- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
I cry "bovine scatology"
If the 1/4" KO was for drainage, why is there a slug to knock out?
If that were true it would just be a hole and not a KO.
GEC entering panel
- Thread starter Hacky
- Start date
- Status
I cry "bovine scatology"
If the 1/4" KO was for drainage, why is there a slug to knock out?
If that were true it would just be a hole and not a KO.
romex jockey
Senior Member
- Location
- Vermont
- Occupation
- electrician
One can run a GEC to meter OR panel Mr Infinity>>>>
110.28 Enclosure Types. Enclosures (other than surrounding
fences or walls covered in 110.31 ) of switchboards, switchgear,
panelboards, industrial control panels, motor control centers,
meter sockets, enclosed switches, transfer switches, power
outlets, circuit breakers, adjustable-speed drive systems, pullout
switches, portable power distribution equipment, termination
boxes, general-purpose transformers, fi re pump controllers,
fi re pump motors, and motor controllers, rated not over
1000 volts nominal and intended for such locations, shall be
marked with an enclosure-type number as shown in Table
110.28.
~RJ~
goldstar
Senior Member
- Location
- New Jersey
- Occupation
- Electrical Contractor
I completely agree with this but, I'd just like to point something out. Logically speaking (and aside from any Code violations) would it make any difference, from a mechanical point of view, whether the GEC wiring enters the panel through the small hole(s) or through a 1/2" KO without any type of connector ? They're still getting landed on the ground bar in the panel. Now, although a 1/2" squeeze connector is not listed for use with single conductors wouldn't it make more sense to strip the insulation off the wire(s), have the clamp on the connector squeezed down on the bare wires and the lock nut tightened where it cuts into the metal of the cabinet and then land the wires on the ground bar ? I would think that would be more of an assurance that the GEC wiring had a better connection to the cabinet. If you don't agree with that method then the entering through the small hole is the only way to go and doesn't use up a KO.
And, BTW, years ago when I was young, bullet-proof and unafraid of the voltage I was dealing with, I was working in a newly installed residential breaker panel that was live and I brought an NMC into the panel. Not paying close attention, the ground wire whipped around and landed across both phases. Quite an arc flash and it actually blew that green ground screw out of the panel. So, the only thing bonding the ground bar(s) to the cabinet is that green ground screw. I think the squeeze connector is a better method. Just my opinion. No Code reference to back it up.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
The following two cases seems qualitatively similar to me physics-wise:
a) The GEC exits a steel enclosure through a small hole, unbonded.
b) The GEC exits a steel enclosure through a steel conduit, which it exits at an open end, unbonded.
In both cases a portion of the GEC is enclosed in electrically continuous steel, with no bond where the GEC exits the steel enclosure. 250.64(E) prohibits (b), but the majority view here is that (a) is allowed. Does the physics support this distinction? I.e. if the choke effect is a function of the length of the enclosed conductor, and of the distance to the steel enclosure, then perhaps the choke effect is small enough to ignore in (a), but not in (b).
Cheers, Wayne
a) The GEC exits a steel enclosure through a small hole, unbonded.
b) The GEC exits a steel enclosure through a steel conduit, which it exits at an open end, unbonded.
In both cases a portion of the GEC is enclosed in electrically continuous steel, with no bond where the GEC exits the steel enclosure. 250.64(E) prohibits (b), but the majority view here is that (a) is allowed. Does the physics support this distinction? I.e. if the choke effect is a function of the length of the enclosed conductor, and of the distance to the steel enclosure, then perhaps the choke effect is small enough to ignore in (a), but not in (b).
Cheers, Wayne
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
I'd say the code has to draw the line somewhere. Surely the length of the conduit is a factor, but there's probably no tenable reason to say that a certain length needs to be bonded and another does not. Total lack of ferrous conduit extending from the enclosure is probably a more reasonable line to draw.
peter d
Senior Member
- Location
- New England
I land the GEC on the neutral bar and I always bond a separate ground bar with a wire so this very thing doesn't happen.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I agree, besides there typically already is drainage holes (no knocking out necessary either) near the corners of the bottom wall of such enclosures. Occasionally those holes are even large enough to pass a 6AWG solid bare conductor through (usually not quite big enough for 4 AWG though) and I have done so.
