Intro and inverter ground fault question

steverstever Registered Users Posts: 5 ✭✭
Hi folks, Steve here from BC Canada. I have a 17 Bigfoot and recently added a Samlex Inverter PST-2000-12 and transfer switch.
I just built a new pad on the other side of my house to store the trailer. Of course there was no power there so I added an external plug, GFCI, to be compliant on an outside wall of the house...the previous location had a non GFCI outlet in the inside wall of the garage. The Bigfoot has a 30amp external power cord and I use an adapter to plug it in to the house supply. It connects into a Siemens main breaker box that has a separate ground bar and neutral bar. There is no neutral ground bond there. The new GFCI outlet trips every time I plug the trailer in. Tested it with a trouble light and the outlet works fine. 
I tested the neutral and ground on the trailer plug and discovered i have continuity. So I went searching for a ground fault.
For the rest of the picture, the 30a main feeds to a Boondocker Transfer switch, as does the Inverter. Priority goes to external supply. But the transfer switch has a built in delay before it switches from the inverter supply to the external supply.

The output from the transfer switch goes to an AC subpanel built into the Parallax charger controller, which in turn flows through a number of breakers for the fridge, microwave and outlets. This AC subpanel has a separate neutral bar and a separate ground bar. No intentional neutral ground bond here either. The 30amp main also subs to a 15amp breaker that feeds directly to the charger controller, to supply the 12v conversion.
I tested everywhere for neutral ground continuity, disconnecting and reconnecting, and as soon as I disconnected the inverter, my ground fault disappeared. The Samlex has a panel that has a GFCI outlet in it (not used) and the panel is removed to access the terminals where I connected the hardwire to hot, neutral, and ground. I removed the panel, and there was continuity between the neutral and ground. I think this is the source of my problem tripping the GFCI. 
The transfer switch delay allows the external GFCI to detect the neutral ground bond in the inverter, concludes ground fault, and trips. 

I searched in this forum, and everywhere else I could to try and decide what to do. 
Since I use external power from the grid, as well as a Honda 2000 Inverter genny, I decided to remove the neutral ground bond from the Samlex. Easy...just had to remove the green ground wire from the neutral slit on the GFCI outlet.
So there is no neutral ground bond in the RV. Re-connected everything, tested, and no ground fault. Plugged into the external GFCI and it didnt trip. The Samlex has a case ground lug that I have connected to the Bigfoot common ground.
The inverter works fine. Everything seems to be working fine.

my bad...I guess Ive had this problem since I installed the inverter, but never knew it until I plugged into a GFCI outlet.

My question: Have I created a new problem for myself by removing the neutral ground bond from the Inverter? Is it safe?
Samlex clearly documents that there is a neutral ground bond in the unit, but says nothing about whether it should be removed if installing in an RV that also uses external power.  I have to be able to plug into a campsite that may or may not have GFCI outlets.

Thanks for reading through my longwinded story.....am I good to go?




Comments

  • mcgivormcgivor Solar Expert Posts: 2,506 ✭✭✭✭✭
    Interesting story, what I'm having trouble understanding is, how the grid source is connected to the inverter output before the transfer is made, they should be isolated at all times in a break before make mode. The only thing I can think of is the internal voltage monitoring  circuitry which initiate the transfer leaks enough current to cause the GFCI to trip, typically 5mA.

    Check with a current CEC code book if the GFCI on the house is actually needed, if there is an overhang of a given amount it may not be necessary, going on memory 30 years back doing residential, things may have changed, commercial was my field, different rules.

    As it stands, the trailer whilst on inverter power, will have a floating neutral, the grid power will provide a neutral bond, a generator may  have an internal neutral bond but only effective if chassis grounded, in any configuration there should only be a single neutral ground bonding point, for any given source.

    Should the GFCI not be needed on the house and everything works without, reconnect the Samlex bond and chassis ground the inverter, if GFCI protection is desired do so at point of use, replace the existing recpticals, however GFCI recpticals can be a nuisance, if the whole system hinges in one device, the whole system is lost when a trip occurs.


    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system. 
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
  • EstragonEstragon Registered Users Posts: 3,127 ✭✭✭✭✭
    My boat inverter has an internal transfer switch which operates in a similar way.  When it senses shore power, it switches from inverting to battery charging mode, and passes shore power through to other loads.

    What I don't grok in your case is why you got n/g continuity on the shore power cord.  A transfer switch for a mobile shore power application should switch both line and neutral, so with the switch in the inverter position, the neutral should be open on the shore side.  That you got continuity leads me to think the switch is only switching line.

