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Bro Shark
buyin' gear
Joined: 13 Jan 2006
Posts: 567
Location: SF
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 Posted: Wed Jun 06, 2012 2:41 pm Post subject: Ground question |
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| I'm renting an old house in San Francisco, built in 1930. Unfortunately the wiring has no ground. This sucks because I want to record electric guitars direct at the house, and I can't get rid of the annoying hum/buzz. Any idears? |
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MoreSpaceEcho
on a wing and a prayer
Joined: 07 May 2003
Posts: 5780
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| Posted: Wed Jun 06, 2012 4:01 pm Post subject: Re: Ground question |
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i only know enough about electricity to be dangerous, but could you swap one of the old outlets for a grounded one, and just ground that outlet to the box?
*pages goose134 to thread*
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Bro Shark
buyin' gear
Joined: 13 Jan 2006
Posts: 567
Location: SF
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| Posted: Wed Jun 06, 2012 4:54 pm Post subject: Re: Ground question |
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| MoreSpaceEcho wrote: | i only know enough about electricity to be dangerous, but could you swap one of the old outlets for a grounded one, and just ground that outlet to the box?
*pages goose134 to thread* |
The outlets are 3-prong, but there is no ground wire attached. What does "ground that outlet to the box" mean? I know nothing about electricity. An electrician friend said "run ground wire to copper water pipe" but my spider-senses are telling me I'll do something dumb and burn the place down. |
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MoreSpaceEcho
on a wing and a prayer
Joined: 07 May 2003
Posts: 5780
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| Posted: Wed Jun 06, 2012 5:15 pm Post subject: Re: Ground question |
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the outlets are in a metal (not plastic) box? you'd just run a ground wire from the green screw on the outlet to a ground screw in the box. fwiw the conduit feeding the box should ground itself, despite there not being a separate ground wire. i believe you can also buy self grounding outlets.
again, i'm talking out my ass here, so def don't take my word on any of this stuff! get your electrician friend over and have them sort it for you.
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goose134
takin' a dinner break
Joined: 22 Mar 2009
Posts: 194
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| Posted: Wed Jun 06, 2012 6:59 pm Post subject: Re: Ground question |
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If your system is from 1930 then you at least have it run in a version of BX as there was no non-metallic raceway to be had back then. BX is mechanically grounded via the fittings to the metal boxes. SO there won't be a wire connected to your outlets as the outlets are bonded to the box via the mounting strap.
A few basic questions to proceed:
1. Is the panel in question the main panel or a sub panel? (Sub panels would be fed from the main)
2. What size service do you have. The main breaker should be marked, but if not, the cover will have the info.
3. Is the water pipe serving the structure metallic?
4. Are the circuits going into the panel in flexible metallic conduit (BX) or conduit?
Let me know the answer to these questions and it'll be a cinch. Your electrician friend is right. We'll make sure you do it right.
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I make a living as an electrician, not recording in the basement. |
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Bro Shark
buyin' gear
Joined: 13 Jan 2006
Posts: 567
Location: SF
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| Posted: Wed Jun 06, 2012 7:15 pm Post subject: Re: Ground question |
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| Thanks, goose134. I'll check that stuff out in the next few days and post back here. Thanks to MSE also! |
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Snarl 12/8
moves faders with mind
Joined: 20 Dec 2008
Posts: 2708
Location: Portland
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| Posted: Wed Jun 06, 2012 9:42 pm Post subject: Re: Ground question |
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Do you have one of those outlet testers with the 3 or 4 LEDs? Are you sure it's not grounded even though there's no wire? Sometimes just screwing a grounded outlet into a grounded metal box will provide a contact ground. I've got some outlets in this 1920's house I live in that work that way.
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goose134
takin' a dinner break
Joined: 22 Mar 2009
Posts: 194
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| Posted: Wed Jun 06, 2012 10:49 pm Post subject: Re: Ground question |
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| Snarl 12/8 wrote: | | Do you have one of those outlet testers with the 3 or 4 LEDs? Are you sure it's not grounded even though there's no wire? Sometimes just screwing a grounded outlet into a grounded metal box will provide a contact ground. I've got some outlets in this 1920's house I live in that work that way. |
The only problem with these types of testers (at least the inexpensive ones) is that they won't tell you if your ground is achieved through neutral bonding in the box. The ground will be a normal read, but your raceway will be carrying current. But they are at least a good way to start.
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Snarl 12/8
moves faders with mind
Joined: 20 Dec 2008
Posts: 2708
Location: Portland
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| Posted: Thu Jun 07, 2012 12:21 am Post subject: Re: Ground question |
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| goose134 wrote: | | Snarl 12/8 wrote: | | Do you have one of those outlet testers with the 3 or 4 LEDs? Are you sure it's not grounded even though there's no wire? Sometimes just screwing a grounded outlet into a grounded metal box will provide a contact ground. I've got some outlets in this 1920's house I live in that work that way. |
The only problem with these types of testers (at least the inexpensive ones) is that they won't tell you if your ground is achieved through neutral bonding in the box. The ground will be a normal read, but your raceway will be carrying current. But they are at least a good way to start. |
I did have that problem recently. What's a better tester?