I tried to say that earlier - so how long can the "continuous steel closure" be before choke effect becomes significant. Panel wall thickness will have an effect - but I think most will agree fairly insignificant effect - yet if we were to pass normal current carrying conductors of a circuit through separate holes in a cabinet wall many also agree we need to cut slots between the holes to effectively make just one hole to reduce inductive heating and choke effects.
peter d
Senior Member
- Location
- New England
It should also be pointed out that an NEC GEC is NOT a UL listed lightning protection system. An actual LPS is worlds apart from what we install to be compliant with the NEC. So even if the sheet metal somehow "choked" the current heading to the ground rod, does it matter with a lighting strike? We have all seen lighting damage on houses that don't have an LPS and it's quite significant.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Absolutely agree with you, "dirt worshipers" like to exaggerate things, the GES on many installations isn't as critical as they want us to believe it is. And if you have a direct lightning strike the choke effect on the hole the GEC passes through or even the metal pipe it may pass through is likely the least thing to be concerned about, you are going to have significant damage either way.
jwelectric
Senior Member
- Location
- North Carolina
I am surprised that with the number of electrical engineers on this site not one has step up to explain the effects of eddy currents. Someone please explain why it is so important to bond both ends of a rigid pipe but not the enclosure, please :?
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Where passing a GEC through a hole in cabinet wall that would mean you have to bond it inside and outside wouldn't it?
Otherwise the cabinet is usually bonded - usually via a screw in the neutral bar.
romex jockey
Senior Member
- Location
- Vermont
- Occupation
- electrician
Gentlemen, let's review please>>>
250.64(E) Raceways and Enclosures for Grounding Electrode
Conductors.
(1) General. Ferrous metal raceways and enclosures for
grounding electrode conductors shall be electrically continu‐
ous from the point of attachment to cabinets or equipment to
the grounding electrode and shall be securely fastened to the
ground clamp or fitting. Ferrous metal raceways and enclosures
shall be bonded at each end of the raceway or enclosure to the
grounding electrode or grounding electrode conductor to
create an electrically parallel path. Nonferrous metal raceways
and enclosures shall not be required to be electrically continu‐
ous.
^^^'at each end of raceway or enclosure'
Thus terminating within it means bonded at MBJ AND enrty
110.28 Enclosure Types
definitionally covers anything with a GEC run into or through it.
&&&
312.5 Cabinets, Cutout Boxes, and Meter Socket Enclosures.
Conductors entering enclosures within the scope of this article
shall be protected from abrasion and shall comply with
312.5(A) through (C)
(A) Openings to Be Closed. Openings through which
conductors enter shall be closed in an approved manner
'closed' is when a connector is used
in an 'approved manner' is when it's listed for such use
&&&&
IEEE142 , a very detailed doc , describes lightning strikes anywhere from 44,000 Amps to 270,000 amps
I don't need to do the math to see the concern for any choke effect becoming relevant in what may be 4-6" of #4 CU mitigating that charge
If there's an EE in the house that would, have at it
~RJ~
250.64(E) Raceways and Enclosures for Grounding Electrode
Conductors.
(1) General. Ferrous metal raceways and enclosures for
grounding electrode conductors shall be electrically continu‐
ous from the point of attachment to cabinets or equipment to
the grounding electrode and shall be securely fastened to the
ground clamp or fitting. Ferrous metal raceways and enclosures
shall be bonded at each end of the raceway or enclosure to the
grounding electrode or grounding electrode conductor to
create an electrically parallel path. Nonferrous metal raceways
and enclosures shall not be required to be electrically continu‐
ous.
^^^'at each end of raceway or enclosure'
Thus terminating within it means bonded at MBJ AND enrty
110.28 Enclosure Types
definitionally covers anything with a GEC run into or through it.
