Isolated ground panel

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cplinc

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I have a situation where we have an isolated ground panel which feeds a dozen or so cash registers that has a lot of unused spaces. The customer would like to add a heated air curtain to their exit/entry way. Airing on the cautious side I don't think it's a good idea to come out of this panel. On the other hand we could save a significant amount of money if we used this option. Would you guys please explain why this is a bad idea.( if it is) What could happen? Thanks
 
I don?t see a problem at all. An ?isolated ground panel? will have three bus bars on which to land conductors. One will be for neutrals, and one will be for equipment grounding conductors, and these two will be electrically isolated from each other. The third will be for the connection of equipment grounding conductors for isolated ground receptacles, and this will be electrically isolated from both of the other two. This configuration allows you to plug something into a receptacle, and not have this item?s EGC connect to any other EGC, or to any bonded metal enclosure or other bonded component, anywhere other than at the N-G bond point at the main panel. It is a method of reducing the impact of any ground issues on sensitive electronic equipment, a category that may or may not actually include your cash registers. I have not heard any statements lately that support the value of isolated ground systems. They have been described as a total waste, but I cannot say anything one way or the other on that subject.

If you add a load to a panel that has the isolated ground feature, and if you connect the EGC for that load to the ?normal EGC bus,? and not to the ?isolated ground bus,? there will be no adverse impact on the existing equipment that does use the isolated ground bus. That is because the two ground bus systems are only connected back at the source.

So I say, ?go for it.?
 
OK, Marc beat me to the draw on this one, but only because my answer was longer. :wink::smile:
 
charlie b said:
OK, Marc beat me to the draw on this one, but only because my answer was longer. :wink::smile:
Click to expand...
I hate it when that happens. Maybe we need the posts to be sorted by when the response was started instead of finished. (I know: software.)

My opinion:

As long as the EGC's remain separated back to the service as they are now (and presuming it's properly done now), the main concern to me would be adding the new equipment load to this panel, which supplies only electronics now.

If there is an issue later, you're most likely to hear from the register people, when they start having system glitches. I have been 'blamed' for POV system hiccups, and found refrigeration equipment plugged into IG circuits.

One could argue that, in reality, everything is in parallel with everything (short of isolation transformers), but we still endeavor to keep sensitive equipment separate from noisy equipment. It certainly can make a difference in performance.

My point is that the grounds may only be part of the possible problems. Noise on the power lines can be worse.

I suggest pricing it both ways, explain the risks as well as you can, suggest that they ask the register provider for their opinion, and let the customer make the choice, with the understanding that changing it would cost more later.
 
LarryFine said:
I hate it when that happens. Maybe we need the posts to be sorted by when the response was started instead of finished. (I know: software.)

My opinion:

As long as the EGC's remain separated back to the service as they are now (and presuming it's properly done now), the main concern to me would be adding the new equipment load to this panel, which supplies only electronics now.

If there is an issue later, you're most likely to hear from the register people, when they start having system glitches. I have been 'blamed' for POV system hiccups, and found refrigeration equipment plugged into IG circuits.

One could argue that, in reality, everything is in parallel with everything (short of isolation transformers), but we still endeavor to keep sensitive equipment separate from noisy equipment. It certainly can make a difference in performance.

My point is that the grounds may only be part of the possible problems. Noise on the power lines can be worse.

I suggest pricing it both ways, explain the risks as well as you can, suggest that they ask the register provider for their opinion, and let the customer make the choice, with the understanding that changing it would cost more later.
Click to expand...

I took the liberty of undelinimng portions of Larry's response. He took the words out of my moyth and highlighted areas are ones where I learned by bitter experience dealing with some customer IT folks and
hidden requirements" they neglect to tell you up front.
 
Charlie,
I would like your comment.

You wrote:
"" I have not heard any statements lately that support the value of isolated ground systems.""

While I worked in research, I designed several instrumentation amplifiers.
We were able to hear three different AM radio stations, depending on where we connected the ground for the instruments.
I designed a Faraday room, and again tried three different grounds. Only the one that had the instrument ground connected with the Faraday sheild and connected to a #4 to a ground rod solved the problem. But, open the read door by 6 inches, and one station would leak into the instruments.

I had designed into the boards a very exact equi-potential ground, and plut ferrites on all input lines, and all output lines, and all power lines. We ended up with a special ground for the AC lines. I don't recall now (25 years later) whether the equipment ground (egc) was connected to the normal EGC to the Load Center at the service point.

I recall that if that if this regular EGC were the only connection, there was a problem. If we used the conduit (EMT) as a ground, then there was a slightly different problem (different radio station), but when connected to the special #4 to a GEC then the problem was under control.

Now, on another note, a friend called me from a multi-building electrical manufacturing concern. I consulted.
They had PC based equipment operating in two buildings. They strung a tele link between them, and were doing data transfer, something like serial port to serial port, but with external communication equipment.
Under certain conditions, the serial boards would quit (with damage to the board). What was happening was that the ground level reference between the buildings was changing due to some adverse load in one.
In analysis, the comm equipment was referencing its power supply to the ground, not the neutral, and as this ground reference shifted, the regulated voltage would shift, sometimes violating the max voltage allowed to the electronic equipment. The problem was resolved when the two equipment sets were grounded together,
something like an equi-potential ground.

I can't go back 25 years and check anything.
Just relating something that I believe is accurate, and interesting, about the possible value of isolated grounds, and the concept of Equi-potential grounding systems.

Ever heard of anything like these scenarios ?
 
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If we can send a man to the moon, but can't build a darned cash register that won't go bananas on a "regular" ground, then we've got some serious problems on our hands.
 
mdshunk said:
If we can send a man to the moon, but can't build a darned cash register that won't go bananas on a "regular" ground, then we've got some serious problems on our hands.
Click to expand...

I've often said the same thing, but many times that's exactly how it works out.
 
mdshunk said:
If we can send a man to the moon, but can't build a darned cash register that won't go bananas on a "regular" ground, then we've got some serious problems on our hands.
Click to expand...
That's a false analogy: spacecraft have isolated grounds. :grin:
 
The isolated ground aspect of this does not worry me in the least and if that was the only consideration I would as Marc said do it in a heartbeat.

Now that said, it is very typical in my experience that these IG panels that supply registers are supplied by a dedicated transformer, often 'K rated' but sized fairly small, often with less capacity then the panel itself would lead you to believe.

This is done to keep the power going to the registers to be free from outside inferences like motor loads starting and stopping.

If as it sits today the panel only runs registers, hubs and servers I would not be the one to add a motor load to it. Down the road if the registers start having problems it could come back to you regardless if the motor you added is the problem or not.
 
glene77is said:
I can't go back 25 years and check anything.
Just relating something that I believe is accurate, and interesting, about the possible value of isolated grounds, and the concept of Equi-potential grounding systems.

Ever heard of anything like these scenarios ?
Click to expand...

There are very few installations that benefit from IGs and even fewer that where IGs are installed that they do not become corrupted almost immediately.

With computers the IGs came about as the computers used to use interconnections that carried a grounding referencing, like RS-232 or the old IBM style connections or coax connections.

Now as far as I know few computer interconnections use a ground reference. Which has eliminated the need or benefit for IGs.
 
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