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#194541 06/09/10 08:37 PM
Joined: Aug 2006
Posts: 356
Niko Offline OP
Member
One of my clients wants me to ground the receptacles because he is under the impression that an ungrounded outlet is not safe for the computer. The existing two conductor circuit is protected by an ungrounded GFCI receptacle, which i told him is perfectly fine and is up to code.

But he still wants me to ground the receptacles. (he is a hardware/software engineer)

Besides the ground being there for safety, can you explain why&if the computer needs the equipment ground to operate properly?
what effect does the EGC have on the performance of PC (personal computers).

Thank you.




Be kind to your neighbor, he knows where you live

Niko #194546 06/09/10 09:23 PM
Joined: Oct 2004
Posts: 806
Member
Most UPS and surge strips rely on a good ground to properly protect the computer against surges.

Additionally, a ground helps to protect the computer against static electric discharge damage.

Bottom line, run a proper ground according to Code or install a dedicated circuit with proper ground.

Otherwise you risk damage to the computer.


Stupid should be painful.
Joined: Oct 2005
Posts: 12
D
Member
Without an actual grounding conductor, the surge protector has no way to drain a surge to ground.

The ungrounded GFI receptacle can shut off the power on a ground fault, which would protect a person, but a surge protector on such a circuit would be useless.

Joined: Aug 2006
Posts: 356
Niko Offline OP
Member
Aren't most surges initiated outside of the computer from an outside source? Utility, motors, appliances...

If that is the case then isn't the computer better off without the ground. besides ground fault, unless the ground is there for static discharge from the operator.

please help me understand this thoroughly.


Be kind to your neighbor, he knows where you live

Niko #194550 06/10/10 12:57 AM
Joined: Oct 2006
Posts: 745
E
Member
Oh boy, is this one of my latest hot buttons. I'm going to assume that this situation involves a UPS.

Either use the building ground 100% or use a UPS's ground which effectively isolates the ground for all devices attached to the computer. In my travels, what I see is that people use a UPS for the actual computer, yet they plug the printer, monitor, etc. into non-backup power. It is all or nothing when using a UPS, PERIOD!

The supposedly-protected electronic equipment, be it phone systems, computers, or whatever are now being hit in two directions under lightning/surge conditions. Double-whammy exposure and double risk for damage. Secondary surge protection devices are just a marketing ploy that actually increases equipment damage in my book.

These devices are sold with "guarantees" for the protected equipment from surge damage, but any claims filed are impossible to collect upon. These guarantees are so loosely-written that the manufacturers of these devices rarely pay out a dime. I've never succeeded in a single claim on a customer's behalf.

Surge "protectors" can only do so much when they are expected to do what they are not designed to do when placed in an isolated environment.


---Ed---

"But the guy at Home Depot said it would work."
Joined: Jul 2004
Posts: 9,672
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G
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Since the pan of the computer is "ground" and also DC common it will get it's ground from the cable company or the telco if you don't give it one. Unfortunately the path is through the LAN card and the system board.
We even went as far as bonding PC cases on the LAN together when grounding from the electrical system was dodgy. It reduced blown parts from surges dramatically.


Greg Fretwell
Joined: Jul 2002
Posts: 8,412
Likes: 3
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Niko,
Is this in a commercial or residential installation?
Is this also a place that has dedicated computer circuits, not just where any old thing can be plugged into any given recept on that given circuit?

Trumpy #194559 06/10/10 06:28 PM
Joined: Aug 2006
Posts: 356
Niko Offline OP
Member
Trumpy,
it is residential and they don't have dedicated circuits.

but my questions is on the ground. why does the computer need a ground to operate properly. Another words, if they use a cheater adapter, will the computer malfunction? why or why not? is the ground there strictly for safety or for performance of the computer?

Thanks.


Be kind to your neighbor, he knows where you live

Niko #194560 06/10/10 08:01 PM
Joined: Jun 2004
Posts: 1,273
T
Member
The solid state logic of modern computer chips uses DC impedance.

( Yes, impedance is not just an AC phenomenon. In DC SWITCHING CIRCUITS the impedance exists for a fraction of a second upon a change in state. This wave pulse is the actual basis for triggering the logical state function from 1 to 0 or from 0 to 1.)

One aspect of such high speed switching is the absolute need for a stable ground state -- ie ground path. If the last pulse is not instantaneously flushed/drained to zero faster than the next machine cycle ( switching frequency ) then logical errors pop up. What should be now zero ( 0 ) is still strong enough to read as one ( 1 ).

Modern chips have just about half of their internal wiring dedicated to ground paths. That's why you see such wide ribbon cable running to and fro. When you discover the pin-outs you'll find repeated isolated paths to ground so that each drain run is wide open for each pulse.

Ultimately, the whole system needs a stable ground with a drain to the ultimate earth. Even laptops have ground drains when they are hooked up to the power supply.

When a laptop is running on battery power, it gets its stable ground by reference to the battery pack.

------

Other items that use DC impedance: VFDs...

AC is rectified into a capacitor 'tank' -- then IGBTs switch the DC at ultra speed and efficiency to 'stack up' AC wave forms at the desired frequencies. ( Study Fourier Series and Wave Physics for the reason it works.)

At higher frequencies such 'tank' circuits produce metal melting induction beams. You'll only find these in industry since they are high cost, high power, high output.

More commonly, intelligent ballasts/power supplies use the same method to power high efficiency fluorescent lighting. In this case, the power supply doesn't care what the input voltage is! it can handle 100 to 300 V Ac and still work. ( the 120 & 277 V rating on the package is just an industry term of art. 208 or 240 volts would work, too.)

----

WRT your situation, the grounding path/drain line does not have to follow the hot & neutral. You can even use bare copper outside of a raceway. You do want to bond it back to the GEC so that you have a one point connection between your neutral and GEC and EGCs.

Ground loops are another no-no for digital logic.

Cheers.

Last edited by Tesla; 06/10/10 08:04 PM.

Tesla
Tesla #194565 06/10/10 09:02 PM
Joined: Jul 2004
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I doubt you will ever have a problem with machines that don't have a ground, until you connect to another machine.

I have a lot of PCs in wood cases (no ground plane) and PCs running off inverters (in cars) that have no ground.
The problem there is if you plug the "sound out" into a dash radio. You get a 60 hz hum that will rattle the windows. The fix is to ground the PC to the car. If you use a set of PC speakers plugged into the inverter it works fine.


Greg Fretwell
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