Neutral required? Conflicting opinions.

[iwire]

To me, that's another reason to have the primary run all the way. I'd rather have the POCO be responsible for as much of the run as possible.

I rather that as well, who wouldn't 24/7 free repair service.

But that would not be possible in my area.

The power company will not run into the property like that here.

The customer would be footing the entire bill.

We often end up running the primary's, building the pads, provide the transformers etc. for the power company on private property.

 

[winnie]

Jon, are you saying that an EGC need not be run with the 600v conductors?

Yup. Either this is a service (iwire's interpretation), in which case the _grounded conductor_ is the fault current return path back to the transformer, and any EGC would be bonded to the grounded conductor at the service disconnect, _or_ this is an outside feeder run between detached structures, where again the grounded conductor can serve as the fault current return path, with any EGCs bonded to the grounded conductor at the building disconnect.

Winne if the 600 volts is coming right from the power company than this is a service.

A grounded system service must have the grounded conductor brought with it, there is no 'EGC' to use.

Agreed. If this were a 600V single phase three wire service where the transformer center tap is grounded, then a grounded conductor would need to be carried from the transformer to the service disconnect.

But what code _requires_ that the grounded conductor be connected to the _neutral_ tap of the transformer secondary. See 250.26(1); this could be a single phase _two wire_ service with one of the conductors grounded. Such a design would introduce other expenses, for example any OCPD would need to be rated for 600V rather than 'slash rated' for the lower hot to ground voltage of the center tapped system, and I am sure that there would be other design differences.

-Jon

 

[winnie]

Bump. Is my thinking here reasonable, or am I still out to lunch ?

-Jon

 

[Smart $]

Simply speaking, if only two-wire service is needed, the poco should configure their xfmr as such, grounding one leg of the service.

 

[hillbilly]

Bump. Is my thinking here reasonable, or am I still out to lunch ?

-Jon

I'll jump in here....Although your scenario is not the way that it's done where I live, On Undergrounds, the POCO runs high voltage underground (in the customer's trench) to a POCO provided transformer located near the home. From there the POCO will run to the customer's meter can (through customer's trench and riser).
I haven't had any experience with your problem, so, any opinion that I give will be fwiw.
When I first read your post I thought..no way. It understood it to say that you wanted to run 2 ungrounded (hot) conductors to the 600/240 transformer and not run a grounded (or grounding) conductor. Then use a earth ground to provide grounding and bonding for the transformer case and center (neutral) tap of the wye connected transformer. This earth ground also providing the grounded (neutral) for the house.

After reading the posts, I think that what you mean is to run 1 ungrounded (hot) and (1) grounded conductor from the first transformer to the second transformer disconnect. At that point you will install a earth ground and bond this grounded conductor to the transformer case, grounded conductor (supplying the house) and center tap of the wye connected transformer. Am I doing OK so far?
If that is the case, then IMO the disconnect (service rated) at the second transformer will be the service Main. From this main disconnect the grounded (neutral) and grounding conductors need to be seperate, requiring a 4 wire feed from the transformer to the house. A Grounding electrode will also need to be installed at the house and bonded to the grounding conductor from the transformer and the breaker panel in the house.
(IMHO) this set-up is OK.

As I said, I don't have much experience with service transformers as the POCO does all of that.
Just thinking out loud.
Any comments? Am I off base?
steve

 

[chicar]

That's the way it's done here. Also include a fuse link switch on top of last pole ungrounded conductor feeding transformer.
Don't forget your hotstick. No EGC.

 

[M. D.]

Steve, are you saying the disconnect @ 600 volts feeding the second transformer is the main disconnect for the house.
Would this make the transformer service equipment??
I have never been involved in anything like this.
Why 2 transformers?? I don't understand what is gained??

 

[bob]

Cant he run two 750kcm cables from the 600v transformer to the step-down transformer, then ground the tap at the load side and run it to the house?Thanks

I do not see the need for 750 kcm for the 600 volt cable. Voltage drop for
100 amps at 600 volts is 0.64% or 4 volts. VD for 4/0 is 12 volts or 2.0 %.
100 amps x 600 volts = 60 kw load. Does the house have that much load?

 

[petersonra]

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Why would I put a service disconnect at that end?

We need more info but I see it this way.

The power company is providing a 600 volt service, from the service point to the 600-240/120 step down transformer are customer owned 1000' long service conductors and do not require a disconnecting means until they get to the structure served.

That being the case their will be no EGC to bring along, it will have to be the power company's grounded conductor.

But maybe I see the job differently than the rest of you.

That seems reasonable.

I kept thinking if an EGC was required in service conductors as some have suggested in previous posts in this thread, why does no one do it?

 

[hillbilly]

Steve, are you saying the disconnect @ 600 volts feeding the second transformer is the main disconnect for the house.
Would this make the transformer service equipment??
I have never been involved in anything like this.
Why 2 transformers?? I don't understand what is gained??

