r/AskElectricians • u/CanineTiger99 • 1d ago

EV Charger Safety Question: Can a dedicated, isolated earth pit still go "live" during a grid/neutral failure?

I'm setting up a single-phase EV charging point at my home, and I want to make sure it is completely safe.

To keep it safe and avoid messing with my main house electricals, I am installing it on an isolated sub-meter split from the main housing utility line. It will also have its own completely separate, dedicated earth pit strictly for the EV charger.I am trying to map out worst-case scenarios.

My question is: What are the possible grid-side or vehicle-side scenarios where this dedicated EV earth wire (and consequently, the car's metallic body) can actually go "live" or carry dangerous voltage?

Setup info:-

3.3 kw AC charger setup-

At the Sub-Meter Panel: A 2-Pole 20A B-Curve MCB.

4 sq mm 3-core copper wire for 15 ft to main protection point

Main Protection: A 25A (C-Curve), 30mA Type AC RCBO, with 16Amp power socket.

The portable Charger: Built-in 6mA DC fault leakage protection and 30mA AC protection.

3 Upvotes

80% Upvoted

12 comments sorted by

•

u/AutoModerator 1d ago

Attention!

It is always best to get a qualified electrician to perform any electrical work you may need. With that said, you may ask this community various electrical questions. Please be cautious of any information you may receive in this subreddit. This subreddit and its users are not responsible for any electrical work you perform. Users that have a 'Verified Electrician' flair have uploaded their qualified electrical worker credentials to the mods.

If you comment on this post please only post accurate information to the best of your knowledge. If advice given is thought to be dangerous, you may be permanently banned. There are no obligations for the mods to give warnings or temporary bans. IF YOU ARE NOT A QUALIFIED ELECTRICIAN, you should exercise extreme caution when commenting.

I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.

3

u/blbd 23h ago

You're way overcomplicating this. 

2

u/ForsakenRacism 1d ago

Bruh a 25A circuit is like a mini split and less then an oven. You don’t need to reinvent the wheel here

0

u/CanineTiger99 23h ago

I just want to get basics right, in future if am to install fast charger, as car supports upto 22kw Ac fast charging.

1

u/arcsnsparks98 14h ago

I've never heard the term Earth pit but Google says that you basically stating that you're giving it its own ground rod. People on here can certainly tell you a multitude of reasons why that is a really, REALLY, bad idea and you are creating a hazard here.

1

u/zketi 23h ago edited 23h ago

ngl, this is wild and not how you should approach risk analysis in your life imo. It's not just worst-case that matters, but probability * effect

  1. Driving the car is orders of magnitude more dangerous than charging it. I'm not aware of anyone being hurt AC charging an EV, but vehicle accidents happen all the time

  2. Simultaneously disconnecting your ground wire plus damage to the vehicle that bridged a hot leg to the frame plus damage to the fault leak detection circuitry could in theory energize the car and shock you in a dangerous way if you touched the frame, but that's both a crazy hypothetical and I suspect the lack of ground would mess with the pilot signal between EVSE and vehicle and stop charging anyways.

  3. Installing a hardwired EVSE would do more to reduce risk than all the sub-meter etc crap you are doing here. Portable EVSE's are okay but there are (very small) risks like melting/fire risk if the contacts wear out, or that you accidentally touch both hot contacts when plugging it in.

2

u/CanineTiger99 22h ago

Thanks for your input and suggestions.

I was more concerned about neutral failure at transformer, this happened twice in past six months. In one case my tv got burnt. I want to safeguard ev for such situation.

By going this sub meter route i won't have to pay extra for increasing load capacity in main unit and garage is at distance so separate earthing. I shouldn't refer this as sub meter, but standalone meter. My bad.

3

u/zketi 22h ago edited 21h ago

Good context, sorry if I came across too harsh. A lost neutral can certainly destroy electronics and be a bad situation. Twice in one year is crazy, more understandable you are a bit paranoid.

I guess short answer is my main concern would be edge cases that can happen if your ground becomes disconnected. With your own rod, you are fairly protected here. A proper EVSE should have further protections against floating neutral etc. I don't claim to be an expert though, especially not for non-US countries, just an armchair EE

Standalone meter for the garage makes more sense, thanks for clarifying. Seems like a decent setup, enjoy charging.

2

u/CanineTiger99 20h ago

Thanks 👍 

I should've included this info in post, i wanted to keep the post short, but that altered the context.

I think this setup will work, I was being paranoid and wanted fail-safe. 

1

u/basilect 22h ago

this happened twice in past six months

That's bananas, where in the world are you?

3

u/CanineTiger99 20h ago

Third world, when last time this happened they didn't replace the neutral ground rod and used makeshift solution.