NFPA 70E-2012 vs. IEEE 1584 language

[HuskyFC450]

Has the issue with NFPA 70E – 2012; Article 130 Work Involving Electrical Hazards; Section 130.5 Arc Flash Hazard Analysis -Exception No. 1 (Revision)been resolved (or clarified)? See below:

NFPA 70E – 2009 (obsolete)
Article 130 Work Involving Electrical Hazards
Section 130.3 Arc Flash Hazard Analysis -Exception No. 1
Exception No. 1 read as follows:
“An arc flash hazard analysis shall not be required where all of the following conditions exist:
(1) The circuit is rated 240 volts or less
(2) The circuit is supplied by one transformer
(3) The transformer supplying the circuit is rated less than 125 kVA.”

The above exception was eliminated in NFPA 70E-2012 and instead the 2012 edition has the following informational note 5 in section 130.5:

NFPA 70E – 2012 (current)
Article 130 Work Involving Electrical Hazards
Section 130.5 Arc Flash Hazard Analysis -Exception No. 1 (Revision)
This exception is based on language found in Institute of Electrical and Electronics Engineers (IEEE) Std. 1584—Guide for Performing Arc-Flash Hazard Calculations. Exception 1 stated that an arc flash hazard analysis shall not be required on circuits rated 240 volts (V) or less and supplied by one transformer if the transformer is less than 125 kilovolt-amperes. This exception has been deleted. In addition, an informational note will state that an arc flash hazard analysis may not be necessary for some three-phase systems rated less than 240V. It will then reference the IEEE standard for more information.
“See IEEE 1584 for more information regarding arc flash hazards for three-phase systems rated less than 240 volts.”

There are two major reasons for the change:

1. There was an unintentional inconsistency between 70E-2009 and IEEE 1584-2002. Whereas, 70E stipulated 240 volts or less, 1584 stipulated less than 240 volts. So, if you were following 70E you would not perform an analysis for 240 three-phase systems, but you would perform an analysis for 240 volt three-phase systems if you were following 1584.

2. There is considerable disagreement over the need for an arc flash hazard analysis for systems less than 240 volts. The next revision of IEEE 1584 will address the need for an analysis and will provide new guidelines depending on test results and consensus of the committee.

I have many 3-phase 208v machine control cabinets in my facility and we are "sitting on the fence" as to what we should do in regards to Arc Flash Analysis because of the above ambiguity.

Can anyone offer clarification on this?

Tom

 

[dpc]

I think you are mis-reading a few things.

IEEE 1584-2002 - the statement reads "Equipment below 240 V...." NOT "240 V and below". So for 240 V THREE-PHASE systems, IEEE 1584 equations can be used. The sentence is dealing with systems below 240 V - mainly 208 V systems, at least in the US. But keep in mind that the IEEE 1584 equations are only supposed to apply to three-phase systems. Also, we know that these equations are not as accurate below 250 V.

NFPA 70E-2012. The Exception you refer to does NOT include the "Informational Notes" below. These Notes are NOT part of the actual standard.

Having said that, it is true that the two standards not consistent regarding arc-flash hazards below 250 V. Article 130 in 70E applies down to 50 V. I would not say that these inconsistencies were "unintentional". The differences just reflect what language was approved by the 70E committee. I'm sure everyone on the committee was fully aware of what is in IEEE 1584.

For smaller 208 V systems, you could rely on the Hazard/Risk Classification Table in NFPA 70E. You will end up with a maximum HRC of #1.

The NESC used by utilities also used a 4 cal/cm2 max for 240 V and below.

Some level of PPE is required, even at 208 V. It is difficult to sustain an arc at 208 V, but test data shows molten metal being ejected from the fault and this could cause burns without proper protection. There is no definitive answer in the standards at this time on how to deal with the systems where the IEEE 1584 equations do not apply, unless you fall under the NESC.