I'm setting up a new server room with one Rack. 2 servers will go into the rack and a new telephone system will also be installed in the rack in March which will require a #6 ground. The server room will be in a separate small stand alone building and is approximately 80 feet from the main service panel. There is a secondary panel fed from the main panel which in turn feeds the room. The secondary panel is on the building and is grounded with #4 solid copper going from the ground bus in the panel to 2 8' grounding rods. Is this a sufficient ground and if so can we have an electrician run a #6 stranded ground cable from the grounding bus bar on the rack to the grounding bus in the secondary panel or does it need to go all the way to the main panel? It does not seem practical to have to run it all the way to the main panel but I'm no an electrician so any help would be appreciated. Thank you.
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Grounding Question 3
- Thread starter Timmkatt
- Start date
jimbopalmer
Programmer
I am not an electrician, more specifically I am not YOUR electrician. I do not even play one on TV. But I did sleep in a Holiday Inn Express last night, so here goes.
The main point to grounding is to prevent electrical shock to humans. You want your computer ground to be the same as your electrical ground in this building, not some other building far away. Ideally there is not even a ground wire between the two buildings, just power. If there is one, it should be as large as the power cables.
By the way, it would be a good idea to run network fiber between buildings, so it can't accidentally be a ground wire.
I tried to remain child-like, all I acheived was childish.
The main point to grounding is to prevent electrical shock to humans. You want your computer ground to be the same as your electrical ground in this building, not some other building far away. Ideally there is not even a ground wire between the two buildings, just power. If there is one, it should be as large as the power cables.
By the way, it would be a good idea to run network fiber between buildings, so it can't accidentally be a ground wire.
I tried to remain child-like, all I acheived was childish.
-
1
- #3
If the MAIN SERVICE DISCONNECT for the Server room is in the main building, that is where the main equipment bonding/grounding conductor needs to terminate, unless the equivalent is available at the sub-panel in the Server room. It would also need to be sized according to NEC, which a qualified electrician can do for you. So, just for your own education in these matters you might want to read article 800 and other related sections of the NEC Code.
One of the main points of bonding/grounding is to provide an electrical return path for fault currents to trip the circuit breaker, or protection device, in order to protect lives and property. So you want the lowest possible resistance in the return path, since electricity will always return to the source to complete the circuit. The earth is a very poor conductor and is extremely resistive.
....JIM....
One of the main points of bonding/grounding is to provide an electrical return path for fault currents to trip the circuit breaker, or protection device, in order to protect lives and property. So you want the lowest possible resistance in the return path, since electricity will always return to the source to complete the circuit. The earth is a very poor conductor and is extremely resistive.
....JIM....
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1
- #4
As far as safety for the human factor any proper grounding will work.
But not for sensitive equipment.
What you have asked about is called an 'isolated dedicated ground'. Google it. Tons of info. I traveled the country for a short time installing NCR equipment that required it.
I was required to meet with the electrician, have him show me the isolated dedicated ground wire and disconnect it so I could test it and prove there was no ground on the dedicated outlets, if my meter showed no ground it passed, if ground was still present he had to fix it. The corporation did not want the equipment on the building ground in any way.
There are alot of dirty grounds out there because in some instances it is legal to just jumper it back to the neutral bus. Plus other enviromental issues as well contribute to dirty grounds.
Bo
Remember,
If the women don't find you handsome,
they should at least find you handy.
(Red Green)
But not for sensitive equipment.
What you have asked about is called an 'isolated dedicated ground'. Google it. Tons of info. I traveled the country for a short time installing NCR equipment that required it.
I was required to meet with the electrician, have him show me the isolated dedicated ground wire and disconnect it so I could test it and prove there was no ground on the dedicated outlets, if my meter showed no ground it passed, if ground was still present he had to fix it. The corporation did not want the equipment on the building ground in any way.
There are alot of dirty grounds out there because in some instances it is legal to just jumper it back to the neutral bus. Plus other enviromental issues as well contribute to dirty grounds.
Bo
Remember,
If the women don't find you handsome,
they should at least find you handy.
(Red Green)
I said "any proper" will do for safety purposes. Key word being proper which I assumed would translate as "to code".
Sorry for 'any' misinterpretation or misunderstanding.
Edited version:
As far as safety for the human factor any ground that meets code will work.
