chapter 6 selection, installation and wiring of ex certified electrical equipments

8/3/2019 Chapter 6 Selection, Installation and Wiring of Ex Certified Electrical Equipments

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CHAPTER 6SELECTION, INSTALLATION AND

WIRING OF Ex CERTIFIEDELECTRICAL EQUIPMENT

Under the Division 1 classification, wire terminations

are considered ignition sources.

6.1 UNDERSTANDING THE DIFFERENCE INZONE VS DIVISION INSTALLATION METHODSTerminations are the key to understanding the differences in

installation methods of Zone and Division rated equipment.

Under the Zone system wire terminations rated as Ex-e,

increased safety, are not considered sources of ignition.

Terminations are tested to ensure that they do not heat up or

vibrate loose and have sizable creepage and clearance

distances to prevent arcing. Under the Division 1 classification,

wire terminations are considered sources of ignition as it is

assumed they could vibrate loose, short out and create an arc.

This results in major differences in the way products are

designed. To illustrate this refer to the push-button control

stations shown below. Both stations contain an explosion-

protected contact block. The one on the left is rated

explosionproof for Division 1 and has an explosionproof metallic

housing. The one on the right is rated flameproof and increased

safety for Zone 1 and has a non-metallic housing. Each contact

block prevents arcs from switch operations inside from igniting

gases within the control station. Why then must the contact

block located in a Division 1 area be housed in an

explosionproof enclosure while the Zone 1 rated control

stations is in a non metallic enclosure?

The Division 1 control station has a metallic enclosure.

The Zone 1 version has a non-metallic enclosure.

Under the Division 1 system, wire terminations areconsidered ignition sources. If volatile gases and air accumulate

inside an explosionproof enclosure and are ignited by the spark

from a wiring fault on the terminals, the enclosure must contain

the explosion. As the hot gases escape the enclosure by passing

across a flat or threaded or serrated joint, they cool so they can

no longer ignite gaseous mixtures in the hazardous area. In a

Division 1 area, the contact block must be housed inside an

explosionproof enclosure rated for the area.

Explosionproof Contact Block in Division 1 Area

Wire terminations are considered sources of ignition for Division 1 products.

An explosionproof enclosure for the contact block is required.

Under the Zone system, wire terminations are not considered

an ignition source if they are rated as Ex-e or increased safety.

If the contact block is rated flameproof with increased safety

terminals, the switch can be housed in an increased safety

housing, e.g. a non metallic enclosure that has a suitable

construction and an IP rating to protect against moisture and

dusts.

Ex-de Contact Block with Increased Safety

Terminals in Zone 1 Area

Ex-e Wire terminations are not considered sources of ignition for Zone 1

products, and Ex-de contacts can be housed in non metallic enclosures

suitable for Zone 1.

Determining which system is safer, less expensive or easier to

install is very difficultsomewhat like comparing the metric and

US systems of measurement. Each application has its own

merits and depends on user preference, as well as how the

areas are classified, and the wiring systems used in the facility.

At the present time North American users have the advantage

of being able to use either type of product in Division 2.

Cooper Crouse-Hinds Ex DigestSelection, Installation and Wiring of Ex Certified Electrical Equipment

Division 1 Vs. Zone 1

Potential Ignition Source?

Not a Source of Ignition


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Equipment listed and marked for use in Class I,Zone 0, 1, or 2 locations shall be permitted in Class I,

Division 2 locations for the same gas and with asuitable temperature rating.

6.2 STANDARDS AND INSTALLATIONPRACTICESEx Electrical equipment certified to U.S., Canadian, CENELEC,

IEC or any other national standards must be installed and

maintained correctly. To ensure that correct installation is

achieved, every industrial country will use a recognized

installation rules or a code of practice.

