Overcoming bonded neutral issues in the setting of a GFI protected Ford Lighting 7.4kw inverter.....

[zanydroid]

They are then setting themselves up foe liability.

But generators often allow this. What is different about Ford? More at stake than Harbor Freight? :laugh: I guess then we can ask if Honda allows it -- they also make generators. I guess maybe the LLC's are designed so that generator subsidiary getting sued won't kill the mama ship

 

[zanydroid]

I kept re-reading this though. Lets say I have a L fault somewhere between the transfer switch and and its NOT faulted to neutral, but to something else and it finds an alternate path back to the main panel G and then "rejoins" the N wire where it is bonded to G. Now current out on L1 and L2 should still equal current back on N. Pickup cannot see ground anymore. I sooo much want to not understand this and have you be right, BTW.

How does having the EGC protect against this?

On most GFCIs nothing directly "sees" the EGC. On some (like EVSE) there will be additional checks to see if the EGC is bonded correctly somewhere in the system. I don't believe the truck can make this check since it already has N-G bonded internally.

This is a low probability event. This somewhat reads like "I don't believe in GFCIs, because in some cases there will be a fault that will have balanced current still". OR. "I want EGC in addition to GFCI because there is additional protection". True in some cases, but I don't think it applies here. In the case of connecting something non-double insulated or with a big honking metal chassis, I described a few posts earlier why having both EGC in working order and GFCI are helpful (and in fact code requires this in many cases to get two chances to save your bacon from a line-ground fault).

In my mind the system is equivalent safety/unsafety with/without the in the cable. The system is bonded normally at the house. So any problem is on the cord->truck side.

I think also bonding EGC in cable to the transfer switch, but leaving it unbonded on the truck side, is quite similar to a truck where the internal N-G bond can be removed. The difference would come in wrt how the truck itself is bonded internally. If this makes you feel better wire the cable as such.

Another way to look at this is. 99% of the time when you're connecting power to the house, you're inside your house. Things are OK in the house, based on what makes sense to you today. Stay away from the backfeed cable or protect it extra.

IMO the backfeed cable is equivalent in risk to having a 12/2 cord with 120V connected to the generator. My UL listed corded leaf blower uses this kind of cord, no ground. I use a GFCI with this and I feel safe from electricity.

 

[zanydroid]

I think what you want the EGC to do is to increase the probability that a fault will come back along a path that bypasses the GFCI sensing. I think touching L1 on the supply cable with one hand and N or G of house with the other hand would not trip the GFCI. I don't see this as likely if you avoid running equipment inside your house that's supplied from an extension cord running to your truck.

You can try feeding through an isolation transformer to guard against this.

 

[cdherman]

How does having the EGC protect against this?

You are right, doesn't. Listen, you all that are willing to have the ground disconnected -- some of us far less experienced guys take it as gospel that every circuit ought to have a ground. I am just trying to figure out in my mind where an inspector would have a problem. Frankly, you have brought me into agreement. My only concern is coming across an inspector who would ask me for that same coherent explanation and under pressure it makes it harder.

Anyhow, big thanks again for those patient enough to keep trying. The Ford Lightning forum was less helpful.

 

[zanydroid]

Cool.

I don’t think an inspector would have an issue with modifying the temporary backfeed wiring, it is not really subject to inspection at a house. But it is a bit of a gray area.

There is a new section of Residential Code (not in effect in all states) where it requires you to follow the vehicle manufacturer’s instructions when powering a house with it.

You would want to keep the inlet box and receptacle bonded though, that would actually be inspected.

 

[CoolWill]

You are right, doesn't. Listen, you all that are willing to have the ground disconnected -- some of us far less experienced guys take it as gospel that every circuit ought to have a ground. I am just trying to figure out in my mind where an inspector would have a problem. Frankly, you have brought me into agreement. My only concern is coming across an inspector who would ask me for that same coherent explanation and under pressure it makes it harder.

Anyhow, big thanks again for those patient enough to keep trying. The Ford Lightning forum was less helpful.

The inspector doesn't have much to say about portable sources of power. He is chiefly concerned with the wiring of the building. If you're not willing to modify the inverter in the truck and you're not willing to separate the neutrals and grounds at the panel, you only have two choices:

1) Abandon the project
2) Disconnect the ground at one end of the cord

Keep in mind that you aren't leaving the cord ungrounded. The ground will still be connected at one end. Let's say you disconnect the ground at the plug. The inverter and truck are still grounded by the neutral-ground bond at the inverter. The green wire in the cord is connected to ground at the panel, so if the cord were to be compromised somehow, the green wire will still carry fault current.