But again, may or may not protect equipment. (see previous post)
Bo
Remember,
If the women don't find you handsome,
they should at least find you handy.
(Red Green)
Sorry for 'any' misinterpretation or misunderstanding.
Edited version:
As far as safety for the human factor any ground that meets code will work.
But again, may or may not protect equipment. (see previous post)
Bo
Remember,
If the women don't find you handsome,
they should at least find you handy.
(Red Green)
- Thread starter
- #7
After further evaluation more information on my server room electrical feed/ground. The secondary panel is fed from the main panel with 3 #4 stranded cable (Black insulator). There is a hot, a common and a third lead which is connected from the grounding bus in the secondary panel to the grounding bus in the main panel. The main panel has a #4 stranded bare copper cable from it's ground bus run to a cold water pipe nearby and a 4AWG solid bare copper cable connected to 2 8'grounding rods and as mentioned in the original post the secondary panel also has a #4AWG solid copper running from it's ground bus to 2 8' grounding rods. I'm not sure how much more grounding can be done but this sounds like it should suffice to have the copper TGB in the rack bonded to the ground bus in the secondary panel and complete the loop. Wouldn't it be redundent to now run another cable from the grounding bar in the rack all the way to the main panel 80-90 feet away rather than the 8-10 feet to the grounding bus in the secondary panel since it is already connected to the grounding bus in the main panel via the third leg of the feed? I'll be consulting an electrician but want to be educated for future reference. Thank you
I have seen electricians do it. Mostly in strip mall shopping centers.
Not saying its correct, but again, I have seen certified electricians do it. Go get them, I didn't do it.
Bo
Remember,
If the women don't find you handsome,
they should at least find you handy.
(Red Green)
Not saying its correct, but again, I have seen certified electricians do it. Go get them, I didn't do it.
Bo
Remember,
If the women don't find you handsome,
they should at least find you handy.
(Red Green)
-
1
- #10
misseditbythatmuch
Technical User
Where did you get this idea? "
It borders on gnit picking, but one of several places ...
......................
NEC 250.24 Grounding and Bonding at Service Equipment
4) Main Bonding Jumper. When the grounded neutral conductor is bonded to the service disconnecting means [250.24(B)] by a bus bar [250.28], the grounding electrode conductor can terminate to either the grounded neutral terminal or the equipment grounding terminal within the service disconnect.
......................
Neutral-to-Ground Bonding: Not An Option
The National Electrical Code® explicitly
defines grounded conductors and grounding
conductors as follows: A grounded conductor is
the wire common to all phases in a multi-phase
system. This conductor is more commonly
known as the system neutral conductor.
A grounding conductor is the grounding
electrode for the multi-phase electrical system.
This is the conductor most often referred to as
the ground conductor.
Article 250-26 discusses the grounding of a
separately derived alternating current system and
states that “…a bonding jumper shall be used to
connect the equipment grounding conductor of
the derived system to the grounded conductor.
This connection shall be made at any point on
the separately derived system or at the source of
a system that has no disconnecting means or
overcurrent devices. The intent of this section is
to permit this connection at the transformer.”
Why is a missing bond a problem?
If a short occurs between a phase and ground
without the presence of a neutral-to-ground bond
at the upstream transformer, the distribution
system’s neutral conductor will “float” or lose its
reference to ground. The floating neutral
condition can cause voltages to float to a
maximum of 208 volts RMS relative to ground,
subjecting loads to a sustained overvoltage
condition.
Even if one assumes light or balanced loading,
the electrical distribution system may operate
without any apparent side effects for quite some
time. Should the loading become unbalanced or
an electrical short occur, the phase voltages will
fluctuate severely.
How does sustained overvoltage
cause problems with SPDs?
Most SPD manufacturers include 25 percent
“headroom” in their products to accommodate
normal voltage fluctuations routinely generated
by the local utility provider. By utilizing 150
Vrms MOVs (metal oxide varistors), the device
should be safe from the 10 percent voltage
deviation a utility is likely to produce.
However, any voltage exceeding the value would
cause the components to conduct. The
continuous conduction is what the SPD
components are not designed to handle.
