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Ground Current... Caused by motors?
- Thread starter waltppiva
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hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Ground Current... Caused by motors?
Thank's as I'm still learning too.
Thank's as I'm still learning too.
Re: Ground Current... Caused by motors?
Don/Wayne (or anyone else who would like to answer), Is there a code requirement stating that there must be an isolation transformer installed if the main service entrance panel is more than so much distance from a UPS? With this site we've been discussing the main feed is 208/120. So, there is no isolation transformer installed on the primary side of the UPS. Could this be an issue if the main service N-G bond is too far from the UPS? This still would not cause ground current, right?
Don/Wayne (or anyone else who would like to answer), Is there a code requirement stating that there must be an isolation transformer installed if the main service entrance panel is more than so much distance from a UPS? With this site we've been discussing the main feed is 208/120. So, there is no isolation transformer installed on the primary side of the UPS. Could this be an issue if the main service N-G bond is too far from the UPS? This still would not cause ground current, right?
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Ground Current... Caused by motors?
Walt directly I don't know of anything that could be used but indirectly, This could be an issue in providing a fault path sufficient to open a OCPD. But It still would be a hard call to prove. as far as current on the grounding conductor have you been able to determined if there is a ground/neutral bond in the UPS? if not have you checked if this current is also present on the load side of the UPS? if it is it could be coming from a circuit on the load side that might have a bad/miss-wired equipment cord plugged in. or a ground to neutral fault in one of the circuits. or even in the load panel might have a ground/neutral bond. But I don't see where this would cause the delay your experiencing. Have you been able to get your down time window yet?
[ January 12, 2004, 07:00 PM: Message edited by: hurk27 ]
Walt directly I don't know of anything that could be used but indirectly, This could be an issue in providing a fault path sufficient to open a OCPD. But It still would be a hard call to prove. as far as current on the grounding conductor have you been able to determined if there is a ground/neutral bond in the UPS? if not have you checked if this current is also present on the load side of the UPS? if it is it could be coming from a circuit on the load side that might have a bad/miss-wired equipment cord plugged in. or a ground to neutral fault in one of the circuits. or even in the load panel might have a ground/neutral bond. But I don't see where this would cause the delay your experiencing. Have you been able to get your down time window yet?
[ January 12, 2004, 07:00 PM: Message edited by: hurk27 ]
Re: Ground Current... Caused by motors?
Walt
We use a clamp on ground resistance meter from AEMC instruments to check our resistance to earth. We have discovered that it is a handy tool to check for ground neutral loops without isolating the circuit. If you clamp the instrument around the bounding jumper between the transformer neutral and the ground buss you will read the resistance of your grounding electrode system. If you have a ground loop the reading you get will be the resistance of the ground loop, normally .1 or .2 ohms. You should be able to check each circuit by clamping the meter around the grounded conductor. If the circuit doesn?t have a ground loop the reading will be the resistance of the load in series with the resistance of the transformer windings. If there is a ground loop you will get a very low reading (.1 to .2 ohms). The only drawback is that the meter will not work if you have more than five amps of current flowing in the conductor under test. Their web site is www.aemc.com.
Don McLain
[ January 13, 2004, 07:05 AM: Message edited by: mclain ]
Walt
We use a clamp on ground resistance meter from AEMC instruments to check our resistance to earth. We have discovered that it is a handy tool to check for ground neutral loops without isolating the circuit. If you clamp the instrument around the bounding jumper between the transformer neutral and the ground buss you will read the resistance of your grounding electrode system. If you have a ground loop the reading you get will be the resistance of the ground loop, normally .1 or .2 ohms. You should be able to check each circuit by clamping the meter around the grounded conductor. If the circuit doesn?t have a ground loop the reading will be the resistance of the load in series with the resistance of the transformer windings. If there is a ground loop you will get a very low reading (.1 to .2 ohms). The only drawback is that the meter will not work if you have more than five amps of current flowing in the conductor under test. Their web site is www.aemc.com.
Don McLain
[ January 13, 2004, 07:05 AM: Message edited by: mclain ]
Re: Ground Current... Caused by motors?
