PDBFS220 datasheet(19/23 Pages) COOPER

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Proper Application

When applying Power Distribution Blocks (PDBs) and

terminal blocks, there are several requirements that must be

satisfied, based upon various UL Standards, the NEC®, and

the specific application. Some of the requirements and ratings

include: voltage, continuous current, wire range (load and line

side), conductor terminal temperature rating, short-circuit

current rating or withstand rating (SCCR), type and amp

rating of upstream overcurrent protective device (fuse or

circuit breaker) and spacing (between uninsulated live part

and uninsulated grounded part or uninsulated live parts of

opposite polarity). The requirements vary, based on the

application for industrial control panels (feeder circuit or

branch circuit), field applications, or HVAC applications.

New requirements in the 2005 NEC® for a marked short-

circuit current rating (SCCR) on industrial control panels

(NEC® 409.110), industrial machinery (NEC® 670.3A), and

commercial/industrial HVAC equipment (NEC® 440.4(B)) have

resulted in considerable attention being placed upon the

proper selection and application of power distribution blocks

and terminal blocks. In addition, UL508A Industrial Control

Panels has a requirement that the assembly be marked with

its short-circuit current rating. Per UL508A, each power

circuit component in the panel, such as a PDB, has a SCCR

expressed in amperes or kiloamperes and voltage. The

SCCR shall be established by either being marked on the

product, the instruction sheet provided with it, or from

UL508A Supplement SB Table SB4.1. If an assembly short-

circuit current rating above 10,000 amperes is desired, a

power distribution block or a terminal block with a high

short-circuit current rating must normally be utilized.

The following material includes some application notes on

power distribution block and terminal block SCCR, UL Listed

1953 vs UL Recognized 1059, spacing requirements,

conductor ampacities, conductor termination ratings affecting

conductor ratings, and SCCR for multi-lug switches and

circuit breakers.

UL Listed 1953 vs. UL Recognized 1059

Listed products simply require checking to ensure that the

product is used in accordance with its listing and labeling.

However, for recognized products, such as terminal blocks,

the “Conditions of Acceptability” must be investigated to

ensure the product is suitable for the specific application, and

then the procedure description must be documented in the

manufacturer’s procedure for the assembly.

Most power distribution blocks available today are actually

terminal blocks, and are recognized to UL 1059, the terminal

block standard. Terminal blocks may or may not meet the

spacing needed for OEM applications. Terminal blocks are

marked with a UL recognition mark to ensure that the

designer and UL inspector checks, among other things, that

there is adequate spacing for the OEM application in which

they are being applied. Power distribution blocks are

evaluated to UL1953, the power distribution block outline of

investigation and are listed for general installation, which

means they have adequate spacing for most OEM and field

applications. These power distribution blocks are marked with

a listing mark, which means that the inspector does not need

to check ”conditions of acceptability” as is needed with

recognized products. As listed products, PDBs evaluated to

UL1953 are suitable for use in the field. For example, an

electrical contractor may install them in a metal wireway,

something that may not be done with a recognized product

such as a terminal block.

Marking Equipment with SCCR

Marking the equipment with its short-circuit current rating

(SCCR) is another important consideration in the proper

application of PDBs and terminal blocks. This datasheet

provides the details on Cooper Bussmann power distribution

blocks and terminal blocks that have high short-circuit

current ratings. Using these PDBs and terminal blocks with

appropriate overcurrent protective devices makes it easier to

achieve a high short-circuit current rating for the entire panel

assembly.

SCCR for Wire Management Products

There are different ways to determine the SCCR for wire

management products (power distribution blocks, terminal

blocks and multi-lug connectors) per UL508A Supplement SB:

(1) Use tested and listed combinations, which consist of a

specific part number and a specific type and maximum size

overcurrent protective device. For instance, the power

distribution blocks in this datasheet are all SCCR tested and

listed combinations with fuses. An upstream current-limiting

fuse of a specific class and maximum ampere rating as

shown in the tables can be used to achieve the SCCR in the

tables. Otherwise, the SCCR of the power distribution block

will be determined by (2) or (3).

Combination SCCRs

Up to 200KA

Use Tables

Specified fuse class

with amp rating no

greater than maximum

shown

1011

SB-BU09622

Page 19 of 23

Data Sheet 1049

Application Notes

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