Electrical Code (NEC) Snake Tray Cable Management Solutions

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C bl P th

U

d

Cable Pathway Use and

Selection and the National

Electrical Code® (NEC)

By Eric J Sadler BSME MIT By Eric J. Sadler, BSME MIT

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R f

References:

All references to the NEC in this presentation are taken from the National Electrical Code

Handbook, Twelfth Edition – With the complete text of the 2011 edition of the National Fire

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• Common Terms versus code terms for

• Common Terms versus code terms for types of circuits in pathways:

– Power = Conductors for General Wiring

P i i ll d b A ti l 310

• Principally governed by Article 310

– Premise Data = Class 2 and Class 3 Circuits • Principally governed by Article 725Principally governed by Article 725

– Utility/Service Provider Data = Communications Circuits

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• We will consider aspects of some

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Raceways – conduits, tubing and the like

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Cable Tray

Devices to hang cables from the building structure – Hooks and Continuous Cable Routing Assemblies

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• Our goals in this hour: • Our goals in this hour:

– Identify a few important rules,

Di th i it f th l

– Discuss the spirit of those rules, – Dispel of few myths

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The Spirit of the NEC

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In the beginning . . .

There were 10 laws

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• And that was eight too many • And that was eight too many.

All l b b il d d t t

• All laws can be boiled down to two:

– Do not hurt anyone

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• To enforce these two laws we used to • To enforce these two laws, we used to

have the feudal system

• The kindly lord would judge whether a person had hurt someone or touched their stuff, and dole out a sentence

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• However, the decisions of the kindly (or not so kindly) lord were arbitrary (literally and figuratively)

• So we decided to enact laws to precisely • So we decided to enact laws to precisely

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• Fast forward 1000 years or so • Fast forward 1000 years or so

• We now have the NEC and its Handbook, • a 1500+ page document to essentially say:

– Do not hurt anyoneDo not hurt anyone

– Do not touch their stuff . . . With electricity ;)

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Even with 1500+ pages we

Even with 1500+ pages, we

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• The Authority Having Jurisdiction (AHJ) • The Authority Having Jurisdiction (AHJ) • We can do our best to interpret the NEC • What he says, goes

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• The NEC is written to protect people andThe NEC is written to protect people and property from the hazards of electricity.

• These hazards can be categorized by:

– Fire

– Electrocution

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Part of fire prevention, is to

prevent the spread of fire and

products of combustion

products of combustion.

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• Don’t let the fire spread

• The NEC 300.21 calls for firestop

h

th

t t fi

where pathways penetrate

fire-resistant walls

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• Don’t let the smoke spreadDon t let the smoke spread • The NEC 300.22

– Redefines plenum (in 2011) as “other spaces usedRedefines plenum (in 2011) as other spaces used

for environmental air”

• Discouraging wiring in areas whose sole purpose is air distribution

distribution

– Requires wiring methods in plenum spaces to be totally enclosed

• Examples: conduit, MC cables

– Specifically allows cable tray as a support system for wiring methods

for wiring methods

– Further allows and qualifies cable trays with solid tops, sides, and covers as completely enclosedp , , p y

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• Better still prevent the fire from starting • Better still, prevent the fire from starting.

NEC 310 15 (A)(3) D t ll h t t

• NEC 310.15 (A)(3) - Do not allow heat to build to unsafe temperatures that would ignite cables or surrounding materials ignite cables or surrounding materials

NEC 250 4(A)(1) Di i t h t t d

• NEC 250.4(A)(1) - Dissipate shorts to ground

– Properly grounding wiring methods helps both to prevent fires and to prevent electrocution

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• Heat is generated by current in cables

Safe c rrents for e er common

• Safe currents for every common

cable are well documented in the

NEC

• Baseline currents for cables in “free

air” are in NEC 310.15(B)

( )

