chevyx92
Senior Member
- Location
- VA BCH, VA
I know you have to terminate isolated grounds on an isolated ground bar but I dont understand why you dont ground the isolated bar to any type of ground. Its seems to me that the ground is ineffective.
Isolated ground bars
- Thread starter chevyx92
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- Massachusetts
Re: Isolated ground bars
You absolutely must ground the isolated grounding bar!
It should be connected at the main bonding jumper of the system it serves.
You absolutely must ground the isolated grounding bar!
It should be connected at the main bonding jumper of the system it serves.
chevyx92
Senior Member
- Location
- VA BCH, VA
Re: Isolated ground bars
As I dont have much experience with isolated grounds, from what I was told it didnt because you defeat the purpose of it. Is what you stated in the code?
As I dont have much experience with isolated grounds, from what I was told it didnt because you defeat the purpose of it. Is what you stated in the code?
- Location
- Massachusetts
Re: Isolated ground bars
pierre
Senior Member
- Location
- Westchester County, New York
Re: Isolated ground bars
Sometimes a little common sense should be exercised. If any conductor.... that is any conductor, is connected to a terminal that is isolated and goes absolutely no where, what is it really doing? Nothing!!!
It does actually do one thing... it becomes a potential hazard.
Sometimes a little common sense should be exercised. If any conductor.... that is any conductor, is connected to a terminal that is isolated and goes absolutely no where, what is it really doing? Nothing!!!
It does actually do one thing... it becomes a potential hazard.
chevyx92
Senior Member
- Location
- VA BCH, VA
Re: Isolated ground bars
So lets say you have 20 isolated grounds that are part of 20 amp circuits coming back to the IG bar, how do size a ground to run from that IG bar to the main bonding jumper?
[ January 29, 2006, 07:34 PM: Message edited by: chevyx92 ]
So lets say you have 20 isolated grounds that are part of 20 amp circuits coming back to the IG bar, how do size a ground to run from that IG bar to the main bonding jumper?
[ January 29, 2006, 07:34 PM: Message edited by: chevyx92 ]
- Location
- Massachusetts
Re: Isolated ground bars
By the way, it can terminate before the MBJ, but the MBJ is the best spot.
What you can not do is leave it 'floating'.
[ January 29, 2006, 07:40 PM: Message edited by: iwire ]
It would only have to be as large as the largest conductor on the bar.
By the way, it can terminate before the MBJ, but the MBJ is the best spot.
What you can not do is leave it 'floating'.
[ January 29, 2006, 07:40 PM: Message edited by: iwire ]
chevyx92
Senior Member
- Location
- VA BCH, VA
Re: Isolated ground bars
Thank you for the info, as this was a topic of discussion with a guy at work on friday, like I said I have little experience with isolated grounds and I thought what he was telling didnt sound right but I didnt know. Then from what you're saying, would running a ground to the building steel be legal?
Thank you for the info, as this was a topic of discussion with a guy at work on friday, like I said I have little experience with isolated grounds and I thought what he was telling didnt sound right but I didnt know. Then from what you're saying, would running a ground to the building steel be legal?
pierre
Senior Member
- Location
- Westchester County, New York
Re: Isolated ground bars
"Then from what you're saying, would running a ground to the building steel be legal? "
That would most likely create more of a problem with "noise" added to the grounding system.
Read 250.146(D) and Bob's posts a little more closely.
"Then from what you're saying, would running a ground to the building steel be legal? "
That would most likely create more of a problem with "noise" added to the grounding system.
Read 250.146(D) and Bob's posts a little more closely.
peter d
Senior Member
- Location
- New England
Re: Isolated ground bars
Seriously though, I like the new terms and they make much more sense, but I think it's going to take some time before we start using them and getting used to them.
[ January 29, 2006, 07:56 PM: Message edited by: peter d ]
Don't you mean we must BOND the isolated grounding bar???
Seriously though, I like the new terms and they make much more sense, but I think it's going to take some time before we start using them and getting used to them.
[ January 29, 2006, 07:56 PM: Message edited by: peter d ]
chevyx92
Senior Member
- Location
- VA BCH, VA
Re: Isolated ground bars
It says "directly at an equipment grounding conductor terminal of the applicable derived system ". Well if you bond the isolated ground bar back to the MDP equipment ground terminal, then isnt that the same thing as just bonding it to the equipment ground bar in the panel with the IG bar?
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Re: Isolated ground bars
The derived systems or service does not mean the MDP. A derived system or service is where a neutral to ground bond would have occurred (typically a step down transformer or a utility service disconnect electrically "closest" to your isolated system).
