The requirements and purpose of overcurrent protection devices (OCPDs) for electrical circuits up to 1,000 volts, nominal. Here’s a breakdown of the key points:
General Requirements: The section outlines the general requirements for devices designed to operate at voltages up to 1,000 volts, nominal. These requirements ensure the safe operation of electrical circuits within this voltage range.
Purpose of OCPDs: The main purpose of overcurrent protection devices (such as circuit breakers and fuses) is to protect conductors and insulation from high or dangerous temperatures that could result from excessive current flow.
Supplementary Articles: Articles 690 and 705 in the National Electrical Code (NEC) supplement and modify the requirements outlined in Article 240. These articles specifically address photovoltaic (PV) systems (Article 690) and interconnected electric power production sources (Article 705), providing additional and specific guidance for these types of installations.
Operation of OCPDs: OCPDs are designed to either trip open (in the case of a circuit breaker) or blow open (in the case of a fuse) before the current in a circuit reaches a level that could damage the circuit conductors and equipment, such as inverters and PV modules. This protective action prevents damage to the electrical components and ensures safe operation.
Conductor Ampacity: The size of the conductor (wire) and the OCPD must be appropriately matched to ensure adequate protection. This means selecting an OCPD with a rating that will protect the conductor without exceeding its ampacity, the maximum current it can safely carry.
AIC Rating: The OCPD must have the correct Ampere Interrupting Capacity (AIC) rating for the available fault current on the supply side of the terminals. The AIC rating is the maximum fault current that the device can safely interrupt without failing. Ensuring the OCPD has the appropriate AIC rating is crucial for preventing potential damage or failure during fault conditions.
In summary, this section emphasizes the importance of selecting and installing the correct overcurrent protection devices to ensure the safety and integrity of electrical circuits, particularly in PV systems, by preventing excessive current that could cause damage to conductors and equipment.
240.15 Ungrounded Conductors
OCPD must be installed in series with each ungrounded conductor.
On AC side implement on split phase, need OCPD on each hot lines or phase conductors; so Line 1 and Line 2 receive OCPD on a 120/240 system. If 3 phase on Line 3 as well.
On the PV system side, 1 OCPD must be used on either the positive or negative but not both