The current NEC says it is wrong. Whether anyone wants to update an unsafe condition is up to them, my job stops at pointing it out.
Good point. 
Would you report it as not meeting the current code, as a recommended upgrade or both?
It does not say that at all. You need to read Article 90.
The NEC also says that an existing 3 wire feeder can continue to be used. It simply says any new installations need to be 4 wires. It does not call for replacement.
Good point, the NEC explicitly permits the 3 wire feeder to remain.
If this really were a US National Electrical Code (NEC) Enforcement matter a new code cannot be enforced retroactively unless the Authority Having Jurisdiction (AHJ) for code enforcement wants to hang their hat on Clear and Present Danger. If an enforcement agency does that they are in for a hard ride. Trying to make something illegal after it has occurred runs against the very spirit of constitutional law. Every citizen must be able to know what the law is when they do something not years or even days later when someone gets their undies in a twist. Ex post facto is Latin for “from after the deed.” In law it is any statutory enactment which has the intent or effect of prohibiting something that has already occurred. That is why work that was done at a specific time can only be judged by the code adopted by the legislative body of that town, city, charter county, or state.
I’m no lawyer, nor did I play one on the local access cable tv channel, but I had to take 4 semesters on various aspects of law as they relate to the actions of local government and it’s agents in order to get my fire protection degree. The first semester covered the basic principals from which local and/or State government get the authority to even enter a privately owned property to suppress a fire, mitigate a hazardous materials spill, rescue a human being from immediate peril… We had to know certain aspects of law by rote. The idea was to give us a strong sense of the limits on the exercise of the police power of the state. When firefighters enter a private property to conduct fire suppression, hazard abatement, or rescue operations they are exercising the police authority of the State. The State has no legal power to rescue you from your own lawful but ill advised actions. The State does however have the authority to protect your neighbors from your actions and on that authority stands most of what the fire service does. The fire service is a close cousin of the AHJ for the building standards enforcement in this regard. They are only cousins in that the law does not recognize the same level of urgency in their actions. Every thing that code enforcement officials do is limited by the statute that grants them the authority to do it. Since the legislature is constitutionally prohibited from passing a statute which has a retroactive effect there is no legal mechanism by which AHJs can require changes to older buildings unless they are being substantially modified or changed in use. Anything that an AHJs staff do that even feels “arbitrary and/or capricious” is like opening the city treasury and telling every attorney in the State to take what they want. No AHJ has; or in my opinion should have; that kind of authority.
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Tom Horne
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How is it dangerous. It is no different from a separately derived system.
Please read what I was commenting on. 3 wire and the ground(s) are isolated from the grounded conductor(s)?
Did I read that wrong?
It would leave the earth as the only Equipment Grounding Conductor. I’ll get to why that is dangerous next but first I will point out that practice is specifically forbidden by the US National Electric Code (NEC).
Leaving the earth as the only Equipment Grounding Conductor means that you would have to install and test 2 Grounding Electrode Systems (GES) that must present a total resistance between the 2 points of ~5 Ohms (5Ω). Unlike a derived system the current has to flow back to the secondary of the transformer from whence it came via those 2 GESs. The Total impedance of that pathway has to be low enough to permit enough current to reach the supplying transformer secondary winding to exceed the set point of the Breaker. The only way to build such a low impedance pathway is to use a low impedance conductor that connects the two points. The earths conductivity varies at any given location by the season of the year and the recent weather at that location. Depending on a pathway that will change it’s conductivity in the course of a single hour would be imprudent at best.
