Overhead Distribution Transformer 120/240v 3w

[wwhitney]

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.

FWIW, that would only happen in a fault situation, where a primary conductor energizes the secondary, or vice versa. In normal operation this jumper sees no current from the circuit conductors. Which is why electrofelon said it could be omitted.

Cheers, Wayne

 

[mtnelect]

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

Just posted under "Education", Part One, Pages, others to follow.

 

[ramsy]

is this a preferred practice, best practice, or recommendation any where in document form from NESC/IEEE?

You wont see anyone on this forum quote the NESC. You need to search that yourself.

Without conduit you will see smaller conductors carrying more current in free air.

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....

Yes, that single distribution line entering top of xfmr needs a return line.

Each transformer also bonds to an electrode traveling down the pole to the earth, which is a grounding electrode system (neutral).

and has killed the men that work these lines.

When traveling as a groundman for linemen crews repairing storm damage, they said lighting strikes that hit power lines can kill linemen miles away, and nearby strikes have killed everybody on the ground.

One of my clients witnessed a lineman fall from their backyard pole, followed by a blue flame, which continued to emerge from his chest after he hit the ground. That is consistent with geomagnetic storms that are most intense in northern latitudes during solar maximum.

I have personally seen ball lighting floating down our pole transformer, and read about serious burns to curious people that got too close.

 

[jim dungar]

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 utility puts a ground at regular internal along their neutral/grounding conductor, which is strung from pole to pole, this is why it is called a Multi-Grounded Neutral system. How are they using the homeowners system.
The only thing they save is the redundant neutral/ground conductor between their transformer and the service point.

There are lots of engineering advantages and disadvantages to an MGN distribution system. I don't think I have ever read, a peer reviewed, paper that listed cost savings from using the grounding system from the customer.

 

[electrofelon]

There are lots of engineering advantages and disadvantages to an MGN distribution system.

It's good to hear this stated again by another member. It seems many people like to oversimplify things, and just boil it down to "it's the greedy utility companies, MGN=bad". I think part of the problem is most on this forum are more familiar with premise electrical systems, so let me try this: think about grounded versus ungrounded premise electrical systems. Both have advantages and disadvantages. The advantages of grounded are Less poles and overcurrent devices and insulation levels, more automatic operation so better for untrained persons. Advantages of ungrounded systems are low (first L-G) fault currents, can still be operated after a first fault, less stray current issues.

 

[Jpflex]

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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.

After thinking about this, if you were to actually place a bonding jumper between the primary winding and secondary winding and wanted to know the proper size wire i would think


1) the bonding jumper would have to atleast equall to the primary size wire or perhaps it may have to follow tap rules if smaller or

2) sized to NEC 250.122 based on the size of the primary upstream OCPD (cutouts) or

3) based on 250.102 C If no upstrram OCPD brraker or

4) simply bond the primary and secondary windings (typically midpoint or derived neutral point) to the transformer can. This will iliminte the need for a bonding jumper and it would appear that the can would suffice to replace bonding wire size similar to how EMT is considererd the proper size as EGC since it is already sizee large enough to contain conductors. This also assumes you have internal access to windings

 

[Jpflex]

I don't think I have ever read, a peer reviewed, paper that listed cost savings from using the grounding system from the customer.

If you think of all the services multiplied by the number of redundant ground rod electrodes and GEC iliminated by using the homeowners grounding system, the savings is apparent

 

[ramsy]

the savings is apparent

Are the pole electrodes actually missing in some urban areas?

 

[mtnelect]

If you think of all the services multiplied by the number of redundant ground rod electrodes and GEC iliminated by using the homeowners grounding system, the savings is apparent

Part 2 has been posted.

 

[jim dungar]

If you think of all the services multiplied by the number of redundant ground rod electrodes and GEC iliminated by using the homeowners grounding system, the savings is apparent

No it is not.
The utility provides ground rounds per the NESC.
The customer provides ground rods per the NEC.
Ground is ground, so what is being saved?

Do you mean the issue of the utility using a combined grounding and neutral conductor on their primary, negating the need to run both a grounded and a grounding conductor between their transformer secondary and the customer service point? Isn't some of the savings the customer's?