The GFCI topic

[TEG]

EVDL Archive / Forum Interface - Electric Vehicle Discussion List

...You generally don't want two GFCI in series. Sometimes this can make them trip falsely...

Perhaps that is why some customers are/were having GFCI trip problems? It looks like Stephano's Milbank panel install to Tesla charger is using double (in series) GFCIs on the 120V:


(note the test buttons both on the Tesla cord, and on the small GFCI breaker above it)

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Perhaps that is why some customers are/were having GFCI trip problems? It looks like
(note the test buttons both on the Tesla cord, and on the small GFCI breaker above it)

I told SP about the double GFI Roadster trip problem when Doug posted the info on his Milbank installs. About that time Tesla announced the "fix".

[TEG]

Did the fix work?

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Did the fix work?

Apparently not all who have had the firmware upgrade have had a resolution. Many have replaced the GFCI plug on the MC120 with a standard plug. Don't know if the MC240 has any GFCI issues.

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In the home GCFIs are required outdoors and in rooms like kitchen and bath. I was told yesterday that bedrooms are next (very soon) and you might as well just do the whole house if you are building new.

Could this be another tiny time bomb issue for charging future EVs?

[TEG]

I don't know if this info is correct, but here is a site that claims "experts" say that two GFCIs are more dangerous than one:
2007 HOT SPRINGS SAFETY SEMINAR - Tips from industry experts

Breakers and fuses protect equipment, GFCI's protect you! Never connect two GFCIs together on the same power cord. All it takes to kill a person is 50 miliamps and a GFCI is set to trip at 30 miliamps. If you connect two together it will ramp up to 60 mili amps before they trip, potentially killing anyone receiving the jolt.

Questioning the accuracy of the above... For one, I think many GFCIs are 5ma, not 30ma. For another, I am not sure I believe that two in series doubles the ma rating before trip. I would think it would be the lower of the two, but supposedly the above site was advice from an expert.

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I spoke with someone who was frustrated that the MC120 had a GFCI because they said that the code required that the outdoor outlet, not the plug have the GFCI so there would be many cases where the outlet already had GFCI. Perhaps there should be two versions of the MC120 - the existing one for indoor / garage use where there is no GFCI on the socket, and another for outdoor use (which doesn't include a GFCI) that expects the outlet to already have the GFCI?

Apparently the firmware change ramps up the current draw more slowly to avoid tripping one (or more) GFCIs in the circuit.

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Perhaps there should be two versions of the MC120 - the existing one for indoor / garage use where there is no GFCI on the socket, and another for outdoor use (which doesn't include a GFCI) that expects the outlet to already have the GFCI?

What if they only made the non GFCI and included one of these:
Prime Wire & Cable Portable GFCI Adapter and Surge Protector, Model# GFP10000 | Switches + Fuses | Northern Tool + Equipment

http://www.tycothermal.com/assets/Am..._DS_032006.pdf

Tower Shock Buster Portable GFCI

[TEG]

Yep, that might of worked... I guess they didn't want to take the risk that someone would forget to install the add-on GFCI when there wasn't already one behind the socket.

By the way, more GFCI fun:
Two GFCIs in series - OK or not? [Archive] - Straight Dope Message Board

The code allows for multiple GFCI outlets in one line, although generally you only need to have the first in line protected.

Here's something I found out the hard way. A ground fault circuit interrupter works by measuring the current flow in the hot leg, and comparing it to the current in the neutral leg, and if it detects that the currents don't match, it assumes the extra current has "gone to ground" and trips the breaker.
If you are not grounded, and grab both legs so that current can flow from one leg to the other through your body, the GFCI doesn't mind this a bit. It was the late seventies, and GFCI were fairly new, and I didn't know how they worked, and tested one this way. It was only 110V, but it kind of caught me by surprise. I have to admit, there were beverages involved.

Part of the process is to bleed a tiny bit of current into the ground wire if I remember correctly. If you have too many GFIs in the circuit, the sum of al those tiny losses might trip the protection.
And it doesn't do any good to have more than one. Once one opens the circuit is dead and the others won't see any current to be unbalanced.
This is not correct.
A GFCI doesn't even need the "third prong" connected to earth ground in order to work. If you want proof of this, consider that the NEC allows 2-prong, ungrounded receptacles to be replaced with 3-prong, GFCI receptacles (assuming it is properly labeled).

I don't know what the NEC says about GFCIs in series, but my younger brother, a Master Electrician, advises against it. According to him, series GFCIs can lead to undesirable effects including nuisance trips (I have seen this myself) or failure to trip properly (I have not seen this nor pretend to understand how it could occur).

Here's an example of how a "shared neutral" might happen:

Let's say a bunch of receptacles, lights, and whatnot are connected to the load side of the GFCI. We say these things are "downstream" from the GFCI, and thus they are all GFCI-protected. Afterwards, someone decides to install a ceiling light. They connect the ceiling light's "hot" to a circuit that is not GFCI protected (or they run the ceiling light's "hot" wire directly back to a circuit breaker in the panel). They connect the ceiling light's "neutral" wire to a neutral that is downstream from the GFCI. This creates an automatic imbalance on the downstream side of the GFCI when the ceiling light is used, and the GFCI will trip.

Here's an example of how a "shared hot" might happen:

Let's say a bunch of receptacles, lights, and whatnot are connected to the load side of the GFCI. We say these things are "downstream" from the GFCI, and they are all GFCI-protected. Afterwards, someone decides to install a ceiling light. They connect the ceiling light's "hot" to a circuit that is downstream from a GFCI. They connect the ceiling light's "neutral" wire to a circuit that is not GFCI-protected (or they run the ceiling light's "neutral" wire directly back to the CB panel). This creates an automatic imbalance on the downstream side of the GFCI when the ceiling light is used, and the GFCI will trip.

Additionally, GFCIs don't like poor connections in downstream circuits. Granted, it shouldn't make a difference, but when I installed GFCIs in my late 70's home to upgrade electrical compliance, nuisance tripping was common. Only after I opened each device box, removed backstab connections and remade them to the screw terminals did the tripping stop. I can't explain it, but making good connections on the downstream receptacles alleviated the problem.

Your main problem is likely to be discrimination.

We in the UK call these things Residual Current Devices(RCDs), they work particularly well for us because our entire system is neutral grounded using a 3 wire system.

The problem with multiple RCDs is that they not only will have a tripping current, they also have tripping times, so that a surge will not cause unwanted interrupts.

Ideally you put RCDs with longer trip times further toward the incoming supply connection, so that those further down the line trip first.

Your problem comes when you install units with ostensibly the same tripping time, because the reality is that there will always be some small differance.
This can then lead to unwanted upstream tripping, and leave the downstream device still on and can then lead to problems working out which is the faulty circuit.

This is where you pay for a person who knows what to look for in manufacturers specifications instead of doing the job yourself.

This can happen with fuses as well, but fuses tend not to be used in the same way so the safety issues are differant.

[W.Petefish]

Has anyone, other than me, had their HPC's GFCI trip?

[bonnie1194]

What if they only made the non GFCI and included one of these:
Prime Wire & Cable Portable GFCI Adapter and Surge Protector, Model# GFP10000 | Switches + Fuses | Northern Tool + Equipment

http://www.tycothermal.com/assets/Am..._DS_032006.pdf

Tower Shock Buster Portable GFCI

I bought one of those and threw it in my bag when I removed the GFCI from my cable assembly. Had Tesla done that to begin with, it would have saved me from much charging frustration on a roadtrip.