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Draw the schematic for a user transformer. There is a solid connected conductor from the service 480/277 volt neutral to the neutral of the 120/208 secondary X-O. This electrical connection is complete to the utility MV MGN. Please explain; where is the separation?

A separately derived system will prevent the dairy cattle issue. The normal load carrying conductor being electrically connected to other systems is not the defining issue, this is not even in the consideration. The common connection of the ground fault conductor is the reason for a separately...

Sorry dpc, MGN is Multi Ground Neutral. This is the most popular distribution system in use. Through fault containment is provided at each transformer, by a shorting effect. Single bushing pots can be used. The neutral can serve as the third phase on open wye and delta banks. This conductor...

I was active in the industry when the term "separately derived system" was coined. The term "separately derived system" never has appeared in the transformer article of the NEC. "Separately derived system" is a procedure for connecting to ground, the equipment...

On a MGN distribution system, the primaries and secondaries of all transformers, including the end user equipment, are electrically connected under the definition of NEC section 200.3. The only transformer configuration that meets the definition of a separately derived system, is when the...

I will try this another way; Draw a distribution transformer, MGN system, as a supply to a building. Now draw an end user transformer, connected as required in the NEC for a separately derived system. What is the difference in electrical connections?

Thanks very much, Maybe my problem in understanding this issue is the NEC use of words not in the English language; ie, Grounded, and Grounding. Very well composed response. Thanks again.

Another reason I would like to run this issue by the professional engineers on this, and other forums is; The schematic of a transfer switch, in the Soares Grounding Publication, is identified as a separately derived system, due to the neutral being switched. Please examine the equipment...

Another issue; The illustrative technical publications, describing a separately derived system, specify that all transformers meet the definition excluding an auto-transformer. The reason is the supply neutral is connected to the auto-transformer. How about a grounded wye/grounded wye...

busbar: I like your approach.I still question the equipment ground conductor with the transformer supply, not being regarded as a circuit conductor. The origin of the terminology "Separately Derived System" section 250-26 first appeared in the NEC in 1968. In the 1965 Edition title...

I wrote the above to quick. Sorry if it is not clear. I wish there was an edit feature on this forum. I would like to know the technical facts that determines an equipment ground conductor to not be a circuit conductor. Any conductor that carries current or is capable of carrying current is a...

Thanks for responding. The supply conductors originating in another system are four wire secondary to a delta primary. The ground/neutral of the supply, connects to the X-O secondary of the user transformer. The MGN is complete to the transformer secondary. This is a MGN system, not a...

1.5 KVA 120/240 single phase transformers are a standard KVA size. The physical size is 10"H, 6"W, 6"D. Weight 40 lbs. This procedure is common for voltage matching. Safety considerations are; Ambient temperature, duration of load at full demand, Temperature rise is 115ºC...

I have been involved in research and design of ground systems at some of the most unique locations in the world. The conditions covered both extremes of earth impedance. The coral islands in the Pacific constituded a variable resistor. The impedance changed in relation to the ocean tide. The...

Gentlemen: You don't know how much I value this information. I only hope it is not wasted on me, at the ending of my career. I only wish the internet was active 50 years ago. I,m sure others will read this thread and benefit from the years of searching my brain. I agree a transformer is a...

Yes, this is known as a V/V, which can be an open delta or open wye. Open delta is usually 120/208 with a stinger leg. The secondary neutral is grounded and directly connected to the supply MGN, for through fault containment. Open wye is usually 480 secondary phase volts. The center...

Has anyone ever connected a transformer bank in open wye/open wye configuration?

Now I am really getting interested. I can not tolerate an unsolved issue, even if it is only trivia. I worked on the construction of an IBM data center in California for So. Cal Edison. They moved their computer mainframes from San Onofre Nuke plant. I understand a radiation leak will erase the...

I am seeing current from the load imbalance and from exterior sources on the equipment ground conductors. I read high EMF on these conductors.

I mis-stated the last message. The equipment ground conductors with objectionable current are from the service neutral/ground bus to the X-O of the transformer secondary. This X-O is connected to effective grounded building steel at closest point.