Eelctrical Snafu

[cope]

When I bought my house in 1986, I added a second breaker box for the garage because the garage had only one 15 amp circuit. I ran 6-3 Romex from a 50 amp 220 breaker for my Miller arc welder. In previous garages I had used 8-2 w/ ground because I only had to run a 6' run from the breaker. The 6-3 had black/red/white insulated wires where the 8-2 had blck/white/bare copper. Without a second thought I used black and white for the line and red for the ground. This wasn't correct, but since it was done at both ends there was no problem. Three years ago I added a 20 amp recepticle from the welder recepticle for my table saw. When I realized that this violated code I removed it. In the process I wired the recepticle correctly(black/red line and white ground). Fortunalely I did not plug my PowCon in. I discovered the mistake the other night when I reached for my tire inflator chuck which was hanging next to the conduit the 6-3 runs in and got a healthy tingle. Even with the breaker off there was 150 volts feeding through one leg. I now have the whole circuit re-wired correctly.

Morale of the story is pay attention to details.

[Scott V]

Cope,try a green ground next time!

[cope]

Originally posted by Scott V
Cope,try a green ground next time!

Scott, the 8-2 had bare copper and the 6-3 had black/white/red. I guess they figure that 6-3 isn't used too often for 110 volt apps? Green would have made it a no-brainer though.

[Sberry]

Yes, green or bare and there are lots of rules for remarking wires, too many to list here and some exemptions in certain places. Remember, a sub panel in the same structure ALWAYS requires a 4 wire feed with the neutral and the ground unbonded at the subpanel. The ground and neutral are seperate in a sub. The only time you can use 3 wire is in a detatched building with no other metal inerconnecting parts,, such as phones or metal gas lines, then you bond the neutral. Remember also that a ground isnt what it sounds like in most instances, it is to be a fault return path back to the neutral at the service entrance. For the purposes of grounding a welding machine the ground wire goes back to the panel,,, not to a ground rod. You may know this but it is an important for others to understand this when hooking up machines.

[Scott V]

Try here.

Aaron,homework!

http://www.practicalmachinist.com/ubb/Forum1/HTML/001887.html

[pontiac]

Disclamer First.. IANAE (I am not an Electrican)

If I understand what they are getting at you should at a minimum bond the rod for your table to the main panel ground bus with a heavy gauge insulated wire.

Better yet would be to dicconect the grounding rod and run a dedicated ground from the table to the main pannel ground bus.
(I think)

[Sberry]

The grounding system for equipment saftey and lightning grounds are different. As well as carrying lightning strikes the ground rod eqeulizes the potential of the structure and the ground you are standing on. It has nothing to do with ground faults from the power source. There is only to be one grounding system within the same structure to eleminate potentials and so there are not alternative ground paths with seperate potentials. (essentially and as easily as I can explain it here, maybe we have EE here somewhere) So, one ground rod system. In detatched buildings its slightly different and it requires another rod so a lightning strike is carried to actual ground as soon as possible and hopefully not carried on the wiring system. Also the reson for 4 wire in a detached building where there are interconnecting metal pipes or wires is so that the grounding conductor is along WITH the current carrying conductors which helps clear faults (shorts) and that one of the wires or pipes doesnt become an alternate path. A ground rod to the bench would provide no use and grounding to the electric system is not required unless there is an electric supply from the service. Sometimes it may even cause a problem under certain circumstances. My explanations may not be clear sometimes but thats the basics.

[cope]

When did the 4 wire rule come to be? I knew about it because my daughter rented a duplex with the 4 wire recepticle for the 220 dryer, but my house was built in 1964 and my last one in 1977 and I didn't have 4 wire 220 in either one.

[atucker]

If you want to "muddy the water" a little more, check a Miller Owners Manual for one of the TIG machines - check the "High Frequency" section.

Neutral/Ground discussions can get real interesting depending on who you are talking to, what municipality, etc. Many of the municipalities around here still require an Earth ground (rod) AND a water pipe ground.

Allen T.

[Old Man Stick]

Originally posted by cope
When did the 4 wire rule come to be? I knew about it because my daughter rented a duplex with the 4 wire recepticle for the 220 dryer, but my house was built in 1964 and my last one in 1977 and I didn't have 4 wire 220 in either one.

