NEC 2023, Art. 240 Overcurrent Protection. 240.2 Protection of Conductors. Added item.

[James Williams]

NEC 2023, Art. 240 Overcurrent Protection. 240.2 Protection of Conductors.

New Text

240.2 Protection of conductors.
(A) Power Loss Hazard. … Short-circuit protection shall be provided.

(?) Current-Transformer Secondary Conductors. Conductor overload protection and short circuit protection shall not be provided for current transformer secondary conductors. An open current-transformer secondary circuit presents a high-voltage hazard.

(B) Overcurrent Devices Rated 800 Amperes or Less. …

Substantiation: Open CT secondaries can develop voltages of several thousand volts. This is a hazard to equipment and personnel. See https://www.nrc.gov/docs/ML1713/ML17137A031.pdf [Public Domain document] for example data.

 

[don_resqcapt19]

Is there a question here?

 

[infinity]

How would the CT circuit suddenly open? If the CTs are still properly connected how could they have an open?

 

[jim dungar]

Article 240 is about overcurrent protection.
The OP is about an overvoltage concern. He appears to want language added for the purpose of saying something is not required.

 

[wwhitney]

He appears to want language added for the purpose of saying something is not required.

An explicit allowance to omit overcurrent protection in the CT conductors, as opening them could create a voltage hazard.

Perhaps such allowance is already present in a less explicit form?

Cheers, Wayne

 

[infinity]

My take is that the OP is saying there is no current code section that would prohibit an OCPD in the CT circuit. If an OCPD were used then the opening (tripping or fuse blowing) of that OCPD could cause a runaway high voltage condition.

 

[James Williams]

Typo in the original post, for 240.2 read 240.4

 

[James Williams]

How would the CT circuit suddenly open? If the CTs are still properly connected how could they have an open?

This section of the code is the part that requires OCPDs. The 240.4(A) part omits the requirement for overload protection for circuits that would result in problems worse than overloaded conductors, but it still requires short-circuit protection. Examples of part (A) circuits are (1) Fire Pumps and (2) Ammunition Lifts on naval ships. Both are allowed to "run to destruction" because of the vital service they provide.

CTs make a hazardous condition if their secondaries are opened, much worse than the conductors being compromised.

Article 450 Transformers … Part 1. General 450.1 Scope. This article covers the installation of all transformers other than the following:
(1) Current transformers (2) …

Thus 450 is not the part to place the short-circuit protection restriction.