Previous in Forum: How Could I Find Electrical Run Out in Probe Area   Next in Forum: Voltage Drop Calculation and Cable Sizing
Close
Close
Close
18 comments
Commentator
Philippines - Member - New Member Engineering Fields - Control Engineering - New Member Engineering Fields - Instrumentation Engineering - New Member

Join Date: Jun 2007
Location: Philippines
Posts: 85

Intrinsically Safe Cables

12/01/2010 3:13 AM

Mga Henyo,

Im creating Instrument Cable routing plan, some of my cables are IS-Cables, is there a requirement to separate them with non-IS cables in loading them on cable trays? In cable tray loading, cables are separated depending on their noise level, how about IS-cables and non IS cables?

__________________
"Autobots.......TRANSFORM!!!!" -- Optimusprime
Register to Reply
Pathfinder Tags: cables instrument
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Anonymous Poster
#1

Re: Intrinsically Safe Cables

12/01/2010 6:59 AM

Yes IS cables to be seperated from NON-IS cables, Generally they can be laid 100-150 mm apart. If u need any futher details let me know.

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30339
Good Answers: 818
#2

Re: Intrinsically Safe Cables

12/01/2010 8:20 AM

Intrinsic safety is a method of protection, and is not a type of cable.

In the UK, SWA cables with a blue sheath are generally in use on IS circuits. Cable separation standards vary across installations. There are creepage and clearance requirements between individual conductors, and these requirements apply within panels.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply Score 1 for Good Answer
Commentator
Philippines - Member - New Member Engineering Fields - Control Engineering - New Member Engineering Fields - Instrumentation Engineering - New Member

Join Date: Jun 2007
Location: Philippines
Posts: 85
#3
In reply to #2

Re: Intrinsically Safe Cables

12/01/2010 3:50 PM

Yes its a method of protection and I've read about the color coding, but lets say I have two panels, one is IS-Panel, one is non-IS, their cables have the same route, do I have to separate them on different cable trays?

__________________
"Autobots.......TRANSFORM!!!!" -- Optimusprime
Register to Reply
Anonymous Poster
#4
In reply to #3

Re: Intrinsically Safe Cables

12/01/2010 10:41 PM

Not required.

Register to Reply
Guru
United States - Member - New Member Engineering Fields - Mechanical Engineering - New Member Engineering Fields - Petroleum Engineering - New Member Hobbies - Target Shooting - New Member

Join Date: Jan 2008
Location: Spring, Texas
Posts: 3403
Good Answers: 149
#5
In reply to #3

Re: Intrinsically Safe Cables

12/01/2010 11:03 PM

I don't know if there is a specific requirement (I suspect there is, and the ruling standard will probably vary depending on what part of the world you are in or where the product is going.) but I certainly would separate them because if the cables were to ever be chafed/damaged then you may have non IS voltage and current levels appearing on your IS equipment which would then make them non-IS (and probably damaged as well.) and could lead to a explosion hazard. whenever in doubt, always choose the most safe method and you'll rarely regret it.

__________________
Who is John Galt?
Register to Reply Score 1 for Good Answer
Guru

Join Date: Jul 2007
Location: Commissariat de Police, Nouvions, occupied France, 1942.
Posts: 2599
Good Answers: 76
#18
In reply to #3

Re: Intrinsically Safe Cables

07/26/2018 9:42 AM

How come these two panels are in the same place, then?

__________________
Good moaning!
Register to Reply
Active Contributor

Join Date: Aug 2010
Posts: 22
#6

Re: Intrinsically Safe Cables

12/01/2010 11:09 PM

Required as per NEC, in nomal practive (oil and gas field) we separated IS-cable and non IS cable into separated tray.

Register to Reply Score 1 for Good Answer
Commentator
Philippines - Member - New Member Engineering Fields - Control Engineering - New Member Engineering Fields - Instrumentation Engineering - New Member

Join Date: Jun 2007
Location: Philippines
Posts: 85
#7

Re: Intrinsically Safe Cables

12/02/2010 2:13 AM

Thanks guys...big help, just finished my deliverable

"petiks mode(siesta)"

by the way I'm currently in Saudi Arabia and working for Korean company...=?

__________________
"Autobots.......TRANSFORM!!!!" -- Optimusprime
Register to Reply
2
Power-User
United States - Member - New Member

Join Date: Aug 2008
Location: KY, USA
Posts: 367
Good Answers: 18
#8

Re: Intrinsically Safe Cables

12/02/2010 9:33 AM

NEC Article 504 - Intrinsically Safe Systems generally states that Intrinsically Safe (IS) conductors running in raceways, cable trays, and in cables should not be run in the same raceway as non-IS conductors, but it does give some exceptions.

Perhaps the most notable exception is that you can run in IS and non-IS conductors in the same raceway if you maintain at least 50mm of separation between the IS and non-IS conductors or if your raceway has a partition of 20 gauge sheet metal (or equivalent) installed to keep IS and non-IS conductors separated.