I think the 4 wire 220 came in 2000 ?? or maybe 1999. Thats SOO nice now! NOT LOL My dad has rental houses. I had to go in and add the 4 wire plugs on the dryers and rainge. You never know what the new people moveing in will have and man are thay UNHAPPY when there new dryer wil NOT plug in to there new place!

I thougth it would have come out sooner with all the questions about grounded and grounding.

Nope im not a EE just the old man was and still has his electrical Inspector Cert. for Ohio. So I got to grow up in the feild and work in the family bussness for a few years untill he retired and I did nto feel like carrying it on...... Some days I do feel really DUMB too!!!

OMS

[INTP]

The 1996 version of the National Electric Code (NEC) introduced a fourth conductor for dryers, ovens, and a couple other home appliances. (Old= R/B/G, New=R/B/W/G) Cities often trail the NEC by a couple years or more, so it may or may not have taken effect where you live for some time.

The point of the fourth (W) conductor feeding these appliances is that many of them are starting to come with features that use only 120V. Timers, lights (in the oven), etc. are often 120V. If the appliance uses just one leg of the 240V circuit, it still needs a 0V wire to complete the 120V portion. If there's no neutral (white), then it has to use the ground, which is also 0V, but is not insulated. This introduces a voltage into an un-insulated ground wire, and depending on many variables, presents a possible shock hazard.

The concept is similar for subpanels, since they also have 120V and 240V circuits run off them. If the ground and neutral are connected to each other in the subpanel, then there is a likelihood that a voltage will be introduced into the ground wire. In addition, grounds are not necessarily the same voltage in different locatioins, so connecting the subpanel ground back to the main panel ground helps to make sure that the ground voltage is consistent.

There is a whole section of the NEC dedicated to grounding/bonding, and it's apparently one of the most perplexing sections. It's no wonder that it seems unclear at times.

I hope that makes sense.

[Sberry]

I am going to post this in both threads because its important. Yes, there tends to be some confusion but there doesnt need to be. For 99% of the people on this forum there is only one thing that is really important about grounding. When you read the instructions it says "Must be connected to an electrically grounded circuit." This doesnt mean water pipes or ground rods but only one thing. That the grounding conductor comes with the current conductors and ends up back at the neutral bar at service entrance. If you are on a properly wired subpanel you will hook the ground wire to the seperate equipment ground bar not the neutral bar. Its really that simple for the most part.

[Old Man Stick]

Originally posted by aweaver
As I understand it then, I should remove the earth ground (rod) from the welding bench. I should then attach the the rod to the sub panel in my welding shop. I should also add a rod to the sub in my garage. Both the garage and weld-shop are separate buildings from my house.

Do I have this correct? When I upgraded my homes electrical the inspector require me to use 2 ground rods. Should I use 2 at the outbuildings as well?

Aaron

Yes you should. For one the inspector will red tag the panel if you do not. There should be two grounds. Water pipe if you have a copper/iron water pipe thats in the ground and a grounding rod. If you DO NOT have the water pipe then you must put in 2 rods. In a subpanel you should have pulled 4 wire out ot each panel. two hots, a Neutral, and a ground. If you pulled the 4th wire for ground then ... depanding on your local code you should be able to only drive one ground rod. I do know know the code in your area or your inspector. Some inspectors are funny and really dont fully understand the whole grounding / grounded thing. I would just say drive two rods and be done with it.

OMS

[Sberry]

Yes, Old Man Stick is correct about all of that. They want a ground rod at the garage to carry lightning strikes and to eleminate potentials between the building and ground that you may be standing on. He is right that normally tey require only one there unless the local inspects feel that for some reason of soil conditions and such may require 2. You could put as many as you want as long as they are all connected together. Funny stuff happens once in a while especcially when there are more than one residence or service are connected to the same transformer especially in urban areas. Here is another tidbit related to grounds.
(B) With Circuit Conductors. By an equipment grounding conductor contained within the same raceway, cable, or otherwise run with the circuit conductors.
NEC HANDBOOK COMMENTARY;
One of the functions of an equipment grounding conductor is to provide a low-impedance ground-fault path between a ground fault and the electrical source. This path allows the overcurrent protective device to actuate, interrupting the current. To keep the impedance at a minimum, it is necessary to run the equipment grounding conductor within the same raceway or cable as the circuit conductor(s). This practice allows the magnetic field developed by the circuit conductor and the equipment grounding conductor to cancel, reducing their impedance.
Magnetic flux strength is inversely proportional to the square of the distance between the two conductors. By placing an equipment grounding conductor away from the conductor delivering the fault current, the magnetic flux cancellation decreases. This increases the impedance of the fault path and delays operation of the protective device.