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The percent of baseline current

allowed or “correction factor”

allowed, or correction factor

is both temperature and

th

d

d t

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• Temperature correction factors for cables • Temperature correction factors for cables

normally rated at 30 deg C (most

common) are in 310 15(B)(2)(A) and vary common) are in 310.15(B)(2)(A) and vary from 1.29 to 0.29

• Temperature correction factors for cables normally rated at 40 deg C are in

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• For single conductors in raceways or in the jacket of a cable NEC Table

310.15(B)(3)(a) gives adjustment factors. • The factors are dependent only on the

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• As per NEC 392 80(A) For multi • As per NEC 392.80(A) For

multi-conductor cables in cable tray, you use the same chart:

the same chart:

– You adjust for the cable, not for the tray

• Except where there is 1.8m (6ft) or more cover on the tray, apply an additional

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• The NEC 392 80(A)(2) governs singleThe NEC 392.80(A)(2) governs single

conductors in a cable tray cabled together (bunched)

(bunched)

– 0.75 correction factor for cables 600kcmil or larger

larger

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• As per a special provision in article • As per a special provision in article

690.31, for photovoltaic (PV) installations single conductor cables less than 1/0 are single conductor cables less than 1/0 are permitted in exposed wiring methods such as tray within the PV array

as tray within the PV array.

• The NEC has not caught up to this with Tables, so correction factors must be

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• Class 2 and 3 and communications circuits do not carry sufficient current to cause a fire nor power to cause electrocution

• This did not stop them from writing entire

sections of the NEC to govern their installation • It does mean fewer, and “less strict,” regulations

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A NEC 725 24 Cl 2 d 3 i i

• As per NEC 725.24, Class 2 and 3 circuits can be attached directly to building structure

• This is usually accomplished with devices listed for that purpose UL 2239 “Hardware for the

for that purpose, UL 2239 Hardware for the Support of Conduit, Tubing, and Cable”

• Various hooks and continuous cable routing assemblies are listed this way

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UL 2239 listed Cable Hooks UL 2239 listed Cable Hooks

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Myth #1:

If you choose to put your

y

p

y

cables in a cable tray, you

t

th t i UL

must use a tray that is UL

listed

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Fact:

Repeat after me:

p

Th

i

h thi

There is no such thing as

UL listed cable tray!

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As per NEC 392.60(B) Tray

can be (UL) Classified as

E

i

t G

di

an Equipment Grounding

Conductor (EGC) if:

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• It is identified as an EGCIt is identified as an EGC

• The cross sectional area of the conducting members g of a cable tray meets the requirements of Table

392.60(A). (Greater than 0.2 in sq total cross section) • That area is marked on the tray (for trays of channel

or one-piece construction)p )

• Sections are connected in accordance with 250.96, using bolted connectors or bonding jumpers

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• As per the table in NEC 392.60(A), the greater the cross-p ( ), g section, the greater the allowable ampacity

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Myth #2:

Your cable tray must be a

y

UL Classified EGC

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Fact:

NEC 392 60(A) says that

NEC 392.60(A) says that

metallic cable trays,

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• Not:Not: – Will be – Must be – Ought to be – Would be swell if – But: Sh ll b itt d t b d

• Shall be permitted to be used as equipment grounding conductors

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• NEC 392 60(A) goes on to say that cable • NEC 392.60(A) goes on to say that cable

trays that support electrical conductors shall be “electrically continuous, and be effectively y , y bonded and grounded as per 250.96 and Part IV of 250.

• And trays containing only non-power

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• Therefore • Therefore

• Cable trays containing only non power circuits • Cable trays containing only non-power circuits

are NOT required to be grounded and bonded, only electrically continuous.

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Th th t d Cl 2 d 3 • There are other reasons to ground your Class 2 and 3

and communications circuit pathways, such as cable performance

p

• And to prevent possible surges from other devices in

i h Cl 2 d 3 bl h

contact with Class 2 and 3 cable pathways • But it is not required by the NEC

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Another Fact:

• EGC are explicitly required for power circuits

• But nowhere in the code does it state that you can use metallic raceways as EGC, and for wireways and gutters metallic raceways as EGC, and for wireways and gutters it explicitly states that separate EGC is required.