If the second transformer is going to belong to the customer, it is part of the service equipment (again IMHO). If the customer ever has to have service performed on "his" transformer, he will require a disconnect. This (fused) disconnect on the primary of the transformer then becomes the main disconnect for "his" service. If this is not correct, somebody with a different opinion please jump in. I'm here to learn.
I didn't say that I thought this was the best way. IMO, high voltage underground to a utility supplied transformer (near the house) is the best way. I was just responding to the op.
I've never seen anything like this before either.
Two transformers, and feeding this distance with 600V is a waste of money. Not only in initial cost, but also in the energy that will be wasted in the long run.
Again, just my opinion.
steve

 

[dnem]

I thought that I understood the situation until I started reading the replies. I have more question about the replies than I have about the installation.

The question is about the conductors between a 1.7kv-600v transformer and a 600v-120/240v transformer, right ? Unless it has been posted otherwise, I would assume the main disconnect is on the 120/240 conductors, so why is the subject of an EGC coming up when talking about the conductors between the 2 transformers ? Is an equipment ground ever used on the line side of the main disconnect ?

If you have transformer to transformer supply wiring, why would you ever run more conductors than the primary on the second transformer needs ? Run your phase conductors and then either add a neutral if the primary on the second transformer is wye or just ground one of the phase conductors if the primary on the second transformer is delta.

Am I missing something ?

The replies on this thread are leaving me scratching my head.

David

 

[tom baker]

"As an interesting side note, his neighbor in this rural area is an electrician with the local water district and he mentioned that they run similar installations with just two wires all the time. However, it is possible that they are only using 240 and not 120. They also are likely to have different regs. to follow."
This is a violation of 250.20. Think of the grounded conductor as a white wire with an green stripe, its either/or for unbalanced current or to clear a line to case fault.
Ask the electrican how a fault is cleared.

 

[LarryFine]

If you have transformer to transformer supply wiring, why would you ever run more conductors than the primary on the second transformer needs?

Suppose a 600v line wire were to short out against, say, the inside of a transformer can (600-to-240/120) at the house (which would be bonded to the house neutral). With no EGC (or neutral), there would be no low-impedance pathway back to the street-end transformer(s) to assure operation of the fuses.

 

[dnem]

Suppose a 600v line wire were to short out against, say, the inside of a transformer can (600-to-240/120) at the house (which would be bonded to the house neutral). With no EGC (or neutral), there would be no low-impedance pathway back to the street-end transformer(s) to assure operation of the fuses.

If what you're saying is true then there are thousands upon tens of thousands of corner grounded 3phase delta primary transformers that are incorrectly installed.

You don't need either a equipment ground or a neutral to operate the OC. A grounded phase conductor can operate the OC every time.

David

 

[LarryFine]

If what you're saying is true then there are thousands upon tens of thousands of corner grounded 3phase delta primary transformers that are incorrectly installed.

You don't need either a equipment ground or a neutral to operate the OC. A grounded phase conductor can operate the OC every time.

Agreed. I've been under the impression from the start of this thread that the installation would be done with two ungrounded conductors.

If one of the conductors is, or can be, grounded, this entire thread has been moot.

 

[sandsnow]

I read through everything looking for one thing and did not see it.

Is this overhead installation with pole top XFMR or undergraound with a padmount XFMR. The XFMR in my question being the 600V - 120/240V XFMR.

I'm kinda thinking it's overhead given the distance involved.

If the XFMR is pole top, I see no reason for an EGC or Neutral to be used for bonding the case. 250.110(1). It is over 8 feet in elevation.

If it is a padmount, then yes some bonding means needs to be provided. Same code section

 

[iwire]

If the XFMR is pole top, I see no reason for an EGC or Neutral to be used for bonding the case. 250.110(1). It is over 8 feet in

Larry I don't think you reading 250.110 correctly.

250.110 Equipment Fastened in Place or Connected by Permanent Wiring Methods (Fixed).

Exposed non?current-carrying metal parts of fixed equipment likely to become energized shall be grounded under any of the following conditions:

So I agree it gets by 250.110(1) but it certainly is required to be grounded by 250.110(6)

 

[sandsnow]

Good one Bob

Now that you forced me to put more thought into my answer, how about Exception #2, same section.

I love it when I can bail myself out ;-)

 

[iwire]

how about Exception #2, same section.

Looks quite possible assuming pole mount.

I love it when I can bail myself out ;-)

Bail yourself out?

Naw, you where just seeing if we where paying attention.

I have to say though I really do not like that exception.

So now if we have a case fault on the primary side the OCP will never open but it will raise the potential of the secondary grounded conductor supplying the house.

 

[sandsnow]

Thanks Bob, but that's like playing slop shot in 8 ball. Ok, I'll take it ;-)

So now if we have a case fault on the primary side the OCP will never open but it will raise the potential of the secondary grounded conductor supplying the house.

Isn't that one of the reasons (we've always been told) we take the neutral to earth at the house? I have no idea if this thing is a feeder or service.

The secondary neutral of that XFMR should be bonded and grounded on the pole. There's a code requirement for that or used to be. Can't find it at the moment.

The POCO's do this on their distribution XFMR's all the time. I would have to assume after all these years if it was a problem, that they would discontinue the practice.

Or maybe this is one of the causes of all that stray voltage, especially in livestock areas??? A little out of my area of expertise.