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Old 07-20-2015, 08:21 AM   #21
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Originally Posted by mike837go View Post
I will argue "There is no connection between the GFI system and the 12 volt system."

All 3 electrical systems share a common ground. 12VDC negative is connected to 120VAC ground. So the converter's 12V+ is routed through the fan to 12DC- (ground) and the GFCI sees that flow as a ground fault.

Why the rest of the factory 12VDC items don't trip an external GFCI is beyond me.
"connection" as in function, not physical wire. But, even so, the GFCI is not connected to ground.

GFCI does not see ANY 12 VDC current flow. GFCI only sees 120 VAC current on the hot and neutral. Has nothing to do with the ground. What triggers a GFCI to trip is current went from the hot to ground without returning on the neutral. Has nothing to do with the 12 VDC system.

Additionally, the reason a GFI will trip when an RV is connected to it is because the ground and neutral are bonded together at the converter. If this connection is absolutely perfect the GFI will not trip. But the slightest imperfection in this bond will result in the GFI tripping. Many times this bond is not perfect but is not dangerous. This is why it is not recommended plugging your RV into a GFI receptacle.
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Old 07-20-2015, 08:54 AM   #22
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Originally Posted by tnchuck100 View Post
"connection" as in function, not physical wire.

GFCI does not see ANY 12 VDC current flow. GFCI only sees 120 VAC current on the hot and neutral. Has nothing to do with the ground. What triggers a GFCI to trip is current went from the hot to ground without returning on the neutral. Has nothing to do with the 12 VDC system.
Its not supposed to but Our Hero seemed to have found a way.

It would appear that the added accessory fan draws enough power from the 12VDC system to exceed the GFCI's .005A threshold. From the pix, he picked up +12VDC from the back of the fridge, but the -12VDC connection is not shown. If that is just to the fridge's case, we have our ground fault.

In DC circuits, the wiring is the function. Modern Household wiring has been made more complicated by law for safety reasons. You only need 2 wires to complete a circuit. (Unless you get into what Mr. Tesla was experimenting with. Then wires tend to get irrelevant).

The ground wire in house and commercial wiring is there to keep people from getting hurt or killed when something goes wrong.

But, in low-volt systems, there is no danger to people so ground is one side of the circuit. By convention, the negative - electron source - side.

So the 12VDC for lighting, controlling appliances, radio, etc. shares the -12VDC with the Stop/Turn/Tail lights and Ground (not neutral) with the 120VAC 'house' wiring.

These systems are interconnected!

To take it a step further, the tow vehicle keeps the battery charged while driving.
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Old 07-20-2015, 11:23 AM   #23
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Its not supposed to but Our Hero seemed to have found a way.

It would appear that the added accessory fan draws enough power from the 12VDC system to exceed the GFCI's .005A threshold. From the pix, he picked up +12VDC from the back of the fridge, but the -12VDC connection is not shown. If that is just to the fridge's case, we have our ground fault.
Wow! thanks for all the help. I am fairly adept at electrical wiring (non-electronic), so your explanation helped.

The -12vDC connection is inside the frig. The fan design uses an alligator clip attached to the cooling fins. On some model fans, the alligator clip also serves as the on/off switch. My model has an independent micro toggle switch. I can keep the fan mounted in the frig, then turn it on/off by the switch. The switch was loose in the fan body, so I don't know if that is also a cause of the .005a fault.

In any event, I am not sure if the fan is doing any good. It is noisier than I expected. I will probably take it off.
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Old 07-20-2015, 12:00 PM   #24
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Wow! thanks for all the help. I am fairly adept at electrical wiring (non-electronic), so your explanation helped.

The -12vDC connection is inside the frig. The fan design uses an alligator clip attached to the cooling fins. On some model fans, the alligator clip also serves as the on/off switch. My model has an independent micro toggle switch. I can keep the fan mounted in the frig, then turn it on/off by the switch. The switch was loose in the fan body, so I don't know if that is also a cause of the .005a fault.

In any event, I am not sure if the fan is doing any good. It is noisier than I expected. I will probably take it off.
Abso-100-per-cent-lutely!

