Success with 2-wire charging?

[wwhitney]

I still stand by my original advice - If you're going to mickey mouse some stupid crap, at least get that ground connected to SOMETHING. Even a crappy ground will give the EVSE an opportunity to trip the GFCI (through the crappy ground) BEFORE you touch the car.

I'm not convinced that effectively attaching a ground rod to your car, when there's no EGC going back to the main panel, increases personnel safety. I'm fairly sure that for any electrical equipment intended to be attached to an EGC going back to the main panel, attaching the ground pin instead to a local ground rod will not enhance personnel safety and may decrease it.

Cheers, Wayne

 

[btmspox]

I looked outside and there are only 2 wires coming down from the power pole. I assume those are 2 legs of 120 Volts and they use earth as ground.

Typically there's a third wire referred to as a messenger cable that the two 240/120 split phase wires are supported by. It can easily be overlooked as simply a support cable but it is the neutral wire and will come in your service entrance. In the main panel for a structure the ground and neutral are bonded together, which can be confusing if you're trying to understand just by looking in a panel, but it is there.

If you didn't have this third wire, you'd experience lots of bizarre behavior from your 120v loads, like light bulbs dimming, from the load being unbalanced between the two legs due to having a poor return path to the transformer. If that was the case you would really need to put your EVSE plans on hold until you could get that sorted out.

 

[Pigwich]

I'm not convinced that effectively attaching a ground rod to your car, when there's no EGC going back to the main panel, increases personnel safety. I'm fairly sure that for any electrical equipment intended to be attached to an EGC going back to the main panel, attaching the ground pin instead to a local ground rod will not enhance personnel safety and may decrease it.

Cheers, Wayne

Hi Wayne,

I'm intrigued (no, sarcasm, honestly here) as to the theory and conditions that may cause a decrease in personal safety by a local ground. I know that in some cases having multiple grounds can cause current to flow over the grounds, which is I believe what's referred to as a ground loop, and I know this is important in some cases (especially analog signaling, hence the use of differential signaling in critical applications) but in a two-wire system, in the absence of a second ground where one should be (in the plug) I don't see how a loop could be formed by grounding the charger locally, so I guess that rules out a ground loop?

My charger at home is firmly bonded to the service entrance box (which is bonded to rods) by a piece of 6 ga copper, so no worries there, but god knows what's going on in other houses. I'm interested in making this discussion as productive and informative as possible.

 

[LeftieBiker]

On a related note, I have a 7500 watt dual fuel backup generator. It requires a grounding rod or other solid ground. My house and garage have a copper cable lightning rod setup. Can't I simply use the nearest lightning rod grounding cable to ground the gen?

 

[wwhitney]

I'm intrigued (no, sarcasm, honestly here) as to the theory and conditions that may cause a decrease in personal safety by a local ground.

Sorry to have been slow to respond, I've been traveling.

Before I directly answer your question, let me first give some important background. The third wire on a receptacle or plug that we call the ground really has very little to do with the earth. This Equipment Grounding Conductor, or EGC, would more properly be called an Equipment Bonding Conductor, or EBC. Its job is to bond together all the conductive parts of an electrical installation that aren't supposed to conduct current during normal operation. In a "grounded" system, as is typical, this EGC is further connected to one of the circuit conductors (the "neutral" or "grounded conductor") at one point in the system (and one point only), the main service panel.

As such, should any of the other circuit conductors (the "hots") inadvertently short out to the non-current carrying conductive parts, a circuit is completed that should trip the circuit breaker protecting the wires. On a grounded system, without that EGC, in the event of a fault, the conductve parts would instead stay at an elevated voltage until someone or something that is also grounded comes along and completes the circuit, likely at a high enough resistance that current would flow but the circuit breaker wouldn't trip. That would be very dangerous.

Thus, a ground rod can not create an EGC, as it isn't bonded to the grounded service conductor at the main panel. In the event of a direct fault form a hot conductor to a ground rod, the current that will flow won't be enough to trip a circuit breaker. (Earth electrode resistance is on the order of 100 ohms (maybe 10 to 1000 ohms) while tripping a 15 amp breaker at 120V requires a resistance under 8 ohms.)

Let me stop here for a moment.