In North America the installation requirements for Hazardous

Locations is specified in Section 18 of the Canadian Electric

Code and in Article 500 of the National Electric Code. Prior to

1997 most Countries produced their own National Standards for

installation in hazardous areas, which allows the use of Ex

Electrical Equipment certified to CENELEC and other national

standards. In 1997 the IEC Standard, IEC 60079-14 wasadopted as a European standard EN 60079-14. This was a

large step forward toward on worldwide standard for the

installation of electrical equipment in hazardous areas.

6.3 SELECTION OF EX PROTECTEDELECTRICAL EQUIPMENTThere are considerable international differences in the

approach to hazardous area electrical installations. Therefore, it

is important to clearly establish the documented safety rules

that will be applicable to the installation before the selection

process is undertaken. To illustrate this problem, hazardous

area electrical equipment may be manufactured and certified to

comply with the requirements of a Zone classification but may

not be considered suitable for Division 1 Hazardous Locationclassified by the North American (USA and CANADA) Class

and Division concept.

This has become more relaxed with the addition of Article 501-

1 in the NEC which states:

Equipment listed and marked in accordance with Section 505-

10 for use in Class I, Zone 0, 1, or 2 locations shall be permitted

in Class I, Division 2 locations for the same gas and with a

suitable temperature rating.

This has given North American users a wider range of products

to select from. Products which are rated for the IEC Zone

classification system, and are adapted to North American wiringand installation practices can be installed in Division 2.

Cooper Crouse-Hinds has received UL and cUL approvals on all explosion

protected equipment manufactured by Cooper Crouse-Hinds CEAG in

Europe. This product line, called SpecOne, is made out of either metal or

plastic which will accommodate either cable or conduit installation methods.

The SpecOne products include fluorescent lighting, control stations and

panels, power distribution panels, terminal boxes, plugs and receptacles and

disconnect switches.

While there are still many differences between the standards

and installation practices in North America and Europe, not to

mention others in Latin America, Japan, Australia and South

Africa, the gaps are narrowing. The main differences are:

Local safety and fire codes for ordinary locations.

No direct correlation between Class/Divisions and Zone

classification.

Different wiring methods for conduits and cables.

Cable entry hole threads, NPT versus metric openings.

Gas Groupings are different.

Conductor cross sectional areas and current ratings.

Nonacceptance of the Increased Safety concept in Class 1

Division 1 Hazardous Locations. (Connections & terminations

are still considered sources of ignition.)

These differences define the way equipment is selected,

installed and maintained and must be taken account of when

projects are designed.

6.4 BACKGROUND OF WIRINGIn the early 1900s when industry was converting from the use

of natural gas to electrical wiring, it was natural for contractors

to use the gas pipe as a raceway or conduit to run the electrical

conductors. Although this sounded easy, a need developed to

also have junction boxes and elbows to pull and terminate

cables and fixture hangers to assemble the new light fixtures.


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Two entrepreneurs

from Syracuse, N.Y.,

Jesse L. Hinds andHuntington B.

Crouse, made outlet

boxes for the new

conduit wiring

systems. They coined

the term condulet,

which was a

combination of

conduit and outlet box

as seen in an early

advertisement.


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In the 1920s when oil refineries were being constructed, there

was a new need for outlet boxes, fittings and fixtures which

would prevent electrical sparks and heat generating products

from causing explosions. The industry came up with the

concept of Division 1 to define these locations where volatile

gases would be present.

Mr. Crouse and Mr. Hinds engineered and manufactured explosionproofproducts for the oil and gas industry.

In the 1980s Canadian industry readily adopted the use of

TECK cable which is similar to metal clad cable except with an

extra PVC jacket. Now the industries with Hazardous Locations

use a variety of wiring methods ranging from rigid conduit to

various types of cable.

6.5 TYPICAL INSTALLATION CONDUITVS. CABLEThere are primarily 3 different types of wiring systems used:

rigid metal conduits, armored cables, and non-armored cables.

The use of each method is embedded in the electrical

installation culture of the area.

6.5.1 RIGID CONDUITThis system is widely used by specifiers and installers in the

USA and parts of Canada as well as parts of South America,

Middle East and Asia where the NEC is used. This method

ensures the maximum protection of conductors against

mechanical and chemical attack.