&&&
312.5 Cabinets, Cutout Boxes, and Meter Socket Enclosures.
Conductors entering enclosures within the scope of this article
shall be protected from abrasion and shall comply with
312.5(A) through (C)
(A) Openings to Be Closed. Openings through which
conductors enter shall be closed in an approved manner
'closed' is when a connector is used
in an 'approved manner' is when it's listed for such use
&&&&
IEEE142 , a very detailed doc , describes lightning strikes anywhere from 44,000 Amps to 270,000 amps
I don't need to do the math to see the concern for any choke effect becoming relevant in what may be 4-6" of #4 CU mitigating that charge
If there's an EE in the house that would, have at it
~RJ~
Last edited:
peter d
Senior Member
- Location
- New England
You keep grasping for straws but it's not working. That article doesn't apply to a single bare conductor not in a raceway. You still can't provide a code article to support your position.
jwelectric
Senior Member
- Location
- North Carolina
How about 250.64(E) where it says, " to create an electrically parallel path." To be parallel it needs to be electrically joined on both ends, once on the terminal bar and the other where it passes through the enclosure. UL says that the 1/4 inch hole in outside panels are for drainage not conductors as has already been posted.
Yes I know that a SOP is hard to defeat but a SOP is not code
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Stepping away for a moment from the Code and just looking at the physics, the reason to bond both ends of a ferrous raceway enclosing a GEC is the choke effect. You have an effective partial turn of the conductor around (through) an iron core. In the case of lightning induced current that could cause the current to seek another path, possibly arcing through air, or develop a harmful voltage difference to earth ground. The duration is short enough that eating from eddy currents can be ignored.
In the case of a sheet metal enclosure the series inductance is not likely to cause a problem, but the eddy current heating over a sustained period of time for conductors that normally carry current will be noticeable. The loss mechanism is similar to that which motivates making a transformer core out of separate laminations instead of solid metal.
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romex jockey
Senior Member
- Location
- Vermont
- Occupation
- electrician
Grounding & Bonding via '11 NEC
The effectiveness of a grounding electrode is significantly reduced if a ferrous metal raceway containing a GEC isn't bonded to the GEC at each end. This is because a single conductor carrying high-frequency induced lightning current in a ferrous raceway causes the raceway to act as an inductor. That severely limits (chokes) the current flow through the GEC. ANSI/IEEE 142, "Recommended Practice for Grounding of Industrial and Commercial Power Systems" (Green Book) states: "An inductive choke can reduce the current flow by 97%."
~RJ~
The effectiveness of a grounding electrode is significantly reduced if a ferrous metal raceway containing a GEC isn't bonded to the GEC at each end. This is because a single conductor carrying high-frequency induced lightning current in a ferrous raceway causes the raceway to act as an inductor. That severely limits (chokes) the current flow through the GEC. ANSI/IEEE 142, "Recommended Practice for Grounding of Industrial and Commercial Power Systems" (Green Book) states: "An inductive choke can reduce the current flow by 97%."
~RJ~
Mgraw
Senior Member
- Location
- Opelousas, Louisiana
- Occupation
- Electrician
From a GE meter socket publication. Bold by me.
Ringless meter cover
Revised catalog number and ground labels
Latches and Hasps changed to Stainless
Mounting bosses moved toward corners of enclosure
9/32” ground wire hole K/O in bottom
Single latch centrally located hasp on Meter cover
Ringless meter cover
Revised catalog number and ground labels
Latches and Hasps changed to Stainless
Mounting bosses moved toward corners of enclosure
9/32” ground wire hole K/O in bottom
Single latch centrally located hasp on Meter cover
peter d
Senior Member
- Location
- New England
I don't agree. The GEC is bonded to the neutral terminal in meter sockets, thus satisfying the rule for it to be in parallel. They are at the same potential and no further bonding is needed.
It's common to use PVC to enclose the GEC going to meter sockets here. The GEC still passes through the enclosure unbonded in the same fashion it does through the 1/4" hole.
Mgraw
Senior Member
- Location
- Opelousas, Louisiana
- Occupation
- Electrician
You do realize that section was talking about ferrous metal conduit being used to protect the GEC.
goldstar
Senior Member
- Location
- New Jersey
- Occupation
- Electrical Contractor
I'm trying to keep up with the gist of where this thread is going and I'm not sure if it matters where the GEC gets terminated. We used to be able to land a GEC inside the meter pan here in NJ but many EI's now will not allow it citing that it is not "serviceable" once the POCO locks the meter pan. So, all grounding wiring has to be done inside the panel with the first or main over-current device. Now we're back to the green ground screw as being the only thing bonding the neutral bar to the cabinet (assuming everything upstream was either PVC or SE cable).
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