Triplex Service Drop

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Joseito

Member
Location
Illinois
Hi everyone... my understanding is that a typical triplex service drop has an outer cover for weather protection but it is typically not rated as insulation. Is this true for all service drop conductors? I understand that if they are marked with type SE/USE, then, that outside jacket IS insulation but otherwise, it's just for weather protection. Where can I find information that will either confirm what I understand or clarify my knowledge? (NEC, UL, ANSI...?) Thanks everyone!
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Art 310.13 of the NEC ('08) identifies the insulated conductors recognized by the NEC.
ACSR with no other marking is not listed among them.
"Approval" as noted in Art 90.4 of the wiring method is left to the AHJ.
 

John120/240

Senior Member
Location
Olathe, Kansas
The outer cover on SE or SER cable is not insulation. It is just a covering that keeps all of the conductors in the cable together. Tri Plex or Quad Plex for overhead installations would not have an outer covering. Two or three insulated conductors (XXHW maybe) & a bare conductor used for Neutral & as the messenger cable in a Tri Plex situation. For Quad Plex you would have three insulated conductors, (two hots, one neutral) & a bare messenger cable used as ground.
 

jumper

Senior Member
From Southwire:

CONSTRUCTION
Southwire Type SE cable is constructed with AlumaFlex AA-8000 series aluminum alloy, compact stranded conductors. The conductors are covered with a sunlight resistant Type XHHW-2 or Type THHN/THWN-2 insulation. A reinforcement tape is wrapped around the conductors for added strength and conformity. A gray sunlight resistant polyvinyl chloride (PVC) outer jacket covers the entire assembly. Style SEU cable has two phase conductors surrounded by a concentric neutral while the SER style has two, three or four phase conductors and a bare neutral.

http://www.southwire.com/products/Aluminum-SE-Cable.htm
 

Joseito

Member
Location
Illinois
Thank you everyone for your responses.... here is a picture of the type of cable I was referring to. The black jacket on the first picture (left) does not have any letters or markings... are those conductors insulated or covered?

http://forums.mikeholt.com/attachment.php?attachmentid=13378&stc=1&d=1442441105


The black jacket on the second picture (right) shows Type USE... is it safe to say that those conductors ARE insulated because they are marked with usage, etc?

http://forums.mikeholt.com/attachment.php?attachmentid=13379&stc=1&d=1442441398

Thanks again for the help... this is a great forum and I have been learning quite a bit reading everyone's comments and opinions.
 

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meternerd

Senior Member
Location
Athol, ID
Occupation
retired water & electric utility electrician, meter/relay tech
You picture is overhead triplex aluminum conductor with a bare ACSR neutral. No, the covering is not rated as an insulator, but it does, in fact, insulate the conductors from the neutral and each other. Underground would have a jacketed neutral, but would still be three separate conductors with no outer jacket. Quad would just have one more jacketed phase conductor. I haven't seen any service drops that supply a ground.
 

Iron_Ben

Senior Member
Location
Lancaster, PA
Top picture is overhead triplex; two hots and bare grounded neutral. Bottom picture is underground triplex; two hots and insulated neutral (yellow stripe). The underground triplex that we used at the POCO had a neutral that was two sizes smaller, so if the phase conductors were 4/0, the neutral was 2/0, etc. Other utilities might spec something else, don't know.
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
Ok now Im confused...:blink:

Being the two hots are in contact with a bare messenger acting as the neutral that has to be functional insulation.

At the 5kv level and above that would certainly be classified as a covering. Some POCOs do use covered overhead cables (and will probably act is a perfect insulator on 600 volts and under) but must keep them up on insulators or HV rated spacers. The reason for using covered conductors is to cut down on momentary outages from flash overs when a tree branch temporarily comes in contact with a phase conductor. It works well provided its temporary. Extended or permanent contact with anything grounded (heck even an insulator with a different dielectric constant) will cause the covering to track and burn away. For this reason all conductor kept on insulators must be treated as live because the covering might have tracked through. Even then Ive heard from linemen that with good covering it can still give you a nasty shock from corona.
 

Joseito

Member
Location
Illinois
Is it permissible that the overhead triplex hot conductors are just covered and therefore, uninsulated? If so (or if not), where can I find that requirement in the NEC or elsewhere? Is there a specific reason for the overhead one to not be insulated? I'm interested in any specific NEC requirements about insulation in both instances.
 

meternerd

Senior Member
Location
Athol, ID
Occupation
retired water & electric utility electrician, meter/relay tech
Is it permissible that the overhead triplex hot conductors are just covered and therefore, uninsulated? If so (or if not), where can I find that requirement in the NEC or elsewhere? Is there a specific reason for the overhead one to not be insulated? I'm interested in any specific NEC requirements about insulation in both instances.