There are an equal number of proponents as there are

opponents to the use of rigid conduit. While some maintain that

conduit leads to higher installation costs, others argue the

merits of greater mechanical protection. A recent survey

showed that Canadian users favor TECK cable over rigidconduit. The USA industry is equally divided between favoring

cable over conduit. For example, offshore installations favor

cable over conduit, which is more susceptible to corrosion.

Conduit systemsprovide

mechanical

protection of

wires and

conductors.

6.5.2 TECK CABLEInstead of conduit, cable systems are used more often under

the Zone concept. There are 5 types: TECK, steel wire

armored, steel wire braided, lead sheathed and unarmored.

TECK cable is a variation of the armored cable which is used

primarily in Canada. The TECK cable is a metal clad (mc) cablewith an extra PVC sheath for additional insulation. Special

TECK connectors are used to secure and terminate the cable

into enclosures.

Teck cable has an extra PVC sheath for additional insulation.

6.5.3 ARMORED CABLESArmored cables are widely used in the United Kingdom and

former commonwealth countries and ensures the mechanical

protection and earth continuity. Special cable glands must be

used to guarantee the earth continuity (ground).

6.5.3.1 STEEL WIRE ARMORED (SWA)SWAcable consists of individual PVC-coated conductors within

an aluminum screen surrounded by a PVC coating, then by a

series of steel wires within an exterior PVC coating. The steel

wires are conical in shape and protect the conductors in the

same way as metal-clad cable. SWA is a very high-strength,

durable cable and used in many power applications.



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6.5.3.2 STEEL WIRE BRAIDED (GSWB)GSWB cable consists of individual conductors within an

aluminum screen surrounded by an inner sheath, then by a

steel braid, similar to a basket weave, underneath an outer

sheath. The braid makes this cable more flexible than SWA.

This durable cable is used in many instrumentation applications

or where shielding is required for signal applications.

6.5.3.3 LEAD SHEATH (LWA)

LWA cable consists of individual conductors surrounded by alead sheath for protection from hydrocarbons. A PVC coating

then surrounds the exterior. This cable is popular in the oil

industry and is usually buried in the ground. The lead sheath

protects the conductors from ground spills of oil byproducts.

Crouse-Hinds offers brass,

stainless steel, steel and and non-

metallic cable glands for

any type of cable or thread.

6.5.3.4 NON-ARMORED CABLEThis cable is similar to tray or SO-type cable and normally

contains a ground conductor or earth core. Since the cable is

not considered a source of ignition, under the Zone concept the

cable does not require its own mechanical protection. The

protection is usually provided by open conduit or other cable-

tray type protection called a cage or mounting grid. This

method, which is used in France, Germany, Italy and parts ofAfrica and Asia, can be very flexible, fast and economical. If the

installation is subject to mechanical risks, it is advisable to use

armored cable or an open conduit system. Most exposed

vertical cables are housed in open conduits or pipes to avoid

mechanical abuse.

Cooper Crouse-Hinds non-metallic mounting plate on mounting grid offers a

quick installation method of control stations and switches.

Table 6.1

Typical Cable Systems by World RegionAREA CABLE TYPE THREAD

TYPE

Canada TECK NPT

North America Metal Clad Aluminum NPT

Central Europe Unarmored Cable Metric*Germany

Europe offshore Steel Wire Braid Metric

Ireland, Norway, Steel Wire Armor MetricHolland, Belgium, Unarmored CableSpain

Italy, Belgium Steel Wire Armor Metric

Unarmored Cable & NPT

Middle East Steel Wire Armor MetricUnarmored Cable NPT

Far East Steel Wire Armor MetricUnarmored Cable & NPT

CIS States Steel Wire Armor Metric(Azerbaijan, Unarmored CableKazakhstan)

* Metric threads have replaced Panzer gage (PG) threads


(Saudi Arabia & Kuwait)

Steel wire

braided cable

is more flexible

than SWA

Crouse-Hinds NCG non metallic cable glands are offered with

NPT or metric males threads for tray and other flexible cables.


