Posted: 3/26/2013 6:54:42 AM EDT
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Is it ok to bond a 480V ground to a 120V ground at arbitrary places? To me this would be a parallel path - I think there should only be one connection bonding the separately derived 120V system to the main grounding electrode conductor on the 480V end. What say you? |
| Depends on what you are trying to do. Is there any reason to need the separate supplies to float at different potentials? If these systems are wholly isolated, it shouldn't matter if they share a ground, as long as your ground is properly engineered (read: to code) |
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The problem encountered when bonding grounds like that is a phase divergence occurs resulting in an inverse reactive current.
Instead of power being generated by the relative motion of conductors and fluxes its produced by the modial interaction of magneto reluctance, and capacitive duractance. A ground consisting of a base plate of prefamulated amulite surmounted by a malleable logarithmic casing will prevent all of the above. |
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The neutral needs to be bonded across the transformer to prevent leakage from picking up the secondary to the primary input voltage through the inter-winding capacitance.
(Just like it does on a pole transformer for kV down to 120/240 V split phase). The safety ground also crosses, but is isolated from the neutral on the secondary side (everything on the secondary side is treated as a sub-panel with separate grounding an grounded conductors. |
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Quoted: Depends on what you are trying to do. Is there any reason to need the separate supplies to float at different potentials? If these systems are wholly isolated, it shouldn't matter if they share a ground, as long as your ground is properly engineered (read: to code) That's exactly what I don't want. It's not my system, so I don't know if the system is to code. I just need to fix an issue in my very small area. The 120V equipment SHOULD be bonded to the 480V equipment, but we have evidence of varying potentials, which is what I need to eliminate. I just don't want to create a parallel path back to the ground electrode conductor. |
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Quoted: The problem encountered when bonding grounds like that is a phase divergence occurs resulting in an inverse reactive current. Instead of power being generated by the relative motion of conductors and fluxes its produced by the modial interaction of magneto reluctance, and capacitive duractance. A ground consisting of a base plate of prefamulated amulite surmounted by a malleable logarithmic casing will prevent all of the above. Do you have a part number? 
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Quoted: The problem encountered when bonding grounds like that is a phase divergence occurs resulting in an inverse reactive current. Instead of power being generated by the relative motion of conductors and fluxes its produced by the modial interaction of magneto reluctance, and capacitive duractance. A ground consisting of a base plate of prefamulated amulite surmounted by a malleable logarithmic casing will prevent all of the above.  |
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Quoted:
Quoted:
Depends on what you are trying to do. Is there any reason to need the separate supplies to float at different potentials? If these systems are wholly isolated, it shouldn't matter if they share a ground, as long as your ground is properly engineered (read: to code) That's exactly what I don't want. It's not my system, so I don't know if the system is to code. I just need to fix an issue in my very small area. The 120V equipment SHOULD be bonded to the 480V equipment, but we have evidence of varying potentials, which is what I need to eliminate. I just don't want to create a parallel path back to the ground electrode conductor. What is the voltage between the two grounding points? |
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Quoted:
Quoted:
The problem encountered when bonding grounds like that is a phase divergence occurs resulting in an inverse reactive current. Instead of power being generated by the relative motion of conductors and fluxes its produced by the modial interaction of magneto reluctance, and capacitive duractance. A ground consisting of a base plate of prefamulated amulite surmounted by a malleable logarithmic casing will prevent all of the above. Do you have a part number? I think the Rockwell Retro-encabulator will work for you, but I don't remember the exact part number... |
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Quoted: Quoted: Quoted: Depends on what you are trying to do. Is there any reason to need the separate supplies to float at different potentials? If these systems are wholly isolated, it shouldn't matter if they share a ground, as long as your ground is properly engineered (read: to code) That's exactly what I don't want. It's not my system, so I don't know if the system is to code. I just need to fix an issue in my very small area. The 120V equipment SHOULD be bonded to the 480V equipment, but we have evidence of varying potentials, which is what I need to eliminate. I just don't want to create a parallel path back to the ground electrode conductor. What is the voltage between the two grounding points? 300mV |
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300mv isn't enough to worry about. generally, unlyss it causes a problem with your equipment,
