Grounding wire size


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Old 02-09-04, 04:55 AM
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Grounding wire size

I'm working on installing some separate ground wires for an older house that was not built with grounded receptacles or cabling. Is it acceptable to ground a 20A circuit with 14 gauge wire? There seems to be a lighting ground system made with 14 gauge wire in the attic, and I'm wondering if its acceptable to connect new receptacle grounds to that. Thanks!
 
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Old 02-09-04, 05:57 AM
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No.

A 20 amp circuit must be grounded with a 12 gauge wire, green, running all the way back to the panel and connected with the other ground wires.
 
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Old 02-10-04, 04:01 PM
imjerry
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Sounds Like

Knob and tube wiring to me, no ground, you are not going to like this but there is no way to do it that meets code requirements!!!

Sorry bout that, wiring should be replaced !!! Jerry
 
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Old 02-10-04, 09:30 PM
bungalow jeff
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K&T should not be on a 20 Amp circuit. So, if it is K&T, there is a bigger problem.

The first generation of metallic sheathed cable did not have a ground wire and the early connectors did not create a ground path from box to sheath. If this is the material in question (I have removed this from my house, but it was installed in 1942), then 12 gauge green wire run from each outlet back to the box is acceptable. However running all of the individual ground wires is not much less work than replacing the existing wiring with new NM-B cable. This would allow other code updates, such as 20A circuits as necessary and new circuits for computers and AV equipment.
 
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Old 02-11-04, 04:46 AM
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If the wiring is in good shape then I recommend adding a ground wire only where necessary. Most of our lamps appliances are not grounded anyway, so those devices don't care if there is no ground.
 
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Old 02-11-04, 08:19 AM
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Originally posted by racraft
If the wiring is in good shape then I recommend adding a ground wire only where necessary. Most of our lamps appliances are not grounded anyway, so those devices don't care if there is no ground.
I am in 100% agreement with the above quote. First off, it is not K&T wiring. The house was built in 1959. It is 12 gauge metallic sheathed cable, and the boxes are non-metallic. Generally speaking, the wiring is in good shape otherwise. My plan is to provide grounded outlets for all bathrooms (with GFCI), the kitchen (with GFCI), laundry area and garage. In addition, I think I will provide one grounded outlet in each of the three bedrooms, to accomodate a computer/monitor, etc. or other specialized electronic equipment. In a brief, informal survey of electrical/electronic devices out there today, I'm finding that very few these days even require a grounded outlet! So why go overboard on grounded outlets, except where required by code or absolutely needed. Its somewhat of a pain to add an external ground to an in-situ non-grounded outlet.

Since we're on the subject of grounding, here's a quick question. Let's assume there is a fault in the device and the outer metallic enclosure (say a washing machine) becomes energized by a broken hot wire (non GFCI circuit, but with a "green wire ground"). Will a person still feel a shock (perhaps a mild one)? Will the circuit breaker trip? If no to both questions, how would you know the device is now faulty?
 
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Old 02-11-04, 08:46 AM
arcspark
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If there is a fault between your hot wire to the metal frame of any non-grounded metal appliance, you will feel the shock when you touch the appliance. If YOU are sufficiently grounded, the shock could be lethal. Properly installed, the ground wire in a circuit ties the appliance frame back to your main electrical panel ground (which is bonded to the neutral). When the fault occurs with the hot wire to metal frame, there should be sufficient current flow to trip the fuse or breaker - shutting off the circuit.
A Ground-fault receptacle or ground-fault breaker works a little differently. In a normal operating circuit, the amount of current flowing out in the hot wire should be the same that returns in the neutral wire (assuming it is not a split wire circuit). A GFCI device compares these two current flows and will trip off if there is more than 5 milliamps (.005 amps) difference between the two wires. It assumes the current is leaking off the circuit through a person, or whatever else. It takes approx 20 milliamps across a normally heathly person's heart to stop it. You may feel the shock, but it shouldn't hurt you. GFCI devices are code acceptable when there is no third ground wire present. A GFCI receptacle will also protect all down stream receptacles, so only one need be installed at the beginning or each circuit.
 
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Old 02-11-04, 08:49 AM
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The metal outside of major appliances (washing machines, dryers, stoves, refrigerators, etc.) is connected to ground via the ground wire in the cord and plug.

If a fault occurs in the appliance and the hot wire contacts the metal, a short will occur via the ground wire in the cord back to the outlet. if the outlet is properly grounded then this short will trip the circuit breaker.
 
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Old 02-11-04, 09:18 AM
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Ok that's what I thought. If the circuit trips virtually instantly after the fault takes place, then wouldn't a smaller ground wire be sufficient (say 14 gauge versus 12 gauge on a 20A circuit), as the ground wire won't have had time to heat significantly? That was my thinking in bringing up the original question.

Also, what if there is some resistance (e.g. from corrosion, etc)present in the "hot wire-to-metal housing" ground fault, such that the ground fault current is less than 20 A? Then it seems that the circuit breaker wouldn't trip, even though the appliance metal housing still might be dangerously energized. Or is this just not likely?
 
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Old 02-11-04, 09:26 AM
arcspark
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Code requires 12 guage on a 20amp circuit. I would not go down in size. When a fault occurs, you're not talking about 20amps of fault current, you have in the hundreds of amps. The last thing you want to happen is to have your ground wire fail before the hot wire fails or before the breaker has time to trip. There is not but a penny or two difference in cost/ft of the wire. Stick to the 12 guage. Is your life or your family's life not worth that much to protect it?
 
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Old 02-11-04, 02:08 PM
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Originally posted by arcspark
Code requires 12 guage on a 20amp circuit. I would not go down in size. When a fault occurs, you're not talking about 20amps of fault current, you have in the hundreds of amps. The last thing you want to happen is to have your ground wire fail before the hot wire fails or before the breaker has time to trip. There is not but a penny or two difference in cost/ft of the wire. Stick to the 12 guage. Is your life or your family's life not worth that much to protect it?
Great answer. My question was intended more along the lines of "why is the code that way?" as opposed to "this is my justification for cutting corners". I'm going to ground with the 12 gauge. Thanks for your time!!

 
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Old 02-11-04, 04:03 PM
arcspark
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Thanks. Glad to see you are trying to understand the technical aspects of your project. Electrical is not that hard once you get some basic theory understood. Grounding and bonding is one of the most misunderstood applications, even among some electricians! Good luck with your project, keep asking questions, and b-safe.
 
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Old 02-11-04, 10:19 PM
noxx
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While it's acceptable per NEC 250.130(C) to bring an external ground to these receptacles, you'll run into a host of other code violations running the wire, especially providing entrance into the nonmetallic (bakelite?) boxes for a single conductor without damaging the boxes and violationg one of the cardinal codes, 110.12.

I'd recommend using GFCI protection as allowed by 406.3(d). A grounded recep may be installed on an ungrounded two-wire cable if protected by a gfci recep or cb. This is more costly in terms of material, but will save quite a bit of time and other hassles. Be advised also that any external ground needs to be connect to the grounding electrode conductor, and that in a home of that age the GEC may be non-existent or wholly inadequate.
 
 

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