.005A @ 120VAC= .6 of a watt. So if that fan draws more than 50ma, there's the power the GFCI saw go out on the Hot leg and not return on the neutral.

The fins, cooling unit and the case are connected to house wiring ground via the power cord. -12VDC comes in only on the controller. IIRC on my trailer, there are no ground straps to frame ground.
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Old 07-20-2015, 01:30 PM   #25
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Abso-100-per-cent-lutely!

.005A @ 120VAC= .6 of a watt. So if that fan draws more than 50ma, there's the power the GFCI saw go out on the Hot leg and not return on the neutral.

The fins, cooling unit and the case are connected to house wiring ground via the power cord. -12VDC comes in only on the controller. IIRC on my trailer, there are no ground straps to frame ground.
Abso-100-per-cent-lutely FALSE!

Mike, you know just enough electrical theory to mis-lead people. I have no doubt you sincerely believe what you are posting is accurate. However, you are coming up short when it comes to relating that knowledge to the real world. The 12 VDC system does not have ANY affect on the GFCI system. I will not debate this issue with you any further.
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Old 07-20-2015, 02:08 PM   #26
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Originally Posted by tjpolsin View Post
The -12vDC connection is inside the frig. The fan design uses an alligator clip attached to the cooling fins. On some model fans, the alligator clip also serves as the on/off switch. My model has an independent micro toggle switch. I can keep the fan mounted in the frig, then turn it on/off by the switch. The switch was loose in the fan body, so I don't know if that is also a cause of the .005a fault.

In any event, I am not sure if the fan is doing any good. It is noisier than I expected. I will probably take it off.
Tjpolsin, I probably have the same fan setup inside the frig as you have, actually I have two of them. You are right they are noisy. I have never tripped my GFC by using them. Difference is I do not have any type of switch to control them.
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Old 07-20-2015, 02:30 PM   #27
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I have a 12v fan wired exactly as tjpolsin described his. I have never had any problem with my GFCI and I doubt if his problems with the GFCI have anything to do with the fan.

Are there any electrical engineers here who would like to take a stand on this?

Lots of lost time is wasted troubleshooting a problem when a incorrect idea is accepted as fact.
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Old 07-20-2015, 02:38 PM   #28
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I have a 12v fan wired exactly astjpilsin described his. I have never had any problem with my GFCI and I doubt if his problems with the GFCI have anything to do with the fan.

Are there any electrical engineers here who would like to take a stand on this?

Lots of lost time is wasted troubleshooting a problem when a incorrect idea is accepted as fact.
Let's check a couple of facts, then.

Let's see how well our fridges are grounded. Tonight I'm going to get out my DVM and see how well connected the fins inside my fridge are to the frame ground of the trailer and whether that connection is through the fridge's 120VAC cord.

How about all of us that participated in this thread, perform this test and compare notes. We all know the theory I hold. Let's all see if it stands up to reality.
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Old 07-20-2015, 03:10 PM   #29
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Originally Posted by tnchuck100 View Post
"connection" as in function, not physical wire. But, even so, the GFCI is not connected to ground.

GFCI does not see ANY 12 VDC current flow. GFCI only sees 120 VAC current on the hot and neutral. Has nothing to do with the ground. What triggers a GFCI to trip is current went from the hot to ground without returning on the neutral. Has nothing to do with the 12 VDC system.

Additionally, the reason a GFI will trip when an RV is connected to it is because the ground and neutral are bonded together at the converter. If this connection is absolutely perfect the GFI will not trip. But the slightest imperfection in this bond will result in the GFI tripping. Many times this bond is not perfect but is not dangerous. This is why it is not recommended plugging your RV into a GFI receptacle.
Correction: The neutral is NOT bonded to the ground in the converter or anywhere in the RV. Please disregard that complete bolded statement.
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Old 07-20-2015, 03:24 PM   #30
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Frame ground, fridge ground and AC common are all within 1.5 ohm of each other on my rig.
It has no bearing on whether the fridge is plugged in or not.
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