 

[Checkthisout]

You are right, doesn't. Listen, you all that are willing to have the ground disconnected -- some of us far less experienced guys take it as gospel that every circuit ought to have a ground. I am just trying to figure out in my mind where an inspector would have a problem. Frankly, you have brought me into agreement. My only concern is coming across an inspector who would ask me for that same coherent explanation and under pressure it makes it harder.

Anyhow, big thanks again for those patient enough to keep trying. The Ford Lightning forum was less helpful.

Use a generator inlet plug at the house and a main breaker interlock on the backfeed or just a regular 8, 10 (or whatever circuit) transfer switch.

The inspector isn't going to inspect your truck and cord so that never comes into play.

 

[Shimmy]

Safest solution is to have an isolation transformer between the truck and SolArk. Getting rid of the ground connection could cause significant risks if there is ever a low level ground fault in the system.

 

[Checkthisout]

Safest solution is to have an isolation transformer between the truck and SolArk. Getting rid of the ground connection could cause significant risks if there is ever a low level ground fault in the system.

Give an example of a real-world failure mode that would result in significant risks as a result of not having an EGC between the truck and house?

What if I plug a hairdryer into the trucks outlet? Hairdryers only have a 2 prong cord, hot and neutral.

Why is the Hairdryers plugged into the truck less "risky" than hooking a house panel up to the truck without and EGC between the truck and house?

 

[zanydroid]

Hair dryer is double insulated so isn't the best example to use.

If you run an extension cord from truck with EGC disconnected in the cable, plug a splitter on the cord, plug one side of cord into transfer switch and another side into a tool with a metal frame (one way to not be double insulated).

Plugging the transfer switch into the house provides a path from concrete pad / soil -> N-G bond -> N extension cord -> truck

Now let's suppose the tool has a line-to-ground fault due to a loose wire. Then the GFCI on the truck is defeated since there can be fault current from energized frame -> human -> concrete pad -> N-G bond -> N extension cord -> truck. (***)

If you plug double insulated hair dryer with L-N only cord into either Truck, House, or mistakenly added splitter adapter, the double insulation of case provides the protection against the fault scenarios listed here.

If you plug the metal framed tool into house(*), a standard breaker alone will trip immediately. If you plug metal framed tool into truck (**), same thing. If metal framed tool has a double fault - Line to chassis short, chassis to EGC bond broken. Then case (*) will be bad, breaker will not trip, you need GFCI. (**) will still have GFCI available to protect. In fact (*) and (***) would be equivalent since there is a broken EGC bond, the difference is where it is.

I don't think it would be safe to keep a cable with EGC removed on a jobsite where people may not be aware of this. Unless it somehow has a inlet receptacle type that is ungrounded, so that it is impossible to plug the wrong kind of tool or splitter into it. Like inlet and cord should use NEMA 10-30 instead of 14-30.

 

[Checkthisout]

Hair dryer is double insulated so isn't the best example to use.

If you run an extension cord from truck with EGC disconnected in the cable, plug a splitter on the cord, plug one side of cord into transfer switch and another side into a tool with a metal frame (one way to not be double insulated).

Plugging the transfer switch into the house provides a path from concrete pad / soil -> N-G bond -> N extension cord -> truck

Now let's suppose the tool has a line-to-ground fault due to a loose wire. Then the GFCI on the truck is defeated since there can be fault current from energized frame -> human -> concrete pad -> N-G bond -> N extension cord -> truck. (***)

If you plug double insulated hair dryer with L-N only cord into either Truck, House, or mistakenly added splitter adapter, the double insulation of case provides the protection against the fault scenarios listed here.

If you plug the metal framed tool into house(*), a standard breaker alone will trip immediately. If you plug metal framed tool into truck (**), same thing. If metal framed tool has a double fault - Line to chassis short, chassis to EGC bond broken. Then case (*) will be bad, breaker will not trip, you need GFCI. (**) will still have GFCI available to protect. In fact (*) and (***) would be equivalent since there is a broken EGC bond, the difference is where it is.

I don't think it would be safe to keep a cable with EGC removed on a jobsite where people may not be aware of this. Unless it somehow has a inlet receptacle type that is ungrounded, so that it is impossible to plug the wrong kind of tool or splitter into it. Like inlet and cord should use NEMA 10-30 instead of 14-30.

