Can you elaborate?

Great info, thank you!

Exactly understanding and monitoring ungrounded systems in an OR is also the responsibility of medical staff beyond just maintenance electricians.

As an example, the "safe" 0.54mA in his picture is well more than enough to excite the multimeter and show a voltage.

If we used a voltage meter with "low impedance function" like the Fluke 117, do you think the measurement would finally be 0v?

Yes, I service quarterly a Marine Well Containment platform, and it has an ungrounded system. It thru me for a loop the 1st time I opened the service panel to throw the breaker for a fire alarm panel and found it to be 20A double pole. I was installing a Surge Protection Device on the fire panel's primary 120Vac power. When measuring across safety ground and either line conductor I also read somewhere around 50 - 60 volts.

I work in a shipyard and onboard shore power fed vessels I read about 60v on each leg to ground. When looking for ground faults with a 3 light ground detector installed at the panel, it has been pretty easy to isolate by shutting of breakers until the ground fault disappears. However, I have ran into a ground fault on a breaker connected to an audio system with back up power and hit a wall going further with isolation. I heard that it is not necessarily a fault in the equipment but a lack of capacitive balance between the three phases. It's new to me and I'm learning about it as I post this.

For recording studios it is very similar (60/120V), but it is a grounded system.

I believe that both the common marine galvanic isolator and the uncommon marine isolation transformer both retain a bonded connection of the secondary neutral wire and boat ground wire. The neutral bond is inside the secondary wiring of the transformer, and the shore ground is there but completely isolated from the secondary boat ground. In a marine isolation transformer the difference is that shore ground is completely separate from boat ground, and in a galvanic isolator the two grounds are connected but separated by a set of parallel, opposite polarity diodes with a 1.4V forward drop either way. So, the marine setup is fundamentally different than the isolation described here in operating rooms, where ground and neutral are separate when testing with a multimeter.

Thanks!

Thank you! Good luck to Poland against France this weekend.

@@RyanJacksonElectrical thanks , and also keep finger cros for US

I've never heard that before. Interesting!

I think the main benefit there is for diagnosing faults; i.e. keep the system running even though it has a ground fault.

this is similar to using an old school light bulb with a filament in stead of a safety fuse: the resistance of the filament goes up when current goes up. This helps with diagnosing an overcurrent inside the equipment.

Please allow me to ask in earnest, is there a way to synchronize the phase and frequency of these inverter generator systems or is it done automatically looking at cumulative voltage considering summing vs subtractive interference?

​@@jeffreystroman2811 Yes. Automatic synchronization is done by every grid connected solar inverter. What's more interesting are AC generators. In that case, the hard part is determining when they line up to connect them. Once that happens, the electrical coupling forces both systems to spin at exactly the same speed.* So as long as you use timing lights, or an automated equivalent, you can manually synchronize AC generators and tie them together into a larger system. Note that doing this at home using home-made timing lights might be an interesting project, but it is dangerous and almost certainly violates the NEC. Connect them at the wrong time and things will go bang. * Simplifying

Thanks Brian! I can't think of a reason why it would matter.

Electrically it doesn't matter - I honestly think the strict adherence to color matching the legs is more about ensuring every single bit of the highly protective system is built perfectly - so don't leave anything to chance of the whims of a lazy electrician.

@@RyanJacksonElectrical Here's a scenario it prevents: Take two devices which both expose the operator to voltage in the exact same manner. Say two tools or lights which both have a part which is "live" from the brown wire, but is not contacting ground. If everything is wired the same nothing happens when someone touches both lights at that point. However, if the second light was plugged into an outlet which was wired with the opposite polarity, that person would be electrocuted. A defect could mean that all lights manufactured within a certain period of time are defective in the exact same way. Bulk purchasing means having two from the same batch is extremely likely. It's not likely, but it's a "free" risk mitigation.

Correct, the primary is a grounded system. The enclosure of the transformer (metal parts) would be connected to the equipment grounding conductor of the supply circuit (the primary), so there would be a voltage there.

yes, it's like a split phase system, but there's no grounded service conductor, aka "neutral". So it's a floating system. If you take earth as your reference, there is still a potential, you can still get shocked. I bet the operating table is very well insulated, and for wet conditions.