I can't address the NEC question, but I can give you some info about the bare wire. Mainly, it is because the bare conductor is used as a support wire for the other two conductors...that's why it's ACSR (aluminum conductor steel reinforced). It is "tied off" at the structure with clamps (we call them "cowboys") that hold the weight of the wire. Same at the pole. The bare wire is bonded to the neutral and ground at the pole and the customer's service riser wire at the structure. We don't use it for UG because the bare wire would damage the conductors when being pulled through conduit. Price is about the same, so cost isn't really a consideration.
 

Joseito

Member
Location
Illinois
Thanks again for the info and comments... I still have the doubt on what the black plastic that surrounds the hot conductors actually is (on the overhead triplex shown on my first picture)...

How can I tell if that black jacket on the first triplex picture (overhead one) is insulation or not? It does not have any markings of any type on the outside.
Is that black plastic always rated insulation or is it just a weather protection cover?
Is there any requirement that that jacket has to be rated as insulated (if so, which one(s))?
How can I tell if that overhead triplex has insulation or if it's only covered for weather protection?
 

Iron_Ben

Senior Member
Location
Lancaster, PA
It's insulation all right. As far as how you can tell, how about because there are millions of feet and probably millions of miles of this installed in this country? It's energized at 240 volts from one black covered wire to the other 24/7/365. And in the case of quadruplex, it's often 480 from any of the three black wires to one of the others. And it's in service outdoors in all temperature extremes and weather conditions. We routinely worked on overhead services that were over 40 years old with no issues. Sometimes at the 50 year or so mark, the insulation would get brittle and not hold up as well to physical contact and abrasion. But as far as a reliable component of an electric distribution system, it's pretty close to the top of the list.
 

kwired

Electron manager
Location
NE Nebraska
Those conductors (the overhead cable assembly) are insulated - just that the conductor insulation type is not marked and/or is not a type that complies with NEC.

This type of cable is commonly used by POCO's but they don't have to comply with NEC.

Acceptable conductor types was mentioned by Augie - 310.13 in earlier editions of NEC. They have been moved (I think in 2011) to 310.104.

This kind of conductor is not listed in that section, nor is the cable assembly mentioned anywhere else in chapter 3 wiring methods - therefore it is not a NEC recognized wiring method or conductor.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
....
This kind of conductor is not listed in that section, nor is the cable assembly mentioned anywhere else in chapter 3 wiring methods - therefore it is not a NEC recognized wiring method or conductor.
While most do not agree with me, it is my opinion that the use of triplex or quadplex cables is not prohibited by the NEC. I believe that the following from Table 396.10(A) would permit the use of those cables.
Other factory-assembled, multiconductor control, signal, or power cables that are identified for the use.
Identified (as applied to equipment). Recognizable as suitable for the specific purpose, function, use, environment, application, and so forth, where described in a particular Code requirement.
The very extensive long term use of these cables by utilities makes the "recognizable as suitable for the specific purpose".
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
Is it permissible that the overhead triplex hot conductors are just covered and therefore, uninsulated? If so (or if not), where can I find that requirement in the NEC or elsewhere? Is there a specific reason for the overhead one to not be insulated? I'm interested in any specific NEC requirements about insulation in both instances.
If you are asking about the triplex that is installed by a Power Company worker, there is NO National Electrical Code (NEC) on that side of the Service Point (see the Article 100 Definition).

However, if you are installing the triplex to, say, power an outbuilding off of the Premises service, then I like the NEC explanation that Don offers above.
 

kwired

Electron manager
Location
NE Nebraska
While most do not agree with me, it is my opinion that the use of triplex or quadplex cables is not prohibited by the NEC. I believe that the following from Table 396.10(A) would permit the use of those cables.


The very extensive long term use of these cables by utilities makes the "recognizable as suitable for the specific purpose".
That may be one way to accept them. I know that kind of cable is still used around here other then by the POCO's at times, but only is allowed as an aerial cable.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
That may be one way to accept them. I know that kind of cable is still used around here other then by the POCO's at times, but only is allowed as an aerial cable.
Yes, using the triplex as it was made to be used, as an overhead cable.
 
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