Usually induced voltage runs around that,. But, dont try to bond the systems at a point in the field. You can have a fault that isn't tripping a breaker causing the erratic condition due to an improper intersystem ground. The fault current would pass through your bond, causing an electrocution hazard or burn hazard when your jumper burns up. The separately derived system should be connected to the same grounding electrode system the primary service uses on the secondary side of the transformer. The neutral should also be bonded to the case of the transformer inside the transformer, and there should be a separate ground and neutral coming from the transformer , though the bonding can be done at the first disconnect after the trans, but the former method is more common. The 480 system should have a bond to the building steel, a ufer or ground rod , and any other metal that can become energised also needs to be bonded, eg water, gas, sprinklers, etc. best to have maintenance get an electrician to check things out since most of these connections are only accessible by removing panel covers and that can be very hazardous. But they need to check continuity on the grounding and bonding system. |
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Quoted:
300mv isn't enough to worry about. generally, unlyss it causes a problem with your equipment, Usually induced voltage runs around that,. But, dont try to bond the systems at a point in the field. You can have a fault that isn't tripping a breaker causing the erratic condition due to an improper intersystem ground. The fault current would pass through your bond, causing an electrocution hazard or burn hazard when your jumper burns up. The separately derived system should be connected to the same grounding electrode system the primary service uses on the secondary side of the transformer. The neutral should also be bonded to the case of the transformer inside the transformer, and there should be a separate ground and neutral coming from the transformer , though the bonding can be done at the first disconnect after the trans, but the former method is more common. The 480 system should have a bond to the building steel, a ufer or ground rod , and any other metal that can become energised also needs to be bonded, eg water, gas, sprinklers, etc. best to have maintenance get an electrician to check things out since most of these connections are only accessible by removing panel covers and that can be very hazardous. But they need to check continuity on the grounding and bonding system. I generally try to keep the different grounds separate. But only because I deal more with electronic systems instead of higher voltage and in that case you could have some cross talk. If your connecting something like a computer on the 120V that doesn't have a signal conditioner and a welder or noisy motor on the 480V side then you might have issues. I also like to think about what it takes to do LOT and if there are any extra precaution to lock out 480V for your facility. I know by the book everything below 600V is "low" voltage so that might not be an issue for you here. I would suggest an electrician to get in there and have them take care of it. |
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Quoted:
The problem encountered when bonding grounds like that is a phase divergence occurs resulting in an inverse reactive current. Instead of power being generated by the relative motion of conductors and fluxes its produced by the modial interaction of magneto reluctance, and capacitive duractance. A ground consisting of a base plate of prefamulated amulite surmounted by a malleable logarithmic casing will prevent all of the above. 
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Quoted: 300mv isn't enough to worry about. generally, unlyss it causes a problem with your equipment, Usually induced voltage runs around that,. But, dont try to bond the systems at a point in the field. You can have a fault that isn't tripping a breaker causing the erratic condition due to an improper intersystem ground. The fault current would pass through your bond, causing an electrocution hazard or burn hazard when your jumper burns up. The separately derived system should be connected to the same grounding electrode system the primary service uses on the secondary side of the transformer. The neutral should also be bonded to the case of the transformer inside the transformer, and there should be a separate ground and neutral coming from the transformer , though the bonding can be done at the first disconnect after the trans, but the former method is more common. The 480 system should have a bond to the building steel, a ufer or ground rod , and any other metal that can become energised also needs to be bonded, eg water, gas, sprinklers, etc. best to have maintenance get an electrician to check things out since most of these connections are only accessible by removing panel covers and that can be very hazardous. But they need to check continuity on the grounding and bonding system. That's what I thought. The problem is that I'm having arcing between the 120V equipment and the 480.... and to be more specific, the 120 is converted to 240DC and the 480 is converted to 24DC, and the arcing is between two chassis grounded parts. |
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Quoted:
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300mv isn't enough to worry about. generally, unlyss it causes a problem with your equipment, Usually induced voltage runs around that,. But, dont try to bond the systems at a point in the field. You can have a fault that isn't tripping a breaker causing the erratic condition due to an improper intersystem ground. The fault current would pass through your bond, causing an electrocution hazard or burn hazard when your jumper burns up. The separately derived system should be connected to the same grounding electrode system the primary service uses on the secondary side of the transformer. The neutral should also be bonded to the case of the transformer inside the transformer, and there should be a separate ground and neutral coming from the transformer , though the bonding can be done at the first disconnect after the trans, but the former method is more common. The 480 system should have a bond to the building steel, a ufer or ground rod , and any other metal that can become energised also needs to be bonded, eg water, gas, sprinklers, etc. best to have maintenance get an electrician to check things out since most of these connections are only accessible by removing panel covers and that can be very hazardous. But they need to check continuity on the grounding and bonding system. That's what I thought. The problem is that I'm having arcing between the 120V equipment and the 480.... and to be more specific, the 120 is converted to 240DC and the 480 is converted to 24DC, and the arcing is between two chassis grounded parts. So the way you have explained it, your system looks like this? </plaintext>120V(AC)<--XForm-->480V(AC) | | V V 240DC 24DC</plaintext> |
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Quoted: Quoted: Quoted: 300mv isn't enough to worry about. generally, unlyss it causes a problem with your equipment, Usually induced voltage runs around that,. But, dont try to bond the systems at a point in the field. You can have a fault that isn't tripping a breaker causing the erratic condition due to an improper intersystem ground. The fault current would pass through your bond, causing an electrocution hazard or burn hazard when your jumper burns up. The separately derived system should be connected to the same grounding electrode system the primary service uses on the secondary side of the transformer. The neutral should also be bonded to the case of the transformer inside the transformer, and there should be a separate ground and neutral coming from the transformer , though the bonding can be done at the first disconnect after the trans, but the former method is more common. The 480 system should have a bond to the building steel, a ufer or ground rod , and any other metal that can become energised also needs to be bonded, eg water, gas, sprinklers, etc. best to have maintenance get an electrician to check things out since most of these connections are only accessible by removing panel covers and that can be very hazardous. But they need to check continuity on the grounding and bonding system. That's what I thought. The problem is that I'm having arcing between the 120V equipment and the 480.... and to be more specific, the 120 is converted to 240DC and the 480 is converted to 24DC, and the arcing is between two chassis grounded parts. So the way you have explained it, your system looks like this? 120V(AC)<--XForm-->480V(AC) | | ||| V V VVV 240DC 24DC Corrected ETA: Lol, you probably have it right. Spacing doesn't work right once posted. 24 is from 480. |
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You have to remember that transformer isolation is NOT infinite.
Their is leakage across the insulation, and capacitive coupling also. Yes, even at 60 Hz there is capacitive leakage. Separate earth grounds should be bonded. Just use a large enough conductor. How much current is flowing? Use a lower value resistor (100 ohms) and measure the voltage drop across it. You may find the current is VERY small. indicating it is coming from a high source impedance, like insulation leakage or capacitive coupling. Keep in mind that 120 V over a 10 mega ohm impedance still gives you 12 micro amps. Easily measured with a modern digital meter (though a cheap meter may load it slightly). |
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Quoted:
The problem encountered when bonding grounds like that is a phase divergence occurs resulting in an inverse reactive current. Instead of power being generated by the relative motion of conductors and fluxes its produced by the modial interaction of magneto reluctance, and capacitive duractance. A ground consisting of a base plate of prefamulated amulite surmounted by a malleable logarithmic casing will prevent all of the above. Came here to post this ^. |
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The problem encountered when bonding grounds like that is a phase divergence occurs resulting in an inverse reactive current. Instead of power being generated by the relative motion of conductors and fluxes its produced by the modial interaction of magneto reluctance, and capacitive duractance. A ground consisting of a base plate of prefamulated amulite surmounted by a malleable logarithmic casing will prevent all of the above. Do you have a part number? I think the Rockwell Retro-encabulator will work for you, but I don't remember the exact part number... The large electrical supplier Anus Distributing has the best deal on it. |
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Quoted: Quoted: Quoted: The problem encountered when bonding grounds like that is a phase divergence occurs resulting in an inverse reactive current. Instead of power being generated by the relative motion of conductors and fluxes its produced by the modial interaction of magneto reluctance, and capacitive duractance. A ground consisting of a base plate of prefamulated amulite surmounted by a malleable logarithmic casing will prevent all of the above. Do you have a part number? I think the Rockwell Retro-encabulator will work for you, but I don't remember the exact part number... P/N 87 duh |