The derived systems or service does not mean the MDP. A derived system or service is where a neutral to ground bond would have occurred (typically a step down transformer or a utility service disconnect electrically "closest" to your isolated system).
Re: Isolated ground bars
Chevy, do not feel bad about being in the dark over IGR. I know many electricians, engineers, and manufactures with ?Mushroom Syndrome? when it comes to IGR.
IMO the confusion in part comes from the NEC itself, by not specifying where the IGR conductor should originate. Again IMO the NEC is too lenient or vague in its description. Per the NEC it can originate any where from the service disconnect to any point downstream from there. This leads to a lot of misinterpretations from all across the electrical disciplines like separate, isolated, insulated, dedicated, clean, quite, signal, computer, electronic, or other improper form of earth bonding for use as a point of connection of the IG EGC.
Isolated earth grounding electrode designs have no means for limiting the potential developed across the intervening impedance in the commonly shared grounding medium (e.g. earth) when a current is caused to flow through it. As a result, lightning may create a few to tens of thousands of volts between two such earth grounding electrodes. AC system ground faults may create similar problems in relation to the AC systems nominal L-G voltage and the fault-current magnitude.
Which brings us to the question of where should the IG EGC originate? Well it has already been answered, but I will try to simplify. The IG EGC should originate at the N-G bond point from where the power is supplied from. It is really that simple. Don?t go away with a narrow mind set of that the service disconnect is the only place it should originate frome because that is not true. We have separately derived systems like isolation/step-down transformers and UPS thrown in the mix. Which brings up another point? The only way for an IGR circuit to be even remotely effective is by using a separately derived system like a isolation/step-down transformer or UPS. These are the only two systems that can effectively reduce or eliminate common mode noise. The kicker is if you use a transformer or UPS, then there is no need for an IGR circuit.
OK flame away folks; I got my thinking cap on today.
[ January 30, 2006, 10:28 AM: Message edited by: dereckbc ]
Chevy, do not feel bad about being in the dark over IGR. I know many electricians, engineers, and manufactures with ?Mushroom Syndrome? when it comes to IGR.
IMO the confusion in part comes from the NEC itself, by not specifying where the IGR conductor should originate. Again IMO the NEC is too lenient or vague in its description. Per the NEC it can originate any where from the service disconnect to any point downstream from there. This leads to a lot of misinterpretations from all across the electrical disciplines like separate, isolated, insulated, dedicated, clean, quite, signal, computer, electronic, or other improper form of earth bonding for use as a point of connection of the IG EGC.
Isolated earth grounding electrode designs have no means for limiting the potential developed across the intervening impedance in the commonly shared grounding medium (e.g. earth) when a current is caused to flow through it. As a result, lightning may create a few to tens of thousands of volts between two such earth grounding electrodes. AC system ground faults may create similar problems in relation to the AC systems nominal L-G voltage and the fault-current magnitude.
Which brings us to the question of where should the IG EGC originate? Well it has already been answered, but I will try to simplify. The IG EGC should originate at the N-G bond point from where the power is supplied from. It is really that simple. Don?t go away with a narrow mind set of that the service disconnect is the only place it should originate frome because that is not true. We have separately derived systems like isolation/step-down transformers and UPS thrown in the mix. Which brings up another point? The only way for an IGR circuit to be even remotely effective is by using a separately derived system like a isolation/step-down transformer or UPS. These are the only two systems that can effectively reduce or eliminate common mode noise. The kicker is if you use a transformer or UPS, then there is no need for an IGR circuit.
OK flame away folks; I got my thinking cap on today.
[ January 30, 2006, 10:28 AM: Message edited by: dereckbc ]
pierre
Senior Member
- Location
- Westchester County, New York
Re: Isolated ground bars
Hello Derek
If one has 2 different CPUs that are plugged into 2 different receptacles, each receptacle being on a different phase and the Data cable between the 2 CPUs has a ground connection; other than installing them on the same circuit,how can that problem be alleviated?
Hello Derek
If one has 2 different CPUs that are plugged into 2 different receptacles, each receptacle being on a different phase and the Data cable between the 2 CPUs has a ground connection; other than installing them on the same circuit,how can that problem be alleviated?
Re: Isolated ground bars
Optical Isolation Modem is the best bet. Otherwise get away from signal protocols that use ground or grounded conductors as a signal path and avoid shielded cable. A good example of a bad signal protocol is RS-232 and coax mediums. Use ethernet.
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