Grounding Conductor

[Another C10]

I always seem to pull a ground, I remember one service call in particular at a car dealership were a 200 Amp splice box supporting some massive kernies, one being pressed up against the enclosure which had became so saturated inside from rain water pouring in through a "SS Conn", that before isolating it had noticed at the gear it fed you could literally see and hear arcing across all the nearby concentrics and connectors, it was a pretty amazing sight. That sold me on why using the metal enclosure isn't necessarily the best path for fault current. The main never tripped.

 

[romex jockey]

If you guys have branch in ALL EMT do you run ground wire to each receptacle along with the hot/neutral or use the conduit as EGC? Just a regular 20A duplex.

What works best?

Assume a typical scenario, industrial setting run of #10's in 1" emt , 20A OCPD's

what is the AIC w/EMT ?, what is the AIC w/EGC? what is the AIC w/both EMT & ECG?

figure a 500' fault, maybe a 1000' fault

consider resistance and reactance of each fault path, or multiple paths


~RJ~

 

[flashlight]

I pull one. I see a lot of emt in commercial situations such as warehouses that has been banged into, or stepped on. or
compromised in some way.

 

[romex jockey]

2020 Code Language:

N 250.109 Metal Enclosures. Metal enclosures shall be permitted to be used to connect bonding jumpers or equipment grounding conductors, or both, together to become a part of an effective ground-fault current path. Metal covers and metal fittings attached to these metal enclosures shall be considered as being connected to bonding jumpers or equipment grounding conductors, or both.

~RJ~

 

[infinity]

What you are asking about is Equipment Grounding Conductors.

Correct, I fixed it.

 

[Eddie702]

Common sense should prevail. If the emt is strapped good its a non issue weather to pull a ground or not, personally I always do and new jobs I see in my area in the last 20 years always have a ground

On a roof on blocks its going to get stepped on, bent, tripped over etc. Die cast fittings especially don't take a lot of abuse.

I think you have to pull a ground there

 

[romex jockey]

I always seem to pull a ground, I remember one service call in particular at a car dealership were a 200 Amp splice box supporting some massive kernies, one being pressed up against the enclosure which had became so saturated inside from rain water pouring in through a "SS Conn", that before isolating it had noticed at the gear it fed you could literally see and hear arcing across all the nearby concentrics and connectors, it was a pretty amazing sight. That sold me on why using the metal enclosure isn't necessarily the best path for fault current. The main never tripped.

One of many real world scenario's C10

so how is it 250.109 debuted in '20?

rationale?

science?

stats?

~RJ~

 

[electrofelon]

I pull a ground wire.
I don't know if I've ever seen a 40-year-old installation that still has all of the joints intact.

I'm sure it has to do with expansion and contraction, not installation issues.

So from what I've seen, it's almost a guarantee that your receptacles are not going to be grounded at some point in the future if you only rely on those fittings

I think I have been around my fair share of 40 year old EMT that didn't have the best workmanship and I just have not seen all these pulled out fittings some talk about. In fact I literally can't remember one instance of it. In fact, the die cast fittings everyone used to use are usually a bear to get apart. I see bad/weak/loose/improper wire nut connections FAR more frequently than conduit connections, thus I find a conduit EGC to be a much better EGC.

 

[infinity]

One of many real world scenario's C10

so how is it 250.109 debuted in '20?

rationale?

science?

stats?

~RJ~

It's likely that this is nothing new because we've been using metal enclosures for a grounding path for 100 years. Here's a good discussion.

2020 NEC 250.109

Would this apply to the requirements of 250.24(A)(1) having the GEC terminate at the grounded conductor bus ? If I’m not mistaken , unless you have a wire type or busbar connecting the grounded conductor buss and the EGC buss, the GEC must terminate at the grounded conductor buss? If a screw...

forums.mikeholt.com

 

[garbo]

If you guys have branch in ALL EMT do you run ground wire to each receptacle along with the hot/neutral or use the conduit as EGC? Just a regular 20A duplex.

