Grounding ( Bonding) recptacles for PCs

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mb5412

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Hi, I've been replacing 2 wire receptacles ckts w/ 3 wire receptacle circuits for use w/new PC's in residences.
What I'd like to know, for the sake of installation time is, does installing a GFCI w/ no equipment grounding (bonding) conductor attached to it, affect the operation of the PC?
Even w/the absence of a grounding (bonding) conductor connected to the GFCI, I do understand that the GFCI will still open any line-to-case faults of anything plugged into it.
Is there some electronic thing going on within the PC that requires them to be connected to a 3 wire receptacle?
 
Re: Grounding ( Bonding) recptacles for PCs

Hello-

Computers (excluding laptops) generally need an EGC for a zero reference point to correctly distinguish between highs and lows (1's and 0's). Since you are installing new computers, you may not observe any problems at first. As the equipment ages, the EGC will become more and more important.

Generally, computer systems should not be installed on GFCI circuits to prevent any unexpected surprises if the device trips.


Mark
 
Re: Grounding ( Bonding) recptacles for PCs

A gfci without an equipment ground is the lesser of two evils. Its is felt to be safer to allow a GFCI than for users to cut off the ground pin or use an adapter. Some equpment should have an equipment ground, for example TVSSs, but even they divert most surges back to the line and not to ground.
 
Re: Grounding ( Bonding) recptacles for PCs

Computers (excluding laptops) generally need an EGC for a zero reference point to correctly distinguish between highs and lows (1's and 0's). Since you are installing new computers, you may not observe any problems at first. As the equipment ages, the EGC will become more and more important.

Noooo, I don't think so. :roll:

-Hal
 
Re: Grounding ( Bonding) recptacles for PCs

Good catch Hal
I have used many a computer that was plugged into a non-grounded receptacle.

I do understand that the GFCI will still open any line-to-case faults of anything plugged into it
Click to expand...
This will only happen if there is enough return to source leakage that will exceed the 5ma threshold of the GFCI. even the three light tester will not trip the GFCI because there is no return path to source for the tester to use without a grounding conductor but the GFCI will still function when there is a path to source that would also be a shock hazard.
This is one of the biggest myths I see posted allot. Electrical equipment does not need Earth to function or a ground path. If wires need shielding it is the connection of this shield at the input of the signal that is the reference not the building wire. if equipment need a "0" volt reference it will be the "0" volt reference from the equipments power supply again not the building wire. Equipment grounding is for fault path back to source and for elimination of voltage potential between equipment. ;)
 
Re: Grounding ( Bonding) recptacles for PCs

If wires need shielding it is the connection of this shield at the input of the signal that is the reference not the building wire. if equipment need a "0" volt reference it will be the "0" volt reference from the equipments power supply again not the building wire.
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That's right. I think some confusion comes from the fact that both the 0 volt equipment supply reference and the EGC, if both exist, are usually both bonded to the equipment chassis. The EGC is not responsible for the equipment's 0 volt supply reference. Just connected to it.
 
Re: Grounding ( Bonding) recptacles for PCs

Sam I remember the old networks that used the MUX 25 pin system It had the "0" volt reference in the cable. I installed many of these systems what a pain! Sitting at a desk and soldering each end on. :roll:
 
Re: Grounding ( Bonding) recptacles for PCs

Originally posted by pqtest:
Hello-

Computers (excluding laptops) generally need an EGC for a zero reference point to correctly distinguish between highs and lows (1's and 0's). Since you are installing new computers, you may not observe any problems at first. As the equipment ages, the EGC will become more and more important.


Generally, computer systems should not be installed on GFCI circuits to prevent any unexpected surprises if the device trips.


Mark
Click to expand...
The EGC statement is just plain false. A lot of laptops don't even bring the ground wire through the power supply into the computer itself. Further, how would you explain how any computer would work if it was unplugged? Lots of laptops still work with no powerline or EGC connection at all!!!

As for false tripping of GFCIs, that can happen because a lot of PCs have filtering on their mains and these can exhibit some leakage current. But PCs are not the only devices that can have some leakage current due to filtering. GFCIs should only be used where absolutely necessary, and not installed where they are not needed, since unnecessary use of them can indeed lead to nusiance trips. Even commonly seen power strips can trip GFCIs because they have internal TVSS and they sometimes exhibit a bit of leakage.
 
Re: Grounding ( Bonding) recptacles for PCs

Hello all-

Most computers do in fact require a low impedance ECG for correct operation. If you have access to it, take a look at IEEE Standard 1100, Powering and Grounding of Electronic Equipment, or take a look at this IBM Service note:

http://www-307.ibm.com/pc/support/site.wss/document.do?lndocid=NETV-SAFETY&velxr-layout=print

and scroll down about half way. This reads:

Grounding requirements
"Electrical grounding of the computer is required for operator safety and correct system function. Proper grounding of the electrical outlet can be verified by a certified electrician."

I use this IBM note for a quick reference, but they have many product standards which state the same. (GOOGLE IBM and grounding) IBM generally requires an EGC impedance of .25 ohms or less.

