Isolated Ground Testing

[Jlmyers82]

Hello everyone.
I am building a restaurant i Ft Lauderdale Florida. The Owner has requested meto provide a test or certification for all of the Isolated Ground Point of Saleoutlets. The reason for this is they always have problems with the POSequipment and the POS company blames the problems on the receptacles sayingthat the power is bad or whatever. So the owners want to get them tested andcertified so that they POS folks have nothing to fall back on? My question toyou guys is, What exact test needs to be done for this situation and who inSouth Florida can provide this for me if any?

 

[stickboy1375]

This one should be interesting...

 

[zbang]

My question to you guys is, What exact test needs to be done for this situation ?

Get a competent POS vendor? (I always smile when using that acronym.)

No really. If the POS boxes need 'clean' power, and usually they're just PCs, put a UPS under each one. In my limited experience with them, the problems were almost always serial comm related. If they're using serial cables over a long distance, they an isolated ground system might help, but if they're twisted-pair ethernet, there's complete isolation already. All that said, I'm not aware of a certification for isolated grounds, but there are much smarter people than me here.

 

[gar]

120803-0813 EDT

The first post needs clarification. The terms need definition. What is the real question? What is the real problem that needs to be solved?

Zbang has probably identified what may be the real problem.

The thread title is "Isolated Ground Testing". What does isolated ground mean here, and how does that relate to whatever is the problem needing a solution?

If the problem is reliable RS232 communication, then my I232 Isolator product is possibly a solution. See http://www.beta-a2.com .

.

 

[zog]

Hello everyone.
I am building a restaurant i Ft Lauderdale Florida. The Owner has requested meto provide a test or certification for all of the Isolated Ground Point of Saleoutlets. The reason for this is they always have problems with the POSequipment and the POS company blames the problems on the receptacles sayingthat the power is bad or whatever. So the owners want to get them tested andcertified so that they POS folks have nothing to fall back on? My question toyou guys is, What exact test needs to be done for this situation and who inSouth Florida can provide this for me if any?

You need to clarify, are they asking for a ground resistance test? Did they provide a spec?

 

[dkidd]

Take a look at

http://www.idealindustries.com/prod...cuit_analyzers/suretest_circuit_analyzers.jsp

From the instructions:


#61-176 Isolated Ground Adapter
This adapter allows the operator to verify that a receptacle is completely isolated from the
system ground that is bonded to other devices on the branch circuit. Test the ground
impedance of the receptacle and record the ohms value. (See the section on Line
Impedance Testing for details on obtaining the ground impedance value). Remove the
SureTest and plug it into the isolated ground adapter. Attach the alligator clip to the center
receptacle screw or metal junction box, and re-insert the SureTest into the receptacle and
record the ohms value.
The isolated ground adapter creates a parallel pathway to ground, which results in a lower
ground impedance reading with the adapter versus with the receptacle with the isolated
ground. If the two readings are the same, then the receptacle does not have an isolated
ground. If the reading taken with the isolated ground adapter is lower, then the receptacle
has an isolated ground.

 

[kwired]

You need to clarify, are they asking for a ground resistance test? Did they provide a spec?

I think, based on past experiences, his owner is simply asking for a good enough grounding system so that the equipment repair guys don't blame the power supply and its grounding for problems. Those guys are pretty good at putting blame on that when nothing else is obvious, yet you come in and try to fix the "grounding" problem and the problem with the equipment does not go away. He wants to have some way of verifying the grounding system meets the demands these guys ask for so when they point to that he can tell them to do their job and quit pointing the finger at something else, and is asking how to verify this.

 

[gar]

120803-1444 EDT

kwired:

What is a definition of a "good enough grounding system"?

CNC machine suppliers will say you need a good ground when there is a communication problem. They never define a good ground. Often times they will suggest a ground rod at the machine as a good ground. A ground rod probably is not a good ground. Even if someone suggests 0.1 ohms as a good ground however they obtained the ground, this may not solve the problem. Also one has to define what is meant by ground.

What is really important is to find out what is the problem that is in need of a solution that requires the so called good ground. In other words asking the correct question when you do not know the question to ask.

.

 

[jeremysterling]

...My question to you guys is, What exact test needs to be done for this situation and who in South Florida can provide this for me if any?

Don't make this harder than you have to.

If you are the installer, you should be able to provide certification that IG conductors and receptacles were installed using best practices. An as-built drawing should be sufficient. I'll certify that all day long.

Testing can be done by any electrician with an ohm-meter, linemans and a screwdriver.

 

[kwired]

120803-1444 EDT

kwired:

What is a definition of a "good enough grounding system"?

CNC machine suppliers will say you need a good ground when there is a communication problem. They never define a good ground. Often times they will suggest a ground rod at the machine as a good ground. A ground rod probably is not a good ground. Even if someone suggests 0.1 ohms as a good ground however they obtained the ground, this may not solve the problem. Also one has to define what is meant by ground.

