NFPA 70E Approach to Considering DC Hazards - efcog.org Working Group/_Worker... · HOYDAR- BUCK,...

HOYDAR-

BUCK, INC.

2013 NFPA Conference and Expo

Chicago, IL

NFPA 70E® Approach to Considering DC Hazards

Bobby Gray Consultant

HBI

Steve McCluer Sr. Manager /External Codes & Standards

Schneider Electric

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BUCK, INC.

David Dini was Assigned New Chair of NFPA 70E The New Chair Assigned Various Task Teams Including: DC Hazards Task Team


BACKGROUND

2012 NFPA 70E®

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BUCK, INC.

1. Review Complete 2009 Standard 2. Identify Inadequacies 3. Generate Proposals for 2012


BACKGROUND

2012 DC Hazards Task Team’s Charter

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BUCK, INC.

- Academia - Power and Manufacturing Industries - Research and Development - IEEE Stationary Battery Working Group


BACKGROUND

2012 DC Hazards Task Team Invited Industry Experts

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Shock Hazard

“Chapters 1 and 2 apply to electrical equipment that operates at frequencies normally supplied for consumer use.” --2009 NFPA 70E® Handbook


BACKGROUND

2012 DC Hazards Task Team Results of 2009 NFPA 70E® Review

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The Generic Threshold for Electrical Hazard Is 50 volts Shock Approach Tables are Based on Phase-To-Phase Voltage


BACKGROUND

2012 DC Hazards Task Team Results of 2009 NFPA 70E® Review

Shock Hazard

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BUCK, INC.

1. IEC 60479, Effects of Current Passing Through the Body - referenced in NFPA 70E-2012®, 340.4

2. Published Research Papers by Dalziel, Geddes, Knickerbocker, LB Gordon, etc. 3. NIOSH Data


BACKGROUND

2012 DC Hazards Task Team Shock Hazard Research Papers

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“The current and voltage thresholds for physiological effects are at least twice the values for dc as compared to ac.“ --IEC 60479

See also: NFPA 70E-2012 Handbook


BACKGROUND

2012 DC Hazards Task Team Shock Hazard Research

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1. “DC arc models and incident energy calculations,” Ammerman, R.F.; Gammon, T.; Sen, P.K.; Nelson, J.P.; Petroleum and Chemical Industry Conference, 2009, Record of Conference Papers,14–16 September 2009. 2. “Arc Flash Calculations for Exposures to DC Systems,” Doan, D.R., IEEE IAS Electrical Safety Workshop, 2007, Record of Conference Papers, March 2007. 3. DC Arc Hazard Assessment Phase II Copyright Material Kinectrics Inc. Report No. K-012623-RA-0002-R00.


BACKGROUND

2012 DC Hazards Task Team Arc Flash Research

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1. DC Shock Approach Table 130.4(C)(b) 2. DC Arc Flash Hazard Risk Category Table 130.7(C)(15)(b) 3. DC Incident Energy Calculation Method Annex D, Paragraph D.8.1


BACKGROUND

2012 DC Hazards Task Team 2012 Proposals

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1. Determine Polarity Difference of Potential 2. Determine Nearest Approach Boundary To Be Crossed Based on Table 130.4(C)(b) Approach Boundaries to Energized Electrical Conductors or Circuit Parts for

Shock protection, Direct-Current Voltage Systems

3. Apply Proper Shock Protection Techniques


DC ELECTRICAL HAZARD ANALYSIS

Shock Hazard Analysis 130.4(A)

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TABLE 130.4(C)(b) Approach Boundaries to Energized Electrical Conductors or Circuit Parts for dc Shock Protection (1) (2) (3) (4) (5)

Nominal Potential Difference Limited Approach Boundary Restricted Approach Boundary; Includes

Inadvertent Movement Adder

Prohibited Approach Boundary Exposed Movable

Conductorb Exposed Fixed Circuit

Part

<100 V Not specified Not specified Not specified Not specified

100 V–300 V 3.0 m (10 ft 0 in.) 1.0 m (3 ft 6 in.) Avoid contact Avoid contact

301 V–1 kV 3.0 m (10 ft 0 in.) 1.0 m (3 ft 6 in.) 0.3 m (1 ft 0 in.) 25 mm (0 ft 1 in.)

1.1 kV–5 kV 3.0 m (10 ft 0 in.) 1.5 m (5 ft 0 in.) 0.5 m (1 ft 5 in.) 0.1 m (0 ft 4 in.)

5 kV–15 kV 3.0 m (10 ft 0 in.) 1.5 m (5 ft 0 in.) 0.7 m (2 ft 2 in.) 0.2 m (0 ft 7 in.)


45.1 kV– 75 kV 3.0 m (10 ft 0 in.) 2.5 m (8 ft 0 in.) 1.0 m (3 ft 2 in.) 0.7 m (2 ft 1 in.)





A All dimensions are distance from exposed energized electrical conductors or circuit parts to worker. B This terms describes a condition in which the distance between the conductor and a person is not under the control of the person. The term is normally applied to overhead line conductors supported by poles.

