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?
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?
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.
Touching a bare wire that carries many amps is not a hazard as long as there is no (or small) voltage difference to ground.I realize it is not required, but it still carries amps. Is that not a hazard?
I realize it is not required, but it still carries amps. Is that not a hazard?
And that service neutral is bonded to all that readily accessible exposed metal there at the service- so what does that tell you?
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."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?....
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.
Does anyone know any others?
Basically it can stay bare where it is still an MGN, once it really becomes an NEC neutral it must be insulated.
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.
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.I'm not familiar with the initialism "MGN". Does that mean a wire that is acting as both an EGC and a neutral?
Basically it can stay bare where it is still an MGN, once it really becomes an NEC neutral it must be insulated.
230.41 exceptions tell us places it can be bare - all are on supply side of service disconnecting means though.
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 struggle to understand you sometimes.:huh:
You quoted me, then you basically repeated what I have said. :?
It does in 250.184(C)....NEC doesn't use the term MGN (that I am aware of).
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