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Neutral Ampacity & Re-closers

September 8, 2011

Neutral Ampacity & Re-closers

Q:

In Exhibit E of your proposal you state that cable replacement should be utilized rather than cable injection if the “cable neutral has lower than required ampacity …”  I was able to find on Novinium’s website the limits for neutral corrosion, but nothing on the neutral ampacity limits. What are the neutral ampacity limits? Keep in mind that on three phase cable installs we use one-third neutrals.

In Exhibit F of your proposal you define “Abnormal Operational Excursion(s).”  One of the identified excursions, item (3), is “repeated operations of re-closers.” We use re-closers on all of our circuits. Does this mean that the warranty is void?A:

There are three primary purposes for neutral wires:

  1. Provide a low resistance path for fault currents to protective devices.
  2. Assure a grounded and uniform potential to the insulation shield, which in turn provides uniform electrical stress along the cable axis and circumference.
  3. Carry the return current of unbalanced loads. Since multi-phase circuits have lower unbalanced loads, lower-ampacity neutrals such as your one-third neutrals are possible in many applications.
[dt_fancy_image type=”image” image=”http://www.novinium.com/wp-content/uploads/2015/08/Neutral-Ampacity-Reclosure.png” style=”2″ width=”600″ padding=”10″ margin_top=”0″ margin_bottom=”0″ margin_left=”0″ margin_right=”0″ align=”center” animation=”none”]Novinium can detect and quantify the extent of neutral corrosion.Each circuit owner must decide upon an appropriate value for the required neutral ampacity. This analysis is required on a case-by-case basis. That neutral ampacity requirement is communicated to Novinium so that candidate cables for rejuvenation can be screened for their neutral condition. If a circuit owner requires guidance on appropriate requirements for a specific circuit, they need only ask the world’s foremost rejuvenation experts. They are all at Novinium. Typically less than 2% of a population of candidate cables do not meet circuit owner neutral ampacity requirements.

With regard to “Abnormal Operational Excursion(s)” I have reproduced the full definition below and I have underlined the portion about repeated re-closer operations. Note that the recloser operations are abnormal only if the recloser is operated to clear overhead faults. Most people would agree that this is not a “best practice.” Life insurance doesn’t payout if the insured commits suicide and neither does the Novinium warranty. If the recloser operates normally, but is not abused in an attempt to burn a branch on an overhead line, then the warranty is not suspended.Abnormal Operational Excursion(s) includes non-routine maintenance or operations prior to the segment failure such as: (1) conductor currents or neutral current greater than circuit design constraints; (2) operating temperature greater than circuit design; (3) repeated operations of re-closers, whether manually or automatically operated, as a method to clear overhead faults; (4) physical manipulation of the segment including dig-ins; or (5) any other operational practice inconsistent with the cable’s original manufacturer’s specifications, act of a third party, or act of God (except lightning strikes), which is believed to degrade the reliability of connected circuits