[Sberry]

Here is another from Bob Keis, National code expert. If you have an interest read,, if not,, dont. With the amount of equipment we hook up it is important and I am sure some of the engineers will have an interest.
Then, we ground the system grounded conductor, the neutral, to earth, no equipment to earth, the system neutral to earth. Stop for a minute and consider where you put all the equipment grounding conductors at home. Most of you wired with Romex and the bare ground is landed directly on the neutral bar in the main service disconnect. Not in a subpanel, but at the main itself. Then you grounded the neutral. Thus all the equipment in you house is grounded to the neutral, just like is supposed to be.
Remember this also, the code requires a low impedance ground-fault return path for fault current. In order to obtain this, we must keep all the circuit conductors and the equipment grounding conductors in close proximity in the same raceway or cable. The is also required in "300.3 (B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (4)."
Everything stays together, including the IG ground.
Section 250.54 allows for what the code calls "supplementary grounding electrodes". Some electronic equipment in the installation instructions require this electrode. Why they want these I have no idea, but some electronic people think that if it isn't connected to earth, then it isn't grounded. They don't understand that the earth is loaded with stray currents from many things, but so be it. These stray currents come from many sources. One is the fact that between your grounding electrode at home the system transformer, there are currents through the earth in parallel with your service neutral. These are a fact of life and how much current depends on a lot of things. Also, you, or your neighbors could have a piece of UF going out to a yard light that has a nick in the insulation. Black or white, it don't matter. Some current is leaking out of this nicked insulation and will find it's way back to the electrical system through the earth. Then there are the installations that now grounded to a ground rod because that is the way they were put in. A good example of these are mall parking lot lights, or any large area lighting. A lot of these have no ground wire to them, they are grounded by way of a rod. If one of these lights develops a ground-fault, the current flow is down the rod, then back to the source through the earth. There are many references in the code that prohibit using the earth for an equipment grounding conductor, but these installations exist by the hundreds. If a ground rod is driven into an area that has any of these conditions, the current will be imposed on the equipment connected to this "isolated ground rod". This creates a shock hazard when touching the equipment grounded this way, and any equipment in the building that is connected to the building grounded system.
Take at least one example: A piece or equipment is grounded to a ground rod to satisfy the electronic people. They insist that the equipment be connected to an isolated ground. The average ground rod will megger well over 100 ohms. But just suppose you are lucky and manage a 10 ohm ground rod. 120 volt divided by 10 means that leas than 12 amperes will flow in case of a ground-fault. Will this clear a 15- or 20-amp overcurrent device? No way, but there is 120 volts going down the rod, and 120 volts on the metal of the equipment, just waiting for someone to come in contact with it. Where is this current going from the ground rod. Pretty much where ever it wants, and if there is a swimming pool nearby that for some reason wasn't properly bonded, or has a bad bonding connection, this could be time for an electrocution. About the overcurrent device, in order to clear a standard 20 amp circuit breaker in a reasonable time, it must have close to 80 to 100 amperes pass through it. Kind of hard to do when the rod will only pass 10 or 12 amperes.
I strayed, back to 250.54. This section permits a supplemental grounding electrode at the equipment, but the electrode must be connected to the equipment grounding conductor in the circuit to the equipment. A lot of mall lighting is installed this way. The supplemental electrode is bonded to the equipment ground of the light, and it provides added safety for lighting hits. A lot of the lightning energy will dissipate down the rod. Otherwise it would go back on the equipment ground in the circuit and since the insulation is only 600 volts, it causes a lot of damage to conductors.
As for isolation transformers, these are no different electrically than any other transformer. All transformers, other than autotransformers, are isolation transformers. By this I mean the primary is isolated from the secondary. The difference between a standard and an isolation transformer is the addition of a grounded metal shield between the primary and the secondary winding. All separately derived systems, transformers, must be grounded and bonded to comply with section 250.30. No exceptions are made for isolation transformers, nor for electronic equipment Again, some people feel that these transformers are neither bonded or grounded because they are special. If the bonding connection is not made, there is no way at all to complete the ground-fault return circuit for opening the overcurrent device. You wind up with phase voltage imposed on the entire structure, and this can be deadly.