New Code for 5kV class cables and higher?

[pdlocator]

I need advice and direction. I have been made aware that due to deregulation, some industrial and commercial facility inspectors are being forced to inspect medium and high voltage installation (5kV and above) without proper understanding, inspection tools, or guidelines. I also understand that the NEC is now looking to provide code for medium voltage cable systems. Is this information accurate? Would you provide background on this subject and suggest who I might contact for more information? Medium and high voltage cable reliability and installation safety happens to be my area of expertise and I would be happy to support any code development efforts. I also happen to be the vice chair of working group responsible for IEEE 400, the standard guide to field testing medium and high voltage cable systems. I look forward to your response.

Kind regards,


-Ben

 

[zog]

Re: New Code for 5kV class cables and higher?

Ben,

That scares me, as you know MV cables are a whole different world and a visual inspection of the installation is not enough to say it was installed right. The cable needs to be tested, and even that is a big debate regarding what is the best method (DC, AC, VLF, Tan Delta, PD, etc). The different methods of cable testing is the main topic of the upcoming NETA conference in March, it should be a interesting debate.

Expecting an inspector to be able to sign off on these cables is just asking for trouble IMHO.

 

[stevearne]

Re: New Code for 5kV class cables and higher?

This is not an electrical instructor topic, so I am moving it to a code discussion area. Please feel free to continue your discussion there.
Thanks.

 

[pdlocator]

Re: New Code for 5kV class cables and higher?

Zog,

The thought of NEC inspectors inspecting MV/HV cable startled me too! I agree with you. I think the industry should very cautious. In my travels I see that there is a lot of confusion and debate in the industry. However, for me answers are quite simple. If one can define the objective of the test, the limits prescribed by IEEE standards will dictate which test to use.

I happen to be the vice chair of the working group responsible for IEEE 400 ? the standard guide for field testing shielded power cable systems. This opportunity has given me a pretty good overview of all the tests that are available. I am looking forward to the NETA conference too, as I am scheduled to be one of the panel members on the subject.

Unfortunately, NETA is far behind IEEE with their cable testing standard. Although IEEE 400 mentions just about every test on the planet, it no longer supports a DC high potential (HIPOT) test for and acceptance test or maintenance test of extruded cable (e.g. XLPE and EPR). If the test objective is to do a destructive HIPOT withstand, a low frequency AC is the test of choice. However, if the objective is to make a non-destructive condition assessment, the document states that the only test which will provide convincing evidence that the cable is excellent condition is one that can repeat the factory PD test in the field. The factory test is a 60Hz Off-line PD test performed in accordance with manufacturer and IEEE standards.

So what?s the debate about? ;-) I look forward to meeting you at the NETA conference.

Regards,

-Ben

 

[Nick]

Re: New Code for 5kV class cables and higher?

Wait a minute! Medium voltage cables and installations have been in the NEC for a long time. This is nothing new. Electrical inspectors have been responsible for inspecting customer owned (non utility)medium voltage installations for as long as the requirements have been in the NEC. This is nothing new either. The fact that many (or most) of them have not been trained properly to do this is a topic for another discussion. I don't see where deregulation has changed any of this.
Visual inspection is not enough, agreed. However I know of nothing in the NEC that requires proof testing of cables. Don't get me wrong, I am not trying to dispel the benefits of testing, I'm just pointing out it's not an NEC requirement. If I am wong on this please point me to the appropriate section.

 

[iwire]

Re: New Code for 5kV class cables and higher?

Ben I agree with Nick, this is nothing new and has little or nothing to do with de-regulation. Grab the NEC and read through the scope 90.2 and you will see that there is no voltage limitation to the NEC.

If the wiring and equipment is customer owned it is covered by the NEC regardless of voltage.

I will give a few examples.

110.30 General.
Conductors and equipment used on circuits over 600 volts, nominal, shall comply with Part I of this article and with the following sections, which supplement or modify Part I. In no case shall the provisions of this part apply to equipment on the supply side of the service point.

ARTICLE 328 Medium Voltage Cable: Type MV
I. General
328.1 Scope.
This article covers the use, installation, and construction specifications for medium voltage cable, Type MV.

328.2 Definition.
Medium Voltage Cable, Type MV. A single or multiconductor solid dielectric insulated cable rated 2001 volts or higher.

ARTICLE 450 Transformers and Transformer Vaults (Including Secondary Ties)
450.1 Scope.
This article covers the installation of all transformers.

450.3 Overcurrent Protection.
Overcurrent protection of transformers shall comply with 450.3(A), (B), or (C). As used in this section, the word transformer shall mean a transformer or polyphase bank of two or more single-phase transformers operating as a unit.

(A) Transformers Over 600 Volts, Nominal. Overcurrent protection shall be provided in accordance with Table 450.3(A).

I have the NEC on CD-ROM and a search of the phrase "over 600 volts" came up with 91 'hits'.

Typically a job that has equipment over 600 volts will have job specifications that ensure a safe installation.

[ October 12, 2005, 05:22 AM: Message edited by: iwire ]