How do I derive my Neutral when I use Step Up/ Step Down transformers?

[LarryFine]

You keep using grounded and grounding interchangeably, and they are not the same thing.

The difference matters so we can discuss it correctly.

#1 is a grounding conductor, for bonding metallic parts.

#2 is a grounded conductor, which is your derived neutral.

Added: Okay, green wire #2 is the electrode wire for your derived neutral.

Green #1 is the EGC for your primary and feeder circuits.

 

[LarryFine]

Also, remember that there is an option to use an H1 and N in your (relatively) high-voltage feeder if desired.

 

[Installer]

Thanks Mr. Fine. Now I understand . Grounded Conductor 1 does not exist, it should have been called the EGC. I'm going to study 250.30 very carefully the next few days.

 

[Strathead]

There is no requirement that the system bonding jumper be in the transformer. It is permitted to be in the transformer or at the first OCPD enclosure. In either case a supply side bonding jumper, not a system bonding jumper, must be run between the transformer and the panel.

Thank you. I don't know what I read last year that I misinterpreted, but after seeing you post I verified and see that 250.30 clearly states the system bonding jumper can be in either location.

 

[kwired]

Connect X2/X3 to a grounding electrode, run the neutral from that point to the panel neutral bar. Install a system bonding jumper at either the transformer or the panel and install a supply side bonding jumper between the panel and the transformer.
Note that since the 600 volt system is an ungrounded system, 250.21(B) will require a ground detector.

Or ground/bond one of the 600 volt system conductors.

 

[kwired]

IT was all quick and dirty, I am open to corrections . Yeah I googled the part number for the transformer, but you can go with another brand and they are much cheaper, I See one for $685.

Nassua national shows #4 XHHW for .31/foot. Will be cheaper if you ask them for a quote.

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Is there minimum quantity to get that price?

 

[kwired]

Thanks Mr. Fine. Now I understand . Grounded Conductor 1 does not exist, it should have been called the EGC. I'm going to study 250.30 very carefully the next few days.

The secondary of a transformer like the ones you have is not electrically connected to the primary. There is no ground reference until you make a reference - which theory wise can be any outgoing lead, code wise often must be the "neutral conductor" if one is used. Also the X2/X3 of the final output here is the neutral of the derived secondary of this arrangement, to get a solid 120/240 out of this you must connect to it with your secondary neutral conductor. Otherwise you will just end up with a so called "floating neutral" that does become the topic of many threads here and will have line to neutral voltages that vary greatly depending on loading conditions.

 

[electrofelon]

Is there minimum quantity to get that price?

I don't believe so. After a certain amount, maybe $1000, they give you free shipping.

 

[Installer]

Just wanted to thank everyone here. I made all the corrections. Think I got this right.
Ironic that someone can do all kinds of complicated calculations but hooking up transformers -- I'd rather sand my driveway with 400 grit -can't find any information or book so have to relearn it every time
"If this is outside, you can use 250.30(A)(1) exception #2. So you ground one of the 600V legs and treat it like a service, so it’s a grounded conductor and your EGC. This saves you having to run a third conductor."


"The system bonding jumper (250.102) is required to be installed in the transformer. Then you will run a system bonding jumper (250.102) in the conduit with the transformer secondaries and land it on the ground bus in the panel. The neutral will run to the neutral in the panel. The neutral and ground will not be bonded in the panel. 1 Consult the transformer instructions to be sure, but it looks like your neutral at the step down secondary can be brought out from either X2 or X3. That is not shown in the drawing. If you don't do this you'll fry the loads."


The NEC gives you two options for bonding and grounding: either do both at the transformer, or do both at the first disconnect. I believe you also need the panel on right to have a main breaker or a disconnect in between it and the transformer.


Or ground/bond one of the 600 volt system conductors.

 

[LarryFine]

It looks god at the second transformer now, I think. Just looking elsewhere now, a couple of observations:

1. You show H2 and H3 as taps on single 600v windings on both transformers. Is that accurate, or are there actually two 300v windings that should be connected in series like the 120/240v windings are?

2. If the 600v windings do have center taps (once my observation 1 is confirmed), will you ground the first transformer's center tap, or will you use the option to ground one of the line conductors instead?

You show the 600v feeder as floating right now, which is why I'm asking.

 

[Installer]

I'm glad you noticed that.
I checked several sources and and this is the winding Diagram . Guess there are no center taps
I grounded one of the 600V line conductors at the left (at the Building. If that turns to be hard to do, (we can't get to structural steel) could we instead ground the 600V line conductor at the right out in the Field , at a ground rod
Thanks

 

[kwired]

Can't, or at least should not do that.


You are applying 120 volts to whatever electrode you connected to. Amount of current that will flow will depend on resistance to earth of said electrode. Typical rod will be high enough resistance to not trip breaker but will be undesirable current flowing through the electrode and a voltage gradient in the earth in the vicinity of the rod. If you connected to something rather solidly grounded you will have high fault current and trip the supply breaker.

 

[Installer]

"You are applying 120 volts to whatever electrode you connected to. Amount of current that will flow will depend on resistance to earth of said electrode. Typical rod will be high enough resistance to not trip breaker but will be undesirable current flowing through the electrode and a voltage gradient in the earth in the vicinity of the rod. If you connected to something rather solidly grounded you will have high fault current and trip the supply breaker."




Thanks for being so alert. That was unintentional. I was grounding one of the 600V Hot legs per your and Mr. Fines guidance.