__________________
The most valuable of all talents is that of never using two words when one will do. ~Thomas Jefferson
Register to Reply Good Answer (Score 2)
Commentator

Join Date: Dec 2010
Posts: 89
Good Answers: 1
#9

Re: Intrinsically Safe Cables

12/02/2010 5:27 PM

There is a correct answer, IS cables are cables that are protected to a greater degree than normal cables of the same amperage - voltage and watts are not relevant - Is cables are for use in high risk situations eg. explosive gasses spark hazards, high heat or chemical environments. The separation of the two cable types is simply because there is a fear than a non safe cable may cause damage to a safe cable. It is in fact a contradiction - in a building that requires IS cables they will require all cables that are a risk to be IS cables or the inspector should reject them, where are cable is not required in the building to be IS it is because the cable is of a benign nature such as a fibre optic cable as such are incapable of causing a damage to an IS cable anyway. Any cable capable of causing a damage would be a cable that would be required to be IS in the first place. So the correct answer provided the building/environment has a need for IS cables, is no, because the non IS cables should be no threat or danger. Though common sense say you keep them apart for the opposing reason, data cables are subject to electromagnetic field interference as would be surrounding an item such as a high voltage IS cable. So no there is no requirement, but separate if you want optimum performance of the non IS cables.

Archie

Register to Reply Score 1 for Off Topic
Guru
United States - Member - New Member Engineering Fields - Mechanical Engineering - New Member Engineering Fields - Petroleum Engineering - New Member Hobbies - Target Shooting - New Member

Join Date: Jan 2008
Location: Spring, Texas
Posts: 3403
Good Answers: 149
#10
In reply to #9

Re: Intrinsically Safe Cables

12/02/2010 5:52 PM

Archie you must be operating under a different definition of intrinsically safe than I am. Intrinsically safe around here means that the total energy on the conductors is low enough that it cannot arc enough to trigger an explosion. It is an ATEX requirement. Hence the *intrinsic* part of the definition, it CANNOT arc, even if it does short to ground. I'm not a sparky, I'm but a lowly knuckle dragging Mech Designer, but I work with enough equipment that must go into explosive atmospheres that I DO know what intrinsically safe means at least as it is understood by the NEC and IEC.

__________________
Who is John Galt?
Register to Reply
Commentator

Join Date: Dec 2010
Posts: 89
Good Answers: 1
#11
In reply to #10

Re: Intrinsically Safe Cables

12/02/2010 7:00 PM

Yes as i noted it is amperage, and total energy is not how many amps or volts or watts it is energy ratio to product - eg 240 volts 10 amps through a 10 amp line 2.5mm would be safe but max standard - 4mm would be safe-. the section you have read regarding arcing conductors is related to poles and switches not cables, not even non IS cables can arc, they are insulated. if your interpretation was correct there would be no mining companies, go and ask someone to give you a demo of a resistance tester, it is a sparky's tool, 1milli amp at 1000volts, gives you a nice belt, but even at 1milli amp it still arcs.

Items arc when the power is too great for the resistance of the wire or terminal, so it look for a path of least resistance to complete the loop and arcs.

Think of a hose, turn the nozzles so the water jets out, this is a thin wire, open the nozzle and let it pour, out this is a thicker wire, there is less resistance, so too the thin wire gets hot as the electricity is squeezed through the lines, like a light bulb element, a jug element is fat but also gets hot because instead of 100 watts it has 2000 watts trying to go through it, but if you make the element 20 times fatter it will take forever to heat.

Well, arcs work in a similar fashion, high pressure on too thin a line and a close conductor and it will try to find the path of least resistance and jump, change just the thickness of that cable and the power no longer squeezed will not arc. Or increase the power on the heavier cable and the arc will return. Or in short what you read, "the total energy of the conductors is low enough that it cannot arc to cause an explosion" IS cables are more heavilly insulated and have heavier guage wire above that normally used to prevent the total energy from increasing - A side note is that technically the wording is not very good, energy can be a human calorie, it should read the "the conductor resistance is low enough to prevent arcs" and have a distance via insulative properties and distance via non insulated terminals of conductors.

Again total energy : 1000volts at 1 milli amp will spark but is harmless to humans, 1 volt at 1000 amps will cook an elephant in about 5 minutes, all energy even in domestic use is high enough to create an arc, the safety is in the size of the conductor and insulation.

Directive 94/9/EC, commonly referred to as ATEX ("Atmosphères Explosibles")

OBJECTIVE OF THE ATEX DIRECTIVE 94/9/EC

The Directive does not regulate the

use of equipment in a potentially explosive atmosphere which is covered, for instance, by

Directives 1999/92/EC, 92/91/EC and 92/104/EC9.

The above notes are from the Atex directive, the previous directives refer to CE approved products which include cable.

(I have run electrical engineering firms and also been a manager for L&H selling all of this equipment and cable.)

Register to Reply
Commentator

Join Date: Dec 2010
Posts: 89
Good Answers: 1
#12
In reply to #10

Re: Intrinsically Safe Cables

12/02/2010 7:24 PM

Though I am in Australia we do have ATEX requirements for export to the EU in fact I have exported to the EU both UL and EU certified products.

