EVs and the DC Hazard: AC vs DC Arc Flash – What’s the Difference?

With the rapid growth of electric vehicles (EVs), and the infrastructure needed to support them, so too grows the importance of understanding the direct current (DC) arc hazard. That’s where Tyndale comes in! This series lays out the differences between the alternating current (AC) arc hazard and its lesser-known DC counterpart and demonstrates – through first-of-its-kind real-world video footage – the power of DC arcs. Follow along to learn more and witness firsthand the life-saving difference the right arc-rated (AR) clothing makes in the face of a DC arc.

Technology has a habit of outpacing understanding of hazards and safety; DC arc flash is no exception. With the rapid rise of EVs, DC power is expanding exponentially in the USA. DC battery manufacturing, energy storage and DC-to-DC charging are all growing rapidly, and battery replacement, maintenance, and repairs are close behind. 

While AC arc flash has been relatively well understood since the 1990s, you’d be hard-pressed to find DC arc flash experts, and what little expertise exists is often more theoretical than practical. DC is different than AC in that it is “on” throughout the arc, while AC current alternates “on” and “off” (where the curve crosses the zero point) once per cycle of the arc duration. DC arcs are theoretically harder to stop because they don’t drop below the zero point, but beyond that there are far more questions than answers: 

  • What does DC arc look like? 
  • How different are DC versus AC arcs? 
  • Are DC arcs more or less dangerous than AC arcs?
  • How well does common arc flash PPE handle DC arcs?
  • Are arc ratings determined based on an AC arc (ASTM F1959 uses AC) translatable to DC arc hazards?

Recognizing the rapidly-growing DC arc hazard and the lack of practical and reliable information, Tyndale set out to help the industry by beginning to answer these – and other – DC questions. To do this, we worked with the same laboratories and leveraged the same gear we use for AC arc flash analysis to create DC arcs. We also employed the same high-speed, super-slow-motion camaras to capture overhead and close-up views, to fully demonstrate the effects of the events. We placed manikins in front of the arcs, and tested flammable poly/cotton and cotton workwear, as well as various CAT 2 arc-rated garments, 40 cal arc flash suits, layered systems, flammable outerwear, hi-vis vests, and more. We’re pleased to be able to share the videos and results of this leading-edge research throughout this series.

The first video in our series compares an AC arc to a DC arc, using a split screen of super-slow-motion footage which enables you to clearly see the significant visual difference. These two arcs were in the same gear, with the same amperage, voltage, and duration, and filmed with the same camera in the same location. You’ll notice:

  • The AC arc pulses, growing and shrinking with the cycles, while the DC arc remains the same size throughout, without shrinking and surging. 
  • DC arcs also appear to be more “magnetic” (drawn to metal) and perhaps a bit more energetic vs AC arcs of the same input energy. 

Starting in June, we’ll explore what effect, if any, the AC versus DC difference has on ignition of flammable clothing and arc-rated PPE. Tyndale will release one new video every Tuesday, Wednesday, and Thursday throughout June.  Each of these will be brief, narrated, sharable, and downloadable. We hope you’ll follow along so you can learn how to stay safe. 

Look out for our next post to see how non-protective workwear made from poly/cotton blend fabric performs in a DC arc. Spoiler alert: you don’t want to be wearing this type of workwear in the face of a DC arc.


Series: EVs and the DC Hazard

Think you know arc flash? Think again. DC arcs are different. Following along with this series to see how different – and how to stay safe.

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