Static Wire vs. Neutral Conductor

[podobing]

Hello,
I work for an electrical contractor, primarily in the mining and gas industries. A customer installs and maintains their own 12,470 volt power distribution system. They use wooden poles with a cross arm that holds the three phases. There is also a single wire at the top of the pole, where a "static" wire would normally be found. The customer asked us to install a single phase 50 kVA transformer at two different locations along that line. The transformers were single bushing 7200 volt:120/240 volt pole-mounted units.
I mentioned to the customer that I did not think that it was proper to use the static wire as a current carrying conductor. He said that the wire was actually a neutral conductor that also acted as a static conductor. That does not sound correct to me.
I have a few questions:
1) Is it legal to use a static wire as a current carrying conductor?
2) Is it legal to run the neutral wire in the location that the static wire is normally installed?
3) Can a wire be both a static wire and a neutral conductor?
At this time, I do not know if this static/neutral wire is aluminum ASCR or galvanized steel, but I understand that that may affect your answers.
I do not want to upset the customer, so any specific references to code or standard practice would be beneficial.
Thanks in advance.
Regards,
Podobing

 

[Mbrooke]

If the conductor is big enough (and of the right material) it can be used as a neutral regardless of where its placed. Some utilities will place their neutral above the phase conductors or even on a cross arm with a 5kv pin next to the phase conductors.

 

[podobing]

Mbrooke,
I assume that you mean a (galvanized) steel conductor would not be legal.
Would the conductor have to be adequately insulated (5 kV?) from the structure?
Podobing

 

[waross]

I have seen a multiple grounded neutral run high in areas prone to lightning strikes.
The theory is that it will serve as both a static line and as a neutral.
In one system, the neutral was normally run low, but in a few areas at higher, exposed locations the neutral was run high.
I should note that there were no connections in the areas where the neutral was high.
The system was not subject to any codes except possible liability in the event of gross negligence.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[bacon4life]

I have seen steel wire specified at both 12 kV and 115 kV for long span river crossings, so I doubt you would find any sort of code issue specifically with the type of wire used.

It is also common to use aluminum coated wire (i.e. alumoweld) rather than zinc coated wire (i.e. galvanized) for shield wires.

 

[Mbrooke]

No need for the 5kv insulation, just what some POCOs choose to do rather than having the neutral directly tied to a cross arm pin.


What size is your galvanized steel conductor? And is it all steel? (Code name would be the most ideal, if known, or applicable)

 

[podobing]

Mbrooke,
I am not sure if the conductor is steel or not. I hope to find out next week.

bacon4life,
Is alumoweld suitable for use as a current carrying conductor? I am not a lineman. Thanks for the education on wire types. PS- Good name - makes me hungry!

waross,
The wire is run high all of the time. For this proposed installation, they want to "roll" one phase wire and the neutral/static wire off as a lateral with the single phase wire being directly over the neutral and install the transformer at that location. Your comment of "gross negligence" has me very concerned.

Podobing

 

[krisys]

As a first step you should obtain the overall single line diagram (SLD) of the distribution system. Then it will be clear.

Check what is the type of earthing, available fault level, protection schemes etc.
If the distribution system is within the mine area, then the applicable code of practice may be different.

Check in the overall SLD, whether there is any such 1-Ø transformers connected. Then you follow their footsteps. When you are armored with these information, it will be easier to deal with the situation.

 

[bacon4life]

I do not have direct experience using alumoweld as current carrying conductor, but Southwire seems to provides ampacity values for alumoweld:

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheetS2C

 

[Mbrooke]

That is a messenger for spacer cable- but I guess it could also be used as a static wire/neutral by itself.