The more I think about the more i realise the question is moot, you could not be required to install IS cables if there was a requirement, because there could not be Non IS cables in the tray anyway, that would defeat the point of having the others IS - I have a feeling your non IS cables are the data or non dangerous cables, though not rated IS are by their very nature IS anyway. If in fact there are non IS power cables, you should be questioning the engineering plans as unsafe.

Register to Reply
Guru
United States - Member - New Member Engineering Fields - Mechanical Engineering - New Member Engineering Fields - Petroleum Engineering - New Member Hobbies - Target Shooting - New Member

Join Date: Jan 2008
Location: Spring, Texas
Posts: 3403
Good Answers: 149
#13
In reply to #12

Re: Intrinsically Safe Cables

12/02/2010 8:56 PM

Not necessarily, they could (and probably are) instrumentation cables being routed to a control station outside of the explosive zone and intercepting/intersecting another cable tray on the way that is also going to the control station from somewhere else. I'm guessing this is probably a petrochemical facility. And yes, high power conductors can and do get routed to explosive areas, but they must be enclosed in conduit and the joints sealed. And they have to terminate in explosion proof boxes, usually big honking cast aluminum monstrosities (although Hawke makes a welded stainless box that is also ATEX approved, go figure.). the goal being to make sure no explosive gasses can get to the switchgear of course.

__________________
Who is John Galt?
Register to Reply
Commentator

Join Date: Dec 2010
Posts: 89
Good Answers: 1
#14
In reply to #13

Re: Intrinsically Safe Cables

12/02/2010 9:37 PM

Not sure about the conduit theory, use of items that can trap or enclose gases with electrical items would seem a little silly, one crack and its a bomb, even without spark from cable heat, can't say Ive seen it in sealed conduit in mines, have seen in in non sealed protective piping for short distances, but always with openings to prevent trapped gases. Conduit even HD is only a mechanical protective device, I would personally never seal any container that had a heating component inside, kinda goes against physics 101. the termination points and switch gear is always sealed anyway, explosion proof switches, usually not a box, some of the switches are on mobile cables for equipment operation. Doesnt sound like this is the case, again a perto chemical site would have all wires designated as critical and rated IS and conduit is not usually run over cable trays. Still think the design is an error or a misundertsanding on the person doing the job, if it is a danger zone there cannot be any non IS cables at all unless they are outside the zone when they come into contact with each other, in which case as noted before the answer is no requirement to seperate.

Register to Reply
2
Guru

Join Date: Jul 2006
Location: Eastern Kansas USA
Posts: 1420
Good Answers: 121
#17
In reply to #14

Re: Intrinsically Safe Cables

12/05/2010 12:55 AM

Friend,

Education, yes---understanding, questionable. Within explosion-proof equipment, small explosions can and do occur. However, the ground metal joints and multiple turns of threads on piping serve to cool the escaping gases to a temperature below that at which the surrounding atmosphere could burn. Options exist to prevent the occurrence of explosions within the equipment---purging with a non-flammable gas while using controls that turn off the electric energy if the purging fails, and the use of intrinsically safe equipment which is incapable of providing enough energy to cause the atmosphere to ignite or explode.

An intrinsically safe circuit is defined in the NEC (504.1) as: "A circuit in which any spark or thermal effect is incapable of causing ignition of a mixture of flammable or combustible material in air under prescribed test conditions."

Because the point of connection for these circuits is likely to be well distant from the hazardous area boundary, the codes properly require separation of IS circuits from non-IS circuits to minimize the possibility of problems from non-IS cable heating, capacitive or inductive coupling, etc. Note the "Simple Apparatus" limits of 1.5 V, 100 mA and 25 mW. These are very low values and all must be satisfied together (thus 0.1V and 150mA fails even though it is only 15mW).

--JMM

Register to Reply Good Answer (Score 2)
Anonymous Poster
#15

Re: Intrinsically Safe Cables

12/04/2010 1:59 AM

Again, I am saying ..not required.

Register to Reply
Commentator
Philippines - Member - New Member Engineering Fields - Control Engineering - New Member Engineering Fields - Instrumentation Engineering - New Member

Join Date: Jun 2007
Location: Philippines
Posts: 85
#16

Re: Intrinsically Safe Cables

12/04/2010 5:54 AM

My Drawing is done! and approved!

Also, I've on ARAMCO standard(which is generally used on Saudi based projects) that it is required to separate the IS cable from non-IS cables...thanks for your opinions..

__________________
"Autobots.......TRANSFORM!!!!" -- Optimusprime
Register to Reply
Register to Reply 18 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

Anonymous Poster (3); Crabtree (1); EElectrician (1); jmueller (1); Life is Enerventure (4); nguyenkhoadung98 (1); Optimusprime (3); PWSlack (1); Rorschach (3)

Previous in Forum: How Could I Find Electrical Run Out in Probe Area   Next in Forum: Voltage Drop Calculation and Cable Sizing

Advertisement