Wayne, I'm going into the site Saturday 1/24. I'll let you know what I find out.
Regarding the AEMC ground tester, I do have one and I do use it frequently. But, this particular site has up to 16 amps of current on the ground in various locations. So the ground tester would not work too well in this case. Thank you for the idea though.
Wayne, I'm going into the site Saturday 1/24. I'll let you know what I find out.
Regarding the AEMC ground tester, I do have one and I do use it frequently. But, this particular site has up to 16 amps of current on the ground in various locations. So the ground tester would not work too well in this case. Thank you for the idea though.
arcandspark
Member
Re: Ground Current... Caused by motors?
I had a potential difference in a hog production fascility where the lack of an equipotential plane was causing a small voltage to be transferred to the sow when the piglet attempted to suck. She would roll over and refuse to feed.
Once I (at no liability to myself), repaired the previous electricians lack of bonding, the potential difference was reduced to 1-2 volts and thus the problem was eliminated.
I know this all sounds funny, but the parallels are there. In this case, the sow is the UPS and once the ground problem/bonding problem is eliminated, I think your sow will begin to respond properly too.
Good luck
I had a potential difference in a hog production fascility where the lack of an equipotential plane was causing a small voltage to be transferred to the sow when the piglet attempted to suck. She would roll over and refuse to feed.
Once I (at no liability to myself), repaired the previous electricians lack of bonding, the potential difference was reduced to 1-2 volts and thus the problem was eliminated.
I know this all sounds funny, but the parallels are there. In this case, the sow is the UPS and once the ground problem/bonding problem is eliminated, I think your sow will begin to respond properly too.
Good luck
Re: Ground Current... Caused by motors?
I have a 2 part question:
Are there any issues that anyone knows of regarding if the main service panel (main neutral-ground bond) is more than a certain distance away then an isolation transformer is required to bring the N-G bond closer (to the UPS)?
With the site in question the UPS is approx 50 ft away from the main service panel (main bond). But there is no isolation transformer installed. Would this application require a transformer, or would installing a transformer on the primary side of the UPS help to isolate the UPS from ground current that may be created in the electrical system somewhere upstream of the UPS?
Tell me if I'm thinking correctly, but if there is ground current on the building steel (let's say for the sake of this conversation that the source of ground current is upstream of the UPS), if an isolation transformer is installed on the primary side of the UPS, because the XO is bonded to the case of the transformer cabinet, this would also tie the transformer XO (and the N-G bond)to the path of ground current, correct? And therefore would transfer the upstream ground current to the rest of the system on the secondary side of the transformer.
When there is current traveling on the building steel, it will travel on any available path. Therefore any piece of equipment connected to bldg steel (everything) has the potential to have ground current (or current on the metal case of the equipment). BIG SAFETY ISSUE!! Correct? Any thoughts?
I have a 2 part question:
Are there any issues that anyone knows of regarding if the main service panel (main neutral-ground bond) is more than a certain distance away then an isolation transformer is required to bring the N-G bond closer (to the UPS)?
With the site in question the UPS is approx 50 ft away from the main service panel (main bond). But there is no isolation transformer installed. Would this application require a transformer, or would installing a transformer on the primary side of the UPS help to isolate the UPS from ground current that may be created in the electrical system somewhere upstream of the UPS?
Tell me if I'm thinking correctly, but if there is ground current on the building steel (let's say for the sake of this conversation that the source of ground current is upstream of the UPS), if an isolation transformer is installed on the primary side of the UPS, because the XO is bonded to the case of the transformer cabinet, this would also tie the transformer XO (and the N-G bond)to the path of ground current, correct? And therefore would transfer the upstream ground current to the rest of the system on the secondary side of the transformer.
When there is current traveling on the building steel, it will travel on any available path. Therefore any piece of equipment connected to bldg steel (everything) has the potential to have ground current (or current on the metal case of the equipment). BIG SAFETY ISSUE!! Correct? Any thoughts?
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Ground Current... Caused by motors?