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- Be Qualified 130.4(D) or - Be Continuously Escorted 130.4(D)(2) and - Work Under EEWP 130.2(B)(1) and - Use Insulated Tools and Equipment 130.7(D)(1)



To Cross a Limited Approach Boundary you must:

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- Be Qualified 130.4(D)(2) and - Be Insulated from Energized Parts 130.4(C)(1)

or - Guard Energized Parts 130.4(C)(2)



To Cross a Restricted Approach Boundary you must:

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1. Determine Arc Flash Boundary (Where is PPE Required?) 2. Determine Incident Energy At Working Distance (What Rating of PPE is Required?) 3. Choose Arc-Rated and Other PPE Based on Task



Arc Flash Hazard Analysis 130.5

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Arc Flash Hazard Analysis Two Methods to Select PPE [130.5(B)]:

1. Incident Energy Analysis [130.5(B)(1)]

a) Determine Actual Exposure

b) Use 130.7(C) or Table H.3(b)

2. Hazard Risk Category from Table 130.7(C)(15)(b)

& PPE from Table 130.7(C)(16) [130.5(B)(2)]

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BUCK, INC.

NFPA 70E-2012 Table 130.4(C)(b) identifies 4 Conditions at 11 dc voltage ranges. [see next slide]

(It does not address Amperes, Watts, or fault potential)


HAZARD ANALYSIS FOR BATTERIES

Shock Approach Boundaries: Energized dc circuits or conductors

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From Table 130.4(C)(b)

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BUCK, INC.

o NFPA 70E-2012 Table 130.7(C)(15)(b) is for all dc use, including storage batteries, dc switchboards, & other dc supply sources o Hazard risk categories (1 - 4) o Rubber insulating gloves & Insulated hand tools are required in all cases -



Hazard Risk Category Classes for dc Equipment

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Table 130.7(C)(15)(b) Potential Arc Flash Boundaries:

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Annex D.8 Calculated Arc Flash Boundary:

●70E picks up Doan’s method (based on Lee’s work); comments

that “testing completed for Bruce power has shown that the

calculation is conservatively high…”

●Recommends multiplying factor of 3 for “arc in a box”

configurations

●Applicable to systems up to 1000V DC

Schneider Electric 22

Maximum Power Transfer

● Max power is delivered to arc when Arc Voltage = ½ System Voltage

● In other words – impedance matching!

● Power delivered = ½ bolted fault MVA

VA

VS

ZA

IF

VSys

ZS

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HAZARD ANALYSIS FOR BATTERIES Table 130.7(C)(15)(b)

Table 130.7(C)(15)(b)

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Is there such a thing as dc “arc flash?”

• Maybe a spark?

• in most cases a battery cannot sustain an arc

• unlike a utility, which has ‘unlimited’ EMF

• a battery’s stored energy is rapidly depleted

• Literature search reveals shock hazards and

millisecond-long “sparks”

• but no “flash” and no “blast”

• The real hazards are ‘thermal’ and ‘shock’

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Needed: DC Test Data

●NFPA & IEEE are conducting a US $6 million collaborative

research project to characterize arc flash

The joint study includes:

● Heat & thermal effects

● Blast Pressure

● Sound

● Light intensity

● Initial report is for ac only; some dc modeling has been done

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IEEE StaBatt Committee Approach to Considering DC Hazards


● HAZARD and RISK are NOT THE SAME THING

● If there is no hazard, there is no risk

● If there is a hazard, the risk depends upon the

probability of an incident

● Risk can be minimized

● Personal Protective Equipment (PPE) must be

based upon the risk, not the hazard

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Concerns About Required PPE

●Gloves, clothing, and other PPE should:

● protect against both Electrical &Chemical hazards

● allow full freedom of movement & visibility for all

battery-related tasks

● be readily available

● Too much PPE can actually create a

hazardous situation

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●Methods of minimizing risk:

● use insulated tools

● segment battery sections

● insulate exposed dc bus

● prevent contact between + and –

● train, certify, refresh

● perform risk analysis for planned tasks prior to

doing the work

APC by Schneider Electric – BATTCON 2011/ McCluer – West

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BUCK, INC.

NFPA 70E® Approach to Considering DC

Hazards

SIGNIFICANT CHANGES EXPECTED IN 2015 NFPA 70E

● Safe Shock Voltage Lowered back to 50vdc in

Table

● Reformatted Arc Flash Table

● Replaced Arcing Current with SSC Values in

Table

● Added Paragraph to Instruct How to Obtain

Arcing Current in Annex D

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Hazards


Lower Safe Shock Voltage to 50 Vdc in Table

Needed to reconcile with AC threshold in NFPA 70E

and NEC

LAB – 3’6” RAB – Avoid Contact

Justification to Cross Required at 50 Vdc

Qualified or Continuously Escorted

No PPE Requirements

Tools Not Required to be Insulated [130.7(D)(1)]

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BUCK, INC.


Hazards


Two existing arc flash tables – 130.7(C)(15)(B)(a) & (b)

will be merged into one: 130.7(C)(15)(b)

First Table Screens Tasks With Arc Flash Hazard

Second Table Assigns HRC to Equipment

Some DC Tasks Added

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BUCK, INC.


Hazards


Will replace Arcing Current with SSC values in arc

flash table

2012 Requires conversion from SSC to arcing

current to use table

Other changes include defining proper installation

and maintenance

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BUCK, INC.


Hazards


Adds paragraph to instruct how to obtain arcing

current in Annex D

Method is based on IEEE 946

50% of DC short circuit value

Assume 25°C ambient

Maximum available SSC =10 times 1 Minute ampere rating

of the battery

Better: Contact battery manufacturer for specific battery

model short circuit values

HOYDAR-

BUCK, INC.


Hazards

CONCLUSION

●QUESTIONS?

●COMMENTS?

●THANK YOU!

NFPA 70E Approach to Considering DC Hazards - efcog.org Working Group/_Worker... · HOYDAR- BUCK,...

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