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The use of twist-on connectors, known as wire nuts

or marets, is not allowed in Europe as increased

safety terminals.

The Ex-e push in connectors are a major advantage

for OEMs, and for installation of lighting circuits.

6.6 TERMINATION METHODSTraditionally Ex-e connections are made at increased safety

terminal blocks mounted inside of metal or non-metallic, Ex-e

enclosures. The terminals are rated for creepage and clearance

distances.

6.6.1 TWIST ON CONNECTORSThe most popular method of termination in North America is

with the use of twist-on connectors, also known as wire nuts or

marets. For products approved for use in Europe, twist-on

connectors or wire nuts are not allowed. Some form of terminal

blocks or screw terminals must be used. Twist-on connectors

versus terminal blocks are the main differences between theNorth America and European wiring methods. North American

wiring methods will not be quick to abandon using twist-on

connectors in favor of terminal blocks for branch circuits

especially when both systems are safe when they are installed

properly. Until recently, twist-on type connectors were not rated

as increased safety.

Cooper Crouse-Hinds pioneered the first

Ex-e wire nuts which offer major

advantage for OEMs, and for

installation of lighting circuits.

6.6.2 TERMINAL BOXESThe specifications for terminals according to IEC and

CENELEC standards are very stringent. Certified electrical

terminals for connecting wires in hazardous areas will be tested

with the following requirements:

Insulation resistance to tracking (CTI)

Temperature limitation (thermal stability) Measured Creepage &b clearance distances

Voltage and current ratings

Wire pull out test

Antivibration locking

Thermal end to end resistance

Conductor clamping method (pinch screws are

not permitted)

The connection of wires to terminals is most commonly made

via DIN rail mounted terminals. The underlying design principle

for terminals is a pressure plate contact with the conductor and

an antivibration locking feature to prevent self loosening for the

connected conductors. Other types of reliable certified terminals

include saddle clamps, slotted type clamps (often used for

lighting circuit terminations) and screwless cage clamp

terminals.

6.7 TERMINATING ARMORED CABLE ANDCONDUIT IN NON-METALLIC ENCLOSURESThe armor of steel wire or braided cables must be effectively

connected to the earth/ground system. If a phase to armor

circuit fault occurs there can be thousands of amps flowing.

Therefore the armor must have a low impedance to

earth/ground via the cable gland. The enclosure to which the

armored gland is connected may not be tested to carry fault

currents so internal and or external connections are required.

The biggest dilemma of mixing zone and division installation

methods is the practice of using terminating conduits or

armored cable into non-metallic enclosures. The majorconsiderations are: pull out strength of the conduit from the

enclosure and ensuring a continuous and secure path to

ground. There are 2 different methods commonly used, the

zone rated hub or the integral grounding plate.


Under IEC installation

methods it is permitted to

combine two or more

wires in a compression-

type terminal provided

that the terminal is

designed for that purpose,

such as the Cooper

Crouse-Hinds eAZK

enclosures with Ex-e

U-slot terminals.

Ex-e U-Slot terminals,

which accommodate

different sized wires,

are found in Ex-e

terminal boxes (eAZK)

and in some Ex-d light

fixtures


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6.7.1 ZONE RATED HUBSThis hub is specifically designed for Zone applications to be

non-loosening and to have the required IP rating. For through

holes the male threads must have a locking ring which has an

increased safety grounding point and an extra security screw to

ensure against loosening of the locking ring. Either the hub or

the locking ring will have serrated teeth for extra clamping

protection into the non-metallic enclosure. Both of thesefeatures protect the connection from loosening against vibration

and long term use. The hub has an integral silicone rubber o-

ring or gasket to guarantee the require IP rating of the

enclosure. The hubs are machined to accept either NPT or

metric thread form.

The SpecOne Myers

hubs

are rated for

Zone 1 usage.

