Author Topic: Fridge (866.3) makes second ground point.  (Read 235 times)

Offline JohnM

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Fridge (866.3) makes second ground point.
« on: January 18, 2020, 10:54 PM »
NORCOLD Fridge, model 866.3, somewhere in it's wiring, has battery (-) tied to it's frame, AND 120v AC earth tied to the frame, creating a ground loop outside the cabin main electrical (12v fuses & 110vac breakers) panel.


I want to remove the battery (-) earthing on the fridge, and just run it with 110vac earthing. Somewhere, somebody knows where & why the battery (-) was tied to the fridge frame, and if it can be removed, and how to do it.



That is one of those AC/DC/LP mode fridges. Apparently, somewhere in there, by design of NORCOLD, the frame of the fridge is connected to battery (-). The AC cord, which I rarely use, has it's earth screwed into the fridge frame. So I removed that AC earth for now, and tagged it out.



My question is, why would NORCOLD make the fridge metal part of battery (-)? I can understand why it's a good idea to ground the fridge to 110AC earth, but I'm at a loss as why somewhere in the control box, the circuit (I have yet to dive that deep and look) has the frame tied to battery (-).

Offline Rickf1985

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Re: Fridge (866.3) makes second ground point.
« Reply #1 on: January 19, 2020, 10:08 AM »
The fridge controls run on 12 volt. If you take the 12 volts away you will have no fridge. I suppose if all you ever plan to do is run 110 volt you could do that but I don't understand why. Is it causing issues with electronics somewhere? Not being a certified electrician I am not fully in the know about the ground loop thing. All of the 12 volt appliances will have grounds as well as all of the AC powered items. What you are saying is that this particular item has both and that is the issue? If so what does this cause? I am curious, anything like this fascinates me. The reason I ask is that this has been done for 40-50 years. I am getting ready to change my fridge so if this is an issue I would plan on running a dedicated ground from the fridge back to the battery.

Offline Rickf1985

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Re: Fridge (866.3) makes second ground point.
« Reply #2 on: January 19, 2020, 11:16 AM »
It's interesting, I did some research on this subject and there is a LOT of info out there on it. Just on the RV side alone. And ALL of it is conflicting! this thread alone has good info but it is good info on both sides of the fence so which is actually right? (Told you I was truly curious)


https://forum.solar-electric.com/discussion/350524/to-ground-or-not-to-ground-to-chassis

Offline JohnM

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Re: Fridge (866.3) makes second ground point.
« Reply #3 on: January 20, 2020, 05:11 AM »
Hi!


The CHASSIS (the frame of the vehicle) is -12v DC. That stays that way. I don't know if people are discussing not doing that, but it doesn't make a whole lot of sense not to, unless everything in the cabin runs on 110AC or 48vDC, and your entire DC power storage system is a 48v one, while your motor is a -12vDC chassis-ground design. From what i know of DC power, it still works to have your 48vDC system grounded -48v to the chassis, while also having your alternator etc be grounded -12vDC to the same chassis.


I'm saying don't ground your 110vac earth to the chassis. And if it is, remove the ground, and install an RCB/RCBO in your breaker box. It gives more protection to the circuit and any people using it, than a simple earth ground does, and allows your chassis to be ungrounded. I will explain:



Pre-90's, the thinking was by not grounding the chassis to 110VAC earth, meant if you had a live wire (a hot) somewhere that touched the chassis, you would have a live chassis at 110VAC, at 10amps or higher. A person with wet feet, on the grass outside, touching the frame of the vehicle, while shore or generator power was applied, could in that situation, be executed (electrification..). It's the same with an appliance, like a washing machine.


In the above paragraph, is when the only safety equipment available was a fuse, or later,  breakers. Earth ground was thought up so if there was a hot short to the metal case of an appliance (or the whole RV chassis), it would cause a short, and the load would be in excess of the 10amps (or 15 or 30 or 50) that the circuit was rated at. The breaker would then trip, shutting down the circuit.


