Isolated ground system

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TarheelDanno

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have a computer technician and owner wanting an IG for all there computer station at the frontdesk of a new hotel project. I explained to the owner that we then need to pull isolated ground circuits from the service or establish an isolated ground at the panelboard in the computer room from the service. The technician wants a separate grounding electrode from a separate delta outside his computer room to a grounding bussbar. Doesn't article 250 still require all grounding conductors tied together at the main service?
Signed, feelbackedinacorner
 
TarheelDanno said:
The technician wants a separate grounding electrode from a separate delta outside his computer room to a grounding bussbar.
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They can want that but they can not have that.


Doesn't article 250 still require all grounding conductors tied together at the main service?
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In a nutshell yes, specifically take a look at the last sentence of 250.4(A)(5).
 
What they want does not comply with code or any known practice. In fact will more than likely produce the exact opposite results.

The best practice IEEE-1100-2005 Chapter 9 is to use a very simple isolation transformer and run standard SG recepts, IGR is antiquated, no longer used, and discouraged.
 
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TarheelDanno said:
The technician wants a separate grounding electrode from a separate delta outside his computer room to a grounding bussbar.
Signed, feelbackedinacorner
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Is this referring to some sort of grounding electrode?
 
infinity said:
Is this referring to some sort of grounding electrode?
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I think it means 3 ground rods in a triangle pattern, I have had to do that by spec before but they where tied into the buildings GES.
 
Regardless of the code, (that this guy wants to violate) what does he think is going to clear a fault?

Running a conductor from the grounding terminal of the device to the earth will not do anything.

Roger
 
This "delta" 3 grounds rods in a triangle; is the Bermuda Triangle of electronic techs I have seen this spec'd and installed sooooo many times. I think it works like a pyramid, repairing the bad electrons that disappear into the triangle.
 
Running a conductor from the grounding terminal of the device to the earth will not do anything.
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I agree! I do not see qualified electrician in the title (not to beat up on computer techs):
computer technician and owner
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I'm so sick of people trying to tell us how to do our job. I was LOL when I had someone call me and tell me I wasn't allowed to design a plan for lighting. This was her words: You need a separate license to layout lighting!? Hun!!
She must have worked for the State at one point in her life!
 
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It seems that most Computer Techs are young "geeks" that have an Isolated background... I can remember when we faced the same issue with a lot of Electricians and Control Techs.

I did a company safety-meeting on this very subject when I was a young guy and was laughed at by some of the "30 year Electricians".

I work with a lot of Contractors and I find that few want to devote time to personal study. "Homework" ends when you graduate from High School.

We have to help these guys, or they're not going to get it.
 
iwire said:
I think it means 3 ground rods in a triangle pattern, I have had to do that by spec before but they where tied into the buildings GES.
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That's what I thought but didn't want to assume. I'm frequently amazed at the lack of knowledge that some designers actually have.
 
TarheelDanno said:
.......the technician wants a separate grounding electrode from a separate delta outside his computer room to a grounding bussbar.
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This "Sounds" familar. Wonder if the sound and computer techs are taught by the same vodoo priest?
 
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infinity said:
I'm frequently amazed at the lack of knowledge that some designers actually have.
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Trevor, the prints showed specific measurements between the rods and 2 bare cad welled around al of them. :roll:

I really felt like I should also do a 'grounding dance' to the Gods to ensure all bases where covered.
 
As long as the neutrals and grounds are bonded at exactly one point and the engineers did their job correctly the power quality will be fine for the computers. Will they accept the excuse that the NEC specifies how isolated ground receps have to be installed and wired? You can still sell them three rods in a triangle, just bond them properly, and install IG receps properly if they want to pay for them. If you're marking up your materials properly and the installation delivers clean power to the computers, who cares? It doesn't matter if they want to pay for extra, useless material to get the same power quality.

Depending on the details of the "grounding dance," make sure to include a shoe wear and tear allowance, maybe built into a higher labor rate for this specialty skill.

Jeremy
 
If they want "clean" sockets for their IT equipment, then simply arrange the ground wiring as P-A-N-I, and identify some outlets as for IT only, selling them coloured outlets for those circuits at the "I" end of the bar. PANI is entirely compliant, and has been discussed here many times.
 
dbuckley said:
If they want "clean" sockets for their IT equipment, then simply arrange the ground wiring as P-A-N-I, and identify some outlets as for IT only, selling them coloured outlets for those circuits at the "I" end of the bar. PANI is entirely compliant, and has been discussed here many times.
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I am afraid you have a misunderstanding of the MGB (Master Ground Bar) PANI application. It cannot be used to originate an IGR receptacle by any code compliant method.

The best practice that is code compliant is to originate the green/yellow ground wire is at a Neutral-Ground bonding point like at the service entrance point, or down stream at an SDS like an isolation or step-down transformer.

PANI bars as you call then are pretty much used for DC powered equipment racks in telecom industry. They could be used as supplemental grounding on equipment racks in a IT environment, but there is no need to ever do this as the EGC ran with phase conductors serves the purpose and would corrupt any isolation attempts unless extreme measure are taken. I have seen it tried, and failed every time because installers, technicians, electricians fail to understand the concept from lack of knowledge, proper training, and no testing and commissioning practices.
 
"Are they all taught by the same voodoo priest?"

Arrgh. As a full-time instructor - I teach audiovisual folks how to design and install AV systems - I run across a LOT of misinformation - even in recently published materials (2007).

The informed among us in the audiovisual community know that:
1. IG does not mean separate ground electrode - well, it can, but it must be bonded to the electrical system's grounding electrode at the main service entrance. To do otherwise could prove fatal and is a violation of Code.
2. Using grounding adapters (mistakenly called ground lift adapters) can prove fatal and is a violation of Code and is not how to properly solve a hum/buzz issue.

In AV, and specifically in relation to audio, our obstacles are:
1. Typical signal levels running from in the millivolts to about a volt. Noise (especially power) is easily induced onto the audio signals at these levels.
2. Manufacturers (especially consumer and computer oriented manufacturers) don't design their products properly to deal with this induced noise (See the "Pin 1 Problem" as well as Common Mode Noise Rejection).
3. Need of extended signal-to-noise ratios - around 60 dB being minimum. A Performing Arts Center, Theatres, Recording Studio requires even more. Video needs at least 30 dB and Ethernet needs less than video.
4. Wide frequency range - 20 Hz to 20,000 Hz - ten octaves - and guess what? 60 Hz is within that range and can be very audible.
5. Our needs are different than the Ethernet guys. Different frequency ranges (they're in the GHz range now) requiring different approaches to grounding. Additionally Ethernet is actually a very robust standard against noise. And if the signal doesn't get through over Ethernet, it just tries again.

There is also a lot of good and proper information on correct power and grounding relating to audio.

Bill Whitlock is one of many that teaches to anybody willing to listen.
http://www.jensentransformers.com/an/generic seminar.pdf

It's an uphill battle, but it's also why I subscribe here, study electricity, own some of Holt's books and own a copy of the NEC Handbook.
 
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