Transformer grounding

don_resqcapt19

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Illinois
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retired electrician
I agree with this. If the wire from X-0 to the neutral bus isn't white, it's because the transformer maker put it in and didn't use a white wire.
I don't care who put it in, it is a neutral. The manufacturer may not be required to make it white, but I really doubt that wire was installed by the manufacturer. However no mater who installed it, it is a neutral as it is a conductor connected to the "neutral point".
Neutral Point
The common point on a wye-connection in a polyphase system or midpoint on a single-phase, 3-wire system, or midpoint of a single-phase portion of a 3-phase delta system, or a midpoint of a 3-wire, direct-current system. (CMP-5)
Neutral Conductor.
The conductor connected to the neutral point of a system that is intended to carry current under normal conditions. (CMP-5)
 

Rock86

Senior Member
Location
new york
Occupation
Electrical Engineer / Electrician
I don't agree. The conductor from the XO point on the transformer to the terminal block is the neutral. The neutral does not start at the terminal block,
neutral, xo... the connection point is xo (xo being just a lable), the function is to serve as a neutral... imo. its semantics at this point.
 

jap

Senior Member
I disagree with the drawing.

Never in my career have I ever taken a jumper from the XO or Neutral terminal of a transformer to the ground bar, then, from the ground bar terminal to my panel for the Neutral.

I take my panel feeder neutral directly to the XO terminal of the transformer.

The connections shown in his drawing from XO to the grounding terminal would be my bonding jumper on it's own lug of XO, and, I'd land my Neutral directly on the XO terminal on it's own lug, not on the grounding block.

JAP>
 

jap

Senior Member
The primary and secondary phase conductors in the drawing are shown landing on the "black dots" if that's what you want to call them, or,
H1, H2 ,H3, and, X1 X2 and X3.

If that's how they want to portray the terminals on the transformer, then, I'm going to also land my Neutral on the center "black dot" XO,or neutral of the secondary.

Not the grounding bar bolted to the chasis of the transformer.

JAP>
 

jap

Senior Member
The transformer will have some common point usually a piece of bus that is for the connection of the field neutral conductor and it is the point where the one side of each coil terminates. Look at this photo and see if it makes sense. The X0 bus is at the bottom.
View attachment 2557800

The drawing seems to be tailored per this setup which is unlike any modern transformer connection I'm used to seeing.

JAP>
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
I disagree with the drawing.

Never in my career have I ever taken a jumper from the XO or Neutral terminal of a transformer to the ground bar, then, from the ground bar terminal to my panel for the Neutral.

I take my panel feeder neutral directly to the XO terminal of the transformer.

The connections shown in his drawing from XO to the grounding terminal would be my bonding jumper on it's own lug of XO, and, I'd land my Neutral directly on the XO terminal on it's own lug, not on the grounding block.

JAP>
While I would install it your way, I don't think there is anything in the code that prohibits a splice in the neutral conductor, and the installation in the picture appears to be code compliant.
 

jap

Senior Member
While I would install it your way, I don't think there is anything in the code that prohibits a splice in the neutral conductor, and the installation in the picture appears to be code compliant.

I agree, but, if the feeder neutral actually did land directly on the XO terminal of the transformer as usual, instead of the terminal block, I'd consider the "black wire" in the drawing from XO to the grounding terminal a "jumper".

JAP>
 

don_resqcapt19

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Staff member
Location
Illinois
Occupation
retired electrician
I agree, but, if the feeder neutral actually did land directly on the XO terminal of the transformer as usual, instead of the terminal block, I'd consider the "black wire" in the drawing from XO to the grounding terminal a "jumper".

JAP>
Assuming that the grounding electrode conductor connects to that terminal block, the jumper would be the main bonding jumper. If the GEC connection is at the first disconnect, then the jumper would be a supply side bonding jumper, and it would not be permitted to be white. It could be any color other than white or gray.
 

jap

Senior Member
assuming that the grounding electrode conductor connects to that terminal block, the jumper would be the main bonding jumper. If the GEC connection is at the first disconnect, then the jumper would be a supply side bonding jumper, and it would not be permitted to be white. It could be any color other than white or gray.

I'm talking about the jumper that HHSTING is talking about shown in the drawing from the grounding terminal block (where the feeder neutral conductor to the panel and all the grounding electrodes are terminated ) to the actual XO terminal of the transformer.