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The Scum
deaf.
Joined: 04 Jul 2003
Posts: 1994
Location: Denver, CO
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| Posted: Thu Jun 07, 2012 2:04 am Post subject: Re: Ground question |
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| Quote: | | What's a better tester? |
Something like this
http://www.testequity.com/products/3811/
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Snarl 12/8
moves faders with mind
Joined: 20 Dec 2008
Posts: 2708
Location: Portland
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| Posted: Thu Jun 07, 2012 1:42 pm Post subject: Re: Ground question |
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I was afraid of that. ($180) Probably not worth it [for me] for the number of times per decade that I test outlets.
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Seamonster
takin' a dinner break
Joined: 14 Jan 2004
Posts: 192
Location: old Malibu
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| Posted: Thu Jun 07, 2012 3:22 pm Post subject: Re: Ground question |
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| MoreSpaceEcho wrote: | | the outlets are in a metal (not plastic) box? you'd just run a ground wire from the green screw on the outlet to a ground screw in the box.... |
If you have BX, as Goose134 describes, then MoreSpaceEcho's suggestion should work (assuming the BX is providing continuity all the way back to ground at the main service entrance).
If there isn't a ground screw in the metal box, you can run a green wire from the screw on the outlet to a "ground clip" that clips onto the metal box. I happen to be holding in my hands a packet of "green ground clips for N/M cable," Halex brand, #14-#12, 26309. (I likely found 'em at Home Despot.)
And here may be some very slight enlightenment:
http://www.askmehelpdesk.com/electrical-lighting/little-green-grounding-clips-24801.html
- K Hill
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goose134
takin' a dinner break
Joined: 22 Mar 2009
Posts: 194
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| Posted: Fri Jun 08, 2012 1:26 am Post subject: Re: Ground question |
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I think the thing we need to focus on here is whether or not he has a Grounding electrode conductor. Bonding to the box is fine and good, but if we don't have the continuity to the electrode (in this case, the water pipe) then all the bonding in the world won't help. Let's get some answers from the OP and we'll proceed from there.
Something tells me that there is some improper bonding going on in the system for that kind of noise to be generated. Whether it's an outlet or systemic remains to be seen. One thing at a time, people. Simple first, hard later.
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goose134
takin' a dinner break
Joined: 22 Mar 2009
Posts: 194
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| Posted: Fri Jun 08, 2012 1:27 am Post subject: Re: Ground question |
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Oh, and you can just call me Goose
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Seamonster
takin' a dinner break
Joined: 14 Jan 2004
Posts: 192
Location: old Malibu
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| Posted: Fri Jun 08, 2012 6:00 am Post subject: Re: Ground question |
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| goose134 wrote: | | .... Bonding to the box is fine and good, but if we don't have the continuity to the electrode (in this case, the water pipe) then all the bonding in the world won't help. .... Something tells me that there is some improper bonding going on in the system for that kind of noise to be generated. .... |
Goose, you could well be right re. the possibility of improper bonding. For instance, given that a 1930's San Francisco building has gone through a few earthquakes, a break in the BX continuity wouldn't be implausible.
However, in my experience with my house built in the 1940's, outlets that are bonded via BX still can cause guitar amps to exhibit AC hum. I'm not sure why; I'd guess that maybe a BX run can have an unduly high impedance (e.g., with corroded or dirty connections), such that it will still work as a ground against catastrophic failure but nonetheless presents a differential potential(?)
Anyway, given that amps can and do hum on BX circuits that at least test as okay, I figured that bonding the outlet to the box would be a simple test. If Bro Shark does that and the hum goes away, then he's good, right? If the hum is still there, then he'd know that the BX has no continuity – and then your questions about his system would become totally right on.
Incidentally, I circumvented all this by wiring my studio on its own dedicated 60-amp main lug panel, including equipment ground back to the service entrance. I have no AC noise; some clients have been amazed that their amps could ever sound so clean. (I also used 6 AWG Romex for the long run to the main lug panel, to minimize voltage sag.)
Bro Shark, if you yourself take this any further, you might like to get a book like "Wiring Simplified." I got through my studio wiring with that book (along with a high school course in electronics, and some years of flexing my tinkering gene – now I know just enough to be dangerous). Here's a link to the book:
http://www.amazon.com/Wiring-Simplified-Based-National-Electrical/dp/0971977976/ref=sr_1_1?s=books&ie=UTF8&qid=1339148943&sr=1-1
- K
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