In the hope of being very clear let me state that a derived system is in all aspects other than magnetic fields a closed system. The current flows from and to the windings from whence it came. When you install a GES at the origin of a derived system It’s function is entirely different than using the earth as a current carrying conductor. If you bond the Equipment Grounding Conductors to a feeder’s Grounded Current Carrying Conductor (Neutral) you set up the first part of a different type of fault. If the neutral develops a high impedance connection or open, between this added bonding point and the Main Bonding Jumper at the Service Equipment, neutral currents will flow over the exposed conductive parts of the electrical system and any other conductive parts of the structure in conductive contact with them to return, via the main bonding jumper in the Service Equipment enclosure, to the secondary of the utility’s transformer. The impedance of such unintended pathways are entirely unknown but are almost inevitably higher than the impedance of a properly installed insulated Grounded Current Carrying Conductor (Neutral). The greater the impedance the more voltage will be used up in overcoming it to return to the source winding. The voltage used in overcoming the impedance of a conductor which is not a part of an intentional load is called “Voltage Drop.” That is because the power used in moving that current between the source and the load does no useful work. What it does do is raise the “touch potential” to a voltage above ground potential which may become large enough to subject anyone coming in contact with these unintentionally energized conductive surfaces to a dangerous or even deadly shock.
That brings me to the most important difference between a panel supplied through a feeder with no Equipment Grounding Conductor and a separately derived system. Such a feeder creates a situation that is only one failure away from death or serious injury while a Separately Derived System System does not have any such added risks.
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Tom Horne
If I didn’t want to waste their time I would post this on Mike Holt’s forum!!!
There is so much wrong in what you have written that I hardly know where to begin. I’ll start by asking, what is this “US National Electric Code” that you so often mention?
Your last paragraph is nothing short of absurd. Most of what you said, beginning with the mention of “US National Electric Code” to your final sentence is wrong.
Please do we welcome all kinds of debates. I’m sure you get quite a few opinions. 
Thanks infinity - jxofaltrds
The United States is not the only Nation that has a National Electric Code. I add the “US” just to be clear that it is the National Electric Code which is published in the United States. If being insufficiently arrogant to use the word National and assume it could only refer to the United States is some sort of social faux pas then it is my bad.
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Tom Horne
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You’re welcome, Jack of all trades. 
Wrong how? A little bit of specificity would really help if you actually want me to defend what I’m writing. All you have done is make a broadly dismissive statement.
I’m not the one who wrote that there is no difference between a panel supplied by a feeder which has no Grounding Electrode Conductor and a Derived System. So I’ll try to compose an answer to your dismissal by simply quoting the National Fire Protection Association’s National Electric Code (NEC).
“Feeder. All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device.”
“Separately Derived System. An electrical source, other than a service, having no direct connection(s) to circuit conductors of any other electrical source other than those established by grounding and bonding connections.”
What is being discussed here is a Feeder supplied panel. There are Current Carrying Conductors between the busbars which supply all of the Over-current Devices in the panel being discussed and the power utility’s transformer.
If it were a “Separately Derived System” the only conductors which would be continuously and deliberately connected back to the utility’s transformer would be the conductors which supply the primary side of the transformer and the Equipment Grounding Conductor of the branch circuit that those conductors are part of. The conductors which carry the current produced in the windings of a Separately Derived System have no deliberate conductive pathway to anyplace other than the windings of that Separately Derived System and the loads that system supplies. There is no deliberately installed conductive pathway from the Separately Derived System to the Electrical Service of the premises wiring system and the utility’s transformer.
I don’t think that I’m being at all absurd when I say those 2 ways of supplying current to a load are very different indeed and have very different characteristics which have markedly different safety considerations.
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Tom Horne
Michael,
Its a matter of liability… A HI has enough to worry about already, if there is ANYTHING deemed unsafe it should be pointed out! it is then the decision of the buyer to do anything about it or not… I don’t want to get sued when someone gets hurt because I didn’t address something in my report. As long as I did, I wont get sued for it!
I thought we were always supposed to point out when the neutrals and grounds were not isolated on a sub panel. So now there are cases when that is not required?
Just wondering, because this is one big difference to look for in a sub panel that has never been addressed in any of the nachi courses.
3-wire feeder to detached building neutrals and grounds Are Bonded and connected to ground rod at building.
4-wire feeder neutrals are isolated.
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