Cheers, Wayne

 

[wwhitney]

Now, in the absence of any GFCI, what hazards could using a fake EGC (connected only to a ground rod connected) provide over a simple 2 wire circuit? For one thing, in the event of a hot to fake EGC fault, it increases the danger area from just the normally non-current carrying metal parts of the equipment to the earth around the ground rod. Maybe that's it, but I bet with some thought we could come up with other scenarios.

The presence of the GFCI in an EVSE mitigates these hazards somewhat, because a 20,000 ohm connection should be sufficient to trip a GFCI at 120V, and earth electrode resistance is typically less than that. However, the cord of the EVSE is still not GFCI protected, so there is still some increased risk due to a fault in the cord from hot to fake EGC. If the EVSE is hanging by its maximum 18" cord, the strain put on the cord makes that a not-so-remote possibility.

The upshot is that the EGC has very little to do with earth or with ground rods.

Cheers, Wayne

 

[wwhitney]

On a related note, I have a 7500 watt dual fuel backup generator. It requires a grounding rod or other solid ground. My house and garage have a copper cable lightning rod setup. Can't I simply use the nearest lightning rod grounding cable to ground the gen?

Why does the generator require a grounding electrode? What is being powered by the generator? Does it have receptacles on it, or is it hard-wired? Does the generator have a neutral-EGC bond?

Cheers, Wayne

 

[LeftieBiker]

On a related note, I have a 7500 watt dual fuel backup generator. It requires a grounding rod or other solid ground. My house and garage have a copper cable lightning rod setup. Can't I simply use the nearest lightning rod grounding cable to ground the gen?

Why does the generator require a grounding electrode? What is being powered by the generator? Does it have receptacles on it, or is it hard-wired? Does the generator have a neutral-EGC bond?

Cheers, Wayne

I have a generator connection port on the front porch, a 25' 240 volt locking cable, and an either/or interlock on the main panel. So the gen would power the hole house, more or less. I don't think I've ever seen a recently built gen that didn't have a ground screw, and a warning in the manual to connect to a ground circuit or stake. Our little Champion (Chinese Honda clone) has the screw for grounding.

 

[wwhitney]

I have a generator connection port on the front porch, a 25' 240 volt locking cable, and an either/or interlock on the main panel.

If you have a generator connection port on the front porch (a 4-wire inlet), then when the generator is hooked up, it is already connected to the house's grounding electrode system (ground rods, etc). So there is no need for any additional grounding electrodes. The generator will need to have its ground and neutral isolated, in which state it won't be suitable for standalone use, only for use when connected to your house.

Cheers, Wayne

 

[Pigwich]

Now, in the absence of any GFCI, what hazards could using a fake EGC (connected only to a ground rod connected) provide over a simple 2 wire circuit? For one thing, in the event of a hot to fake EGC fault, it increases the danger area from just the normally non-current carrying metal parts of the equipment to the earth around the ground rod. Maybe that's it, but I bet with some thought we could come up with other scenarios.

The presence of the GFCI in an EVSE mitigates these hazards somewhat, because a 20,000 ohm connection should be sufficient to trip a GFCI at 120V, and earth electrode resistance is typically less than that. However, the cord of the EVSE is still not GFCI protected, so there is still some increased risk due to a fault in the cord from hot to fake EGC. If the EVSE is hanging by its maximum 18" cord, the strain put on the cord makes that a not-so-remote possibility.

The upshot is that the EGC has very little to do with earth or with ground rods.

Cheers, Wayne

Hey Wayne - Thanks for the explanation. Yeah, this all does make sense. I've heard that in rural areas, where they use single conductors with earth return for power distribution, they need to drive LOTS of ground rods all over the place, otherwise cows get electrocuted if the "hoof to hoof" voltage gets too high. What a way to go, huh? But those voltages are on the order of a dozen KV, so it makes killing cows a much more straightforward process.

Now, I'm drawing out this circuit, and with a fault of one leg shorted to the chassis, really we just have two resistors in parallel to the ideal, theoretical ground, one being 100 ohms (the fake ground rod) and the other being my body at 500 ohms at the absolute worst. I'd still see full voltage, and the fake ground rod would still see full voltage, so no benefit there.

Oddly however, having the earth potential rise up around said ground rod decreases the voltage differential between the car and the person.... Maybe we suggest putting the grounding rod as close to the charging door of the car as possible? :lol: :lol: :lol: Only problem is that your balls will get zapped if you take long enough strides as you walk up to the car, and who needs that??? Glad the GFCI will still help us though...

