Wire type EGC in the NEC
- Thread starter marcosgue
- Start date
- Status
Buck Parrish
Senior Member
- Location
- NC & IN
According to an article in the ECM. It was introduced in 1956-62 EGC along with three prong outlets . To ground the metal housing of equipment.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
It was introduced to prevent shocks. 12 AWG NM had a 14 AWG. The EGC in some cases presented more of a shock hazard. It was the GFCI that was the shock hazard answer.
Last edited:
I understand the first answer to my questions, we learn every time in this forum and I'm sorry my missing out the second part to my question, but my point is why the use frequently of wire type EGC with metal raceway if it's no necessary?
Dsg319
Senior Member
- Location
- West Virginia
- Occupation
- Wv Master “lectrician”
Some people think it’s redundant to do, others don’t like the idea of a mechanical connection of conduit being their low impedance fault current path to clear a fault.
As well as certain companies and specs a lot of times in my areas of work always require a wire type EGC.
DrSparks
The Everlasting Know-it-all!
- Location
- Madison, WI, USA
- Occupation
- Master Electrician and General Contractor
Yes especially EMT with those cast zinc set screw couplings.
Sent from my SM-A326U using Tapatalk
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
If you make a code proposal for wire type EGC, the metal raceway panel members will say its a installation issue, ie product is safe when installed correctly.
It is a myth that common electrical hardware (metallic conduits, cable trays when properly installed AS an EGC) are inferior to copper cable. Quite the opposite is true. Certain Codes (hospitals) require redundant grounds and an EGC certainly fulfills that role. There are also differences in performance in terms of surge and higher frequencies so a stranded ground conductor is often recommended for lightning protection systems and variable frequency drives.
It is also a myth that grounding is always the solution. The idea is two fold. The first is that it keeps people who are normally grounded close to the same potential as the surfaces of electrical equipment. As distances increase or if ground loops are present such as with bracket grounding or multiple system bonding jumpers this condition may no longer hold. NEC mandates single point grounding and OSHA requires work site (single point) grounding.
The second idea is that given a low enough impedance short circuit protection can do double duty for both phase to phase and phase to ground faults. Again impedance causes major issues on larger systems. For instance say a circuit breaker on a 208 V system uses a 100 A breaker. The short circuit trip will be 1000 A using typical UL 489 B curves. The phase to ground voltage is 120 V so if the impedance exceeds 0.12 ohms, it won’t trip properly. This condition is easily achieved with very short distances.
As cable lengths increase grounding via cables or equipment is no longer effective. However as the following report shows steel conduit and EMT is vastly superior to EGCs.
GEMI Analysis Software | Steel Tube Institute
Download the free GEMI Analysis Software to:– confirm wire-type equipment grounding conductors provide an effective ground-fault current path– confirm steel...
steeltubeinstitute.org
Multi grounded systems become a necessity as Earth has a 2D grounding system actually decreases impedance with distance (see IEEE Green book). Summary: resistance grows linearly with distance but the number of paths grows with the square of distance. So the net result is resistance is proportional to the inverse of the distance. Alternatively we can use common mode detection and tripping (sum of the phase currents should equal zero, the GFCI operating principle) or at extreme distances using distance relays which trip if the measured impedance falls under a certain range.
So if you are working residential this is mostly a lot of detail you never need to know. In a utility environment it’s baked into the design. In commercial and industrial it’s very easy to cross over from effective grounding to ineffective grounding. If anything the GEMI software and some tables produced with it are good at keeping you between the ditches.
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
The purpose of an EGC is to open a breaker or fuse during a fault condition. Doing so eliminates dangerous touch voltage.
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
In what scenario would it present more of a shock hazard?
GFCIs only came into mandate due to missing EGCs stemming from an early lack of theoretical knowledge.
Considering the failure rate of GFCIs, it is not the answer.
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
Post #9 made a valid point, GFCIs do not stop shocks, why was it taken down?
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
A person has to get shocked first, (touch the faulted object) before a GFCI will open.
Where an EGC will remove voltage from the surface of an object regardless.
Where an EGC will remove voltage from the surface of an object regardless.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
It is a fascinating phenomenon. At some point using a 250.118 approved raceway as the EGC started being viewed negatively by most in the industry. I am not really sure why that started happening and no one seems to know. I can just conjecture that it came along with all the excessive obsession with grounding and bonding. I started in the trade in about 1998, and it was well entrenched before then. Best I can tell this ridiculous movement started in the '80s, maybe some of the older members on the form here can comment on the time frame.
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
Most people do not place expansion joints on conduit as needed or correctly. Fitting can loosen. Conduit oxides. Conduit moves.
On the other hand a copper spliced EGC is no different than a phase or neutral splice. We know it holds up.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
I'm not going to argue about it, I'm sick of this topic. The cult of the green wire has you, may God save your soul
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
I'm not going to argue about it, I'm sick of this topic. The cult of the green wire has you, may God save your soul
"Admittance" or Y, is key
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
A GFCI will also clear a ground fault an EGC won't. For instance, suppose someone touched a hot wire and a small amount of current went through his/her body to ground. The small amount of current would not open the OCPD but the GFCI should sense it and clear the fault.
Also a GFCI will not clear a hot to neutral fault at all.
So really for best protection you need both where the risk warrants it.
- Status