Are isolated groung outlets necessary

[roger]

i see the necessity for their use mainly in the medical field where absolute grounding is necessary to remove even static charges outside the electrical system's wiring.... where they terminate in their own ground system independent of any other ground..

Charlie, in medical applications quite the opposite is true, there are very few if any IG's and the ones that are installed are probably in violation or a mistake.

Patient rooms must have an Equipotential of <.1 ohm and this is hard to achieve with isolated grounds and numerous paths.

Most medical equipment manufacturers of equipment like C.T.'s, Xray's, Linear Accelerators, etc... have multiple bonding paths that are connected in parallel by design.

Roger

 

[ryan_618]

Dominic, here is an article on IGs that you may find helpful:

http://www.mikeholt.com/mojonewsarc...ding-versus-Bonding-Part-9-of-12~20050602.php

 

[LawnGuyLandSparky]

Isolated grounds were required to solve some issues with the original IBM mainframes in the 60's and 70's. Since then they've been nothing but an expensive, unnecessary habit. Wave a fancy new or special anything under the nose of an IT tech and it'll be added to the specs.

No need to keep data center at 60 degrees anymore either, but try telling one of them that. They like to treat their data centers like hermeticallly sealed "clean rooms" as if they're manufacturing silicone microchips in there...

 

[Dominic Ramirez]

Good article, explained alot.

 

[ItsHot]

spray paint

spray paint

That's brings me back to one of my original thoughts on IG recs. Give them an orange colored receptacle, and that'll shut 'em up.

A can of orange spray paint!

 

[dereckbc]

Dominec, I have worked in the telecom industry for a number of years dealing with all kinds of ground techniques, most of them proven and sound techniques

So help me out here as I do not have a lot of experience with POS equipment. What topology or protocol is data being transmitted with? Is it Ethernet twisted pairs, or a ground based protocol using RS-232. It is some form of ground based topology like RS232, there is a sure fire way to eliminate the problem via optical modems connected to the terminal equipment that takes out any ground issues,

 

[brian john]

The biggest problem with IG systems is constantly demonstrated on this site, a misunderstanding of how to install the system.

In my expierence if an electrical distribution system is properly installed, IG is of no benefit. If a distribution system is not properly installed and there are PQ issues related to this, IG should not be installed the wiring issues should be corrected.

We (the industry as a whole) would be better served if ALL electricians understood how to install a basic electrical distribution system, free of shorts and free of accidental or intentional ground connections that are inappropriate.

I have seen many IG systems installed and few if any are properly installed, the electricians can't get the basic electrical system installed properly, they sure as heck are not going to install a system with extra grounding requirements installed properly.


Cross connections between IG and "normal" EGC.
IG taken to separate isolated electrode.
IG circuits normal outlets.
NO IG circuits IG outlets.
IG and EGC tied together at the outlet.
IG ground ISOLATED (no connection to anything)
Total isolation (ungrounded system)
Total isolation no EGC, PVC coupling in EMT run to 3 phase 3-wire computer on isolators and unit tied to separate ground electrode (lighting had fun with this isolation).
More rods driven than Cabela's has sold in a decade drive to correct PQ "issues".
And various HOODOO VOODOO the electricians DODO, in attempts to resolve grounding requirements and PQ issues.

 

[LarryFine]

So help me out here as I do not have a lot of experience with POS equipment. What topology or protocol is data being transmitted with? Is it Ethernet twisted pairs, or a ground based protocol using RS-232.

Every POS system I've wired used ordinary CAT-5e UTP ethernet. And every one spec'ed IG for the power circuits.

I usually use 12-3 MC, using the green conductor as the IG and the red (stripped where accessible) as the power EGC.

 

[iwire]

I usually use 12-3 MC, using the green conductor as the IG and the red (stripped where accessible) as the power EGC.

You know that is definitely up to debate if that is legal.

IMO that is not allowed by 250.119(B) in most POS installations.

 

[big john]

EC&M had an interesting article on IGs a few months ago. I've always been skeptical of their value, especially when they are used with interconnected equipment. Like a lot of people I've seen IGs hyped as a panacea for any and every possible electrical problem. However, the article seems to support a position I've also heard form engineers on this site, that IGs do reduce common-mode noise. I have never been able to find a definition (that I can understand) of what common-mode noise actually is and why an IG should reduce it.

We recently installed some flat-screen televisions. Ran 12/2 MC for as spec'd, in some cases for hundreds of feet. The guy doing the datacom wiring (who also works for the company supplying the televisions) shows up with a box of IG receptacles for us to install. Uhhh.... The worst part is that the powers-that-be proclaimed "Just connect the ground wire straight to the receptacle!"
"But where's the ground for the device box...?"
"It's grounded through the MC; do what you're told!"

-John

 

[dbuckley]

No need to keep data center at 60 degrees anymore either, but try telling one of them that. They like to treat their data centers like hermeticallly sealed "clean rooms" as if they're manufacturing silicone microchips in there...

Yes, we do like to keep our data centres cool, and it's getting harder than ever.