To me where the main conductors terminate are the main termination points and other conductors are considered jumpers.

The conductor or jumper in the diagram from the actual XO terminal of the transformer to the grounding block is serving as the neutral.
If the neutral conductor from the panel was terminated directly to the XO terminal instead of the grounding block, then, the jumper from XO to the grounding block would be a bonding jumper.

Per this drawing the panel neutral is connected to the grounding block, not the actual XO terminal of the transformer.
Its getting its connection to the XO terminal of the transformer via a jumper cable which connects the two points.

Yes it is definitely a neutral, but, seeing as how the panel feeder neutral is not connected directly to the XO terminal of the transformer, in this case, it's actually a Neutral Jumper.

Nothing more than an extension of an upper XO termination point to a lower one.

JAP>
 

ActionDave

Chief Moderator
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Location
Durango, CO, 10 h 20 min without traffic from wing
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Licensed Electrician
assuming that the grounding electrode conductor connects to that terminal block, the jumper would be the main bonding jumper. If the GEC connection is at the first disconnect, then the jumper would be a supply side bonding jumper, and it would not be permitted to be white. It could be any color other than white or gray.

I'm talking about the jumper that HHSTING is talking about shown in the drawing from the grounding terminal block (where the feeder neutral conductor to the panel and all the grounding electrodes are terminated ) to the actual XO terminal of the transformer.

To me where the main conductors terminate are the main termination points and other conductors are considered jumpers.

The conductor or jumper in the diagram from the actual XO terminal of the transformer to the grounding block is serving as the neutral.
If the neutral conductor from the panel was terminated directly to the XO terminal instead of the grounding block, then, the jumper from XO to the grounding block would be a bonding jumper.

Per this drawing the panel neutral is connected to the grounding block, not the actual XO terminal of the transformer.
Its getting its connection to the XO terminal of the transformer via a jumper cable which connects the two points.

Yes it is definitely a neutral, but, seeing as how the panel feeder neutral is not connected directly to the XO terminal of the transformer, in this case, it's actually a Neutral Jumper.

Nothing more than an extension of an upper XO termination point to a lower one.

JAP>
It's not a conductor, it's a line on an illustration showing that the main bonding jumper and grounding electrode conductor and wye neutral point all get bonded together in the transformer if you don't do it in the first disconnect.
 

jap

Senior Member
It's not a conductor, it's a line on an illustration showing that the main bonding jumper and grounding electrode conductor and wye neutral point all get bonded together in the transformer if you don't do it in the first disconnect.
I guess I don't understand.

Without that conductor connection you'd have no neutral for the panel feeder.


Jap>
 

ActionDave

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Location
Durango, CO, 10 h 20 min without traffic from wing
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Licensed Electrician
I guess I don't understand.

Without that conductor connection you'd have no neutral for the panel feeder.


Jap>
That illustration is from the NEC handbook in 250.30. It's not showing a panel feeder it's showing how to bond the neutral of a transformer. There is another illustration that shows the bonding in the first disconnect.
 

jap

Senior Member
That illustration is from the NEC handbook in 250.30. It's not showing a panel feeder it's showing how to bond the neutral of a transformer. There is another illustration that shows the bonding in the first disconnect.

If that's the case It's just drawn odd.

Someone ought to get rid of that black dot at the XO point of the transformer.

That way the XO point of attachment would be at the terminal block and forget about the jumper that is drawn.

You wouldn't need it.

Jap>
 

paulengr

Senior Member
I guess I don't understand.

Without that conductor connection you'd have no neutral for the panel feeder.


Jap>

Not everything has a neutral. If all loads are 3 phase or line to line you don’t need it. Motor circuits for instance don’t need it. Heating sometimes. Lighting is better if you use a tranny anyways.
 

DrSparks

Senior Member
Location
Madison, WI, USA
If you really pay attention to that illustration, the line going from the center of the wye diagram to the terminal bar would be carrying all the neutral current, so it is technically a CCC. Would normally be white. Not sure why they made it black as the lines depicting the phase conductors are also black. They may just be callout lines which are typical in diagrams.

Sent from my BE2028 using Tapatalk
 
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infinity

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New Jersey
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Journeyman Electrician
If you look at the windings they're also black so I'm not see where the color representation changes anything. When compared to the two transformer photos posted they clearly show that the black line merely represents the internal manufacturer's connection of the transformer windings to the X0 terminal.
 
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