Walt only the path of the current would be preasent as current on the UPS this would meen that if there is current (amprage) on the grounding wire of the UPS then it is comming from the load side of the UPS and it could be just a neutral/ground bond in a branch circuit or the panel if any on the load side.
Walt only the path of the current would be preasent as current on the UPS this would meen that if there is current (amprage) on the grounding wire of the UPS then it is comming from the load side of the UPS and it could be just a neutral/ground bond in a branch circuit or the panel if any on the load side.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Ground Current... Caused by motors?
Walt I should have added that 50' should not pose a problem in fault current path as the resistance drop accross this short distance is low. Also have you been able to verify the unit is in normal mode? as I still think there should not be any transfer with this type of UPS.
Walt I should have added that 50' should not pose a problem in fault current path as the resistance drop accross this short distance is low. Also have you been able to verify the unit is in normal mode? as I still think there should not be any transfer with this type of UPS.
Re: Ground Current... Caused by motors?
I went into the site this past Saturday night. Oh boy, where do I start. We found 10 neutral-ground bonds in some office furniture circuits. Also, there is a generator that feeds 480 delta through a delta-wye step down transformer. The transformer then feeds through a disconnect switch. This feeds to the ATS. This is a 3-pole ATS which has the neutrals from the generator, utility and load all tied together. In the generator transformer the neutral was bonded to ground on the secondary side at XO. The disconnect switch also had a neutral-ground bond in it. With the transformer bond, in a standard application this may be normal to bond XO, but in this case because we are using a 3-pole ATS where the neutrals are all tied together, the main source neutral-ground bond will be used (at the main distribution panel). With a bond also in the generator transformer this would create a parallel path for neutral current to transfer onto the ground.
What would the code be that addresses the gnerator transformer being used as a secondary source and not a newly derived source, and therefore it should not have the N-G bond on XO.
What would the code be that addresses the N-G bond in the disconnect switch and also the bonds in the load circuits. This code would probably be the same for both. The information I have is from the 1993 code book 250.04 for the 3-pole ATS, and 250.61(B) for the other bonds. I have a 2002 code book, but am having trouble cross-referencing the codes. Any help would be tremendously appreciated.
I went into the site this past Saturday night. Oh boy, where do I start. We found 10 neutral-ground bonds in some office furniture circuits. Also, there is a generator that feeds 480 delta through a delta-wye step down transformer. The transformer then feeds through a disconnect switch. This feeds to the ATS. This is a 3-pole ATS which has the neutrals from the generator, utility and load all tied together. In the generator transformer the neutral was bonded to ground on the secondary side at XO. The disconnect switch also had a neutral-ground bond in it. With the transformer bond, in a standard application this may be normal to bond XO, but in this case because we are using a 3-pole ATS where the neutrals are all tied together, the main source neutral-ground bond will be used (at the main distribution panel). With a bond also in the generator transformer this would create a parallel path for neutral current to transfer onto the ground.
What would the code be that addresses the gnerator transformer being used as a secondary source and not a newly derived source, and therefore it should not have the N-G bond on XO.
What would the code be that addresses the N-G bond in the disconnect switch and also the bonds in the load circuits. This code would probably be the same for both. The information I have is from the 1993 code book 250.04 for the 3-pole ATS, and 250.61(B) for the other bonds. I have a 2002 code book, but am having trouble cross-referencing the codes. Any help would be tremendously appreciated.
Re: Ground Current... Caused by motors?
Hey everybody, I've answered my own question about the code for the generator transformer in my previous post. Because this generator transformer is connected to a 3-pole ATS, in which the neutral is tied together with the utility neutral, this would be covered under 250.20(D)(FPN No. 1). Therefore the transformer is not a seperately derived source and therefore should not be bonded.
Hey everybody, I've answered my own question about the code for the generator transformer in my previous post. Because this generator transformer is connected to a 3-pole ATS, in which the neutral is tied together with the utility neutral, this would be covered under 250.20(D)(FPN No. 1). Therefore the transformer is not a seperately derived source and therefore should not be bonded.
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