Overhead Distribution Transformer 120/240v 3w

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DumbLineman17

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Freedom, Idaho
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Journeyman Lineman
Hello,
Looking to find code references to single phase over head distribution transformers supplying 120/240 3w service. My question is: Does the neutral conductor - usually a 2/0 or 4/0 copper for most 15kVA to 100kVA transformers - for the X2 have to be directly connected to the system neutral on a Wye distribution system? Many utilities I have worked for have a common practice of connecting this neutral (X2) "transformer leg" directly to the system neutral. I have been working under very old standards/"specs" for a small utility that does not do this commonly accepted practice. Instead this old, outdated utility uses a #4 solid copper conductor between the 2/0 or 4/0 copper "transformer leg".
Again, looking for direct words in the NEC or any code reference/s.
Thank you in advance,
Just a dumb lineman.
 
DumbLineman17 said:
Hello,
Looking to find code references to single phase over head distribution transformers supplying 120/240 3w service. My question is: Does the neutral conductor - usually a 2/0 or 4/0 copper for most 15kVA to 100kVA transformers - for the X2 have to be directly connected to the system neutral on a Wye distribution system? Many utilities I have worked for have a common practice of connecting this neutral (X2) "transformer leg" directly to the system neutral. I have been working under very old standards/"specs" for a small utility that does not do this commonly accepted practice. Instead this old, outdated utility uses a #4 solid copper conductor between the 2/0 or 4/0 copper "transformer leg".
Again, looking for direct words in the NEC or any code reference/s.
Thank you in advance,
Just a dumb lineman.
Click to expand...

This is not a popular concept on this forum ... just food for thought !
 

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mtnelect said:
This is not a popular concept on this forum ... just food for thought !
Click to expand...
Thank you for your information. Sorry, just a dumb lineman, but what "concept" are you referencing? For some very apparent reason most utilities are directly connecting the x2 to the system neutral. I'm simply trying to find out the answer to that question. I was sent here by the site administrator... So if there is some type of "rule" I am breaking please let me know. Again, just a dumb lineman, Thank you for you our help.
 
After reading the full IEEE you provided, I would like to be clear. I am asking about the secondary side of the overhead step down distribution transformer. Not the primary (high voltage) side. I see a concept/s in Fig 12 and 13 you may be referencing, but in clear. Again, the question lies on the size conductor that it "linked" between the transformer X2 and the system neutral.
Thank you for your information. Very good read.
 
Welcome to the forum.

Is your question, "Why the secondary neutral is tied to the primary neutral?"
 
DumbLineman17 said:
Thank you for your information. Sorry, just a dumb lineman, but what "concept" are you referencing? For some very apparent reason most utilities are directly connecting the x2 to the system neutral. I'm simply trying to find out the answer to that question. I was sent here by the site administrator... So if there is some type of "rule" I am breaking please let me know. Again, just a dumb lineman, Thank you for you our help.
Click to expand...

They use less copper, and it causes "Stray Current" to flow into the ground. It's great for the utilities but bad for the consumers.
 
First note that the NEC does not cover utility installations. That would be the NESC. Most of us on this form are not familiar with the NESC. And I'm with larry, I'm not exactly sure what you are asking. Are you asking about a connection between the secondary neutral and the primary and neutral? If so, it would help to know some more specifics about the transformers. Most transformers would come with a copper factory installed strap from the can to the secondary neutral. A distribution line with a neutral would almost always be a multi-grounded neutral system, and use single bushing transformers. The primary neutral would land on the can itself, and that factory installed strap I mentioned earlier would make the connection to the secondary neutral. However, utilities that have both MGN and deltas will often use two bushing transformers so they can be used on either system. Maybe this is the case you are talking about where they need a jumper from the primary neutral to the secondary neutral?
 