What is really important is to find out what is the problem that is in need of a solution that requires the so called good ground. In other words asking the correct question when you do not know the question to ask.

.

I don't know. I think that is what the OP is asking how to prove though. Good enough for one service tech for the equipment involved is like you said driving a ground rod, next one wants IG all way back to service, others just want copper EGC and no steel raceway as a ground. When their equipment has problems they can't explain though there is either a power or grounding problem and they make it become the electricians problem. You can then run a new circuit meeting all their criteria and the thing still has same problem:slaphead:

Don't make this harder than you have to.

If you are the installer, you should be able to provide certification that IG conductors and receptacles were installed using best practices. An as-built drawing should be sufficient. I'll certify that all day long.

Testing can be done by any electrician with an ohm-meter, linemans and a screwdriver.

Like I was mentioning before, how do you prove it is good to the technician that can't find anything wrong and blames whatever problems there is on the grounding.

I have had similar issue with flame sensors on gas fired appliances. They are having trouble sensing flame and figure there must not be a good enough ground since they can't find anything else wrong. I have ran new circuits, pulled copper EGC's through metal raceway grounded systems, and still had no result in solving the flame sensor problem. It has gotten to where unless it is obvious there is no equipment ground I will lay out a temporary ground wire and bond the unit to the neutral back at the service equipment and tell them to try it. If it solves the problem fine, I will look into getting a ground/ better ground to the unit. If it doesn't solve the problem I tell them they better look harder for other problems.

 

[jeremysterling]

...Like I was mentioning before, how do you prove it is good to the technician that can't find anything wrong and blames whatever problems there is on the grounding.

Lucky for us the OP doesn't have to. The OP is being asked to certify the IG to the owner, not the POS tech.

 

[kwired]

Lucky for us the OP doesn't have to. The OP is being asked to certify the IG to the owner, not the POS tech.

And the owner asks for this because he has had to deal with the POS tech in the past, but what happens when POS says grounding must not be good enough sometime in the future, and POS tech says warranty does not cover anything unless electrician fixes the grounding problem (that does not exist)

 

[Speedskater]

I would just use an Ohm Meter. Measure the resistance at each "IG" outlet to a known good power system ground point (each should read in the low Ohm range). Then lift each "IG" wire at the appropriate panel board and re-measure each outlet (each should read near infinity).

Anyone who talks about adding ground rods, just doesn't understand what an "IG" is all about.

 

[zog]

We are all just guessing until the OP clarifies what he is talking about, until then any discussion is worthless.

 

[brian john]

1. The POS has no clue what they want or need.
2. Once the system is installed megger the neutrals (with nothing connected) and if the neutral is clear of shorts all issues should be resolved.
3. Hire a testing company and have them test the IG (I assume these are IG for a resistance) write a letter stating the resistance is so many micro-ohms and the POS will look at the letter have no clue but be happy as a pig in doo.

And if they doesn't work tell them the best solution is to install a Iso transformer at each outlet and increase your sales.

http://www.tripplite.com/en/products/model.cfm?txtModelID=228&gclid=CLy_qKTZ0LECFcne4Aodr18Axw

 

[Speedskater]

2. Once the system is installed megger the neutrals (with nothing connected) and if the neutral is clear of shorts all issues should be resolved.

I think that a megger of the Neutrals would answer other wiring questions, not the "IG" one.

And if they doesn't work tell them the best solution is to install a Iso transformer at each outlet and increase your sales.

A isolation transformer and a correctly wired Separately Derived System is a great solution, but not at each outlet.

 

[brian john]

I think that a megger of the Neutrals would answer other wiring questions, not the "IG" one.
[QUOTE}

Meggering the neutrals would resolve most of the issues the writer of the specification was installing the IGs to supposedly resolve.


[QUOTE} A isolation transformer and a correctly wired Separately Derived System is a great solution, but not at each outlet.

Why not I/we see it done quite often, an easy fix in lieu of resolving the actual problem and fattens the installers wallet.

 

[gar]

120806-1715 EDT

What is the problem to be solved? We do not know. So far all we can do is guess.

Connect two computers together via non-isolated RS232 ports and provide an isolated ground to each computer. Doesn't matter whether the isolated grounds are certified or not. Isolation transformers or not I can easily burn out the drivers in the ports unless the ports have clamping diodes and fuses or resistors that serve as fuses to protect the drivers.

.

 

[iwire]

1. The POS has no clue what they want or need.

That is not relevant, the customers believe they do.

 

[brian john]

That is not relevant, the customers believe they do.

And I would bet 3 different companies could submit 3 different reports using a variety of test equipment and the person reviewing the documentation (if they bother) would be happy.