    If so, I'd personally not use it, or if I did I'd be sure to test shore power for polarity etc before plugging in.  RV parks, marinas, etc aren't always meticulous in their wiring.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • steverstever Registered Users Posts: 5 ✭✭
    edited November 2018 #4
    mcgivor said:
    "Interesting story, what I'm having trouble understanding is, how the grid source is connected to the inverter output before the transfer is made, "
    the transfer switch is wired so that the default in a nopower position is the inverter. If the switch detects external power, it moves the relay arms on both line and neutral, disconnecting the inverter, so i never have 2 power sources connected at one time. There is a 10 second delay in the switch, supposedly to give external power such as a genset time for the voltage to level and stabilize, avoiding putting a load on it prematurely.
    it is during the 10 second delay that the gfci outlet thinks there is a problem. It trips instantly.

    the ground wire hardwired into the inverter ac terminal is connected to common ground with all the other ac circuits. I have no way to switch the ground.

    there is an overhang, but our local codes have changed, requiring gfci. I could switch back to a non gfci outlet, but if during travel, i had to plug into a gfci circuit, i have no control over where i might run into one, and would be stuck without power. Some places wont let you run a generator.

    the transfer switch is wired with inverter default, but priority switches to external if present, intentionally, on the advice of the switch supplier. And it seems to be the "normal" approach in RVs. I guess i could reverse the order, and then the inverter would be isolated, but if on the inverter, and grounds are common, if im still plugged into an external source, then the ground fault will appear to the external sources.
  • steverstever Registered Users Posts: 5 ✭✭
    Estragon said:
    My boat inverter has an internal transfer switch which operates in a similar way.  When it senses shore power, it switches from inverting to battery charging mode, and passes shore power through to other loads.

    What I don't grok in your case is why you got n/g continuity on the shore power cord.  A transfer switch for a mobile shore power application should switch both line and neutral, so with the switch in the inverter position, the neutral should be open on the shore side.  That you got continuity leads me to think the switch is only switching line.

    If so, I'd personally not use it, or if I did I'd be sure to test shore power for polarity etc before plugging in.  RV parks, marinas, etc aren't always meticulous in their wiring.
    the transfer switch has two relays in it, one for line, and one for neutral. Grounds are common. I will go back in there and do further testing to verify and report back. 
    I do have a circuit polarity /surge protector plug expressly for use in RV parks where wiring may be an issue.

    Thanks all for the comments, questions. 
  • steverstever Registered Users Posts: 5 ✭✭
    Ok, here is a possibility. 
    The ac grounds are all common.
    inside the Parallax charger converter, there is an AC subpanel used to feed all the appliances that has a common neutral bus and a separate common ground bus. The common neutral bus has connection to the transfer switch, and inturn, to the inverter in default mode. When i ran the ac supply into the charger converter for the 12v side, it bypasses the transfer switch, so that im only charging when on an external source.  i borrowed one of the unused circuit breakers for it, but  connected the neutral input to the common neutral. Line is isolated but neutral is not!  I think i should remove the charger converter neutral input from the common neutral and just isolate it directly into the charger converter. Going to test that now.
  • steverstever Registered Users Posts: 5 ✭✭
    Bingo. By incorrectly connecting the charger converter neutral input to the common neutral in the AC subpanel, the shorepower n/g continuity was basically going backwards from the inverter n/g bond, thru the transfer sw in default mode, to the common neutral in the ac subpanel, then out back to the main shorepower breaker through the separate charger converter circuit. 
    I isolated the charger converter neutral connection with a marrette, then reconnected the n/g bond in the inverter, and voila, no ground fault. Gfci house supply doesnt trip. 

    Clearly this was my mistake and not a Samlex problem. 
    This had me perplexed but thanks to both Mcgivor and Estragon, you asked some questions that forced me to re-think through the circuits, and allowed me to discover the error. Sincere gratitude and thanks to both, and to this forum for giving me an outlet to figure this out.

  • mcgivormcgivor Solar Expert Posts: 2,506 ✭✭✭✭✭
    Good to hear the problem is solved, sometimes all that's needed is a little food for thought, glad to have helped..
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system. 
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
  • Cosuper_EnergyCosuper_Energy Registered Users Posts: 6 ✭✭
    Estragon said:
    My boat inverter has an internal transfer switch which operates in a similar way.  When it senses shore power, it switches from inverting to battery charging mode, and passes shore power through to other loads.

    What I don't grok in your case is why you got n/g continuity on the shore power cord.  A transfer switch for a mobile shore power application should switch both line and neutral, so with the switch in the inverter position, the neutral should be open on the shore side.  That you got continuity leads me to think the switch is only switching line.

    If so, I'd personally not use it, or if I did I'd be sure to test shore power for polarity etc before plugging in.  RV parks, marinas, etc aren't always meticulous in their wiring.
    could you tell me your boat inverter brand? the power, voltage and other parameters about this boat inverter
  • EstragonEstragon Registered Users Posts: 3,127 ✭✭✭✭✭
    It's a 12Vdc Xantrex, 2.0 or 2.5kw 120v output MSW from c.2010.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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