electrofelon said:
First note that the NEC does not cover utility installations. That would be the NESC. Most of us on this form are not familiar with the NESC. And I'm with larry, I'm not exactly sure what you are asking. Are you asking about a connection between the secondary neutral and the primary and neutral? If so, it would help to know some more specifics about the transformers. Most transformers would come with a copper factory installed strap from the can to the secondary neutral. A distribution line with a neutral would almost always be a multi-grounded neutral system, and use single bushing transformers. The primary neutral would land on the can itself, and that factory installed strap I mentioned earlier would make the connection to the secondary neutral. However, utilities that have both MGN and deltas will often use two bushing transformers so they can be used on either system. Maybe this is the case you are talking about where they need a jumper from the primary neutral to the secondary neutral?
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Ok. A single phase 120/240 3 wire service transformer that is less than 200kVA has 3 secondary bushings, each have one conductors as I have explained above (usually 2/0 or 4/0 copper) that is attached: 2 secondary bushing each supply 120 volts X1 and X3, the middle or center bushing X2 is the neutral. After that conductor is attached then follows down to the customer attached neutral, DOES THIS NEUTRAL X2 conductor have to be directly attached to the primary system neutral? Or.....can a small #4 copper link/jumper be used. This is NOT a delta distribution system. It is a Wye distribution system. Regardless of what is going on on the "high side" or primary side (H1 or H2) I am asking about the secondary side. I will post two pictures of either standards. Thanks for your patiences as I understand we line monkeys deal in an entire different code for the same AC theory - that is a whole other discussion.
 

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DumbLineman17 said:
Ok. A single phase 120/240 3 wire service transformer that is less than 200kVA has 3 secondary bushings, each have one conductors as I have explained above (usually 2/0 or 4/0 copper) that is attached: 2 secondary bushing each supply 120 volts X1 and X3, the middle or center bushing X2 is the neutral. After that conductor is attached then follows down to the customer attached neutral, DOES THIS NEUTRAL X2 conductor have to be directly attached to the primary system neutral? Or.....can a small #4 copper link/jumper be used. This is NOT a delta distribution system. It is a Wye distribution system. Regardless of what is going on on the "high side" or primary side (H1 or H2) I am asking about the secondary side. I will post two pictures of either standards. Thanks for your patiences as I understand we line monkeys deal in an entire different code for the same AC theory - that is a whole other discussion.
Click to expand...
Ok , I usually see a copper strap connecting the X2 to the can, in the primary neutral is also attached to the can. Looks like that is not what you have and instead of that copper strap it's just a wire as a jumper. Same thing of course. Anyway, there are advantages and disadvantages to this connection. The advantages are quicker clearing time if a MV line falls on a service drop, and a lower resistance premise grounding system since it is now tied to the utilities grounding system, which may provide better protection from lightning events. Disadvantages are you are now providing a path for distribution neutral current which could result in elevated voltages and stray neutral current.
 
This is off subject ... I have great respect for Linemen. My brother in-law worked his way up to Service planner for SCE, he often stated that the most critical time was when a pole transformer is activated. Told stories of utility workers getting covered with hot oil and restoring power in poor weather conditions. Not to mention the physical problems of climbing poles. Also, mentioned not to park your car next to those gray PVC vent pipes.
 
DumbLineman17 said:
Ok. A single phase 120/240 3 wire service transformer that is less than 200kVA has 3 secondary bushings, each have one conductors as I have explained above (usually 2/0 or 4/0 copper) that is attached: 2 secondary bushing each supply 120 volts X1 and X3, the middle or center bushing X2 is the neutral. After that conductor is attached then follows down to the customer attached neutral, DOES THIS NEUTRAL X2 conductor have to be directly attached to the primary system neutral? Or.....can a small #4 copper link/jumper be used. This is NOT a delta distribution system. It is a Wye distribution system. Regardless of what is going on on the "high side" or primary side (H1 or H2) I am asking about the secondary side. I will post two pictures of either standards. Thanks for your patiences as I understand we line monkeys deal in an entire different code for the same AC theory - that is a whole other discussion.
Click to expand...
Picture shows a single distribution line entering top of can. Is that a Single Wire Earth Return (SWER) ?

Picture shows another distribution line at same level as can, but can't see where it's connected ?

Picture shows what appears to be secondary taps going over and around the can, then disappear at the pole. Where are those going?
 
ramsy said:
Picture shows a single distribution line entering top of can. Is that a Single Wire Earth Return (SWER) ?

Picture shows another distribution line at same level as can, but can't see where it's connected ?

