Ground Loop between transformer primary & Secondary

T

tlona1

Member
I have a 3phase transformer that is 1000 feet away from the primary OCPD. The secondary will have its OCPD 30 feet away from the transformer and the secondary System Bonding Jumper (SBJ) will be at the OCPD along with grounding conductor and ground rod. The Code requires an EGC on the primary side and a Supply Side Bonding Jumper (SSBJ) on the Secondary side. Since both the EGC & the SSBJ are attached to the transformer housing doesn't bonding the two grounding systems together create a ground potential between the two?
 
i'm unsure of your question. a "ground potential between the two"? are you referring to the building's utility EGC and the seperately derived sustem's SSBJ? the entire building (assuming steel building) is an EGC if the building is bonded properly. but you're going to give it an intentional bond back to the source, from the system's bonding jumper.
 
Thank-you
yes there will be a current flow but how is that quantified. Also Concern is if the EGC is disconnected, say form maintenance reasons, then could a have a potential EGC and enclosure.
 
Master Nater - The EGC I am referring to is the one run with the primary feeders which would be bonded buildings Main Bonding Jumper at the service. The ground soil at the service and at the secondary OCPD can be quite different. So yes they are all bonded but the two ends can be at different ground potentials
 
tlona1 said:
So yes they are all bonded but the two ends can be at different ground potentials
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This happens because there is already a neutral to earth voltage back at the utility side of things. Many use the grounded conductor for current carrying. A conductor carrying any current will have a voltage drop across it. At the far end that voltage drop shows up as a potential to earth even if you have quite a bit of length that isn't carrying current, the fact it is connected together way back where voltage drop last occurred, that potential is still there beyond that point. You can have nothing wrong with your site equipment but if there is neutral (grounded conductor) to earth voltage because of voltage drop on utility grounded conductor that passes on through. This is something that is almost always there if you are supplied by a utility that utilizes current carrying grounded conductor in their distribution. Often is rather negligible, but is noticed in places where even a small rise in voltage on the grounded conductor can cause problems. Also is a major factor in why all the equipotential bonding is required at swimming pools.
 
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