it grounding

[zyhml]

There is a workshop with rebar in column as down conductor and foundation as grounding rod, if we want to connect IT grounding to rebar in column, is there any restriction in NEC code? I heard from some one direct connection is banned, it should connect to SPD's PE terminal and kevin wiring is needed.

 

[dereckbc]

Where are you located. From the terms you use I assume UK?

I design IT, Data Centers, and telephone offices in the USA, and a UFER is a prefered method or ground electrode source, or I should say one of the many we use.

 

[zyhml]

i'm from china .

 

[petersonra]

i'm from china .

I spent a month in China once starting up some machines.

 

[zyhml]

welcome. The SPD guy told me there will be huge side flash risk if direct connection between rebar in column and IT grounding panel was made.

 

[don_resqcapt19]

welcome. The SPD guy told me there will be huge side flash risk if direct connection between rebar in column and IT grounding panel was made.

Actually the lack of a bond increases the risk of a side flash.

 

[zyhml]

I might not make my description clear, actually designer want use the down conductor as grounding source of IT, not only make bonding with it. Is it ok?

 

[dereckbc]

Yes it is a common practice.

 

[Pierre C Belarge]

If you mean 'down conductor' in regards to lightning protection, then the answer is no. Lightning protection is not one of the Grounding Electrodes as per 250.52. Also I do not believe it is a good idea to connect your IT to the lightning system.


If you mean 'down conductor' in regards to the grounding electrode system, then I agree with Dereck.

 

[zyhml]

I agree with you, but i only found a restriction in 250.60 "Air terminal conductors and driven pipes, rods, or plate Bare aluminum or copper-clad aluminum grounding conducelectrodes used for grounding air terminals shall not be used in lieu of grounding of other system", is it only consider air terminals?

 

[Pierre C Belarge]

What is it you are trying to achieve with the "grounding" you are describing?

 

[don_resqcapt19]

I believe you will find a requirement in NFPA 780 that requires bonding of most all conductive objects within either 3 or 6 feet of a lightning protection conductor to that conductor. This would be in addition to any electrical safety grounding.

 

[zyhml]

If you mean 'down conductor' in regards to lightning protection, then the answer is no. Lightning protection is not one of the Grounding Electrodes as per 250.52. Also I do not believe it is a good idea to connect your IT to the lightning system.


If you mean 'down conductor' in regards to the grounding electrode system, then I agree with Dereck.

Actually, in this building we use foundation as lightning and electrical grounding system, the part of perimeter column as down conductor of lightning, designer want to use internal column as grounding electrod of IT.

 

[dbuckley]

When you say 'IT' do you mean "Information Technology" or an IT grounding system, ie a system with a high resistance ground path?

 

[brian john]

Could mean it as a pronoun, as in how do you ground "it".

 

[zyhml]

IT mean "information technoledge" in my topic.

 

[brian john]

It. American humor....

 

[weressl]

There is a workshop with rebar in column as down conductor and foundation as grounding rod, if we want to connect IT grounding to rebar in column, is there any restriction in NEC code? I heard from some one direct connection is banned, it should connect to SPD's PE terminal and kevin wiring is needed.

I believe you need an isolated ground connection to serve the IT structure.

Establish an insulated grounding loop connection in the IT area that has no galvanic connection to any metallic structural or other items in the area except the PE point of each IT equipment. Run two - for redundancy - insulated ground conductors to grade level, establish earthing of these connections with 3 meter ground rods. Keep these two runs are 3-5 meters away from lighting and grounding downleads if possible.
The distance of this isolated ground from your standard ground in the earth depends on the earths resistance, but normally 5 meters is sufficient. The two grounding systems should be interconnected with approx. 50 meter of insulated grounding cable that is laid in a snaking pattern about 2 meters, like this /\/\/\/\, making sure that you have no smaller bending radius than 15cm. (This will provide you with a high impedance interconnection between the 'two' grounding system, so that you comply with the intent of the NEC of all grounding should be interconnected, but minimize the potential from surge currents entering the isolated ground from the 'power' grounding side.)

Bring this connection aboveground in a test box. The test box will provide you with two features. One: you can test for circulating current between the two grounding and allowed to isolate the two systems if you discover 'objectionable current' that would interfere with IT equipment. Two: you can test the grounding systems resistance from this test point. (You can also install hall-effect current sensor and record the data. Good for troubleshooting.)

 

[zyhml]

Definitely it's a best way i can figure out, but i still wonder if there is compromised way to establish IT grounding.

 

[weressl]

Definitely it's a best way i can figure out, but i still wonder if there is compromised way to establish IT grounding.

I don't understand your question. What do you consider 'compromised', in what sense? What I have described can be considered a compromise between needing to minimize ground current interference from 'other' sources, yet have all 'grounding' interconnected.

If there is an objectionable ground current between the two segments, as I described it, you are allowed to open the connecting bond.