# Grounded B Phase???



## sparks134

Just wondering if anyone has worked on a grounded B phase service! I ve heard of it but never worked on one!:001_huh:


----------



## RIVETER

*Grounded B phase*

Are you talking about a delta secondary and possibly used in an industrial enviornment?


----------



## sparks134

RIVETER said:


> Are you talking about a delta secondary and possibly used in an industrial enviornment?


yeah!:thumbsup:


----------



## RIVETER

*B phase grounded*



sparks134 said:


> yeah!:thumbsup:


 I have not worked with it extensively but have run across it. What is the question for someone ,out there, that has worked it?


----------



## pjmurph2002

Be careful. 

When I was an apprentice, we were hired to come in on a Saturday and clean transformers and check connections for a facility. The JW I was with shut the line side disconnect off, and went to the bathroom. I figured I would start without him. Prior to starting, I checked the terminals inside the transformer. There was voltage present. At that point the JW returned, and I showed him. We opened the disconnect to find that "B" phase was not fused, in had a copper link in place of the fuse.

This is just something that has stayed with me over the years.


----------



## RIVETER

*B phase grounded*



pjmurph2002 said:


> Be careful.
> 
> When I was an apprentice, we were hired to come in on a Saturday and clean transformers and check connections for a facility. The JW I was with shut the line side disconnect off, and went to the bathroom. I figured I would start without him. Prior to starting, I checked the terminals inside the transformer. There was voltage present. At that point the JW returned, and I showed him. We opened the disconnect to find that "B" phase was not fused, in had a copper link in place of the fuse.
> 
> This is just something that has stayed with me over the years.


That would be scary,but if the disconnect was built in recent years, the line side of the copper should have been separated from the line voltage just as the fuses would be.


----------



## pjmurph2002

I don't recall the exact disconnect make / mfg, howerever, I remember that A and C phase were dead on the load side of the switch, but not B phase.

The facility was an older builing.


----------



## RIVETER

*B phase grounded*



pjmurph2002 said:


> I don't recall the exact disconnect make / mfg, howerever, I remember that A and C phase were dead on the load side of the switch, but not B phase.
> 
> The facility was an older builing.


Being an older building explains a lot. You have to be thankful that whoever originally taught you to "TEST" after turning "OFF" any circuit was interested in teaching you that.


----------



## pjmurph2002

I had the good fortune to work with / under a number of quality JW's and had alot of hard nosed old timers for teachers during my schooling.

I am greatful.


----------



## RIVETER

*Grounded B phase*



pjmurph2002 said:


> I had the good fortune to work with / under a number of quality JW's and had alot of hard nosed old timers for teachers during my schooling.
> 
> I am greatful.


And, apparently, rightfully so. If you get the chance, tell THEM.


----------



## micromind

I've seen a few of them, mostly 480. Usually they feed a motor or a group of motors at some remote location. There are two buildings around here that I know of that have them. One has a single phase transformer for 120, the other a 3 phase. Both are quite old, likely 50's, maybe 60's. 

Rob

Not exactly a service, but it's normal for the secondary of potential transformers to be grounded B. Usually, there are two of them connected open delta.


----------



## RIVETER

*Grounded B phase*



micromind said:


> I've seen a few of them, mostly 480. Usually they feed a motor or a group of motors at some remote location. There are two buildings around here that I know of that have them. One has a single phase transformer for 120, the other a 3 phase. Both are quite old, likely 50's, maybe 60's.
> 
> Rob
> 
> Not exactly a service, but it's normal for the secondary of potential transformers to be grounded B. Usually, there are two of them connected open delta.


I think that you are right. Most likely, some installation with a heavier inductive load than a lighting load...Makes sense.


----------



## Bob Badger

pjmurph2002 said:


> Be careful.
> 
> When I was an apprentice, we were hired to come in on a Saturday and clean transformers and check connections for a facility. The JW I was with shut the line side disconnect off, and went to the bathroom. I figured I would start without him. Prior to starting, I checked the terminals inside the transformer. There was voltage present. At that point the JW returned, and I showed him. We opened the disconnect to find that "B" phase was not fused, in had a copper link in place of the fuse.
> 
> This is just something that has stayed with me over the years.


If you where dealing with corner grounded delta it would be a NEC violtion to place a fuse in the grouded phase.

You can buy 'dummy' fuses just for this use.


----------



## Roger

pjmurph2002 said:


> Be careful.
> 
> When I was an apprentice, we were hired to come in on a Saturday and clean transformers and check connections for a facility. The JW I was with shut the line side disconnect off, and went to the bathroom. I figured I would start without him. Prior to starting, I checked the terminals inside the transformer. There was voltage present. At that point the JW returned, and I showed him. We opened the disconnect to find that "B" phase was not fused, in had a copper link in place of the fuse.
> 
> This is just something that has stayed with me over the years.


As Bob said, that would be correct for a corner grounded delta. I am curious though, where were you reading voltage from, this terminal and ground or load side terminal to terminal?