So I guess this leaves everybody's original advice to the original poster intact and well - Get a real outlet, or risk getting your balls zapped and worse.

 

[LeftieBiker]

I have a generator connection port on the front porch, a 25' 240 volt locking cable, and an either/or interlock on the main panel.

If you have a generator connection port on the front porch (a 4-wire inlet), then when the generator is hooked up, it is already connected to the house's grounding electrode system (ground rods, etc). So there is no need for any additional grounding electrodes. The generator will need to have its ground and neutral isolated, in which state it won't be suitable for standalone use, only for use when connected to your house.

Cheers, Wayne

While I was waiting for you to reply I thought more about it, and came to pretty much that conclusion: that the connection port provides all the ground needed, and the ground connection on the gen is for pretty much all other, standalone, use of the gen. I'm not sure, though, what you mean by "The generator will need to have its ground and neutral isolated, in which state it won't be suitable for standalone use..." Wouldn't that just be not connecting the ground when used for the house, and connecting it (I'm still thinking to the lightning rod cables) to ground when/if I need to use it standalone?

 

[wwhitney]

Leftiebiker, what is the make and model of your generator?

Cheers, Wayne

 

[LeftieBiker]

It's a cheap Home depot Special. GP7500DEB, 6,200-Watt Propane (LPG) or Gas Powered Generator. I had read in the reviews that it was surprisingly good for the price, but was often damaged in shipping, so it was better to pick it up at a store. I did, and... it was damaged in pre-store shipping. I had to replace a wheel, re-bend the frame back to mount the wheel, and replace the starting battery. The manufacturer provided the parts. It's worked fine in test runs, but after years of occasional 3 hour+ outages, once I got that we have had none in two years. So I guess it's doing its job. ;-)

 

[wwhitney]

It's a cheap Home depot Special. GP7500DEB, 6,200-Watt Propane (LPG) or Gas Powered Generator.

OK, there is a mismatch between the type of transfer equipment you have and the type of generator you have.

Recall that the EGC is really a bonding conductor and its connection to earth is of limited importance. And the EGC needs to be bonded to a circuit conductor (the neutral for a voltage system that has a neutral, like the US residential 120V/240V system) so that when a hot conductor shorts to the EGC, enough current flows to trip the circuit breaker. This bond needs to be located at only one place in the electrical system; if it occurs in two or more places, then the EGC is parallel with the neutral, and current will flow on the EGC during normal operating conditions. Having current flow on the normally non-current carrying metallic parts of the electrical system is a safety hazard.

Your main panel has the neutral-EGC bond for usual grid supplied electrical operation. Your transfer equipment is a mechanical interlock between two breakers, the main breaker (for energy from the grid) and a breaker for a feeder from the a generator. This means only the hot conductors are switched, not the neutral.

A stand-alone generator with receptacles on it provides hot(s), neutral, and EGC via the receptacles. In order for the receptacle EGC to function, such a generator must have a neutral-EGC bond within it. You can verify this with the generator off by simply measuring the resistance with an ohmmeter between the neutral and EGC pins on a receptacle.

Now when you hook your generator up to your inlet using your transfer equipment, you have a system with two neutral-EGC bonds in it. While running on generator, some of the neutral return current will flow through the EGC, which is a safety hazard. In order to use a generator with your type of transfer equipment, you need a generator in which you can remove the neutral-EGC bond (and I didn't see any discussion of being able to do that in the manual for your model.) You'd need to restore the bond whenever running the generator stand-alone.

The proper solution to using a generator with a neutral-EGC bond to supply a house is to use transfer equipment that will switch the neutral. That will isolate the main panel's neutral-EGC bond from the electrical system when running on generator. You can read more about that in the UL category description page for "Engine Generators for Portable Use, FTCN" here:

http://productspec.ul.com/document.php?id=FTCN.GuideInfo

Cheers, Wayne

 

[wwhitney]

P.S. As to the original question of using a ground rod with a stand-alone generator, it is close to useless. Earth resistances are too high to have a benefit in tripping circuit breakers at 120V. The main benefit of earthing an electrical system is for higher voltages. In a typical residence, this can occur with an indirect lightning strike imposing higher than normal voltages on the grid, or with a primary (high voltage) utility line falling on the secondary (120V/240V) utility lines, e.g. from a tree limb breaking. For a stand-alone generator these don't seem too important.