The above was at a time without electronics, and without GFCI. On europe, they use something called an RCB or RCBO (equivalent to a GFCI with overcurrent protection), on the SOURCE of power, in the electrical box, instead of at the outlet. It looks similar to another breaker, that is installed in series ahead of the usual breaker, and commonly covering more than one circuit, sometimes the whole panel depending on how much power it handles. Since an RV typically handles only 50 or 30 amps, the RCB would cover the whole panel. That has the advantage of protecting all the downstream circuits.


You would, as normally done, run 110vac earth from the power cable wire end to the breaker box, which is also the junction box where the wire terminates. If you have an autotransfer switch ahead of it, that intermediate location is also earth grounded, and also not bonded to the frame.


That is as it should be, as long as that breaker box is isolated electrically from the chassis. You'd have to be extra careful with the line from shore or genset not contacting the vehicle frame - shielding, double-insulation, etc - and you'd have earth travelling back from the house breaker box, along flexible conduit to where-ever the cord enters the vehicle.


Since, in both cases either short or genset, that incoming power line is a short run, it should be easy to keep that part of the circuit isolated with a metal jacket earth ground.


All of your circuits then terminating outside of the breaker box, are protected with a RCB/O, the slightest leakage from the hot to something other than the neutral, will unbalance the RCB and cause it to trip. That is a much safer way than waiting for 10amps to flow downstream, tripping the breaker. When someone touches an RCB protected hot, or power leaking from the hot, the RCB trips faster than the power leakage through the person can damage them, and at a much lower current.


The fridge was built in the mid-80's, before electronics, and probably based on a design well before that time. It was also designed to be installed by itself, potentially in a cabin, or other stand-alone setup. Therefore, they may not have been concerned about co-mingling a -12v ground with a 110vac earth.


I think they should have, though, and opted for the 110vac earth, and isolated the -12v DC. It doesn't make any sense to ground your chassis (of a fridge or appliance vs an entire RV) because your wire runs are short. In other words, to return to the -12vDC, it takes a small amount of wire to complete the run, instead of using the frame as the return. The purpose of grounding a chassis of an RV, is so massive amounts of copper don't need to be run back to the battery, as you could be talking about 6 to 10 gauge wire, over distances of 40 feet. That's a significant savings in weight, also.


It also makes no sense to connect -12vdc to the chassis of the fridge in the design, because most of those fridges are installed in RV's and trailers, which have their own earth ground system. In other words, by having two places where chassis and -12vdc and 110vac earth meet, it creates a ground loop. It should only be in one place, if any.


On the system I worked on, which was developed in the mid-80's, there was a chassis / -12vdc wire running into the breaker box, screwed to the bus bar where the generator earth and all the power lines were grounded. I removed that and pulled it out of the box, putting it directly to the house battery -12vdc terminal, so the -12vdc and 110vac earth weren't co-mingling. That didn't interrupt the connection between -12vdc and 110vac earth, though, because the fridge had a loop between them.


Temporarily, I've removed the 110vac earth wire from the fridge chassis, as it's usually run on LP. Longer term, the solution is to figure out where NORCOLD was using the frame as a -12DC return, and either replace that with wire or leave it un-earthed for the time being, if it's not possible to easily fix the -12DC lines to have the go back to the fridge control box instead of -12DC using the shell.


Offline Rickf1985

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Re: Fridge (866.3) makes second ground point.
« Reply #4 on: January 20, 2020, 09:55 AM »
I have always wondered about this since a member that used to be here but has not been on in a long time, DRMousseau,pointed out that he got shocked one time getting in his RV. He started checking and found he was getting AC voltage between the RV and a ground rod driven into the ground. His solution at the time until he could find the leak was to drive the rod and run a ground wire from the RV to the ground rod. On Military generators it is specified that you drive a ground rod and ground the genset. So isolating the AC completely from the RV frame will in effect protect the occupants from electrocution in the event of an electrical leak or short to ground?

Offline JohnM

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Re: Fridge (866.3) makes second ground point.
« Reply #5 on: January 21, 2020, 01:11 AM »


I'm going to try to address two of your posts more clearly, now that the information has had time to percolate to the residual neurons and I've slept on it at least once.