Ok.

So why does code allow transfer switches that do not change the NG bond?

And, why do they make portable generators without GFCI?

Are we inventing a problem where one doesn't exist?

 

[zanydroid]

Ok.

So why does code allow transfer switches that do not change the NG bond?

Not sure what you mean by this. There are neutral and non-neutral switching transfer switches to accommodate different N-G bonding scenarios for the power sources being connected. You have to use them in correct scenarios.

And, why do they make portable generators without GFCI?

It's probably allowed in some code/OSHA contexts but not others.

If you have a built-in GFCI you are stuck with the trip threshold that it was baked with. If you plug in enough equipment you may accumulate enough ground leakage to trip this. Not having a built-in GFCI means customer can spec it as they need.

For a small generator it's probably not that easy to plug in enough stuff to hit this problem, so it's probably smart to have GFCI for those by default. But you could still have some upset users with quirky equipment.

Are we inventing a problem where one doesn't exist?

No, I think it's worth having a discussion. I don't think there is a system that will automatically work for all scenarios in a fail-safe way, some intelligent manual configuration is needed. I think the truck's hardwired GFCI and L-N bond errs on the safe for untrained personnel but limits usage scenarios dimension.

We haven't even gotten to what will happen if the accumulated leakage in the house trips the truck's GFCI. In that scenario the isolation transformer would be the least disruptive way to bypass it (if Ford doesn't allow N-G removed they're not going to allow GFCI to be disabled). I would imagine the truck's GFCI is designed for personnel safety, if you have enough, EG, minisplit power supplies in the house it might trip (minisplits come with table to calculate how many can go on a single GFCI/RCD of each protection class, which corresponds to permissible mA leakage before trip).

 

[Checkthisout]

Not sure what you mean by this. There are neutral and non-neutral switching transfer switches to accommodate different N-G bonding scenarios for the power sources being connected. You have to use them in correct scenarios.

It's probably allowed in some code/OSHA contexts but not others.

If you have a built-in GFCI you are stuck with the trip threshold that it was baked with. If you plug in enough equipment you may accumulate enough ground leakage to trip this. Not having a built-in GFCI means customer can spec it as they need.

For a small generator it's probably not that easy to plug in enough stuff to hit this problem, so it's probably smart to have GFCI for those by default. But you could still have some upset users with quirky equipment.

No, I think it's worth having a discussion. I don't think there is a system that will automatically work for all scenarios in a fail-safe way, some intelligent manual configuration is needed. I think the truck's hardwired GFCI and L-N bond errs on the safe for untrained personnel but limits usage scenarios dimension.

We haven't even gotten to what will happen if the accumulated leakage in the house trips the truck's GFCI. In that scenario the isolation transformer would be the least disruptive way to bypass it (if Ford doesn't allow N-G removed they're not going to allow GFCI to be disabled). I would imagine the truck's GFCI is designed for personnel safety, if you have enough, EG, minisplit power supplies in the house it might trip (minisplits come with table to calculate how many can go on a single GFCI/RCD of each protection class, which corresponds to permissible mA leakage before trip).

The generator hooked into a household transfer switch without a switched neutral is more "unsafe" than the GFCI equipped trucked plugged into the house with the EGC severed.

Was my point to @Shimmy.

I don't see how an isolation transformer? would help return "safety" to the system?

 

[zanydroid]

I have no problem supplying a house with generator that does not have GFCI. Most likely those stationary generators do not have GFCI. The protection is no worse than what you get from the utility.

If you look only at the system starting from the transfer switch down, the GFCI equipped truck with EGC severed is pretty safe. But I listed several scenarios above that I would personally want to prevent, where some low levels of ill-informed or accidental usage on the system between transfer switch and truck will lead to problems. Someone could probably make some YouTube clickbait showing how those scenarios have a shock risk.

If I owned this truck -- if nobody touches the house / truck besides me, then EGC severed should have minimal risk and I have no problems with it. Maybe put some permanent tags on the ends of the extension cord:

• on the house side - saying not to use with power tools
• on the truck side - saying not to plug in any tools

Unfortunately this is not bulletproof because it requires people to read, and often code wants physical lockouts against unsafe situations because people don't read.

 

[Checkthisout]

I have no problem supplying a house with generator that does not have GFCI. Most likely those stationary generators do not have GFCI. The protection is no worse than what you get from the utility.

