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Home > Archive > Electrical Engineering > February 2006 > Unsure Ground conductor name
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Unsure Ground conductor name
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| Dear Experts,
I have some trouble with NEC grounding code provisions. I've been doing
this for a long time from Electrical Plans of different Design
Companies for industrial plants & comm'l complexes even in power staion
switchyards & substations but only now that I begin to queston. Here
it is :
I am running an insulated Equipment Grounding Conductor from MCC
grounding busbar to motorised equipments (pumps compressors HVAC equip)
along with the phase wires terminating on motor ground lug or terminal
box itself.
Also I am running a "bare cooper wire from motor chasis to a ground
bus" on the room wall then two wire loops around other ground bus on
other rooms, each ground bus has a wire going to the grounding
electrode (ring & rods or grids) outside.
1. What do I call this "bare cooper wire from motor chasis to a ground
bus" ,seemingly second type of ground wire?
2. Where in the NEC states that it is needed, required or safe to
install this? Is it always required?
3. What is the equivalent of this on the IEC standards? I ve read from
an ABB manual that there is only one PE ( the equivalent of EGC) for
all T-systems.
4. I suspect that this wire can defeat the purpose of GFrelays that
fault current running on the EGC will too weak to de activate the
breakers since fault current will be divided via "second ground wire".
if relays are not set properly. Is it correct.
If its no in the NEC then it is not violation if it is removed?
Really need the views from the Roughnecks out there before I go to Mike
Holt or McPartland.
Thanks Guys
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"dsky" <dsky_max@yahoo.com> wrote in message
news:1140848336.218339.260530@v46g2000cwv.googlegroups.com...
> Dear Experts,
> I have some trouble with NEC grounding code provisions. I've been doing
> this for a long time from Electrical Plans of different Design
> Companies for industrial plants & comm'l complexes even in power staion
> switchyards & substations but only now that I begin to queston. Here
> it is :
>
> I am running an insulated Equipment Grounding Conductor from MCC
> grounding busbar to motorised equipments (pumps compressors HVAC equip)
> along with the phase wires terminating on motor ground lug or terminal
> box itself.
>
> Also I am running a "bare cooper wire from motor chasis to a ground
> bus" on the room wall then two wire loops around other ground bus on
> other rooms, each ground bus has a wire going to the grounding
> electrode (ring & rods or grids) outside.
>
> 1. What do I call this "bare cooper wire from motor chasis to a ground
> bus" ,seemingly second type of ground wire?
> 2. Where in the NEC states that it is needed, required or safe to
> install this? Is it always required?
> 3. What is the equivalent of this on the IEC standards? I ve read from
> an ABB manual that there is only one PE ( the equivalent of EGC) for
> all T-systems.
> 4. I suspect that this wire can defeat the purpose of GFrelays that
> fault current running on the EGC will too weak to de activate the
> breakers since fault current will be divided via "second ground wire".
> if relays are not set properly. Is it correct.
>
> If its no in the NEC then it is not violation if it is removed?
> Really need the views from the Roughnecks out there before I go to Mike
> Holt or McPartland.
> Thanks Guys
Why are you using the ground bus that goes around the room?
GOOD posibility of creating a ground loop this why.
Ground the motors to the MCC or where the over current protection is.
Everywhere I have ever seen ground bars around a room they were for
sensitive electronics. I have never seen a exposed ground bus in a
mechinical room. What is the intention of the ground bus around the room?
Why in the world would you "wrap" a ground wire around a buss bar? Are you
trying to create a current transformer or pulling our legs?
Soars book on grounding.
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| electrician@electrician.com 2006-02-25, 6:21 pm |
| I do not consider myself an expert on this subject but here one
electrician's opinion from the field.
Answer to 1.
I would call your bare copper wire an equipment bonding jumper or just
a simple bonding jumper. We installed many such jumpers on Alaska's
North Slope and in Trans Alaska Pipeline pump stations in Class 1 Div 1
and 2 areas, and as I recall we called them bonding jumpers. The name
was not as important as is the proper installation.
Answer to 2.
We were told that these bonding jumpers are supposed to minimize the
discharge of static electricity. The NEC is not the standard for
static electricity.
>From the 2005 NEC:
For further information on protection against
static electricity and lightning hazards in hazardous (classi-
fied) locations, see NFPA 77-2000, Recommended Practice
on Static Electricity; NFPA 780-2004, Standard for the Installation
of Lightning Protection Systems; and API RP
2003-1998, Protection Against Ignitions Arising Out of
Static Lightning and Stray Currents.
I will leave 3 and 4 for others.
FYI
The NEC mentions equipment grounding conductors in 295 places, main
bonding jumper in 13 places, system bonding jumper in 13 places,
grounding electrode conductor in 145 places, bonding jumpers in 119
places, grounding conductor in 453 places, and equipment bonding
jumper in 24 places. That is a total of 1062 places.
Then there is the NESC for substations and switch yards. It mentions
bonding jumpers in 3 places and grounding conductor in 72 places.
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| This is laid out & required for in the electrical plans that we are
using,It is made by other design company, just implementing them.
I got the motor grounded via the EGC along with the phase wires.
It is the motor chasis & pump chasis bonded together with a jumper.
This terminal point is connect to the wall ground busbar by another
bare copper wire.
Pardon the inaccurate description I used, it describes the way of
interconnecting other busbars, that is, each ground bus have two wires
going into them from other busbars, strung together they form a loop.