The fridge controls run on 12 volt. If you take the 12 volts away you will have no fridge.

Above, looks like you flipped the idea of removing the 12vdc with the 110vac.

TLDR my response: The solution with the OEM Stock Norcold fridge, (the easy way) was to remove the screwed-on earth (green) wire from the fridge chassis, OR (the harder way) leave the earth wire connected, and re-wire the entire fridge so that it wasn't using it's frame as a +12vDC return path to -12vDC. IN EITHER CASE, adding a GFCI/RCB to the main circuit breaker/fuse box in the cabin.

end tldr

Removing the earth wire and taping it up, tagging it off, does not remove the 12v, 110vac or LP gas operation. It DOES remove a 1980's and earlier safety design. Whereby, if there was a leakage from the hot 110vac (black) wire to the fridge chassis, a person would NOT get shocked because, ideally, that leakage would go to ground (it would touch the case), and (hopefully when doing so) pull more than 10 amps (whatever the circuit breaker is rated at) and cause the circuit breaker to trip, killing power to the fridge.

In a washing machine example: visualize some interaction between the hot wire in a washing machine, maybe it comes loose, and either the water flowing through it or the metal body it touches. Without an earth ground, someone could touch the washing machine and a nearby dryer (which we presume is properly grounded) or sink (which with older copper pipes is very likely grounded), and the current would pass from one hand to the other, electrocuting them. This is why earth ground was added.

Enter the RCB/GFCI: it uses a magnetic interlock, that is triggered where there is an imbalance in the flow out of power from the hot to the neutral return. It triggers faster than a circuit breaker. A GFCI can get triggered spontaneously when a piece of equipment is faulty, without a loud 'crack' or 'zap', which can make those conditions slightly more hard to determine the cause - particularly if it's protecting an entire electrical box - as they trigger so fast and at such low current, there isn't the traditional smell of smoke to follow.

However, because RV's have simpler and less lines running from their main circuit breaker box, if one GFCI wired into the panel (looks similar to a circuit breaker and should fit into an existing cabin electrical box), protects all of one phase (in the case of a 30 amp hookup) or two phases (in the case of 50amp hook-ups), then it should not be that difficult to track down the problem piece of equipment.

In an older house or RV setup, when GFCI's first came out, GFCI's were installed only in outlets, protected that outlet, and any subsequent outlets that were downstream from that outlet should have been wired into the LOAD side of that GFCI, chaining it off the GFCI function. So if you have GFCI's in your RV outlets, you will also have outlets that do not have a GFCI/test/reset button. If a neighboring GFCI is reset or tripped, that non-GFCI outlet on the same circuit, should go dead, also.

I believe the trend or standard now is to install a single RCB/GFCI in the main electrical box, which trips whenever AC Hot leaving the box leaks. This also protects the AC wiring in the RV, ahead of the outlets and appliances, as it can take much less leakage to cause a fire than what it takes to trip a circuit breaker.

..he got shocked one time getting in his RV. He started checking and found he was getting AC voltage between the RV and a ground rod driven into the ground. His solution at the time until he could find the leak was to drive the rod and run a ground wire from the RV to the ground rod.

... military 'standards' ...

So isolating the AC completely from the RV frame will in effect protect the occupants from electrocution in the event of an electrical leak or short to ground?

What you are describing indicates he had a leak from his 110vac hot to the chassis. Not enough to blow a 110v AC fuse or trip a 110v AC circuit breaker in his cabin's main electrical box. If he had an RCB/GFCI in the main electrical box, it would have tripped before he felt the buzz.*

* With the caveat, if the hot-to-ground fault condition was AFTER his main cabin electrical box. If it wasn't, for instance, if there was damage to his main shoreline power cord, and it was shorting hot to the RV chassis, at some point where the cord was cracked or rubbing, the GFCI afterwards would not have picked it up. However, the SHORE supply should be GFCI protected imo, and that's an upgrade several people may not have.

