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 Post subject: Battery Bank Arc Flash PPE Requirements- based on task
PostPosted: Sun Jun 16, 2019 10:49 am 

Joined: Mon Jun 30, 2014 12:02 pm
Posts: 1
Perhaps I’m asking the obvious, but I was hoping some of you might educate me on the following. I’ve been more focussed on calculations, than field application requirements.

The battery bank in question is CAT 3 and is as follows, but the question is generic in nature:
• 130 VDC
• 13,620 amps fault capability per the manufacturer.


Question: Though somewhat dated, does the link below on PPE requirements for various battery bank tasks accurately represent your company’s approach to PPE requirements, assuming NORMAL equipment conditions for the battery bank? If not, can you please describe your approach where it varies from those stated below? I did not see a conflict with the retitled table 130.5(C) in NFPA70E 2018.

https://www.ieee-pes.org/presentations/gm2014/2756.pdf

Excerpts from the link are shown below:


Arc Flash PPE is NOT required* for:

– Voltage testing on individual battery cells or individual multi-cell units
– Removing battery intercell connector covers
– Performing infrared thermography and other noncontact inspections outside the restricted approach boundary.
– Insertion or removal of individual cells or multi-cell units of a battery system in an open rack
– Maintenance on a single cell of a battery system or multicell units in an open rack
*…When this activity does not include opening of doors or covers.

Arc Flash PPE IS required on DC Systems for:

– Work on energized electrical conductors and circuit parts of series-connected battery cells, including voltage testing • Such as measuring overall voltage on a string
– Removal of bolted covers (to expose bare energized electrical conductors and circuit parts) • this includes bolted covers, such as battery terminal covers
-Insertion or removal of individual cells or multi-cell units of a battery system in an enclosure
– Work on exposed energized electrical conductors and circuit parts of utilization equipment directly supplied by a dc source

I appreciate your time, Toukow


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 Post subject: Re: Battery Bank Arc Flash PPE Requirements- based on task
PostPosted: Wed Jul 03, 2019 3:10 pm 

Joined: Mon Jan 08, 2018 8:43 am
Posts: 10
A typical VLA, VRLA, or NiCd Stationary Battery will have less short circuit current available at the battery terminals than the rated individual cell short circuit current. Why? External circuit resistance. The individual cell/jar short circuit current rating from the battery manufacturer is the amount of current the cell/jar can deliver to the cell posts/terminals assuming a zero resistance short circuit. This rated short circuit current does not include the resistance of the intercell/jar connectors, or intertier/row cables that are integral parts of the battery. Do to these series resistances a cell rated to deliver a short circuit current of 13,620 amps cannot deliver that same current at the battery terminals.

A cell that can produce 13,620 amps of short circuit current should have an average intercell connection resistance of 5-15 micro-ohms. Assuming an intercell connection resistance of 10 micro-ohms would reduce the battery short circuit current to approximately 12,754 amps. Inserting a single intertier cable with a resistance of 150 micro-ohms would reduce the battery short circuit current to approximately 6526 amps. A single intertier cable connection provides quite a reduction in battery short circuit current which reduces the potential arc flash incident energy.

NFPA 70E recommends using an arc time of 2 seconds on a battery since there is no possible overcurrent protection. Laboratory testing by Bonneville Power Administration in 2017 shows that the maximum sustainable arc time on a nominal 125VDC battery is only 715 milliseconds.

The external circuit resistance within this 125VDC battery and the arc time reduction lowers the incident energy of your battery to approximately 1.40 cal/cm2 at 18 inches.

I normally run my calculations using an arc time of .8 seconds and at normal battery float voltage which should be 133-135VDC depending upon the model cell in use. This raises the incident energy of your battery to approximately 1.688 cal/cm2 at 18 inches which is a significant reduction from the 8+ cal/cm2 at 18 inches that 13,620 amps at 2 seconds works out to…

We require our technicians to wear 8+ cal arc rated clothing, safety glasses, non-melting leather gloves, and standard safety toe electrically rated shoes. We are presently evaluating some light weight arc rated work gloves to provide additional protection.


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