Not trying to pull legs so I did not used the word "wrap" Im really
sorry.
Im just need some legal justification from available codes for having
two grounding wires for the mentioned equipments.
Best Regards
Dsky Max
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| Yes I remember the inspectors calling them equipotential busbars,
Thanks for pointing the NFPA-77,780, finding free copies of this will
be another problem though.
as well as the API.
May I can call it "Equipotential Bonding Conductor" then define it via
NFPA-77,780 since the " bonding jumper " described in the NEC is still
for continuity of fault current path.
I wish the NEC had used the term " Equipment Bonding Conductor " so
that it will coincide as description on sect.250.4 (3) and the intent
of the EGC. and reserve the term "Equipment Grounding Conductor" or EGC
for the purpose as described in the 250.4 (2) and include the
requirements for the lighting and static requirement. Since the Bonding
and Grounding are distinct terms being used. the term EGC is being used
to serve the purspose of Bonding & Grounding. Would you agree? Guys?
But since Static & Lightning Hazards are not always present in all
cases The EGC (with short bonding jumpers as required) can be used for
the Bonding &Grounding describe in 250.4 (2) & (3) in which voltage &
fault current dissipation Hazards in the Electrical sys. are always
present. is it right ?
Thanks again Bro.
dsky_max
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| dsky wrote:
> Yes I remember the inspectors calling them equipotential busbars,
> Thanks for pointing the NFPA-77,780, finding free copies of this will
> be another problem though.
> as well as the API.
> May I can call it "Equipotential Bonding Conductor" then define it via
> NFPA-77,780 since the " bonding jumper " described in the NEC is still
> for continuity of fault current path.
> I wish the NEC had used the term " Equipment Bonding Conductor " so
> that it will coincide as description on sect.250.4 (3) and the intent
> of the EGC. and reserve the term "Equipment Grounding Conductor" or EGC
> for the purpose as described in the 250.4 (2) and include the
> requirements for the lighting and static requirement. Since the Bonding
> and Grounding are distinct terms being used. the term EGC is being used
> to serve the purspose of Bonding & Grounding. Would you agree? Guys?
> But since Static & Lightning Hazards are not always present in all
> cases The EGC (with short bonding jumpers as required) can be used for
> the Bonding &Grounding describe in 250.4 (2) & (3) in which voltage &
> fault current dissipation Hazards in the Electrical sys. are always
> present. is it right ?
>
> Thanks again Bro.
> dsky_max
>
I would understand "equipotential" as a method of keeping the ground
'potential' the same everywhere using many multiple paths. Could
particularly be an issue if there is significant noise sensitive
electronics.
Multiple ground paths aren't a problem. They are common - for instance
attaching panels, conduits to structural steel.
The conductors to the busbar shouldn't be required by the NEC but, as I
read your post, are required by the designer. Could add protection for
events like lightning or be to reduce system ground 'noise'.
For #4, I would assume a ground fault relay would run the phase
conductors through a CT and look at the imbalance (same as a GFCI). Then
the more grounds the better. Metering the ground wire back to the MCC
would mean it is the only ground - no metal raceway, no conduction to
pad or grounded metal pipe.
I believe Mike Holt suggested using the terms "bonding" and "earthing"
which I have grown to like. I think "earthing" is commonly used across
the pond.
bud--
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| Spokesman 2006-02-26, 2:26 pm |
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"dsky" <dsky_max@yahoo.com> wrote in message
news:1140931761.644808.21120@j33g2000cwa.googlegroups.com...
> This is laid out & required for in the electrical plans that we are
> using,It is made by other design company, just implementing them.
> I got the motor grounded via the EGC along with the phase wires.
> It is the motor chasis & pump chasis bonded together with a jumper.
> This terminal point is connect to the wall ground busbar by another
> bare copper wire.
> Pardon the inaccurate description I used, it describes the way of
> interconnecting other busbars, that is, each ground bus have two wires
> going into them from other busbars, strung together they form a loop.
> Not trying to pull legs so I did not used the word "wrap" Im really
> sorry.
> Im just need some legal justification from available codes for having
> two grounding wires for the mentioned equipments.
> Best Regards
> Dsky Max
>
I do not see requirement for two grounding systems on the same motor.
You should check the credentials of the person that designed this
system and see if he is indeed qualified to do this type of work.
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"dsky" <dsky_max@yahoo.com> wrote in message
news:1140931761.644808.21120@j33g2000cwa.googlegroups.com...
> This is laid out & required for in the electrical plans that we are
> using,It is made by other design company, just implementing them.
> I got the motor grounded via the EGC along with the phase wires.
> It is the motor chasis & pump chasis bonded together with a jumper.
> This terminal point is connect to the wall ground busbar by another
> bare copper wire.
> Pardon the inaccurate description I used, it describes the way of
> interconnecting other busbars, that is, each ground bus have two wires
> going into them from other busbars, strung together they form a loop.
> Not trying to pull legs so I did not used the word "wrap" Im really
> sorry.
> Im just need some legal justification from available codes for having
> two grounding wires for the mentioned equipments.
> Best Regards
> Dsky Max
2 paths to grounds are trouble. Ask the design engineer for a
clarification/intent of the use of the second ground. Becareful on how you
ask the question, the engineer might not know either.
I have seen engineers ask for installations that were wrong and dangerous.
After all we are all just people and people make mistakes.
Forming a loop in the grounding path can be dangerous.
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