For instance, humidity can cause a low-level conductance, which the GFCI will pick-up and trip over. But, with only fuses/circuit breakers, enough current could flow through to cause a buzz.

On: military standards
I would personally only do that if the generator didn't have a GFCI. If I'm mounting my own unit, and the genset does not have it's own GFCI, I'm going to make sure that the power cord coming from the generator to the main cabin electrical distribution box in the RV, is double-insulated, or inside of conduit/metal housing that is earth grounded with the earth lead from the generator, and also not connected to the RV chassis.

To reiterate: The incoming shore/genset conduit IS earth grounded, however there's no metal-metal contact between the conduit and the chassis.

The military standards part probably emanates from pre-GFCI protection. There's no reason (I can think of) why you can't have a ground rod in addition to a GFCI. However, if you've noticed, it's required I think, at job-sites to have a GFCI ahead of tools. And several modern tools do not have a ground prong, if they aren't battery-operated already. However, those battery-operated chargers, also don't have a ground prong (although the cases are usually nylon/plastic). The prong is left off, not because someone broke it off, but because in the past, they were broken off, and better insulation along with GFCI, means the leak-to-case (ground) conditions that the ground wire was supposed to protect against, are surpassed by the GFCI.


A typical condition: a tool getting wet.

Quote
So isolating the AC completely from the RV frame will in effect protect the occupants from electrocution in the event of an electrical leak or short to ground?

TLDR Yes.
end tldr

Only if the hot line on that AC is GFCI protected.

If somehow the chassis becomes live because a fault condition, or an appliance does, even to a much less extent than a full connection, the GFCI will sense that there is power flowing out of the hot, that is NOT being returned on the neutral (it's going somewhere else), and trip/disconnect the circuit.

And lastly, searching 'OSHA GFCI' brings up: https://www.osha.gov/SLTC/etools/construction/electrical_incidents/gfci.html

Which reminds me that a GFCI does not protect if some asshat grabs both a hot and a neutral wire. Because in that circumstance, the entire output of the hot is flowing through the neutral.

Offline Rickf1985

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Re: Fridge (866.3) makes second ground point.
« Reply #6 on: January 21, 2020, 09:07 PM »
Good info, So the easy way to make an RV safe is to replace the main breaker with a GFCI, correct? And what is TLDR?

Online TerryH

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Re: Fridge (866.3) makes second ground point.
« Reply #7 on: January 21, 2020, 11:51 PM »
And what is TLDR?
Thank you very much.
I have been following this with interest, but, as per above, TLDR?
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Online TerryH

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Re: Fridge (866.3) makes second ground point.
« Reply #8 on: January 22, 2020, 12:20 AM »
And also, a GFCI Main Breaker will protect everything from the breaker upstream? Not the power pole to the RV, but all else?
How would you best recommend to safe the power directly at and from the 'Park' power pole?
“If you can solve your problem, then what is the need of worrying? If you cannot solve it, then what is the use of worrying?” – Shantideva
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Offline Rickf1985

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Re: Fridge (866.3) makes second ground point.
« Reply #9 on: January 22, 2020, 10:13 AM »
Terry, you can buy (they ain't cheap!) pigtails that are designed to tell you if the power pole is miswired or if the ground is missing. I do not see any that incorporate a GFCI in the setup though. I wonder why?  Here is one below. I would never buy or patronize any of Marcus Lemonis's stores but this is just to show the product. I will also add a link to the manufacturer.


https://www.campingworld.com/ssp-30xl-30-amp-smart-surge-protector-102486.html?cgid=surge-protection#start=6&cgid=outside-rv%2Fpower-protection%2Fsurge-protection


https://www.progressiveindustries.net/ssp-30xl

Online TerryH

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Re: Fridge (866.3) makes second ground point.
« Reply #10 on: January 22, 2020, 07:17 PM »
Thanks Rick. I looked at the Progressive Ind. site and it appears it will only indicate a problem with the park pole or source wiring. It doesn't seem to trip or interrupt the path when there is a problem.
“If you can solve your problem, then what is the need of worrying? If you cannot solve it, then what is the use of worrying?” – Shantideva
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