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Grounding

Grounding

(OP)
I have a ladder rack system in my server room but there is no grounding bus bar for me to ground it to. What I want to do is run a ground wire from the rafters to my first piece of ladder rack then just link all the different pieces of ladder rack. I am experienced in the proper techniques of grounding telecom equipment, I am just curious if it is acceptable to ground telecom cabinets and cable trays to the rafters as I have described?

RE: Grounding

I suppose so as long as those "rafters" are made of steel and connect to ground.

RE: Grounding

I echo that ... make sure the metal you connect to really does go to ground and is not isolated or that will cause you issues.

RE: Grounding

For best results, you would bond it to electrical ground so that there is no difference in potential. If metal components of building are bonded, then you could connect to a metal component. I'd test with good ohm meter first. In reality, any electrical equipment mounted in the rack is providing a ground for the whole rack assembly. But it is still a good idea to bond it separately.

RE: Grounding

If you are going to ground things then they need to be bonded directly to the main electrical service ground point. Lacking that you are better off using the electrical grounding conductor on the supply circuit. This may be already connected via any metal cased power strips mounted to the rack or via equipment installed in the rack as pointed out my mforrence.

Grounding via various building parts is tricky and if done improperly can cause more problems than it solves. During an event like a nearby lighting strike the soil, concrete and various building parts can be at wildly different potentials. A proper grounding system is designed in a star configuration to minimize these differences.

Grounding to a roof structure strikes me as a particularly bad idea.

RE: Grounding

(OP)
I ended up finding a bus bar not far from the ladder racking so my problem is solved. Thanks for all the good advice!

RE: Grounding

Don't think so guys. Avayas instructions for grounding has been consistent through the years. There are two grounds. A protective and a functional ground. The ground plug performs functional ground and the chassis ground performs the protective ground. Functional is from a earth grounded power panel while the prime choice for protective ground is building steel. You can google both grounds to see that Avayas text is consistent with NEC. Also NEC has moved away from cold water pipe for ground since the pipe may not be copper along the entire length.

IPO:
Grounding (IP500): 2013
Use of ground connections reduces the likelihood of problems in most telephony and data systems. This is especially important in buildings where multiple items of equipment are interconnected using long cable runs, for example phone and data networks.

All IP Office control units and external expansion modules must be connected to a functional ground. Where the unit is connected to a power outlet using a power cord with an earth lead, the power outlet must be connected to a protective earth.

In some cases, such as ground start trunks, in addition to being a protective measure this is a functional requirement for the equipment to operate. In other cases it may be a locale regulatory requirement and or a necessary protective step, for example areas of high lightning risk.

WARNING
During installation do not assume that ground points are correctly connected to ground. Test ground points before relying on them to ground connected equipment.

The ground point on IP Office control units and expansion modules are marked with a or symbol. Ground connections to these points should use a 14 AWG solid wire with either a green sleeve for a functional ground or green and yellow sleeve for a protective ground.


Merlin Legend: 1998
Approved Grounds
Approved grounds are listed below, in order of preference:
1. Building Steel. The most preferred ground.

2. Acceptable Water Pipe. Must be a metal, not plastic or vinyl,
underground water pipe at least ½ in. (1.27 cm) in diameter, and
in direct contact with the earth for at least 10 ft. (3 m).
It must be electrically continuous so that the protector ground is
uninterrupted. (Check for insulated joints, plastic pipe, and plastic
water meters that might interrupt electrical continuity.)
A metallic underground water pipe must be supplemented by the
metal frame of the building, a concrete-encased ground, or a
ground ring. If these grounds are not available, the water pipe
ground can be supplemented by one of the following types of
grounds:
— Other local metal underground systems or structures, such
as tanks and piping systems, but not gas pipes
— Rod and pipe electrodes, a 5/8-in. (1.58-cm) solid rod or
¼-in. (0.63-cm) conduit or pipe electrode driven to a
minimum depth of 8 ft. (244 cm)
— Plate electrode, a minimum of 2 square ft. (61 square cm)
of metallic surface exposed to the exterior soil

3. Concrete-Encased Ground. Must be an electrode, consisting of
one of the following:
— At least 20 ft. (6.1 m) of one or more steel reinforcing rods,
each at least ½ in. (1.27 cm) in diameter
— 20 ft. (6.1 m) of bare copper conductor not smaller than #4
AWG, encased in 2 in. (5 cm) of concrete
NOTE:
This electrode must be located within and near the
bottom of a concrete foundation or footing that is in
direct contact with the earth
— Ground ring, consisting of at least 20 ft. (6.1 m) of bare
copper conductor (not smaller than #2 AWG) encircling the
building. The ground ring must be in direct contact with the
earth and buried at least 2.5 ft. (77 cm) below the earth’s
surface.
! WARNING:
Do not use a metal underground gas piping system - this is a
safety risk.



RE: Grounding

Great doc. Thanks.

RE: Grounding

"Don't think so guys."

What don't you think?

