star grounding technique, but to me an isolation transformer is mandatory. The key to what I do is re-bonding the neutral and ground on the secondary of the isolation transformer. That feeds your panel board, and the panel board feeds all the outlets in your studio. When you re-bond neutral and ground on the secondary of the transformer, you are actually, in terms of the electrical code, creating a new service, and 90 percent of your noise — click and pops and other disturbances — comes from voltages between the neutral and ground. So once you've re-bonded neutral and ground, you're off to a new start.

I do soil-resistivity testing to determine what kind of ground reference I have. I shoot for under 5 ohms path-to-ground, and in some cases it's necessary to drive a secondary ground rod. The code is 25 ohms for a service entrance, where the electrical service enters the building and where they bond neutral and ground. The 25-ohm figure is for life safety, but you want to be under 5 ohms for a low-noise ground.

If I don't have a great ground at the service entrance, I'll do a supplementary secondary ground after the isolation transformer. The ground from the service entrance comes to the transformer, goes to a bus bar, the neutral jumpers over to the bus bar and then I'll go from that out to a brand-new ground rod or rods — to get under 5 ohms.

That becomes our new point source for ground. It goes from that point up to the sub-panel, and the sub-panel has an IG [isolated ground] bus in it and an isolated digital bus in it. Then all the neutrals and green wires from the receptacles come back to that point — you never daisy-chain anything. It's a star system from that aspect. Each receptacle or quad box has a dedicated run back to the panel and to its own breaker. That approach has worked flawlessly for me for the past 10 years.

In terms of the ground rod itself, is a standard Home Depot-type, 5/8-inch copper-clad steel rod okay?

Maybe, but you have to make measurements. Ideally, I like to use an ionic electrode [chemical] ground rod, like the Lyncole XIT. It's a 2-inch-diameter tube with weep holes drilled into it and it's filled with a rock-salt material. You core a 6-inch hole, place the rod in the center and backfill it with Bentonite clay/soil conditioner, which you mix into a slurry with the thickness of pancake batter. The Bentonite creates a high-conductivity/low-corrosive mixture.

It's all got to be calculated. I go out to the site, pound stakes into the ground and make Wenner soil-resistivity measurements in 5-foot increments, from five through 20 feet. From that I make a soils profile based on the continuity of the soil and can calculate the required length of the ground rod to have a 5-ohm path-to-ground. This can vary from a single 10-foot chemrod to two or three 15-foot chemrods. When I did O'Henry Studios [Burbank, Calif.], I needed two 20-foot chemrods to achieve five ohms. The facility was in the [San Fernando] valley in very sandy soil, so we needed to go that extra mile. Also, when ground rods are placed too close to each other, they act as one — rather than separate — ground rods. If you're installing 10-foot rods and need two, you need to place them 20 feet apart so they don't interact with one another.






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