# How does electricity from a 3 phase 4 wire 480Y/277v EV meter differ from a standard 120v wall outlet?

I am wondering what the difference is the electricity that comes out of the switchboard/utility meter that is designed to be a separate meter to measure a customer's use of power that only goes to an electric vehicle charger (that is from the utility prior to it being attached to any sort of EV charging device/vehicle) that is 4 wire, 3 phase, and 480Y/277v 2500 amps with a 65,000 amps fault compared to the type of electricity that comes from your standard US wall outlet at 120v?

Is the main difference here the amperage of the electricity, so 20-30 amps vs. 2500 amps and the 277/480v difference in voltage as well? Or is there some fundamental difference in the way that these two sources of electricity behave?

For example: I've been told that generally, the electricity that comes from a 120v wall outlet doesn't pose much of a risk of electrocuting someone because it would return to ground fairly well and that unless someone were very close to the source of the electricity (like touching a wire) that it'd be nearly impossible to feel a serious shock/get electrocuted. Due to the fact that even if this happened to someone who was not located on the ground floor of a building that the relatively small amount of electricity in a 120v 20 amp wall outlet wouldn't be able to pose much of a problem if electricity from it was somehow getting out into the home and would likely only cause something like a person to experience a shock/arc comparable to a very large static electricity shock? If the electricity were coming from the wiring from the EV meter source mentioned above (as in straight from the meter and properly connected to a charging system designed for EV's and not hooked up to a car either) from the utility and at 480v 2500 amps and say passing through the carpeting on its way to the ground then that electricity would absolutely cause a person to notice significantly more serious adverse effects?

Please forgive my lack of knowledge on this subject in general but this is potentially a very serious issue and unfortunately I haven't been able to get advice elsewhere, including the utility.

• well it's a different voltage and it's three-phase instead of single-phase...? – Hearth Mar 16 at 14:20
• I'm having trouble understanding whether you're actually getting shocked or are concerned about it, but regardless, for such concerns you need an electrician, not an electrical engineering forum. All we can tell you with this context is that three-phase, 480/277V is a) three-phase and b) a higher voltage. It still behaves like electricity and follows the same physics. – nanofarad Mar 16 at 14:23
• The electricity still uses electrons in the same way. – Andy aka Mar 16 at 14:24
• I’m voting to close this question because it belongs in diy.se as it pertains to advise about household wiring and tradeoffs for ev charging , this is within the scope of the diy (home improvement) forum. – crasic Mar 16 at 14:30
• 2500 amps is a sh*tload of amps, even for an EV, are you sure it's not 250 amps? – user253751 Mar 16 at 17:34

All household mains voltages pose a threat to human life if they are found where they should not be.

The additional voltage of your three phase is not enough to be shocked when touching an insulated wire.

The largest risk from household electrics is fire, the three phase supply is capable of causing much more damage than 120V if something goes awry, as evidenced by the much larger amperage rating (20A vs purportedly 2500A)

There appears to be an unanswered part of this question regarding electrical safety and what electricity does to you. The level 3 charging station actually has both 480V 3 phase AC input and 480V capable DC output, so two separate potential dangers. Both, if installed properly have many safety features to decrease the likelihood of a person getting shocked. One of the first precautions in an electrical design with a dangerous voltage is simply to build the equipment so that humans can't come in contact with current carrying parts unless they do something stupid or something breaks. In addition to the insulation that protects you from the wire, assorted means of "mechanical protection" are used to make the wire resilient to a reasonable amount of abuse for its purpose, like placing the wires inside walls, or using armored cable or drawing the wires into pipes which in turn may be poured into concrete or simply buried.

Where metal parts like boxes or pipe are used, they are attached to the ground wire to ensure that if a live wire touches them, instead of being energized to the voltage of the wire, the low resistance ground connection allows a massive amount of current to flow to ground, which in turn trips the circuit breaker very rapidly so that the current surge does not last long enough to damage anything. This deenergises the circuit and the object and removes the danger. The "bang" or "pop" noise you hear along with other signs like smoke, heat or the lights in one half of the building going out, along with knowledge of what has been recently modified or is exposed to abuse and what the blown breaker is attached to will help you locate the fault. You can also get devices called GFCIs (Ground Fault Circuit Interruptor) built into breakers or receptacles or just on their own, that blow the breaker immediately at a small detected ground current. These are usually required where conductive liquids may be present, like in the kitchen, the bathroom, or outside.

Where additional danger is present, like a flexible cable capable of carrying huge current at significant voltage that needs reach the car and could be damaged, additional precautions can be taken, such as using an "intelligent" charger that communicates with the car and doesn't apply voltage until the system is securely connected.

So a whole lot of people have put a lot of effort into design and installation rules to ensure that accidents occur as rarely as possible, but what happens when one does occur?

Well first, how much current flows? That is determined by voltage and the resistance of the load (if you're getting shocked, you're the load). Line voltage sources have a current limit, but a 15A 120V circuit won't just deliver 15A to any load that touches it.

$$\I(Current) = E(Voltage) / R(Resistance)\$$

The resistance you have when being shocked depends on the conditions and the path through you the current must take to reach the other side of the circuit. The resistance from the palm of your hand to the back of your hand will be much lower than the resistance from your hand, through your chest and to your feet. A lot of your resistance is in your skin, so if you are wet or your skin is punctured, you lose resistance.