This condition is what causes the majority of
SPD failures as explained by Dr. Francois
Martzloff in his article “What Are the Lights on
Your Surge Protector Telling You?” (Power
Quality Assurance, July 1998).* Recently, a
major printing plant and high school (which used
different electrical contractors) reported their
SPDs had failed during installation. Upon
visiting the sites, engineers quickly discovered
the problem. In both cases, the neutral-to-ground
bond was not made at the transformers. A short
occurred that caused at least two phases to
encounter sustained overvoltages in excess of
150 Vrms.
It is very important to know that this short would
have occurred regardless of the type of SPD
product or particular manufacturer. That’s
because the MOVs (metal oxide varistors) used
in SPDs are designed to share current at the
microsecond time frame – and not to survive
sustained overvoltages.
The amazing thing is that the electricians for the
school and the printing plant were unaware that
the NEC requires establishing the neutral-ground
bond on the secondary side of the transformer.
The Neutral to Ground Bond
NEC 250-2x
Where is it NEC compliant to bond neutral
and ground? The NEC prescribes two
places. The first place that we find this bond
is at the service entrance inside the main
service panels. Why? Fault current at this
point needs to come from the utility source.
The other place where the neutral and ground
are required to be bonded is on the secondary
side of what the NEC calls a "separately
derived system." The most common separately
derived system is a power transformer
where the primary and secondary windings
are galvanically isolated from one another.
This describes the NEMA-type transformer
widely used to distribute power inside all commercial
buildings.
It borders on gnit picking, but one of several places ...
......................
NEC 250.24 Grounding and Bonding at Service Equipment
4) Main Bonding Jumper. When the grounded neutral conductor is bonded to the service disconnecting means [250.24(B)] by a bus bar [250.28], the grounding electrode conductor can terminate to either the grounded neutral terminal or the equipment grounding terminal within the service disconnect.
......................
Neutral-to-Ground Bonding: Not An Option
The National Electrical Code® explicitly
defines grounded conductors and grounding
conductors as follows: A grounded conductor is
the wire common to all phases in a multi-phase
system. This conductor is more commonly
known as the system neutral conductor.
A grounding conductor is the grounding
electrode for the multi-phase electrical system.
This is the conductor most often referred to as
the ground conductor.
Article 250-26 discusses the grounding of a
separately derived alternating current system and
states that “…a bonding jumper shall be used to
connect the equipment grounding conductor of
the derived system to the grounded conductor.
This connection shall be made at any point on
the separately derived system or at the source of
a system that has no disconnecting means or
overcurrent devices. The intent of this section is
to permit this connection at the transformer.”
Why is a missing bond a problem?
If a short occurs between a phase and ground
without the presence of a neutral-to-ground bond
at the upstream transformer, the distribution
system’s neutral conductor will “float” or lose its
reference to ground. The floating neutral
condition can cause voltages to float to a
maximum of 208 volts RMS relative to ground,
subjecting loads to a sustained overvoltage
condition.
Even if one assumes light or balanced loading,
the electrical distribution system may operate
without any apparent side effects for quite some
time. Should the loading become unbalanced or
an electrical short occur, the phase voltages will
fluctuate severely.
How does sustained overvoltage
cause problems with SPDs?
Most SPD manufacturers include 25 percent
“headroom” in their products to accommodate
normal voltage fluctuations routinely generated
by the local utility provider. By utilizing 150
Vrms MOVs (metal oxide varistors), the device
should be safe from the 10 percent voltage
deviation a utility is likely to produce.
However, any voltage exceeding the value would
cause the components to conduct. The
continuous conduction is what the SPD
components are not designed to handle.
This condition is what causes the majority of
SPD failures as explained by Dr. Francois
Martzloff in his article “What Are the Lights on
Your Surge Protector Telling You?” (Power
Quality Assurance, July 1998).* Recently, a
major printing plant and high school (which used
different electrical contractors) reported their
SPDs had failed during installation. Upon
visiting the sites, engineers quickly discovered
the problem. In both cases, the neutral-to-ground
bond was not made at the transformers. A short
occurred that caused at least two phases to
encounter sustained overvoltages in excess of
150 Vrms.
It is very important to know that this short would
have occurred regardless of the type of SPD
product or particular manufacturer. That’s
because the MOVs (metal oxide varistors) used
in SPDs are designed to share current at the
microsecond time frame – and not to survive
sustained overvoltages.
The amazing thing is that the electricians for the
school and the printing plant were unaware that
the NEC requires establishing the neutral-ground
bond on the secondary side of the transformer.
