Understanding, finding, and eliminating ground loops (2003) [pdf]

http://web.mit.edu/jhawk/tmp/p/EST016_Ground_Loops_handout.pdf

by PascLeRasc • 8 years ago

79 13 8 years ago

web.mit.edu

benji-york• 8 years ago

valenciarose• 8 years ago

Thanks for posting.

jhawkinson• 8 years ago

Just in case it was not obvious from the URL (/tmp/p), this is not a durable URL and not guaranteed to last there.

crispyambulance• 8 years ago

That's a useful read!

One thing I've always wanted to know: Where is the actual "ground rod" in a building/residence? How do I find it? I've assumed it was just the water pipe, but now I am not sure.

Also, don't these rods get corroded to oblivion after decades in the ground from electo-chemical reactions?

koliber• 8 years ago

When we were building our house, we installed an actual ground rod that the electrician connected--somewhere. I remember it being a literal rod getting pounded into the earth, pretty close to where we have the main power enter the house.

The water pipes are not metal at our house, so they would be of no use as an electrical ground.

This was in 2014, in Poland.

opencl• 8 years ago

Generally in the US at least, on older houses it's just the water pipe, newer houses use a rod, very new houses use two rods because electrical code requires it now.

Rods definitely do corrode and need to be replaced regularly. ~10 years for zinc coated steel and ~40 years for copper coated steel rods.

imgabe• 8 years ago

Several different grounding electrodes can be used. It might be a literal rod buried in the ground, a group of 3 rods connected by copper wire, the cold water pipe, the steel structure connected to the concrete encased rebar in the foundation, if available, or a loop of wire buried in the ground surrounding the building.

They do get corroded and are supposed to be replaced every so often. Different materials are used depending on the type of soil to minimize the corrosion. If they're really fancy they might have a cathodic protection system to prevent corrosion.

twothamendment• 8 years ago

Above, someone mentioned rebar in the foundation. That is a Ufer Ground. In places with very dry soil you can pound a stack of ground rods into the earth and still not get a good ground. Ufer figured out that concrete in the foundation provides a good ground.

https://en.wikipedia.org/wiki/Ufer_ground

5 years ago I built my house and did my all my electrical, I needed a Ufer ground in the foundation and 2 ground rods near the meter. Being a newer area, water lines were plastic.

mojomark• 8 years ago

I actually read this document recently for my work on grounding equipment on ocean going vessels. Surprisingly, there is very little in Mil-std-1310 (1) about ground loops on ships. Ships are interesting from a grounding perspective because your grounds are generally attached to the steel hull which represents the "common electrical potential".

People get confused when comparing ships to land based (e.g. building) grounds in which two or more grounds in, say a building's earthen foundation, could have very different potentials for a variety of reasons and thus ground loops can be present in shielded cables grounded at both ends. On ships, however, unless there is some strange disconuity, the ship's hull is a common potential and generally no ground loop will be generated, so you can generally have a doubly grounded cable with little risk of organic noise.

1.) http://quicksearch.dla.mil/qaDocDetails.aspx?ident_number=36...

alricb• 8 years ago

The author, Bill Whitlock, is the president of Jensen Transformers, makers of high-end audio transformers.

chiph2• 8 years ago

I used to be involved in car audio in the late 90's, and the people involved came up with many of these solutions via trial & error.

- Have a central grounding point - a steel car body has higher resistance than copper wire so using multiple ground locations will introduce voltage differences.

- Use a large gauge stranded wire for your ground.

- Use the same gauge wire for the ground as you did for the power wire.

- Keep wire runs short.

- Use twisted-pair wire for audio connections.

So for a multi-amp system, you'd run a large gauge wire from the battery positive to a distribution block, and from there to the head unit and amps. The ground from the head unit & amps would use the same diameter wire and be run to a central point. The ground strap from the car body to the battery negative post would perhaps be upgraded to the same diameter as the positive wire.

janci• 8 years ago

These are just the misconceptions the article talks about.

chiph2• 8 years ago

I suggest you look at my list and read the article again.

He is using ground loop isolators because of the length of his cable runs. In a car, that's not a problem as anything over 3 meters would be rare.

Single point grounding makes sense, because as I said, steel is a worse conductor than copper, so you'll end up with a voltage difference between your grounds (from each to the battery) if you use more than one.

So far as twisted pair, he strongly suggests using them to provide shielding against magnetic induced noise. They also provide good shielding against RFI - remember you've got 4-8 spark transmitters running at 900 to 5000 rpm interval in the engine.

And using the same size wire for both power and ground makes sense because different gauge wire has difference resistance.

Understanding, finding, and eliminating ground loops (2003) [pdf]

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