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Old 12-30-2009, 09:50 AM   #1
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Ground Pigtail


Greetings: A question about pigtailing ground wires in a box. If you have a "plastic" bouble gang box with two seperate circuits in it, do you pigtail all of the ground wires togather and then attach the a ground lead to the device -- switch / recepticle, etc. or should only the grounds for each circuit be pigtailed, as they go back to the service panel anyway?

The reason I ask, as it sort of appears to violate two rules, one in the NEC, although the NEC does not seem to specify that ALL Grounding conductors in a box should be pigtailed togather, but inplies All ground conductors on a circuit should be pigtailed.

One is that is breaks the sub feed rule, that from the service panel, a continious ground to the device should be made.

The other, is more on the electronics side of things, is that gound loops tend to occure when all of the circuit grounds are bonded or tied in anywhere other than back at the service or subfeed panel.

Any comments on this would be appreciated.

Regards;

Peter

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Old 12-30-2009, 09:59 AM   #2
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Ground Pigtail


Connect all ground wires from 2 circuits together, then connect them to the devices.
Don't worry about ground loops.

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Old 12-30-2009, 10:33 AM   #3
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All ground wires in electrical boxes are typically tied together, then pigtails used for grounding the box if metal and switches/outlets.

For certain computers or electronic equipment, you can install an "isolated ground" back to the panel...
http://www.google.com/#hl=en&q=isola...c9c32d20fe6232

Isolated ground receptacle...

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Old 12-30-2009, 10:37 AM   #4
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Ground Pigtail


I've always used a UPS on my Computer & TV to protect them
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Old 12-30-2009, 10:48 AM   #5
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Ground Pigtail


Quote:
Originally Posted by Billy_Bob View Post
All ground wires in electrical boxes are typically tied together, then pigtails used for grounding the box if metal and switches/outlets.

For certain computers or electronic equipment, you can install an "isolated ground" back to the panel...
]
A bit more specific:

all grounds MUST be tied together unless there is an iso ground system which can remain isolated all the way back to the panel so;

if you are concerned about ground loops for electronics, run an iso ground system using iso ground receps. The only ground connected to the iso ground recep would be the ground dedicated to that circuit.
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Old 12-30-2009, 11:50 AM   #6
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Ground Pigtail


Thanks folks:

I was loosing sleep over that one.

On another related note. I have, and will be building a Pro Audio Studio in the near future and as an observation from past experience here is what I know about supplying and grounding some thing like that.

First of all, I use and run a lot of vintage gear -- 1980's -- Synthesizers, Mixers, Effects Processors, Power Amps, etc.

A lot of the newer gear uses the Wall Wort Supples, which are a non issue from a supply or grounding standpoint, other than they can induce a lot of noise / hum if not physically isolated.

The older gear and heavy pro road gear use your typical 2-prong and the newer gear 3-prong cords with an internal switching power supplies. In your typical home / home studio situation, you don't have enough power so you connect things up to multiple outlets throughout the room. Invaribly, you get connected to Both sides of your service, hence can and will have 220V across adjacent Hots on different recepticles, and without polarized plugs on some equipment, you have a case that can be potentially hot.

This can pose a real problem from the stand point of both noise -- 60 Hz Hum -- and a pretty good electrical potential Between Two or more pieces of equipment. You could get a pretty good zap connecting up audio cables, or just grabing two pieces of gear at the same time.

I have subsequently replaced all the power cords on my equipment with 3-prongers and that does solve the problem of the mild electrocution, but still does not kill all the hum.

So what I have done is a number of situations is to be sure everything is on the same side of the service buss and that does eliminate the hum completely.

The question / comment is, would it be advisable to wire the studio I am going to build off of only one leg of the service panel and use isolated grounding recepticles?

Regards;

Peter
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Old 12-30-2009, 05:54 PM   #7
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Ground Pigtail


I don't know what you should do for such a system, but the following gets into quite a bit of detail about this...
http://www.epanorama.net/documents/groundloop

Then I've solved some problems using "shielded cable". Here is the theory behind this...
http://en.wikipedia.org/wiki/Faraday_cage

More on ground loops...
http://www.google.com/#hl=en&q=groun...c9c32d20fe6232
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Old 12-30-2009, 06:16 PM   #8
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Ground Pigtail


The following is on shielded cable (wire). I'm not an "audio guru" and I know you guys REALLY get into this stuff! But this should point you in the right direction.
http://en.wikipedia.org/wiki/Shielded_cable

BTW shielded cable is wiring which is wrapped in a metal shield (Faraday Cage) and you can get almost any type of wire which is also shielded. In some cases the individual wires are shielded from each other inside the cable.

Then if you poke around a bit on the internet about this, you might find discussion about grounding the shield on these wires only at one end (as opposed to both ends and creating a ground loop). I'll stay out of that discussion!

There are all sorts of outside radio transmissions, cell phone signals, wireless devices, etc. these days. Any wire strung can act as an antenna to pick up these signals. The shielding keeps the outside noise out. Following is a story about this outside noise being so bad in some areas, people's vehicle remotes would not work!
http://www.washingtonpost.com/wp-dyn...-2004Jul4.html


Last edited by Billy_Bob; 12-30-2009 at 06:20 PM.
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