Cheers, Wayne

 

[LeftieBiker]

Just so we're on the same page: I don't have a typical transfer switch. I have a generator inlet port that is connected to the main panel though a 30 amp 240 volt breaker. There is a sliding mechanical interlock installed on the panel that prevents both the main 200 amp breaker and the generator feed breaker from being on at the same time - it's one or the other, depending on the position of the interlock plate. I just got up and am a little groggy, so are you saying that I need to be able to provide a separate Neutral feed from the gen (I'm using a NEMA L-6 30 cable from the 240 volt twist-lock port on the generator to the twist lock inlet port on the house) and a way to take the panel's neutral connection out of the circuit whenever the gen is providing power to the panel? I've never seen anything about this is in what I've read about using a 240 volt generator connection...

 

[wwhitney]

don't have a typical transfer switch. I have a generator inlet port that is connected to the main panel though a 30 amp 240 volt breaker. There is a sliding mechanical interlock installed on the panel that prevents both the main 200 amp breaker and the generator feed breaker from being on at the same time - it's one or the other, depending on the position of the interlock plate.

Right, that's what I understood from your initial description. This setup only switches the two hot conductors (that land on the breakers), it doesn't switch the neutral conductor at all. So you would call it a "double pole" transfer switch.

With a double pole transfer switch you need to use a generator that does not have a neutral-ground bond on the generator. All portable generators with receptacles will have that neutral-ground bond, it is required when using the receptacles for stand-alone power.

If you used a 3 pole transfer switch that switched both hots and the neutral, then you could use your existing generator as is.

(I'm using a NEMA L-6 30 cable from the 240 volt twist-lock port on the generator to the twist lock inlet port on the house)

That should be a NEMA L14-30 cable, two hots, a neutral, and a ground. That's what the manual shows.

Your options for code compliance and safer operation going forward are: (a) modify your generator (b) get a different generator or (c) install a 3 pole transfer switch.

Cheers, Wayne

 

[LeftieBiker]

Can I install a disconnect switch for the neutral bond? If no, then I may disable the outlets and de-bond it. Where is the connection between G & N? Also, if the gen isn't grounded, why does it matter if G & N are connected? Wouldn't the gen just become part of the house circuit, albeit a somewhat more vulnerable part?

 

[wwhitney]

Can I install a disconnect switch for the neutral bond? If no, then I may disable the outlets and de-bond it. Where is the connection between G & N?

I don't know anything about that generator, it might be possible to modify it so that the generator's neutral-EGC bond is switchable. You'd need to have a way to ensure that when connected to the house, the generator's neutral-EGC bond is off, but when used standalone, the generator's neutral-EGC bond is on.

Also, if the gen isn't grounded, why does it matter if G & N are connected? Wouldn't the gen just become part of the house circuit, albeit a somewhat more vulnerable part?

Again, the issue is having an electrical system with more than one Neutral-EGC bond in it. It causes neutral current to flow on the EGC, which is unsafe. If it's not clear yet, draw yourself a little diagram with a 120V source (one hot, one neutral), a neutral-EGC bond at the source, some loads, and another neutral-EGC bond elsewhere. Current will take all available paths, so if it can return via the neutral and via the EGC simultaneously, it will.

BTW, there is one rather simple solution to the issue of having neutral-ground bonds at both the generator and the house, but I'm not sure that it is safe or allowed. Namely, the EGC could be omitted in the cord connecting the generator to the house, so that the cord is just two hots and a neutral. Everything would still be properly bonded to an EGC, it's just that the generator's EGC system and neutral-EGC bond would be isolated from the house's EGC system and neutral-EGC bond.

This is an allowed, grandfathered configuration for feeders from one building to another (e.g. a garage or shed) where there is no other metallic path between the buildings. But the 2005 or 2008 NEC disallowed it for new installations. It is also the configuration between the utility's transformer and your house. I'm sufficiently unclear on the subtleties to say whether it is a reasonable solution for your generator, so you'd need to find someone more knowledgeable than me to sign off on it.

Cheers, Wayne

 

[LeftieBiker]

Thanks for the clear explanation. I'll look into it further.