@@wim0104 Just the opposite, operating tables are quite often steel, and grounded via the EGC. 'back to source' just means back to the secondary of the isolation transformer. The reason you read 60VAC is that there is no such thing as a perfect 'open'. Air conducts electricity. Wire insulation conducts electricity. The plastic used to construct the receptacles conducts electricity. None of this is a lot of conductivity, but it is never 'zero'. This means that the ungrounded system IS ever so lightly connected to 'ground' from both legs. If this conductance is near equal, which is likely as the wiring is all parallel, then your high impedance sensitive multimeter will still measure JUST enough current to read the 60VAC you are seeing.

@@CraziFuzzy Thanks for the explanation.

yes. it's all about avoiding breakers tripping for ground faults and interrupting the operation.

For an ungrounded delta, usually people just use the normal black, red, blue or brown, orange, yellow. If it was in a hospital, however, 517.160 specifies the colors.

The specific bits this is talking about is for hospital use, and is only really for equipment likely to come into contact with a patient during a wet procedure - which is all 120V. As such, I have never seen a medical isolated power system that was anything but 120V single phase. There are a number of ungrounded three-phase systems out there - but most are military and marine systems, and as such, not subject to NEC rules anyway.

No, there is no voltage from L to G in normal condition. Under a fault you would get 0V from G to the faulted line, 120V to G on the line that isn't faulted. The faulted conductor really just becomes a grounded conductor at that point.

I thought about it a little longer and figured it out in my head haha! Thanks for the vid!

Most isolation transformers are just a 1:1 transformer. This type of setup is pretty specific to ORs.

same reason you will read 60VAC on the video's ungrounded system - sensitive meters and capacitive coupling between the isolated system and ground.

Thank you

Your question assumes it is grounded but it is not. There is 120 V between the legs. Each leg is 0 V to the ground. Think about a 1.5 V battery. It would make no sense to say each pole is 0.75 V? Voltage is always relative. There is no absolute voltage. This rather confusing. We can say that a leg is 120 V (for example) only because we have grounded the system. That is we have deliberately connected the system to the ground with a ground rod. Note that a system can also become accidentally grounded. An isolated system in that case stops being isolated but it still works. Likely you do not have 240 V equipment there or if you do, you have a separate system for them. . At surface one might ask why do we ground as isolated seems to be safer. Well you are not the first one to think so. In fact before 1899 grounding was banned (do not confuse this with the ground prong on the socket, this has absolutely nothing to do with it). However, it did cause problems so in 1901 it was recommenced and in 1913 mandated. Ungrounded systems can get over-voltage which causes arbitrary voltage to the ground because of lightnings, accidental touching of high voltage lines etc. The ground prong was later added to reduce the risk of shock that grounded systems have. Isolated systems are typically used in things like hospitals and ships. Norway is the only country where they are widely used to my knowledge and they typically have a high impedance connection to the earth for over-voltage. They do not distribute the neutral, just three phases 230 V between each two.

Since they can only reference each other(there are no grounded conductors), the only potential is between each other...120V. Otherwise is undefined/don't care or zero(Static charge only). It does make trouble shooting a bit more difficult since for voltages measurements, earth means nothing. For industrial controls, I always 'ground' a leg of a power supply. It is a real pain to diagnose circuits(control circuits especially) when there is no ground reference(floating system). 'Floating' systems are a tricky thing to diagnose.

@@nhzxboi Well said.

the main feature of this "ungrounded" system, is that the breaker won't trip for a ground fault. GFCI or AFCI trips would be just as bad for the patient.

The locations that require these ungrounded systems ('wet' operating and procedure rooms), can be served by either ungrounded isolated power systems OR GFCI's. The decision is left to the facility on whether to use ungrounded systems (which stay energized with a ground), or GFCI's, which will turn off when grounded. Sometimes the complication of the ungrounded system offsets the risk of vital equipment turning off during a procedure.