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Myth #3:

Y

d

You cannot put conductors

for general wiring and class

2 or 3 circuits in the same

tray unless separated by a

UL listed divider

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Fact:

NEC 725 136(B) states

NEC 725.136(B) states

“barrier”

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Another Fact:

The same is true of cables carrying

600V or less and more than 600V

NEC 392 20(B)(2) t t

“

lid

NEC 392.20(B)(2) states “a solid

fixed barrier of material compatible

with the cable tray.”

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Myth #4:

You cannot put conductors

p

in cable tray of a size less

th

1/0 AWG

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Fact:

NEC 392 10(B) states

NEC 392.10(B) states

“SINGLE CONDUCTOR shall

be 1/0 AWG or larger . . .”

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Another Fact:

You can use tray rated (TC)

cable in cable trays and TC

cable comes as small as 18

AWG

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• NEC 336.2 defines TC Cable as, “A

factory assembly of two or more insulated factory assembly of two or more insulated conductors, with or without associated

bare or covered grounding conductors bare or covered grounding conductors, under a non-metallic sheath.”

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For Class 2 and 3 circuits,

Multi-conductor cables are

permitted in cable tray

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Myth #4a:

You cannot put power

conductors in cable tray of

i

l

th

1/0 AWG

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Fact:

NEC 336.10 specifically permits

(1) Power, lighting, control, and

signal circuits

(2) In cable trays

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• To prevent fire as well as physical

hazards, in addition to ampacity, the NEC also governs allowable fill for most

pathways

• The percentage of a pathway’s cross e pe ce age o a pa ay s c oss sectional area that can be physically occupied with cablep

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• Cheat Sheet: • Cheat Sheet:

Conduit and tubing (more than 2 conductors) NEC – Conduit and tubing (more than 2 conductors) NEC

Chapter 9, Table 1, 40%

– Metal wireways (troughs) NEC 376.22(A) 20%y ( g ) ( )

– Sheet metal gutters (open troughs) 366.22(A) 20% – Solid Bottom Cable Tray 392.22(A)(4) 40%

– Ladder or Ventilated Cable Tray 392.22(A)(2)

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• The percent fill can be easily calculated • The percent fill can be easily calculated

using area formulas (πr2 _{and the like)}

• Percent fills are valid on the presumption that ampacity requirements are met

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The NEC has a section for

each pathway that gives its

installation requirements to

prevent physical hazards

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• Cheat Sheet: • Cheat Sheet:

– Securing and supporting raceways NEC 300.11 • “Securely fastened in place”

• Securely fastened in place

• Where support wires are used they must

– Provide secure support

– Be independent of ceiling grid support wires – Be secured at both ends

– Securing and supporting metal wireways NEC 376.30 • Horizontally every 1.5m (5ft)

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• Cheat Sheet cont’d:Cheat Sheet cont d:

– Cable Tray Installation NEC 392.18(A)-(G)

• Maintain electrical continuity

• Complete the tray before installing cables • Covers must be compatible

• Going thru walls is permittedGoing thru walls is permitted

• Keep trays exposed and accessible

• Attach conduits and boxes as per the rules for conduits and boxes

boxes

• Mark high voltage where applicable

– Building Structure NEC 725.24

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• Myths propagate because we believe • Myths propagate because we believe

them and tell others.

• To be through about cable pathways, or any other aspect of the NEC we need to read the rules and study interpretation. • This is of course true for any laws.This is of course true for any laws.

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• Let’s bring this full circle

• Let s bring this full circle . . .

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Now count them

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• “I am the Lord thy God” and “You shall • I am the Lord thy God and You shall

have no Gods before me,”

I th t t ?

– Is that one or two?

• How about “Thou shalt not covet?”

– So it is against the rules to even wantSo it is against the rules to even want something that someone else has?

Anything? – Anything?

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• Do not hurt anyone

• Do not touch their stuff . . . • With electricity ;)

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