# Safety precautions for working on EV's



## madderscience (Jun 28, 2008)

Anything over 72V is considered "Dangerous". Cables carrying this voltage or greater should be housed in orange conduit. First responders are trained to recognize this.

Make sure all wires/cables insulation is rated for the voltage they are carrying. Make sure to size your cables properly for the expected current. route high voltage cables in places where they are protected, such as within conduit and/or in places like the transmission tunnel. I prefer the gray plastic marine grade conduit you can get at any larger hardware/home improvement store. It is cheap, tough, and easy to work with. You can paint the conduit orange.

Design your battery pack with a fuse in every battery box, or every 72V or so. Also add a manual disconnect and/or DC rated circuit breaker. Put this breaker in the MIDDLE of the pack electrically, such that pulling the disconnect immediately divides the maximum voltage in half. It should be reachable from the driver's seat at least, and ideally from all seating positions in the car. My breaker is located between and just behind the two front seats on what was the transmission tunnel so everybody in the car can reach it. Fuses should have semiconductor (fast blow) and DC voltage rating for the maximum on-charge voltage of your pack, and be rated for amps only a little above the maximum amps that your controller can pull. Too big and they won't blow at all.

Obtain a set of "battery wrenches" (or make them) which are just ordinary wrenches/tools with insulated handles, such that it is impossible to drop them across the terminals of a cell/battery and cause a short.

Work on small sections of your battery (battery == multiple cells) at once, and keep the sections you are not working on covered up. I find old political campaign signs are great for this sort of thing, and they also make great battery insulation and battery covers. Keep other tools, nuts and bolts, people, pets, and fluids away from the battery pack.

When assembling your bus bars, assemble 24V sections at atime, then gang them to 72V, then install the fuses, then finally close the breaker. THis keeps the voltages you are working with as low as possible, as long as possible. Test everything more than once before you add the final connections to make sure polarity is what you expected.

Battery boxes don't have to be airtight, but should have covers sufficient to keep people and junk out in the completed car, and retain the cells in the event of an accident.


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## dragonsgate (May 19, 2012)

I heard that 50 volts was the cut off point for lethal. Other than that everything Madder said is sound advice. years ago I managed to score a couple of those orange rubber insulator blankets the power company workers use. Make sure you have the car jacked up with the drive wheels off the ground when working on the electrical.


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## Matej (Dec 4, 2015)

madderscience said:


> When assembling your bus bars, assemble 24V sections at atime, then gang them to 72V, then install the fuses, then finally close the breaker.


The bus bar assembly seems like the most intimidating part.

Probably because of how on regular ICE cars there are sometimes sparks when hooking up the battery, so I imagine that happening, but a lot bigger and stronger.


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## piotrsko (Dec 9, 2007)

So far every one forgot: use dish gloves or only one hand. rubber soled shoes on dry concrete.

Maintaining a stream of conciousness towards one's safety, too.

Physical spacing is important. I had the positive and negative ends of my FLA pack a wrench distance apart. That wrench kinda went plasma.


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## PStechPaul (May 1, 2012)

Almost any voltage CAN be lethal, or cause injury. Somewhere between 10 and 100 mA through the heart can stop it, and a shock of any magnitude can be startling or cause involuntary muscle contractions that can cause you to slam your hand against a sharp object or throw a tool. If your skin is sweaty, or if you have deep cuts, it does not take much voltage to inject dangerous current through the circulatory system and the heart.

Arc flash from short circuits can cause molten metal to be sprayed at you, so safety glasses are highly recommended. Insulated rubber soled shoes and rubber gloves may help, but since traction battery packs are (or should be) isolated from the car frame and the earth, they may not be essential. Working with one hand in a pocket is a good habit where possible. And also avoid wearing metal jewelry and watches, or cover them with tape.


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## Moltenmetal (Mar 20, 2014)

All good suggestions. Key points to me: 

1) ensure you have perfect isolation between your high voltage system and the car's chassis ground, by design

2) work on the high voltage systems only with the disconnect open and all loads disconnected

3) have a means to separate packs from one another

4) cover the high voltage connections as you go, with durable means. We used masking tape- hint, not durable enough...

5) wear gloves or work one handed, and wear good rubber soled shoes

6) take particular care with wrenches and ratchets- it's easy for a tool to bridge across cells. Insulated tools are a good idea

7) make the entire high voltage system finger safe when you're done. Covers that require tools to remove them are sensible but not essential


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## Sunking (Aug 10, 2009)

dragonsgate said:


> I heard that 50 volts was the cut off point for lethal..


That is NEC line of when metallic objects in an electrical system must be grounded or bonded to something in place of earth. Less than 50 in NEC world can Float. 

It is not voltage that harms, injures, or kills you, it is current. If it were voltage you would have been dead long ago when you received your first static electricity shock. Static electricity is in the 10's of thousands of volts. Most static electricity you come in contact with cannot generate enough current long enough to do any damage other than maybe make you jump and collide with something causing an injury or wet your pants from fear. 

The actual voltage considered to be lethal is undefined because resistance in the human body varies from 1000 ohms to 100,000 ohms depending on conditions. 2700 volts is considered to be fatal in 50% of the population, 11,000 volts is guaranteed fatal.

However voltage is not what you should fear the most. You do not even need to come in contact to be seriously injured or killed Electrocution deaths are quite rare even among professionals who do it for a living every day. Arc Flash on the other hand is the most common injury or death from electricity. Let a cable slip from you hand, drop a wrench on the high voltage battery terminals, motor terminal, ect.. Arc Flash can and will surround you with white hot plasma like this *poor guy in the video*. He went home in a dust pan. Note he was not wearing any PPE gear other than safety glasses.


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## Matej (Dec 4, 2015)

Do you gentlemen have any recommendations for a good pair of rubber gloves and an insulated 3/8" ratchet?

I had no idea how much these things cost. The cheapest ones on Ebay start at 120$ or so.


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## piotrsko (Dec 9, 2007)

Kitchen gloves $12.00 usd dozen acid gloves 5.00 pr, medical gloves sometimes free, mechanics latex gloves 12.00 a box.

Wrap a couple of layers plastic wire repair tape on the handle of the wrench or whatever your sticking into the pack leaving just a minimum bare metal. Or buy a can of dip handle rubber paint.

You wont need this every time just when you are working on possible complete circuits with bare wires, posts, bolts.


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## miscrms (Sep 25, 2013)

Matej said:


> The bus bar assembly seems like the most intimidating part.
> 
> Probably because of how on regular ICE cars there are sometimes sparks when hooking up the battery, so I imagine that happening, but a lot bigger and stronger.


You see the spark because the you are closing the circuit with a load in place. This is why its important to make sure your battery connections are not where you are closing the circuit. One or more contactors should be open and isolating the battery from the loads. Making sure your low voltage power is disconnected is a good idea to make sure your contactors can't be accidentally closed. Checking them with an ohm meter each time before working is not a bad idea either. They can fail closed, which is why its a good idea to have one on both the positive and negative leads. Same with the safety disconnect. Breaking the circuit in multiple redundant ways reduces the likelihood of any one mistake/failure causing a big problem. As long as there is no load / no closed circuit path there will be no current flow, so you shouldn't get any sparking when making battery connections. If you do, stop, because you've got a problem somewhere.

Working with one hand is a really, really, good idea. Just be careful about what you lean against while working. I've gotten a pretty good tingle a few times by leaning a bare forearm in too close to a terminal while trying to tighten another with tricky access.


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