Most computer manufacturers such as Sun, Dell, Gateway, etc. have similar environmental installation standards in which they specifically point out the importance of the low impedance EGC for correct operation.


Mark
 
Re: Grounding ( Bonding) recptacles for PCs

Oh, cry me a river Wayne, :D that use to be a typical activity for me some years back. I didn't really either like or dislike soldering. It was just something I was always doing. But I was never an assembler, that I couldn't have endured.
 
Re: Grounding ( Bonding) recptacles for PCs

I have been itching for this topic too come up. Being a contributing writer to IEEE-1100 chapter 9, 2005 edition, I am familiar with the specifications. The .25-ohms EGC impedance is recommended for equipment operation, but not in the way many may think. It is for the fast, safe, and efficient operation of OCPD on branch circuits. The impedance must include all feeders, and branch circuits to the N-G bond point whether that is a service or a transformer. If common mode noise is a concern additional steps can be taken.

As for the 0-volt reference in PC?s and such, it is true that this point is bonded to the EGC. This comes from the old days when we used signal I/O cables with a ground reference like RS-232 or coax cables to interconnect your PC to peripheral equipment like modems, printers, ect. If a fault were to occur in any of the peripheral equipment and an EGC were not present in all of them, the fault current would flow in the I/O cable shields or ground reference wires that are not thermally capable of dissipating the heat causing a fire danger. The EGC provided the planned path to the source.

The other minor role of the EGC plays is for the built-in TVSS and RFI devices like MOV?s and capacitors installed in the common modes of L-G and N-G. But since the EGC impedance is extremely high @ high frequencies it is practically useless in the common modes, they just dump the noise in the EGC to be seen by other equipment as common mode noise. So if you use a topology like RS-232 the common mode noise can impede signal transfer. Now we have modern balanced signal transmission mediums like Ethernet and optical which have no ground reference what so ever. Make since?
 
Re: Grounding ( Bonding) recptacles for PCs

I have a question about getting high frequencies across an EGC path. In order to impede high frequencies the EGC would have to have significant inductance. It doesn't seem there'd be that much, is there?
 
Re: Grounding ( Bonding) recptacles for PCs

Cool Dereck!

Everything you posted makes good sense. What I note is:
Posted by Dereckbc
As for the 0-volt reference in PC?s and such, it is true that this point is bonded to the EGC.
Click to expand...
Over the decades, I have, from my reading and background, been informed that the EGC, when part of desktop PC supply, is used, in part, as pqtest says:
Computers (excluding laptops) generally need an EGC for a zero reference point to correctly distinguish between highs and lows (1's and 0's).
Click to expand...
One of the images that illustrated this for me was that of two observers, each in the gondola of separate balloons. Each observer has a walkie talkie and is looking at the other through a telescope. The sky is cloudless and blue. One balloon is actually going slowly up, and the other is stationary. Without looking away from each other, is it possible for the two observers, by conversation, to figure out who is moving and in which direction?
 
Re: Grounding ( Bonding) recptacles for PCs

Originally posted by physis:
In order to impede high frequencies the EGC would have to have significant inductance. It doesn't seem there'd be that much, is there?
Click to expand...
More than you think. My memory eludes me at the moment for the formula, but if you really want to know reply back and when I get home I will look it up for you in the Emerald Book.

When I gave a protective/lightning/signal grounding classes @ MCI I always had a couple of trick questions that went something like this:

Q.Which of these two conductors, a #6 AWG or 750 MCM would be better to use as a signal path with a length of 10 feet @ 1 Mhz?


A. Niether, the impedance @ 1Mhz is about 1.2 K ohms for either conductor


The next day with a different spin I would ask:

Q. Lets assume we had two buildings with a a?Ground Electrode System (GES) of a ground ring. One building GES measured 5-ohms, and the other 50-ohms. Now lets assume we could use a Ground Electrode Conductor (GEC)of either a # 6 AWG or a 750 MCM at a length of 10 feet. Assuming lightning current were to pass through the GEC and GES, what is the impedance of the multiple systems assuming a base frequency of 10 Mhz.

A. 12K ohms

FWIW, no one ever got the answer right, I made sure of that :D The point I was driving at the time is single conductor size is insignificant when dealing with high frequency components.
 
Re: Grounding ( Bonding) recptacles for PCs

Well, I don't know which formula you mean. If it's for calucating impedance at a given frequency I don't need that. If it's for how to get the inductance of conductor or conducting material or something related to that I would be interested.

I'm having to fight off the urge to do the math but my viseral assumtion is that 1 or 10 MHz. wouldn't be effected much by the inductance of only a straight wire. Sometimes it can be surprising when you calculate what will actually happen though.
 
Re: Grounding ( Bonding) recptacles for PCs

And Al, I've been seeing you around all morning (for me anyway) and I haven't said hello yet.

Hi Al. :)

[ March 08, 2005, 04:25 PM: Message edited by: physis ]
 
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