One reason we like to keep them cool is electronic equipment life is proportional to temperature, and this factors directly to equipment reliability. Keep it cool, it's more reliable. This property is used in stress testing semiconductor devices to evaluate their reliability at the component level, thhe hotter it gets the quicker it breaks. (see Arrhenius Model)

Back in the day, a rack of equipment might use 1KW of juice and thus put out a KW of heat. Today a rack can put out over 20KW of heat, and heat loads of 20KW/sqm are somewhat hard to get rid of.

And we do like our data centres clean (but not clean room clean), with all that air blowing around muck gets everywhere, especially little shards of metal from a contractor's carelessness, which can cause very expensive and inconvenient equipment outages.

 

[dereckbc]

EC&M had an interesting article on IGs a few months ago. I've always been skeptical of their value, especially when they are used with interconnected equipment. Like a lot of people I've seen IGs hyped as a panacea for any and every possible electrical problem. However, the article seems to support a position I've also heard form engineers on this site, that IGs do reduce common-mode noise. I have never been able to find a definition (that I can understand) of what common-mode noise actually is and why an IG should reduce it.

Big John I did not read the article, but I think you either misinterpreted it or the author is misquoted.

IG cannot possibly reduce common-mode noise, there are no active or passive circuits. If there is garbage at the input, it passes straight through to the output. Its only possible use is preventing common-mode noise from entering a circuit and the effects range from no effect, worse effect, or desired effect. There is an excellent way to reduce or remove common-mode noise, a separately derived system like a transformer or dual conversion UPS

The text book definition of Common-Mode Noise is:
The noise voltage that appears equally and in phase from each current-carrying conductor to ground.

 

[Dominic Ramirez]

Dominec, I have worked in the telecom industry for a number of years dealing with all kinds of ground techniques, most of them proven and sound techniques

So help me out here as I do not have a lot of experience with POS equipment. What topology or protocol is data being transmitted with? Is it Ethernet twisted pairs, or a ground based protocol using RS-232. It is some form of ground based topology like RS232, there is a sure fire way to eliminate the problem via optical modems connected to the terminal equipment that takes out any ground issues,

video cable coax, cat5, and fiber optic.

 

[charlie tuna]

its been a few years-- but we did a large cat scan testing lab and it called for a "chemical" ground network with all the receptacles being IG and their ground wires being dedicated back to the bus connected to the "chemical" ground. this may not be the code today??? but thats the only place i came across where IG receptacles were properly designated for their use...

 

[haskindm]

its been a few years-- but we did a large cat scan testing lab and it called for a "chemical" ground network with all the receptacles being IG and their ground wires being dedicated back to the bus connected to the "chemical" ground. this may not be the code today??? but thats the only place i came across where IG receptacles were properly designated for their use...

Unless the grounding bus was also connected to the Grounded Conductor and the grounding electrode system, this was and is a violation of the NEC. The NEC has never allowed an IG to be "isolated" from the Grounded Conductor or attached to an isolated grounding electrode. The term "isolated ground" has caused much confusion because the NEC really prohibits the use of a ground that is isolated.

 

[Dominic Ramirez]

Low Imp. Trans or Dbl Conv

Low Imp. Trans or Dbl Conv

Now I've been told that for clean power I need a low inpedance transformer to clean up the noise a Dbl Conversion UPS doesn't clean.
Do I need one or the other or both or just a battery backed conditioner (not online dbl conversion type) that has a low impedance transformer built in?

Just a reminder, this is for a fast food restaurant's order taking and processing, communication, PC based touchscreens etc.

 

[brian john]

Give them a off line UPS on a 20 amp circuit if it does not work fire all the cashiers.

 

[dereckbc]

Now I've been told that for clean power I need a low inpedance transformer to clean up the noise a Dbl Conversion UPS doesn't clean.
Do I need one or the other or both or just a battery backed conditioner (not online dbl conversion type) that has a low impedance transformer built in?

Whoever is feeding you this information needs educated. A dual conversion UPS is absolutely the ultimate means of cleaning up common-mode noise (assuming true sine-wave type) and any other PQ problems you can shake a stick at. What rubbish they are feeding you? An extremely close second place finisher with reference to common-mode noise is an isolation transformer. In fact they are so close in (CMR) perfomance it doesn't matter which one you use. The only difference is the UPS will give you backup capability in the event of a power failure, brownout, or other such interuptions. A transformer cannot do that.

If cost is the major concern, then the winner is an isolation transformer. Go back and read my post, this is what I have been trying to tell you all along. FWIW the dual conversion UPS already has the isolation transformer built into it on the output.

 

[dereckbc]

video cable coax, cat5, and fiber optic.

For Cat5 and fiber, IGR is a complete waist of money.

 

[Dominic Ramirez]

Dbl conversion it is.

Dbl conversion it is.

We are going down to Slidell La. next week to install an ONEAC dbl conversion conditioner. Right now they have a Powervar offline UPS conditioner and that doesn't seem to be doing the trick. I went through their wiring last week and all orange isolated outlets seem to be wired right.