Neutral from Power Company

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hardworker

Senior Member
A commercial building in an older part of town has a 400 amp single phase system coming into the building overhead. Two hots and a neutral. The neutral is not insulated? Why?
 

iwire

Moderator
Staff member
Location
Massachusetts
Some code sections

II. Overhead Service Conductors

230.22 Insulation or Covering
. Individual conductors
shall be insulated or covered.

Exception: The grounded conductor of a multiconductor
cable shall be permitted to be bare.

III. Underground Service Conductors

230.30 Insulation.
Service-lateral conductors shall be insulated
for the applied voltage.

Exception: A grounded conductor shall be permitted to be
uninsulated as follows:

(1) Bare copper used in a raceway.

(2) Bare copper for direct burial where bare copper is
judged to be suitable for the soil conditions.

(3) Bare copper for direct burial without regard to soil
conditions where part of a cable assembly identified for
underground use.

(4) Aluminum or copper-clad aluminum without individual
insulation or covering where part of a cable assembly
identified for underground use in a raceway or for direct
burial.

And of course if it is on the utility side of the service point the NEC has nothing to do with it.
 

Carultch

Senior Member
Location
Massachusetts
And that service neutral is bonded to all that readily accessible exposed metal there at the service- so what does that tell you?

It tells you that at one point on your service, it is at the same absolute voltage as the surrounding ground, and the non-current-carrying conductive materials on the premises (building steel, concrete, conduits, equipment housings, etc). Such that if the service neutral comes in to contact with a non-energized conductive material, it shouldn't energize it.

Of course, there will be some ohmic voltage drop across the length of any current-carrying conductor, but we are talking about single digit volts. The voltage difference from neutral to ground at the service bonding point will be zero, and any distance away, the difference will be single digit volts, if any at all. So it is not considered a significant hazard.

This does bring up the question of why a service neutral is not required to be insulated, while all load-side circuit neutrals require insulation. Here are some possible reasons I can think of. Does anyone know any others?
1. Service neutrals are more likely not to carry current, due to a greater chance that the loads are balanced.
2. Service neutrals are less likely to be contained in metal conduit or metal cladding.
3. Service neutrals generally run less distance than load-side circuits, thus having less voltage drop by design, and less circuit length for the hazard.
4. Service conductors don't run inside of a building for nearly as much length as load-side circuits do.
5. Service conductors are designed under less conservative rules, in order to be more consistent with standards that govern the utility.
 
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tom baker

First Chief Moderator
Staff member
On the POCO side, the conductors are not insulated, they are covered, and are not listed.
POCOs have been installing services for 100+ years, they have it figured out. Have you ever noticed that the line trucks only carry two sizes of wire, #2 and #6? We'll wire out a 200 amp service with 250 al and they connect with #2.
Their conductors have a different ampacity then ours.
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
This does bring up the question of why a service neutral is not required to be insulated, while all load-side circuit neutrals require insulation. Here are some possible reasons I can think of. Does anyone know any others?....
You mean you haven't stumbled on the Mike Holt forum standard answer...? "Everybody knows that electrons behave differently on the other side of the service disconnect."
 

user 100

Senior Member
Location
texas
It tells you that at one point on your service, it is at the same absolute voltage as the surrounding ground, and the non-current-carrying conductive materials on the premises (building steel, concrete, conduits, equipment housings, etc). Such that if the service neutral comes in to contact with a non-energized conductive material, it shouldn't energize it.

Of course, there will be some ohmic voltage drop across the length of any current-carrying conductor, but we are talking about single digit volts. The voltage difference from neutral to ground at the service bonding point will be zero, and any distance away, the difference will be single digit volts, if any at all. So it is not considered a significant hazard.

This does bring up the question of why a service neutral is not required to be insulated, while all load-side circuit neutrals require insulation. Here are some possible reasons I can think of. Does anyone know any others?
1. Service neutrals are more likely not to carry current, due to a greater chance that the loads are balanced.
2. Service neutrals are less likely to be contained in metal conduit or metal cladding.
3. Service neutrals generally run less distance than load-side circuits, thus having less voltage drop by design, and less circuit length for the hazard.
4. Service conductors don't run inside of a building for nearly as much length as load-side circuits do.
5. Service conductors are designed under less conservative rules, in order to be more consistent with standards that govern the utility.

:thumbsup:.

I was trying to get the op to understand that there was no risk from someone from touching that intact bare service neutral- if that was the case someone would get would get popped every time they touched the bonded case of a panel - the service neutral is a much better path back to source for that current than he is...

I think to you have covered it pretty well as far the reasoning about the lack of insulation and I also agree with Tom Baker that this is more of a non issue- poco's have this down. Lots of sec's out there with a naked gc but no electrocution.:)
 

Carultch

Senior Member
Location
Massachusetts
On the POCO side, the conductors are not insulated, they are covered, and are not listed.
POCOs have been installing services for 100+ years, they have it figured out. Have you ever noticed that the line trucks only carry two sizes of wire, #2 and #6? We'll wire out a 200 amp service with 250 al and they connect with #2.
Their conductors have a different ampacity then ours.

Well, in a sense, the wires in open air are subject to a substantially different thermal condition than the wiring methods that you would do inside of a house or underground, and therefore could have a different ampacity. Remember that ampacity is a thermal problem, and not an electrical problem. Wire ampacity is a function of how well the wire can reject heat to the surroundings, and how hot the constituent materials can get within a safety margin of known failure modes.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
I'm not familiar with the initialism "MGN". Does that mean a wire that is acting as both an EGC and a neutral?
Multiply Grounded Neutral. The current return conductor that gets grounded every so many poles and at transformers. There are enough grounds that the earth electrode resistance has a minimal effect, especially at distribution voltages.
 

kwired

Electron manager
Location
NE Nebraska
I struggle to understand you sometimes.:huh:

You quoted me, then you basically repeated what I have said. :?
It is an NEC conductor all the way to the "service point" All you mentioned was the MGN, though some may consider it to be that to the service disconnect I guess, others may consider MGN to be on the POCO side. NEC doesn't use the term MGN (that I am aware of).

I quoted what you said to further comment on it, not to try to disprove anything that was mentioned.
 
It's bare because it's safe to touch it!

Really, the POCO knows what will be the maximum load current on the neutral wire based on their transformer built-in limit or other protection device on their side, say 700A max, therefore they used the correct wire size to limit the max voltage drop on the wire to be less than a few volts max (let's say 9v drop at 600A will generate more than 5000 watts of heat) to minimize energy lost. Regardless the amount of current in the wire -- 600A or 100a -- if the wire size is big enough then there is little voltage drop to harm anything. Of course it must be connected to earth ground first before it can bare.
 
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