Current passing through your muscles causes them to flex. DC current is constant and only in one direction and as a result can lock you up (make your muscles flex so you can't let go of an energised object).

So above the currents that might stop your heart, if current is high enough, it will cook you and can cause nerve damage or temporary paralysis. If your lungs are paralyzed, you can't breathe. The 50-100mA that might stop your heart would take forever to cook you, but $$\P(Power) = I^2(Current-squared) * R(Resistance)\$$ is the formula for power (heating) of a resistive load. Because the current is squared, if the current doubles, the power doubles. At high enough currents, people are sometimes vaporised, but you could also get a horrible burn from a more reasonable current.

From the Wikipedia article on electrical injury:

The graph explains itself well and the Wiki article is worth reading. You can find similar graphs or charts for DC or different frequencies of AC as well.

Ok so separate from the damage done if current actually passes through you, high currents that are low enough not to trip the breaker can produce tremendous amounts of sustained heat and spark as ignition sources for fires. If too long of a screw is used for drywall and a wire is hit, it can short out a circuit inside a piece of wood. I once checked out a case where this happened, and previously when they tried to turn it on the breaker had just tripped. They turned it on to show me and the breaker contacts welded together, so it just hummed like crazy and failed to trip until I manually forced it.

Separate from sustained fault currents, damage can be done in the surge of current before the breaker trips. On a 120V 15A circuit, this can burn a small hole and leave a large scorch mark where a wire touched a box or melt wire stripper holes into the cutting edge of a pair of pliers and make a flash that you'll see for a few minutes. The higher the current rating of the current limiting devices and the slower they trip, the more damage can potentially be done. The more voltage is present the more likely it is that the full amount of damage be done. A shorted 50A 347V connection is enough to blow a large metal box right off a wall. When you flip a large breaker, especially for the first time, you stand beside it instead of in front of it for this reason. A 347V dead short to ground through iron on a 15A circuit can make a fireball about the size of a volleyball in open air in the instant before the circuit shuts off and you have to explain to your boss why suddenly only the emergency lighting in the west rink is on. It'll give you an instant sun tan too.

Finally there are an immense number of dangers due to the nature of electrical components. A capacitor exploding at a moderate voltage could ruin your eyes if you aren't wearing safety glasses. Charged Lithium Ion batteries become firebombs when sufficiently mistreated. Similar to a gas vehicle, an electrical vehicle is a potential firebomb that has been carefully engineered in every way possible to never go off. Mistreated Lead Acid batteries can produce significant amounts of hydrogen sulfide, a poisonous, flammable gas. 250kW of power delivery on the level 3 charger represents the potential of a relatively huge disaster. Careful engineering reduces the probability and magnitude of the eventual real disaster to manageable levels.

4 wire, 3 phase, and 480Y/277v would generally have a grounded neutral resulting in 277 volts being the maximum voltage to ground. The phase to phase voltage is 480 volts. In comparison the standard US residential service is 240/120V, split phase that has a grounded neutral that provides 120 volts as the maximum voltage to ground. 120 volts is also the maximum voltage for a wall outlet. 240 volts is provided for large appliance outlets and direct wired equipment like central air conditioners. The available fault current is much lower, allowing for the use of more compact fuses and circuit breakers.

A three phase service has some advantages. It is not inherently more dangerous because of the three-phase configuration, but it is more dangerous because it is usually a higher voltage with higher available fault current. A 208/120V Y service is sometimes furnished for residential use to provide the advantages of 3-phase for larger residential loads particularly when HVAC is provided centrally to multi-family residential buildings. In that situation it is comparable to 240/120 service at the individual residence connection.

Wherever a building receives power at a higher voltage than 240/120V, areas of the building that have 120V outlets are not exposed to the risks of higher voltage or available fault current. Even at a consumer charging station, risks can be reduced by protection measures included in the charging system design.

• Does "available fault current" refer to the 65,000 fault I mentioned in the specifications? From what I've read the voltage is not whats really dangerous but instead the amps but that is what you are calling current right? – David Smith Mar 16 at 18:38
• 3 phase can have some additional dangers in a home environment because of the shared neutrals if present. In a commercial environment you only have electricians meddling, but an average homeowner can easily make a mistake and leave a neutral energised by the other two circuits. Usually the voltage on it isn't much, but I have had a few nasty pokes(shocks) from a neutral wire over the years. – K H Mar 17 at 1:24
• @KH, I would think it would be extremely rare for average homeowner to have access to 3-phase wiring. I don't think that is really what the question is about. I doubt that 3-phase charging stations would be offered to homeowners. The example seems more like something for a parking ramp, commercial building etc. with multiple charging stations. If it is offered for home use, I would expect the distribution system to be designed to make the residential part safe. – Charles Cowie Mar 17 at 3:13
• @CharlesCowie It is. Usually you see it on homes owned by people who would never have to lift a tool because they can always afford an electrician. I've also seen it installed once for a home wood shop though. The 3 phase station is definitely meant for commercial areas now that I read more documentation. At 177A plus losses per phase at 480V, only very wealthy people could afford the service connection. Wow. They even mention in documentation that it's hard on the battery, so you probably wouldn't even want one for an everyday charger unless it has low power settings. – K H Mar 17 at 3:45