The Neutral to Ground Bond
NEC 250-2x
Where is it NEC compliant to bond neutral
and ground? The NEC prescribes two
places. The first place that we find this bond
is at the service entrance inside the main
service panels. Why? Fault current at this
point needs to come from the utility source.
The other place where the neutral and ground
are required to be bonded is on the secondary
side of what the NEC calls a "separately
derived system." The most common separately
derived system is a power transformer
where the primary and secondary windings
are galvanically isolated from one another.
This describes the NEMA-type transformer
widely used to distribute power inside all commercial
buildings.
It borders on gnit picking"
NO it doesn't. How the grounding system works is defined by this very idea. For grounding to work the ground conductor MUST be separate from the neutral conductor at all points except those you list in the NEC.
This is NOT what DTSMAN was referring to when he said "it is legal to just jumper it back to the neutral bus". He was citing a common practice he had observed. One usually sees this in situations where a grounded outlet is installed in a box where there is no ground conductor. Very dangerous and a NEC violation, NOT a nitpick.
NO it doesn't. How the grounding system works is defined by this very idea. For grounding to work the ground conductor MUST be separate from the neutral conductor at all points except those you list in the NEC.
This is NOT what DTSMAN was referring to when he said "it is legal to just jumper it back to the neutral bus". He was citing a common practice he had observed. One usually sees this in situations where a grounded outlet is installed in a box where there is no ground conductor. Very dangerous and a NEC violation, NOT a nitpick.
- Thread starter
- #12
I did not really get an answer here on Tek Tips because this seemed to turn into a Pi**ing match between some of the posters but anyway for what it is worth here is the answer I got...
I had a licensed electrician out yesterday and he and our telecom provider confirmed what would be acceptable. He did the work right then and to remain in code he ran a #6 stranded w/green insulation in 1/2" pvc conduit from the secondary panel grounding bus on the west side of the new server room building around the back wall to the east side of the building and through the wall right to the rack. The telecom provider will be terminating the ground on the rack next week when they terminate the network cables on the patch panel at the top of the rack. Even though I ran the network cabling for the ip phones that will be going in I'm being smart and letting the telecom provider terminate both ends and the ground to eliminate any potential finger pointing when the Avaya IP office phone system goes in if there are issues. Thanks again
I had a licensed electrician out yesterday and he and our telecom provider confirmed what would be acceptable. He did the work right then and to remain in code he ran a #6 stranded w/green insulation in 1/2" pvc conduit from the secondary panel grounding bus on the west side of the new server room building around the back wall to the east side of the building and through the wall right to the rack. The telecom provider will be terminating the ground on the rack next week when they terminate the network cables on the patch panel at the top of the rack. Even though I ran the network cabling for the ip phones that will be going in I'm being smart and letting the telecom provider terminate both ends and the ground to eliminate any potential finger pointing when the Avaya IP office phone system goes in if there are issues. Thanks again
I would think each building has its own isolated ground . your electrician should be able to advise you. Sometimes transient voltages flow into the building on the groung wires. Had one experience of a radio channel comming in on the ground from another building in a strip mall
Best to hire a certified electrician
Best to hire a certified electrician
Dave,
In N. America all service entrance grounds are connected.
"Best to hire a certified electrician" Yes, but make sure that electrician knows their stuff about the type of project they are being hired to do. An industrial guy may not know much about residential or commercial wiring.
In N. America all service entrance grounds are connected.
"Best to hire a certified electrician" Yes, but make sure that electrician knows their stuff about the type of project they are being hired to do. An industrial guy may not know much about residential or commercial wiring.
Mugsiensedgwick
Technical User
Just one more little comment. I am not in any way an expert on grounding, as a matter of fact it pretty much gives me a stomachache just to think about how to fix some of my own issues, but I have found that "Certified electrical contractors" are often in the dark when it comes to bonding and grounding to protect telephone equipment, because it's completely different than protecting people. It's kind of out of the ordinary for them.
That's my comment. I usually hire an old 'Western Electric' installer to come in and show me how it should be done.
He charges a nice lunch at a nice resturant but tells lots of good stories while we eat, and I sleep well at night.
That's my comment. I usually hire an old 'Western Electric' installer to come in and show me how it should be done.
He charges a nice lunch at a nice resturant but tells lots of good stories while we eat, and I sleep well at night.
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