GROUNDING FOR 12470 PRIMARIES

Status
Not open for further replies.
B

BRYAN AMBROGIO

Member
Location
Winter Springs Fl
Occupation
Electrical Designer
An underground primary from utility pole to new service transformer.
(3)#2-15Kv-133%N
It is my understanding that when the above wire is used in a 12470 3-phase utility primary system there is no seperate grounding or neutral conductor required.
The grounding and/or neutral is part of this wire.
Is this correct? I need some advice.
Thank You..... Bryan
 
BRYAN AMBROGIO said:
An underground primary from utility pole to new service transformer.
(3)#2-15Kv-133%N
It is my understanding that when the above wire is used in a 12470 3-phase utility primary system there is no seperate grounding or neutral conductor required.
The grounding and/or neutral is part of this wire.
Is this correct? I need some advice.
Thank You..... Bryan
Click to expand...

What cable brand and type is being used?
Most MV/HV cable is semiconducting with an integrated screen/shield, some have concentric bare conductors that are usually connected to the neutral and or bonded to a ground, but not all cables are constructed as described.
 
Last edited:
If the cables have a concentric neutral which appears by your specs it does, then that would normally be used as a ground/neutral. When terminating the cable one would uncoil the concentric a bond that to the frame of the pad mount, lightning aresters, and the customer LV neutral.
 
Just to expand on this a bit and mention something you may not have considered or had to consider: One of the utilities near me lets us run primary. so we have done that frequently on long runs. The customer ends up being very happy where the distribution system is Wye because we just need to run one cable as it can carry the hot and neutral. The unhappy customer is served with a delta distribution so we have to use two cables. In the latter case the concentrics are just grounded at either end and it is my understanding that grounding the concentrics reduces the stress on the insulation although I am not sure why.
 
I do not specify the the exact type of cable. I do predesign work for an estimating department and just need to know (for estimating perposes) if and additional ground needs to be run.
Most of my work is 480 and below and 12470 is a little foreign to me.
One PM here told me that MV cable with a concentric neutral does not need a separate ground if run overhead, however if run underground the a separate grounding conductor is needed and sized the same as the phase conductor except type THHN. Is he on the right track?
 
BRYAN AMBROGIO said:
I do not specify the the exact type of cable. I do predesign work for an estimating department and just need to know (for estimating perposes) if and additional ground needs to be run.
Most of my work is 480 and below and 12470 is a little foreign to me.
One PM here told me that MV cable with a concentric neutral does not need a separate ground if run overhead, however if run underground the a separate grounding conductor is needed and sized the same as the phase conductor except type THHN. Is he on the right track?
Click to expand...

I am curious, is this for a regulated utility or a private/customer owned installation?
 
BRYAN AMBROGIO said:
An underground primary from utility pole to new service transformer.
(3)#2-15Kv-133%N
It is my understanding that when the above wire is used in a 12470 3-phase utility primary system there is no seperate grounding or neutral conductor required.
The grounding and/or neutral is part of this wire.
Is this correct? I need some advice.
Thank You..... Bryan
Click to expand...

If the wire is shielded, there is no neutral. The wire with the neutral will most likely be stranded neutral. You can get it with full neutral or 1/3 neutral.
Here is a link to wire with a neutral:
http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheetEPR01
 
If your underground cable has a concentric neutral (it should) that will be your ground, you do not need to run a seperate ground, however if this is done to other than utility specs (NESC) it may.
 
BRYAN AMBROGIO said:
An underground primary from utility pole to new service transformer.
(3)#2-15Kv-133%N
It is my understanding that when the above wire is used in a 12470 3-phase utility primary system there is no seperate grounding or neutral conductor required.
The grounding and/or neutral is part of this wire.
Is this correct? I need some advice.
Thank You..... Bryan
Click to expand...

I can tell you how we do it. Primary is 12,470/7200 Grounded Wye. When we run a single phase underground service, we run one primary cable with a center conductor and a concentric neutral. Built like a giant coax cable, except there is a layer of semi-conductor between the neutral insulation and the hot. At the padmount transformer, the hot connects to the center pin of a primary elbow, which plugs into a primary transformer bushing and the concentric is unwound, twisted together and connected to the common primary/secondary neutral bushing. This neutral connection is also connected to the transformer case and a driven ground rod. The secondary consists of tri-plex (two hots and an insulated neutral) connected to two line bushings and a neutral bushing. No separate ground wire. Any other grounding and bonding takes place at the service disconnect. Three phase is the same, except three phases of primary and quad secondary. We don't offer Delta anymore.
 
electrofelon said:
You just cant resist connecting those primary and secondary neutrals together can you ;)
Click to expand...

OK...no kidding....the padmount transformers we buy have the primary and secondary neutrals connected internally to one neutral bushing, labeled H0/X0, so we couldn't separate 'em even if we wanted to. I assume they make underground transformers with isolated neutrals, but I'm not familiar with them.
 
meternerd said:
OK...no kidding....the padmount transformers we buy have the primary and secondary neutrals connected internally to one neutral bushing, labeled H0/X0, so we couldn't separate 'em even if we wanted to. I assume they make underground transformers with isolated neutrals, but I'm not familiar with them.
Click to expand...

They do if you spec it out. When one orders transformers you can pretty much get anything wanted, especially if buying in bulk amounts.
 
Status
Not open for further replies.
Top