Article 240 NEC covers the requirements for selecting and installing excess protection devices (OCPDS), such as valves and circuit breakers. The article determines the appropriate categories, position, applications, and special cases of OCPDS via applications.
What is the excess current?
The excess current occurs when the current exceeds the safe limit of the connector or equipment. This can happen because of:
Excess pregnancy: Many of the current is under normal operation (for example, running multiple high -border devices on one circle).
Short circle: Direct contact between two hot wires or a hot and neutral wire.
Earth’s mistake: The hot wire touches a clear surface, such as a metal box or wet floor.
How to protect OCPDS circuits for equipment
OCPDS protection Circles By opening when the current reaches a value that will wear conductors. This protection works differently for equipment. to equipmentOCPDS stops short circles or ground errors before major damage.
In short, it avoids the protection of the circle, the gradual temperature is high; Equipment protection prevents catastrophic immediate failure.
Standard Amp
OCPDS is manufactured in the standard classifications listed in section 240.6, ranging from 15A to 6000a. When changing the size of the crusher, you are usually:
Determine the ampacity connector
Set ampacity per 310.15
Choose the following standard size (if less than 800A and other conditions are met)
Small Mosul Protection (240.4 (D))
The maximum excess protection is limited to small connections:
14 Awg Copper: 15A
12 Awg Copper: 20A
10 AWG Copper: 30A
12 AWG Aluminum: 15A
10 AWG Aluminum: 25A
These values are fixed and do not allow the “Next Size” base. It is in place to prevent high temperature in residential circles and the most used branch. Note that these are the only sizes of the connectors mentioned in this article.
Exception: The risk of energy loss (240.4 (a))
In life safety or important task systems, Excess pregnancy protection may be deleted If the power turning off will create a greater danger.
example: Fire pump circles must continue to run during emergency situations, even when excessive loading. While protecting the short circle is still required, protection of excess pregnancy can be excluded to maintain system functions.
This exception should be applied with caution and not only when energy interruption is a risk to life or safety.
Next size base
When the ampacity connector does not match the standard size, you can apply for the next standard cruise classification if:
The summit of the conductor should be at least equal to the classification of the bridge if OCPD is more than 800 A.
The site in the circle (240.21)
The OCPDS website should be where it receives energy connectors, except in the following cases:
(A) The branch circles that meet 210.19:
Some fixed devices, such as cooking equipment (stoves), can contain unprotected conductor extensions when the conditions of installation and installation correspond to 210.19.
(B) No taps from other taps:
You cannot create a secondary click of the TAP connector.
(C) Secondary protection transformed across OCPDS:
If the primary OCPD is classified and fixed properly, it can protect the secondary side of the transformer.
(D) Service connectors (230.91):
This follows its own protection rules in the first chapter.
(E) Busway (368.17) taps:
Campaign from Busways is allowed under specific TAP connector bases.
(F) Motors (430.28, 430.53):
The engines are often used separate protection for excess pregnancy and do not require OCPDS in each site.
(G) Al -Mawlidat (445.12, 445.13):
OCPD outputs may be ignored immediately if the underlying protection is provided and the installation corresponds to Article 445.
Click on Mosul Rules with examples
The tap connectors have no categorical in its source, so NEC limits:
length: Common limits are 10 or 25 feet, depending on the circumstances.
measuring: It should be large enough to become pregnant and part of the nutrition.
Completion: It should end in OCPD (for example, crushing or painting) that reduces the risk of error.
example: The size should be at least 25 feet from the feeding unit at least 400a (133A) and it is run in a channel to a protected plate.
Complementary OCPDS (240.10)
These are the inner valves or the eclipse used inside the devices or lamps. It does not consider protecting the sub -circuit and does not need to access easily.
Site in the building (240.24)
It should be OCPDS:
It can be easily accessible (there are no required stairs or tools)
No more than 6’7 “to the top of the handle (with a few exceptions)
Not in bathrooms or wardrobes
It has been installed away from corrosion or dangerous environments
The box requirements (240.33, 240.81)
The packages should be vertical unless it is practical
The handicapped handles should be vertically in the UP mode
The containers are designed for safe operation with the user standing on the side
Circle cutters (240.80-240.88)
It should be manually operating
It can include shock trips or remote operators
Swd or HID must be used to use as lighting switches (120 volts or 277 volts)
Ground fear protection (240.13)
Required for services ≥000A Wye systems on the ground strongly > 150V on Earth. It prevents long -term errors that cause fires.
Selective Coordination (240.12)
It is used in hospitals, emergency systems and elevators. Only the closest device must be a rift trip to prevent the turbulence of large systems.
Series Categories (240.86)
The estimated escort cruels are allowed at the bottom of the rift if they are used with the source OCPDS and to distinguish them properly. It provides space and cost in some commercial facilities.
Sagittarius energy (240.67 for valves, 240.87 for fracture)
Apply when ocPDs ≥1200A. One of the following should be used:
This rule focuses on the safety of workers during the ARC flash events.
Cables suitable for extra protection applications
Thhn/thwn-2 copper wire
For wires for general nutrition and branch circuits in dry or wet locations when installed in the canal.
600V, up to 90 ° C
It is associated with the cutter and valves of the interior and exterior panels.
Xhhw/xhhw-2 wire
Similar to the THN but with a better isolation and flexibility; Used in the channel or race.
600V (xhhw) or 1000V (xhw-2)
It is used for long feeding working in commercial or industrial environments.
MC Cable (Clad Metal)
For nutrition and branch circuits in industrial/commercial environments.
600 volts
It should be listed for the environment (MC, the required wet, the open -air); It is often used from one plate to another with a circuit breaker protection.
NM-B (romex)
For residential branches circles in dry interior sites.
600 volts
Used with 15A or 20A cutters for lighting circuits and bowl. It is not allowed in wet or exposed facilities.
UF-B cable
For the underground branch circles (for example, landscape lighting, outdoor outlets).
600 volts
It is associated with GFCI cutters, not permitted inside the canal where the heat cannot be dissipated.
Stair cable (TC-aer)
This is for industrial sub -circuits in cable box systems or directly from the plate to equipment.
Usually 600 volts
It should be used for each mark (for example, TC-AR for open operation); It is not an alternative to MC unless it is specifically classified.
