Equipment Grounding Conductor History

[anthonyklesta]

Does anyone know when it became more common to pull an EGC, instead of using a metallic conduit as the main EGC? (For feeders and branch circuits) I have been doing research on this topic, but cannot seem to find when this practice changed.

 

[tortuga]

I'd say people starting thinking about wire type equipment grounds in the late 1950's that's when the bonding strip was added to AC cable, MC was coming out with a wire type EGC and grounded romex came out.
By the end of the 60's there was a new batch of electricians who were used to seeing wire type EGC's and grounded receptacles so my guess is around then.

 

[infinity]

I started offically in 1987 and back then we never pulled an EGC in a metal raceway. In my experience we didn't start pulling them until the mid to late 90s when IGs were becoming popular.

 

[Sberry]

60 ish in cable, I see a black wire in a 60 install was connected daisy chain to kitchen and laundry outlets.

 

[don_resqcapt19]

There are still a huge number of circuits being installed using the raceway as the equipment grounding conductor as permitted by the code.

 

[infinity]

There are still a huge number of circuits being installed using the raceway as the equipment grounding conductor as permitted by the code.

In the past few years we've seen more and more projects where there are no wire type EGC's being used. MC-ap or EMT without an EGC is a great way to save money and developers are catching on to the fact that they've been wasting money on wire type EGC's for decades.

 

[LarryFine]

I never use a redundant wire EGC where I don't have to (code, specs, etc.)

 

[Tulsa Electrician]

Google this.

 

[Sberry]

I dont add a wire if I dont have to.

 

[David Castor]

Testing done by GE in the 60s showed pretty clearly that steel conduit is not a good return path when compared to an EGC inside the conduit. This gets worse over time due to corrosion. This testing was prompted by the increasing use of solidly-grounded 480 V systems. For 480 V we ran a separate EGC starting in the early 70s, but continued to use conduit for grounding for lighting and receptacle circuits until the early 1980s. At that point we started running an EGC for all circuits. Obviously the steel conduit manufacturers pushed back hard on any suggestion that the conduit wasn't a good ground, but no one has really refuted the test result, as far as I am aware.

 

[retirede]

Testing done by GE in the 60s showed pretty clearly that steel conduit is not a good return path when compared to an EGC inside the conduit. This gets worse over time due to corrosion. This testing was prompted by the increasing use of solidly-grounded 480 V systems. For 480 V we ran a separate EGC starting in the early 70s, but continued to use conduit for grounding for lighting and receptacle circuits until the early 1980s. At that point we started running an EGC for all circuits. Obviously the steel conduit manufacturers pushed back hard on any suggestion that the conduit wasn't a good ground, but no one has really refuted the test result, as far as I am aware.

Do you have a link to that test? It’s contrary to what I’ve been taught and believed forever.

 

[tortuga]

Google this.

Very cool, I love anything two phase.
On that page 27 you posted I get diagrams 'a' and 'b' 440 3 wire and 440/220 4 wire, but I dont get this diagram 'c'.
How do they come up with 492V to ground on that bottom leg?

 

[drcampbell]

... How do they come up with 492V to ground on that bottom leg?

2⌀, 4-wire circuit, phases at 90° to each other.

 

[LarryFine]

View attachment 2566926

Your diagram shows a connection the previous one does not.

 

[tortuga]

2⌀, 4-wire circuit, phases at 90° to each other.

View attachment 2566926

Of course just a triangle c = √(a² + b²)
That must be it.

 

[tortuga]

Do you have a link to that test? It’s contrary to what I’ve been taught and believed forever.

The NEC equipment grounding tables for a long time (last seen in the 1965 NEC) had pipe and EMT right in the table that we now call 250.122, and it looks like 1/2 IN EMT was good for 100 Amps:

 

[drcampbell]

Your diagram shows a connection the previous one does not.

That connection is the only way 492 volts can be derived.

 

[don_resqcapt19]

Testing done by GE in the 60s showed pretty clearly that steel conduit is not a good return path when compared to an EGC inside the conduit. This gets worse over time due to corrosion. This testing was prompted by the increasing use of solidly-grounded 480 V systems. For 480 V we ran a separate EGC starting in the early 70s, but continued to use conduit for grounding for lighting and receptacle circuits until the early 1980s. At that point we started running an EGC for all circuits. Obviously the steel conduit manufacturers pushed back hard on any suggestion that the conduit wasn't a good ground, but no one has really refuted the test result, as far as I am aware.

Testing done at Georgia Tech for the Steel Tube Institute shows otherwise.

https://steeltubeinstitute.org/wp-content/uploads/2020/11/PT_SteelConduitCircuitAnalysisAndTesting_Final.pdf

 

[David Castor]

Testing done at Georgia Tech for the Steel Tube Institute shows otherwise.

Of course it does...

 

[David Castor]

Do you have a link to that test? It’s contrary to what I’ve been taught and believed forever.

GE Let's Be More Specific About Equipment Grounding | PDF

zero sequence

www.scribd.com

Determination of ground-fault current on common A-C grounded-neutral systems in standard steel or Aluminum conduit

A NEED has been indicated in the electrical industry for information which will enable the design engineer to predict the magnitude of fault current that will flow in a circuit enclosed by metal conduit when subjected to ground fault conditions. The purpose of this paper is to present usable...

ieeexplore.ieee.org

The second one is more specifically on-topic, but not accessible without IEEE Library access.