wwhitney
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Re: charging on generator

Wed Jul 12, 2017 9:12 am

There are several reasons that this topic is so confusing. First, the word "grounding" can mean "earthing" or "bonding" depending on context. By "earthing" I mean connecting some part of the electrical system to the Earth itself. This can be beneficial in the context of lightning or swimming pools or a few other situations.

By "bonding" I mean connecting together normally non-current carrying but conductive parts of the electrical system. For example, the metal frame of your refrigerator is bonded to the metal frame of your stove since both of them are connected to an EGC via their 3 prong plugs. Bonding in this sense is always required. Collectively these bonded metal parts are the "ground" whether or not they are actually connected to Earth.

Second there are three different options with respect to "grounding the system", which means whether one of the circuit conductors is intentionally connected to ground. In an "ungrounded system" there is no such connection; this is also referred to as leaving the ground "floating". In a "resistance grounded system", there is such a connection, via a resistor; this will stabilize voltages between the bonded metal parts and the circuit conductors, but won't allow any significant current to flow. Lastly, there is a "grounded system" in which one circuit conductor is solidly connected to the ground.

Furthermore, there is the question of whether the ground should also be connected to the Earth through a "grounding electrode" such as a ground rod. So we can say that the system is "earthed" or "unearthed".

In the US, residential electrical wiring is a grounded, earthed system. But a floating portable generator without any grounding electrodes would be an ungrounded, unearthed system. Both systems can be safe--for a standalone portable generator (not connected to any house wiring,) it is unclear to me whether there is much safety difference between a grounded and ungrounded system.

With respect to standalone portable generators, I'm not aware of any safety advantage to earthing the system. Maybe there is a scenario with a long extension cord lying on the ground and a lightning strike, but I haven't thought about it.

This thread started because an EVSE that does a "ground check" will not work on an ungrounded system like a floating portable generator. So to get such an EVSE to work you need to switch to a resistance grounded system or to a grounded system. If you believe that for standalone portable generators, an ungrounded system is safer than a grounded system, then switching to a resistance grounded system will let the EVSE work while otherwise retaining most of the features of a ungrounded system. If you don't see any difference in the safety of an ungrounded versus a grounded system on a standalone portable generator, then switching to a grounded system is simpler.

Cheers, Wayne

GerryAZ
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Re: charging on generator

Thu Jul 13, 2017 8:02 pm

wwhitney wrote:
GerryAZ wrote:It should be noted that the resistor will limit ground fault current below the trip levels of GFCI receptacles or the EVSE so they will not trip if there is a true ground fault on the load circuit.

While that is true, if the current flow is below 6ma, there is no shock hazard.

GerryAZ wrote:If actual GFCI protection is needed, then the generator frame must be grounded with a ground rod or connection to a building ground and the neutral must be connected to the generator ground with a wire instead of a resistor.

Installing a neutral/ground bond has the advantage that in the event of a ground fault, the breaker or GFCI will trip. Connecting the generator frame to an earth electrode just expands what counts as a ground fault--it's not clear to me it enhances safety.

GerryAZ wrote:I use the solid ground plug for backup power at the house with the generator frame grounded to the house power panel ground. I leave the generator floating (neither plug inserted) for general portable use.

If "backup power at the house" means connecting the generator to the building wiring, then you probably DO NOT want to use the solid ground plug in that situation. Unless your transfer equipment switches the neutral, then when the generator is connected to the building wiring the resulting system already has a ground/neutral bond at the house's main panel. Adding an additional neutral/ground bond at the generator would result in undesirable neutral current on the grounding system.

Cheers, Wayne


Wayne,

First, I guess I should have been more clear with my explanations. You are correct there is no shock hazard with the resistor connection because the ground fault current is limited to a value below what is considered safe.

Second, I really like your clear explanations of grounding and bonding in your follow up post.

I do not connect the generator to the house wiring for backup power. I just use a heavy duty extension cord to plug in critical items like the refrigerator, a few table lamps, and maybe a TV. The refrigerator frame is connected to the house grounding system through the water line for the ice maker, the TV is connected to the house grounding electrode through the grounded shield of the cable coax, and the table lamps have two-wire polarized cords with exposed metal parts bonded to the neutral conductor. I prefer to connect the generator frame to the house grounding electrode and use my solid neutral grounding plug so that any fault currents from equipment failure or transients have a low impedance path to ground instead of possibly flowing through the refrigerator or TV. I believe the isolated (floating) neutral operating mode is safe for running a few critical loads with an extension cord, but I am trying to minimize the possibility of equipment damage.

Cheers,
Gerry
Gerry
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Silver LEAF 2015 SL purchased 2/7/2015

drdnizz
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Re: charging on generator

Sat Sep 16, 2017 11:48 pm

Hey everyone, I am trying to use an inverter to trickle charge my 2013 nissan leaf from an ungrounded off-grid PV setup. Initially, I got a ground fault error reading on the charger. I tried the ground to neutral bond plug (with a straight wire) at the inverter and that did not work. Then I plugged the neutral-ground plug into a power strip and the charger into the power strip. This initially seemed to work and car started to "charge" but did not pull more than 43 W from the inverter. After about 10 minutes, the charger reads a fault and stops trying to charge. The system is not grounded. Any ideas?