@@CraziFuzzy I totally agree. The one goal that was not discussed, was the prevention of a ground fault on one of the two inputs of a vital (i.e. life support) equipment from becoming a show stopper. Naval Combat Ships have above ground electrical systems with isolation monitors. The grounding of one phase during combat will not become a show stopper. I worked with a retired Navy Electrician Chief who shared with me about searching through out the ship, the better part a day for the location of a ground on a phase when its Isolation Monitor went in alarm.

Retired from a large 560 bed hospital that had two LIM panels in each if the 20 plus OR'S . A GFCI should work off a LIM panel because they use a torrid coil to only measure current imbalance between the black ( energized ) & white grounded conductor ( no such thing called a neutral anymore in the NEC. LIM panels NEVER disconnects power on the circuits. It rings an alarm around 4.7 to 4.8 milliamps. Most times the heating pad on OR table is the cause of leakage current.

at that point, he was talking about if the OTHER leg ALSO went to ground while the original ground was still in place.

No.

They were used. Grounding was banned before 1899. It was mandated in 1913 - just 30 years into the commercial electricity and decades before equipment grounding was adopted to protect from shocks. There must have been really good reasons to ground. Essentially in an ungrounded system one can have arbitrary high voltages because of for example lightnings. Accidental grounding is also a problem. Lets say you implemented the split phase system ungrounded and one of the legs grounded accidentally. Now the other leg would have 240 V to the ground - something it never has on a mid point grounded system.

The problem is that "Faults Happen." GFCI (or variations that measure the center tap voltage to earth) can detect these faults and cut off the circuit. Usually, an isolated system will be provided by center tapped transformer secondary's with 60 volts on each side. The center tap will have a resistive connection to ground. This leaks off any static charge but the resistance is high enough to keep life threatening currents from flowing via the earth. Some equipment used in surgeries uses a lot of power and regardless of some current leaking the equipment must continue to operate. That's why there is a monitoring circuit so that someone can address problems before something important is cut off. The reduced voltage to "earth" provides some protection also. Most hospital important equipment has built in battery backup so that even if a circuit trips the equipment will continue to operate.

@@GilmerJohn Well said.

@@GilmerJohn well done nicely explained 👏🏾

@@mathman0101 -- Well, I think you etc. for the complement. I gathered my knowledge from a combination of an old NEC book I picked up from the library sale, some observations of family folks in the hospitals, and just plain common sense. The folks that write the rules are just trying to make things safer without making it impossible to do business. Personally (& with support from an old electrician friend) I believe that sometimes they go way, Way, WAY to far. The "arc fault" CBs are an example. Even the GFCI are a potential problem. These can "fail un-safe." Personally, I would like to see more "balanced" circuits in households with balanced outlets at 120 and 240 volts. The 120 volt outlets would have a lot less danger from shock. The 240 volt outlets would provide no more shock risk than existing 120 outlets but could be protected at lower current levels for the same power or provide better features. (E.g.: a dishwasher could deliver "bone dry" dishes.)

If the center tap is connected to ground, then it is not an isolation transformer? Each leg is then referenced to ground? @@GilmerJohn

RyanJackson618 at Gmail dot com

I'm trying to keep it simple. I agree that, if the conductors lengths are the same, you'll read equal voltage between them when measured to ground (in this case, 60V). But that is strictly capacitance and charging current, and for the purposes of this discussion I'm comfortable saying zero.

@@RyanJacksonElectrical Saying that the voltage is zero because it is not zero and may cause electrocution. The system capacitance will be the complete circuit that will cause elecrrocution if ungrounded conductor will be touched.

@@bobcocampo No. You're not getting electrocuted from a single ground fault on an ungrounded system. That is the entire point of an ungrounded system.

@@RyanJacksonElectrical Check voltage to ground. It is not zero. Touch potential is not zero. Never touch a hot conductor. The main reason for using ungrounded is continuity of service on a line to ground fault

@@RyanJacksonElectrical This is the reason why single phase 2 wire where one line is grounded and only one hot wire