Eaton Industrial Switchgear - General Information

2010

CA08103002Z-EN

www.eaton.com

Switchgear for North America 22/11

circuit through the circuit-breaker’s

auxiliary contacts. In North America,

combinations of this type are used in

motor control centres (MCC) and

as discrete starters in separate

enclosures. Electronic overload relays

also provide protection for motors with

heavy starting duty. For this duty type,

such combinations are also used in

IEC/EN-standard switchgear systems.

For the switches alone, no short-

circuit rating is given. At locations with

short-circuit currents up to the

switching capacity specified for the

complete“combinationmotor starter”,

they can be used without upstream

short-circuit protection device.

Circuit-breakers

NZM...A(E)…-NA,

NZM…A(E)F…-NA, NZM…VE…

NA, NZM…V(E)F…-NA

In North America these devices are

inverse-time molded-case circuit

breakers to UL 489 and CSA-C22.2

No. 5-09)

They are the normal

switches for power distribution

systems, but can also be used in motor

control centres (MCC) and controllers.

All versions of construction sizes

NZM1…-NA, NZM2…-NA

and

NZM3…-NA are approved as current-

limiting devices and marked accord-

ingly on their rating plate. They are

rated in A, their short-circuit switching

capacity is given in amperes and –

if they are equipped with auxiliary

contacts – contain duty type informa-

tion (pilot duties).

These devices have adjustable

magnetic or electronic short-circuit

releases and fixed-current or adjust-

able bimetallic or electronic trip blocks

for overload protection for non-motor

outgoing circuits. They can be used as

short-circuit protection devices and

for switchingmotor circuits

and their

auxiliary contacts for switching

control circuits. At mounting locations

with short-circuit currents up to their

switching capacity, they can be used

without upstream short-circuit

protection device.

In main current outgoing and incoming

lines, they can be used as main

switches. The letter “E” in the part

number indicates versions with

electronic releases. The letter “V”

indicates electronic releases with

adjustable, tripping times with

adjustable delay. They can optionally

be tripped by shunt or undervoltage

releases or be switched on and off

with remote operators. In North

America circuit breakers with fixed

overload releases are often used to

reduce the required cable cross-

sections. Example: A circuit is to carry

150

A. If the adjustable switch has a

rated operational current of 250 A, it

must be wired for 250 A in North

America (for the highest adjustable

current). A switch permanently set to

150

A must be wired only for 150 A.

At least for large currents and long

lines, this consideration can also

be of interest for IEC/EN-standard

systems.

Circuit-breakers PKZM4- …-CB

From motor-protective circuit-breaker

PKZM4a fully-featured circuit-breaker

to UL 489 has been derived. These

circuit breakers are larger than their

motor-protective counterparts

because of the large clearances and

creepage distances required at their

input- and output-side main power

connections. These devices can be

used as branch circuit protective

devices.

This circuit-breaker has been devel-

oped with the aim of offering devices

for smaller rated operational currents

than are possible with circuit breakers

NZM yet with a high switching

capacity. These circuit breakers have

a switching capacity that is compa-

rable with that of circuit breakers

FAZ…-NA. The need for these protec-

tive devices is that non-motor loads

must be protected with fuses or with

circuit breakers. These loads often

have only low currents. This also

applies for the protection of frequency

inverters, although here, too, the load

is a motor. Exporters prefer the use of

circuit breakers and similar fuseless

solution, which is also Eaton’s

recommendation. In North America,

systems commonly contain a large

number of fuses, even though

standard NFPA 70 E

presacribes

very complex safety measures for

replacing defective fuses.

Switch-disconnectors N, PN

For North America the switch-discon-

nectors N and PN, which are derived

from circuit breakers NZM and which

have a proven track record in the

IEC/EN market, have been replaced

with molded-case switches NS…-NA

to comply with North American

practices.

Molded case switches NS…-NA

Molded-case switches NS…-NA,

to UL 489 and CSA-C22.2 No. 5-09 are

the typical North American switch-

disconnectors. They are the normal

switches for power distribution

systems, but can also be used in motor

control centres (MCC) and controllers,

for example as main switches. where

they are the normal switches for

power distribution systems, but can

also be used in motor control centres

(

MCC) and controllers. They are rated

in amperes, their short-circuit

switching capacity is given in kA and –

if they are equipped with auxiliary

contacts – contain duty type informa-

tion (pilot duties).

These devices feature fixed short-

circuit releases and no overload

release. The short-circuit releases are

intended only for intrinsic protection of

the circuit-breaker. They can not be

used as short-circuit protection for

downstream protecting and switching

devices. Their auxiliary contacts can

be used for switching control circuits.

At mounting locations with short-

circuit currents up to their switching

capacity, they can be used without

upstream short-circuit protection

device. They can optionally be tripped

by shunt or undervoltage releases or

be switched on and off with remote

operators. The North American

standards regard these devices are

switch-disconnectors, while the

IEC/EN standards consider them

circuit breakers of category CBI-X

It should be noted that molded-case

switches NS…-NA have a tripped

position that the switch-disconnectors

do not have. After tripping, they must

be reset.