Stopped using all conduits to supply the ground to a device over 45 years ago. While in most cases it's acceptable never 100% reliable. Saw way too many EMT fittings pull apart, steel rigid conduit rust thru etc. Nothing safer then a copper ground conductor same side as the wires feeding 15 & 20 amp receptacles. Was taught that the ground conductor is the most important wire and that it should be the first conductor connected & last to be removed.

 

[infinity]

Stopped using all conduits to supply the ground to a device over 45 years ago. While in most cases it's acceptable never 100% reliable. Saw way too many EMT fittings pull apart, steel rigid conduit rust thru etc. Nothing safer then a copper ground conductor same side as the wires feeding 15 & 20 amp receptacles. Was taught that the ground conductor is the most important wire and that it should be the first conductor connected & last to be removed.

That's a good all around policy if you can cover the cost but if you had a big job with all EMT and the spec did not call for EGC's (meaning that no one is paying for them) would you still install them? It could be a significant cost that you would have to eat.

 

[Dennis Alwon]

Stopped using all conduits to supply the ground to a device over 45 years ago. While in most cases it's acceptable never 100% reliable. Saw way too many EMT fittings pull apart, steel rigid conduit rust thru etc. Nothing safer then a copper ground conductor same side as the wires feeding 15 & 20 amp receptacles. Was taught that the ground conductor is the most important wire and that it should be the first conductor connected & last to be removed.

I am with you in that we always ran a wire equipment grounding conductor however if emt is so unsafe why does the nec allow it. I hear people say that it is not reliable and the couplings and connectors are often not tightened, especially the screw tight conn and coup. There must not be enough evidence that it is unsafe or it would get changed.

 

[infinity]

I am with you in that we always ran a wire equipment grounding conductor however if emt is so unsafe why does the nec allow it. I hear people say that it is not reliable and the couplings and connectors are often not tightened, especially the screw tight conn and coup. There must not be enough evidence that it is unsafe or it would get changed.

I'm am sure that if you go back through past code change proposals you will find many that were for requiring a wire type EGC in EMT. So far it hasn't happened.

 

[kwired]

In a good installation the metal raceway will have less impedance than the wire type EGC typically installed in it.

 

[don_resqcapt19]

I always seem to pull a ground, I remember one service call in particular at a car dealership were a 200 Amp splice box supporting some massive kernies, one being pressed up against the enclosure which had became so saturated inside from rain water pouring in through a "SS Conn", that before isolating it had noticed at the gear it fed you could literally see and hear arcing across all the nearby concentrics and connectors, it was a pretty amazing sight. That sold me on why using the metal enclosure isn't necessarily the best path for fault current. The main never tripped.

I would expect that it was not a bolted fault and the current flow was limited by the impedance of the fault and not the impedance of the metal enclosure. If the current flow is not great enough to get into the instantaneous trip range the breaker will not quickly clear the fault.

 

[infinity]

It's funny because when I first started in this business in the 80's we never pulled a wire type EGC. In the 90's and 00's we pulled them. In the 10's and 20's we're no longer using them. I'm guessing that someone realized that the cost versus the benefit just wasn't worth it.

 

[James L]

I think I have been around my fair share of 40 year old EMT that didn't have the best workmanship and I just have not seen all these pulled out fittings some talk about. In fact I literally can't remember one instance of it. In fact, the die cast fittings everyone used to use are usually a bear to get apart. I see bad/weak/loose/improper wire nut connections FAR more frequently than conduit connections, thus I find a conduit EGC to be a much better EGC.

You have wire nut fails on your own work?

I'm thinking conduit joint failure through no fault of my own. I don't believe my wire nut connections will fail

 

[electrofelon]

You have wire nut fails on your own work?

I'm thinking conduit joint failure through no fault of my own. I don't believe my wire nut connections will fail

No not mine, others'

 

[romex jockey]

In a good installation the metal raceway will have less impedance than the wire type EGC typically installed in it.

then an ~R~ value would have to apply kwired

where would one reference that ?

~RJ~

 

[infinity]

I think that it's referenced here:

https://steeltubeinstitute.org/