I am installing a 150A 120/240V load center 800 feet away from our meter-main service. I am using (2) 37.5kVA isolation transformers to accomplish this by stepping up voltage to 480V, then back down at the other end. I believe this qualifies as a separately derived system, so presumably the ground from main to load center is unnecessary. I am being told I don't need the neutral conductor as well because it is derived from the transformer on the X2-X3 lugs. Is this possible?
Grounds & Neutrals for Transformers
- Thread starter jtttat
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petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: Grounds & Neutrals for Transformers
SDS -yes.
Still need to run an EGC
Neutral is derived at the transformer by connecting it to an appropriate GE near the transformer.
IMO.
SDS -yes.
Still need to run an EGC
Neutral is derived at the transformer by connecting it to an appropriate GE near the transformer.
john m. caloggero
Senior Member
Re: Grounds & Neutrals for Transformers
It is my understanding that the sevice is single phase, 120/240V. A feeder supplies a 240V/480V transformer which in turn feeds a 480V/240V/120V 3-wire edison connected, secondary where a neutral will be derived. This is a separately derived system. The neutral at the second transformer must be grounded to a grounding electrode system as close as possible to the location of the transformer. See section 250.30(A)(3) and 250.30(A)(7). The grounded conductor from the service disconnect is not required.
It is my understanding that the sevice is single phase, 120/240V. A feeder supplies a 240V/480V transformer which in turn feeds a 480V/240V/120V 3-wire edison connected, secondary where a neutral will be derived. This is a separately derived system. The neutral at the second transformer must be grounded to a grounding electrode system as close as possible to the location of the transformer. See section 250.30(A)(3) and 250.30(A)(7). The grounded conductor from the service disconnect is not required.
Re: Grounds & Neutrals for Transformers
Section 250.30 is hard to read. Being primarily a residential electrical contractor; separately derived systems don't apply too often. This learning experience has clarified quite a bit about the grounded conductor - GEC bonding. Thank you for your responses.
What is meant by IMO?
Jeff
Section 250.30 is hard to read. Being primarily a residential electrical contractor; separately derived systems don't apply too often. This learning experience has clarified quite a bit about the grounded conductor - GEC bonding. Thank you for your responses.
What is meant by IMO?
Jeff
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Re: Grounds & Neutrals for Transformers
IMO=in my opinion
IMO=in my opinion
Re: Grounds & Neutrals for Transformers
I thought I had this section licked, but have since then been staring at 250.30A(2) Exhibit 250.13, and 250.14 of the 2002. What I don't understand is why they show an equipment grounding conductor coming from the line side of the transformer. Can't an equipment ground from the separately derived system satisfy this requirement?
I thought I had this section licked, but have since then been staring at 250.30A(2) Exhibit 250.13, and 250.14 of the 2002. What I don't understand is why they show an equipment grounding conductor coming from the line side of the transformer. Can't an equipment ground from the separately derived system satisfy this requirement?
- Location
- Massachusetts
Re: Grounds & Neutrals for Transformers
Are you asking about the EGC shown at the top of those two exhibits?
If so that is the EGC accompanying the 480 volt primarys from the original system.
That EGC is need to ensure operation the the 480 volt primary overcurrent protection if a ground fault happens in the primary conductors.
Sure enough there would be other paths that would make this happen however they would be of higher impedance than the EGC run with the conductors as required by 300.3(B).
Are you asking about the EGC shown at the top of those two exhibits?
If so that is the EGC accompanying the 480 volt primarys from the original system.
That EGC is need to ensure operation the the 480 volt primary overcurrent protection if a ground fault happens in the primary conductors.
Sure enough there would be other paths that would make this happen however they would be of higher impedance than the EGC run with the conductors as required by 300.3(B).
- Location
- Massachusetts
Re: Grounds & Neutrals for Transformers
By the way, the raceway could serve as that EGC.
By the way, the raceway could serve as that EGC.
pierre
Senior Member
- Location
- Westchester County, New York
Re: Grounds & Neutrals for Transformers
jtttat
try to remember that electrons (current flow) are always trying to get back to the source they came from. With that in mind, if there is a ground fault, the fault current is also trying to get back to the same source.
Now the current traveling because of the fault will travel on the equipment grounding conductor. That is the reason why one needs to install the EGC from the source to the last location on the circuit.
jtttat
try to remember that electrons (current flow) are always trying to get back to the source they came from. With that in mind, if there is a ground fault, the fault current is also trying to get back to the same source.
Now the current traveling because of the fault will travel on the equipment grounding conductor. That is the reason why one needs to install the EGC from the source to the last location on the circuit.
Re: Grounds & Neutrals for Transformers
Thanks again for your input. I have to ask though....When I run the EGC from Transformer 1 to transformer 2 I will be lugging it to the cases w/the EGC's from different systems. Is that okay? Is there a parallel path?
In other words: EGC from meter-main to transformer one lugged to case with the EGC for the 480volt run to transformer two. Transformer two I will have the EGC from transformer one lugged to case with the EGC for the 150amp load center.
Your input is greatly appreciated!
Thanks again for your input. I have to ask though....When I run the EGC from Transformer 1 to transformer 2 I will be lugging it to the cases w/the EGC's from different systems. Is that okay? Is there a parallel path?
In other words: EGC from meter-main to transformer one lugged to case with the EGC for the 480volt run to transformer two. Transformer two I will have the EGC from transformer one lugged to case with the EGC for the 150amp load center.
Your input is greatly appreciated!
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