Current limitation

Current limitation is a feature of

modern circuit breakers that interrupt

short-circuit currents very quickly and

of some fuse types. With specially

developed contact systems, these

circuit breakers interrupt short-circuit

currents before the breaker mecha-

nism can respond. The current is inter-

rupted long before it reaches its limit

value. This is referred to as dynamic

contact disengagement through

magnetic force fields around the

conducting parts of the breaker

mechanism. The fast interruption of

the short-circuit currents results in

much lower let-through currents and

energies.

According to IEC/EN the switching and

protective elements connected down-

stream of a current limiter are dimen-

sioned only for these reduced let-

through characteristics. According to

the North American standards the

current-limiting effect in industrial

control panels for machinery can be

used only partially to UL 508A Part 2

and NFPA 79. Annex SB of UL 508A

does mention these current-limiting

protective devices in the context of the

determining the short-circuit current

rating (SCCR), but demands that all

branch circuit protective devices

(

BCPD)

downstream of the current-

limiting protective device have at least

the same switching capacity as the

current limiter itself. This, in effect,

ignores the physical effect, making the

plants unnecessarily expensive. In

reality, the load on the entire installa-

tion after the current limiter is signifi-

cantly reduced. For dimensioning

apparatus in the control panel

arranged on the consumer side down-

stream of the BCPD

the let-through

characteristic of the current limiter

can then be expected again.

All circuit breakers of construction

sizes NZM1…-NA, NZM2…-NA

and

NZM3…-NA, and the small circuit

breakers FAZ…-NA and FAZ...-RT are

designed and approved as current

limiters and marked accordingly on

their rating plate.

Circuit-breakers NZM4…-NA have

single-pole-interrupting contact

systems that are optimized for current

selectivity. For selectivity at higher

currents and for installation away from

short-circuits, contacts that remain

closed as long as possible are

required. The selectivity requirements

exclude the current-limiting effect.

Series connection of circuit

breakers, back-up protection

(

series rating)

If, according to IEC/EN standards, the

switching capacity of a circuit-breaker

is not sufficient for short-circuit

currents that may occur in specific

applications, a further protective

device with a higher switching

capacity is connected upstream of the

circuit-breaker. Together, the two

series-connected circuit breakers can

handle the higher short-circuit

currents. If the additional protective

device protects or supports a group of

lower-rated protective devices, this is

referred to as group protection.

According to the North American

standards, this interaction of several

protective devices in power distribu-

tion systems (distribution equipment)

is also permissible. For the industrial

control panels for machinery (ICP) to

UL 508A and NFPA 79 that are dealt

with here, a series connection of

circuit breakers, fuses or a combina-

tion of the two is not permissible if the

series connection is intended to

increase switching capacity. Circuit-

breakers FAZ…-NA and FAZ…RT,

which are popular in IEC/EN installa-

tions, have a rated current dependent

switching capacity of 10 or 14 kA.

These circuit breakers are often used

in ICPs. According to the North

American standards it is not currently

possible to increase the switching

capacity with a series-connected

protective device (circuit-breaker or

fuse). In an ICP a circuit-breaker must

always provide the required switching

capacity by itself. While it is possible

to connect two circuit breakers in

series as main switch and outgoing

circuit-breaker, this does not increase

the overall switching capacity. The

switching capacity of every protective

device must always be equal to or

greater than the highest expected

short-circuit current.

Operating elements

for circuit breakers

and molded case switches

Operating elements of the upstream

switches that are used in industrial

control equipment for machines

currently attract the particular

attention of inspectors. This applies

specially to the operation of main

switches with door coupling rotary

handles and to door interlocks. Here

follows a brief explanation of the

complex requirements. A more

detailed Technical Essay on this

subject is also available

North American standards UL 508A,

Part 2, Industrial Machinery

10)

and

NFPA 79

11)

demand that the operating

elements of main switches (supply

circuit disconnecting (isolating)

means)

12)

are permanently connected

with these switches to allow switch

operation at any time and irrespective

of the control panel door’s position.

The operating elements must also be

lockable to prevent their operation

(

closing). A further requirement is that

Notes

The term “inverse time” is usually omitted. It expresses that the tripping

time is inversely proportional to the current.

Except NZM…2-ME…-NA

In combination with an overload relay

NFPA 70 E, “Standard for Electrical Safety in the Workplace”

Category CBI-X circuit breakers are molded case circuit-breakers

without overload release. According to IEC/EN switch-disconnectors

must not contain a current-dependent trip block.

Circuit-breakers for individual branches

e.g. contactors or frequency inverters

Except NZM…2-ME…-NA]]

http://www.moeller.net/binary/ver_techpapers/ver966de.pdf

10)

UL 508A, UL Standard for Industrial Control Panels

11)

NFPA 79, Electrical Standard for Industrial Machinery; subject comparable

with IEC/EN 60204-1

12)

Supply Circuit Disconnecting (Isolating) Means