They are also

available as

metric adapters for

entering

metric threaded

female hubs or

plates.

6.7.2 BRASS BONDING PLATESMany non-metallic enclosures also have integral brass bonding

plates. Because of their nominal thickness these normally have

metric or parallel threaded openings. Each plate must have an

internal and/or external ground point. These plates can be field

drilled or drilled at the factory. If the holes are not used they

must be plugged with a blanking plug certified to Ex-e standards

for the required IP protection.

Ex-e blanking plugs are required to fill in threaded openings for IP

protection as seen on the Cooper Crouse-Hinds GHG 74 Series Ex-e

Enclosures.

For ease of wiring the SpecOne control stations, D2Z distribution panels,

Safety Switches, interlocked 309 receptacles and terminal boxes all have an

brass grounding plates. These have metric female threads for European

armored cable glands. For NPT entries use the Zone 1 Myers metric

adapters which are available in zinc or stainless steel.

6.8 CABLE SEALS

Cable glands have multiple options for material types for Ex-dand Ex-e types of protection. Ex-d cable glands have a brass,

aluminum, steel or stainless steel construction with at least two

seal systems to ensure the flameproof properties and ingress

protection. Ex-e cable glands normally have only one sealing

system for ingress protection and are available in a plastic

construction in addition to brass or stainless steel.

Three types of seal materials are most generally used in cable

glands.

Neoprene, a durable oil-resistant rubber compound with good

weather and ozone resistance. To meet the strict deluge test

requirements of the offshore oil industry, glands employ up to

three neoprene seals. These are used on offshore oilplatforms where they may be submerged for long durations.

Conductive, a neoprene seal with iron filings used to seal lead

sheathed cable.

Silicone, a compound with high fire resistance which holds its

properties well in temperature extremes. This seal may be

used in temperatures as low as -60C to as high as +180 C.

It also does not give off smoke when burning (zero halogen

applications) and is used in tunnels or other similar

applications.

Typical Seals and Application Temperatures

Seal Type Temperature Range

Neoprene (deluge tested) -20 to + 80CConductive -20 to + 80C

Silicone -60 to + 180C



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Typical installation of Zone 1 Myers hubs glands into a Cooper

Crouse-Hinds Ex-e stainless steel enclosure.

6.9 WHEN IS NICKEL PLATING REQUIRED?The inherent corrosion-resistance nature of brass eliminates

the need for plating in most cases. However, brass and

aluminum create a natural galvanic reaction, so nickel plate or

other finishes are required where the brass gland is used with

aluminum enclosures or aluminum cable.

Do not use brass

glands in aluminum

housings, which will

result in corrosion.

Use nickel plated

glands.

6.10 TERMINATING NON-METALLIC EX-eGLANDSIncreased safety non-metallic glands must be certified for

ingress protection, impact resistance and aging resistance.

There are 2 versions, which depend on the use of the glands.

For installations where the cables are secured, the glands have

lower requirements for strain relief. If the cables are not secured

trumpet glands are used. Their main purpose is to provide strain

relief where bending, twisting or pulling is common.

Trumpet glands (on handset)

are used on portable

equipment when support for

the cable is not practical or if

there are extensive tensile or

torsional forces.

Cables should be secured close

to the apparatus.

6.10.1 SELECTION OF NON-METALLICGLANDSCable glands are sold either as separate items mounted on the

apparatus or packaged with the cable. Selecting the proper

gland depends on the following criteria:

Cable type

Hazardous area rating

Seal type

Entry thread

Finish

Cable diameter

Material

Use

The one variable, which usually creates havoc for end users, is

holding the tolerance on the cable diameter especially ifflameproof cable glands are used. If the diameters exceed the

tolerances of the glands, they may not fit or seal properly which

could affect the flameproof integrity of the glands.

Cut-away of trumpet gland

For questions or comments, please contact the author at

[email protected]


Lever prevents pull-out or

torsional twisting.

Seal for IP

Protection

chapter 6 selection, installation and wiring of ex certified electrical equipments

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