GerryAZ
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Re: charging on generator

Sun Sep 17, 2017 2:05 am

Can you post information about the inverter? Are you using Nissan 120-volt EVSE?
Gerry
Silver LEAF 2011 SL rear ended (totaled) by in-attentive driver 1/4/2015 at 50,422 miles
Silver LEAF 2015 SL purchased 2/7/2015

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Marktm
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Re: charging on generator

Sun Sep 17, 2017 7:36 am

Out of curiosity - has anyone tried a 240 VAC (split phase?) Honda Inverter Generator to charge a leaf? The EU7000iS unit has the L14-30r outlet which indicates a separate neutral and ground circuitry (which could be "bonded" internally?). I wonder if this generator can provide the full wattage charge (Leaf charger limited) without any ground detection problems?

A very expensive unit - but considering what you get - maybe worth it for a backup generator?

BTW, I have an OpenEVSE CC, so I can turn off the ground detection circuitry - which does work when using a UPS (uninterruptible power supply) that is a "floating ground" design.
2012 Leaf SL; 36,000 miles. Battery replaced November 1st, 2016.
Rural cabin with 6750 watts Grid tied PV. Off-grid solar Leaf charging capable (level II).

GerryAZ
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Re: charging on generator

Sun Sep 17, 2017 6:50 pm

Marktm wrote:Out of curiosity - has anyone tried a 240 VAC (split phase?) Honda Inverter Generator to charge a leaf? The EU7000iS unit has the L14-30r outlet which indicates a separate neutral and ground circuitry (which could be "bonded" internally?). I wonder if this generator can provide the full wattage charge (Leaf charger limited) without any ground detection problems?

A very expensive unit - but considering what you get - maybe worth it for a backup generator?

BTW, I have an OpenEVSE CC, so I can turn off the ground detection circuitry - which does work when using a UPS (uninterruptible power supply) that is a "floating ground" design.


I suspect the EU7000iS comes with neutral floating since most consumer generators are configured that way. A single resistor or solid bond between neutral and ground would make it work with an EVSE that checks for proper ground. My 3000iS will charge my Leaf fine at 120 volts with a single resistor or solid bond between neutral and ground (I made up several bonding plugs with either resistor or solid bond to make that connection). I also have a 3 kVA transformer that has 120-volt primary and 120/240-volt 3-wire secondary so I can charge at 12 amperes on 240 volts with the generator when necessary (transformer plugs in to 30-ampere twist lock receptacle on generator and has 20-ampere, 4-wire twist lock receptacle for output).
Gerry
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Silver LEAF 2015 SL purchased 2/7/2015

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LTLFTcomposite
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Re: charging on generator

Mon Sep 18, 2017 6:47 am

Marktm wrote:A very expensive unit - but considering what you get - maybe worth it for a backup generator?

Based on my experience with hurricane outages in the event you ever have to actually use the thing it will quickly become apparent why a Honda generator is worth the premium it commands vs some random thing from a big box store. Bargains are best avoided in parachutes and generators.
LTL
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drdnizz
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Re: charging on generator

Tue Sep 26, 2017 2:06 am

Phil, will your 1/2 W resistors plug work with a 120 V AC inverter. The inverter does not have a ground-neutral bond.
I am having trouble charging my 2013 Nissan leaf from my pure sine inverter. The 24VDC inverter is pulling from a 24V battery bank. The PV system and the battery bank setup is not grounded. I am getting a ground fault reading (blinking green light). After reading some forums, I tried to provide a ground-neutral bond between the AC output of the inverter and the 120V charger. The car indicated it was charging but it did not. The inverter read only 43W output and then read a fault (red light) shortly after. How do I properly ground the system to get the charger to work right? Thoughts?

BrockWI
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Re: charging on generator

Tue Sep 26, 2017 5:15 am

What is the inverter your using? Can you check the output voltage? Often if there is voltage sag under starting up load (when the car actually starts charging) it will drop out of charge mode and wait for the voltage to stabilize and try again. Also if it isn't a pure sine wave the car might think something else is wrong and not try to charge, but that usually causes the evse to give you a fault flag.
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JohnG
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Re: charging on generator

Sat Sep 30, 2017 10:58 pm

This is my first post.
I have been reading about all the issues that seem to be involved in charging with a generator, so I decided to take the bull by the horns - and won!
I started my Honda EU2000i, switched off the ECO mode, connected my "Khons" charger to it, set the charger to 10 Amps, and connected this to my Leaf Input port.
The generator took up the load, and seemed quite happy to pump 2Kw into my batteries! I was thrilled!
I ran it for 5 minutes without any problems.
I hope this is useful to others.

In case this makes a difference to the electrical configuration, my 2014 Leaf was imported from Japan (6 weeks ago).

Incidentally, we live totally off-grid on Great Barrier Island, New Zealand, and very seldom use the generator!
We have 2.4Kw Solar input, and regularly charge our Leaf at 1.9Kw for 4-5 hours - totally free of charge - using the same "Khons" charger.

We are thrilled with our Leaf!

Regards
JohnG

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