Picture shows what appears to be secondary taps going over and around the can, then disappear at the pole. Where are those going?
Click to expand...
The picture is typical of one leg and a neutral/ground.
SWER are so rare they should only be taught in advanced classes.
 
jim dungar said:
The picture is typical of one leg and a neutral/ground.
SWER are so rare they should only be taught in advanced classes.
Click to expand...
So, again as the name states, I am only a dumb lineman....so I can not talk on these "advanced classes" you speak of but I am assuming the acronym SWER means Single Wire Earth Return???? The highlights in white of the photo I posted are the system neutral of the 7200v Wye distribution system. The "return" reference is my question. The transformer leeds (conductors) that I have highlighted and have explained above ☝️in all the previous posts is the secondary 120/240 leeds. MY QUESTION IS DOES THE NEUTRAL OF THE SECONDARY NEED TO BE DIRECTLY CONNECTED TO THE SYSTEM NEUTRAL. Because what the standards I have been told to build are to have a small #4 copper jumper between the system neutral and the transformer neutral leed. I feel this "necks down" the current, and also creates a hazard if/when this small jumper is to be removed or torn off in a storm. Sorry, if this is TOO advanced....but if you remove the bond or connection to ground/neutral on a high voltage transformer you are creating and very large metal can energized at 7200v....and has killed the men that work these lines.
 
I have trouble understanding the NEC let alone any utility distribution system. But my gut feeling is that you don't want to modify an existing working distribution system, without engineering guidance. If it isn't broke don't mess with it.
 
DumbLineman17 said:
So, again as the name states, I am only a dumb lineman....so I can not talk on these "advanced classes" you speak of but I am assuming the acronym SWER means Single Wire Earth Return???? The highlights in white of the photo I posted are the system neutral of the 7200v Wye distribution system. The "return" reference is my question. The transformer leeds (conductors) that I have highlighted and have explained above ☝️in all the previous posts is the secondary 120/240 leeds. MY QUESTION IS DOES THE NEUTRAL OF THE SECONDARY NEED TO BE DIRECTLY CONNECTED TO THE SYSTEM NEUTRAL. Because what the standards I have been told to build are to have a small #4 copper jumper between the system neutral and the transformer neutral leed. I feel this "necks down" the current, and also creates a hazard if/when this small jumper is to be removed or torn off in a storm. Sorry, if this is TOO advanced....but if you remove the bond or connection to ground/neutral on a high voltage transformer you are creating and very large metal can energized at 7200v....and has killed the men that work these lines.
Click to expand...
When you say "system neutral" do you mean the primary neutral? I believe I answered your question in post number 10. The connection is not required for proper operation. You could remove it and no one would even notice.
 
LarryFine said:
Welcome to the forum.

Is your question, "Why the secondary neutral is tied to the primary neutral?"
Click to expand...
I would like to ask this question. I have seen transformers in books with both primary and secondary bonded together and ive seen transformers with only the secondary neutral bonded to thr transformer can. This this confusing as which method to use or when?

A buck and boost has primary and secondary bonded but a standard transformer is supposted to have mutual induction rather than direct contact with primary secondary contact. Could some one explain this better?
 
mtnelect said:
This is not a popular concept on this forum ... just food for thought !
Click to expand...
Can you please send the rest of that transformer file i read it but wanted to finish the rest. I see why primary was bonded to secondary to save utility money by using customers grounding system

Also i would like to point out that if utility were gov it would be law for them to compensate homeowners for using their property - grounding system
 
The picture is of a a two bushing primary transformer, you can't see the other bushing. The primary/system neutral (at low amperage) is attached to the transformer with a #4 copper. What I am asking is does the secondary (2/0 or 4/0) copper need to be DIRECTLY attached to the primary/system neutral? Here they use a #4 "jumper". The strap you speak of in #10 is between the transformer case and the X2, yes thru a "daisy chain" of connections it goes back to the system neutral. What I am getting at is that you could have a very large amperage return across this small #4 "jumper" as the size of this single phase transformer gets bigger. When we use the same standard for a 15kVA and 167kVA the amperage will increase with kVA. As many other utilities across the nation directly attached this "jumper" to the primary/system neutral, I ask is this a preferred practice, best practice, or recommendation any where in document form from NESC/IEEE?
 
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