If you look only at the system starting from the transfer switch down, the GFCI equipped truck with EGC severed is pretty safe. But I listed several scenarios above that I would personally want to prevent, where some low levels of ill-informed or accidental usage on the system between transfer switch and truck will lead to problems. Someone could probably make some YouTube clickbait showing how those scenarios have a shock risk.

If I owned this truck -- if nobody touches the house / truck besides me, then EGC severed should have minimal risk and I have no problems with it. Maybe put some permanent tags on the ends of the extension cord:

• on the house side - saying not to use with power tools
• on the truck side - saying not to plug in any tools

Unfortunately this is not bulletproof because it requires people to read, and often code wants physical lockouts against unsafe situations because people don't read.

Agreed.

The stars have to line up though.

Especially when a 30 amp cord/connections are involved.

It also need not involve the cord at all. Just disconnect the EGC going to the power inlet inside the house panel.

Done.

 

[zanydroid]

It also need not involve the cord at all. Just disconnect the EGC going to the power inlet inside the house panel.

This is a code violation. The inlet box / inlet receptacle would no longer be bonded. Not bonding a metal box can probably lead to a Darwin Award scenario.

If you bond the box most likely the receptacle will internally bond the ground pin via the mounting screws unless you go and add insulated screws and other bunch of insulation. This is kind of weird and will also probably fail inspection

My personal favorite so far is to use 10-30 cord end but I’m sure folks will come up with a reason that is bad. IE it will not protect against a fault through something plugged into the truck, back through the grounding system of the house. You need the isolation transformer ($$$) to defeat this.

 

[Checkthisout]

This is a code violation. The inlet box / inlet receptacle would no longer be bonded. Not bonding a metal box can probably lead to a Darwin Award scenario.

Yup. It is.

If you bond the box most likely the receptacle will internally bond the ground pin via the mounting screws unless you go and add insulated screws and other bunch of insulation. This is kind of weird and will also probably fail inspection

Yup.

My personal favorite so far is to use 10-30 cord end but I’m sure folks will come up with a reason that is bad. IE it will not protect against a fault through something plugged into the truck, back through the grounding system of the house. You need the isolation transformer ($$$) to defeat this.

Yes but someone will be killed if the stars line up.

My main point here is they make portable generators without GFCI and people have been connecting these to their houses for years without issue.

A portable generator without GFCI hooked to your house with the EGC in-tact is more "unsafe" than the Ford pickup truck with GFCI connected to your house with the EGC disconnected.

And also, I mean really, we are only talking about this because for some reason guys with $80-$100,000.00 trucks don't want to spend the money to put the proper neutral-switching transfer switch in their house. Something that takes less an afternoon and costs less than $500.00

 

[Hedges]

I would have concerns about interrupting ground between Lightning and house. It might work, using neutral wire only, but I haven't thought through possible failure modes well enough. Maybe an open neutral and a short elsewhere could drive truck chassis to 120V.

An isolation transformer would be a good solution. What may cause you problems is that typical utility power transformers are a far from being an "ideal" transformer and will be a nasty load for an inverter. They draw considerable no-load current, out of phase so returned in the next phase.

I like to feed such transformers at half their rated voltage, which keeps them out of saturation and no-load current more than 10x lower. You will probably need two 240/480 to 120/240 transformers to use them this way.

 

[Dymailbox]

And also, I mean really, we are only talking about this because for some reason guys with $80-$100,000.00 trucks don't want to spend the money to put the proper neutral-switching transfer switch in their house. Something that takes less an afternoon and costs less than $500.00

That is not an accurate statement. I have no trouble spending $500 or $2000. I just need to know what to spend it on, and I've gotten no help from local electricians.

I have 600 amp service with a transfer switch and a natural gas backup generator. I also have a sub panel wired with an interlock that feeds the kitchen and a couple outlets and lights in the master. And an inlet wired to the sup panel.

As you said, I have a $90k truck sitting in the driveway the can power critical loads if I need it and natural gas is out. I just want to know how to do it. I never asked how much it cost.

 

[zanydroid]

And also, I mean really, we are only talking about this because for some reason guys with $80-$100,000.00 trucks don't want to spend the money to put the proper neutral-switching transfer switch in their house. Something that takes less an afternoon and costs less than $500.00

You have to move the loads to the transfer switch's subpanel too, which is a design problem. Vs just using an interlock on the main panel. Another option is to either unbond a convertible main panel (tricky) or move all main panel circuits to a subpanel. That trades design problem for spending more work.

I think I prefer refactoring the main and subpanels over isolation transformer.