I know the following;

1. With very few exceptions the NEC requires all grounds to be bonded to the service ground.

2. The OPs plan is not consistent with ATT-TP-76416.

RE: Grounding

Actually that doc talks about grounding the building steel not to the service panel but to the grounding electrode. If the building is properly grounded then bonding to building steel as a protective ground is desirable. The functional ground is derived from the ground plug for ac outlet. He is trying to ground his rack so if building steel is available then it should be the first choice for bonding as the protective ground. The functional ground will be complete by the plug for the devices in the rack. The chassis protective ground is intended to be a separate grounding point to keep from being chassis shocked due to poor wiring or whatever.

Pretty sure I have this right....

2.4.1. Office Principal Ground Point (OPGP)
2.4.1.1.
The office principal ground point serves as a central connecting point for grounding conductors from within the structure and from all earth electrodes. The most common conductors terminated at the OPGP are:
a) The ac service Grounding Electrode Conductor
b) A bond to the Cable Entrance Facility
c) A bond to the interior gas (with an insulating joint between the entrance and interior pipe) and/or water pipe system in the structure
d) Bonds to structural steel
e) Bonds to supplementary ground fields
f) A CO GRD system vertical riser
g) A bond to the earth electrode system in an adjacent structure
h) Bonds to equipment requiring an earth ground reference
i) Bonds to all earth electrodes

RE: Grounding

Grounding to building steel isn't always a slam dunk. A former contributor reported blowing out multiple Avaya Partner ACS processors because of a voltage differential between the electrical outlet's grounding pin and the building steel. He now grounds to the electrical outlet via a grounding block.

I love2 "FEATURE 00"
http://mysite.verizon.net/vze7n25t/

RE: Grounding

possibly but then that means that the building is not grounded correctly. I understand that there is a case form a lot of building not being grounded correctly however you can test the voltage potential between source power and of the protective ground yourself before you connect the ground lead to a chassis. You can measure the voltage at the outlet(voltage number 1) then measure the voltage at the protective ground by using the neutral lead of the tester to touch the ground point while the hot lead stays attached to source power(voltage number 2). As long as the difference is small-no more than 1/2 volt- then there should be no issues. If the building is grounded correctly the tests should be o.k.

If the tests fail then I would certainly report the testing to the site and their electrician for repair.

RE: Grounding

There is.....however.....no promise that there won't be a voltage potential problem 1 day/week/month/year down the road. Hence connecting the ground screw to the same ground that the 3 prong plug uses.

While the Partner ACS processor is grounded via the 3 prong plug, the supplemental ground is thought to be included to offer protection should the power cord to the system be unplugged while the telephone lines are still connected.

I love2 "FEATURE 00"
http://mysite.verizon.net/vze7n25t/

RE: Grounding

"As long as the difference is small-no more than 1/2 volt- then there should be no issues."

Really?

What voltage difference would you imagine that would go to during a lightning strike of other surge event?

After absorbing much of ATT-TP-76416 I find it interesting that the grounding methods allowed for telephone equipment is much stricter than for computer equipment.

When you look at 2.4.3.6 the requirements for using building steel for telephone equipment grounding:

"Certain types of building columns may be used as a vertical riser. Other types cannot be used for this purpose but require bonding to floor CO GRD bus bars to insure equalization of lightning induced voltage between building and equipment conductive components. When column steel consists of structural steel sections, and all section butt ends of the column are bridged with a weld, a welded steel plate or an exothermically welded or brazed 750 kcmil copper bond, the column may be used as a CO GRD system vertical riser."

However when you get to section 4.10 concerning computer equipment you see:

"4.10.1. Bond to Structure's Ground System

4.10.1.1.
When computer equipment is located in central offices or other buildings equipped with a CO GRD system, grounding electrode conductors or other conductors requiring direct connection to an earth ground system shall be connected to a CO GRD or OPGP bus bar. When expedient, a bond to an effectively grounded structural member of the building is permitted if it results in a run length shorter than one to a CO GRD/OPGP bus bar.

4.10.1.2.
In buildings other than central offices where no ground system similar to a CO GRD system has been provided, all conductors requiring connection to an earth ground system shall be connected to the nearest of either:
a) The nearest available effectively grounded metallic structural member
b) The nearest available effectively grounded metal water pipe
c) Other electrodes as specified in Article 250 of the National Electrical Code where electrodes specified by (a) or (b) above are not available"


So my previous statement "The OPs plan is not consistent with ATT-TP-76416" isn't accurate. AT&T does allow grounding that may not be consistent with modern star type grounding practice.

I cannot overstate my belief that picking up a ground off a steel roof structure would be a particularly bad idea. In general modern computer and network equipment does not need more grounding than is supplied by the AC ground. However IF you want to supply additional grounding you certainly don't want to create more problems than you solve. Running a ground wire back to the electrical service ground isn't that hard and assures you of a good ground.


RE: Grounding

The less than 1/2 volt accounts for proximity to the originating power panel. The closer the two voltages match the closer the proximity of the panel and the building steel ground point. A potential greater that 1/2 volts should cause the protective ground to be relocated closer to the originating panel. Naturally you cannot stop lightning from taking whatever path it desires. Including panels.

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