If the system was bonded properly back to this grounded phase you would have read zero (or very little) to ground.

Roger


----------



## sparks134

Bob Badger said:


> If you where dealing with corner grounded delta it would be a NEC violtion to place a fuse in the grouded phase.
> 
> You can buy 'dummy' fuses just for this use.


I believe if it is 1 phase, you can use a 2 pole breaker!!:detective:


----------



## zenayj

sparks134 said:


> Just wondering if anyone has worked on a grounded B phase service! I ve heard of it but never worked on one!:001_huh:


 The infamous "Ghost Leg." It's all over some ranch we do maintanene on.


----------



## MOGAL

I was working on a grounded B phase this spring. Located in the elevator room on a new tower in a major hospital. They were using it to feed the gear for the elevators. I had never worked around it before, as it was a new installation and not actually terminated at the other end I was not dealing with it hot. But i was a 90% apprentice and had only heard of this configuration in school. It was explained that when hot, there would be no voltage induced on the b phase to ground, which can be a dangerous situation if it is not known before hand it is grounded b phase. We placed large warning stickers on all boxes that were related to the feed that it was grounded b phase


----------



## sparks134

warning sign are good!!


----------



## Benny

I'm a second year apprentice, and I am working at a factory that has several areas still using a service with a grounded B phase. You learn to just check everything over rather than just jump into it. Ben


----------



## knowshorts

How about a "grounded B phase" system, where the B phase is actually the Neutral (grounded)? Anyone see one. Saw it on a WWII Nave vessel.


----------



## sparkyob

Coming up through my apprenticeship, this was one of the first things the old timers taught us if we were on a job that had this system. It is very prevalant in the older parts of the major cities here. The old timers always called this the widowmakers leg!!!!!!


----------



## John

I did one last year. gas station/ mini mart need 3 phase for some new equipment and only had 120/240 V single phase....which was a mess
So I installed a new 240 delta service and new panel. Grounded the B phase and but a big LABEL the panel and hooked up the new equipment, no problem.

Did another one where the customer need 3 phase 575 V but only had 120/208 V. Installed a transformer 120/208 Y 3 phase to 575 3 phase delta. grounded the B phase again and but a big LABEL on the disconnect. 

If you label your work..it will not be a surprise to the guy that works on it sometime later.

A grounded B phase is called a "Bastard Leg" around here.


----------



## ampman

sparks134 said:


> Just wondering if anyone has worked on a grounded B phase service! I ve heard of it but never worked on one!:001_huh:


 allmost all the time they don't call it the bastard leg for nothing


----------



## brian john

Yes grounded delta, ungrounded, resistance grounded, solidly grounded.


----------



## RePhase277

ampman said:


> allmost all the time they don't call it the bastard leg for nothing


You are thinking of the delta high leg, which is alot different than the grounded B (aka: corner grounded delta).


----------



## ampman

InPhase277 said:


> You are thinking of the delta high leg, which is alot different than the grounded B (aka: corner grounded delta).


 yes i misred that


----------



## brian john

InPhase277 said:


> You are thinking of the delta high leg, which is alot different than the grounded B (aka: corner grounded delta).


 
They should call it the bitch leg, Because when you hook up a 120 VAC load on that high leg by accident, you sure as hell are going to say SON OF A BITCH.


----------



## varmit

*Corner Grounded Delta*

You don't see this on new services much these days, but it is very common on older industrial buildings. It is quite common as a separately derived system for 230 volt equipment in a plant with a 480 volt service. 

The purpose of a corner ground is equipment and personnel protection. If you do not ground one of the delta connected phases, there is no ground path to blow fuses/ trip breaker on a ground fault. If one of the lines of an ungrounded system shorts to ground, no overcurrent device will trip and the metal , of the equipment COULD become energized. A phase to phase short will still trip the circuit, grounded or not.

Varmit


----------



## brian john

varmit said:


> Y. If one of the lines of an ungrounded system shorts to ground, no overcurrent device will trip and the metal , of the equipment COULD become energized. A phase to phase short will still trip the circuit, grounded or not.
> 
> Varmit


Actually if it is ungrounded system and one of the phases has a fault to a system wide bonded metallic component of the facility you now have a grounded system. THE EQUIPMENT IS NO MORE ENERGIZED than if it was originally a corner grounded system.

The concern is; do the facility personnel now know the ungrounded system is grounded, hence the requirement for ground alarms.


----------



## varmit

You are correct, in theory, in a perfect world it would work the same wherever the ground was, of course the code requires the ground connection at the point of origin of the separately derived system. The problem would arise in a situation where the equipment where the fault is located is not properly grounded. In this case there could be a voltage potential between the machine and any grounded surface nearby.


----------



## Bob Badger

varmit said:


> You are correct, in theory, in a perfect world it would work the same wherever the ground was, of course the code requires the ground connection at the point of origin of the separately derived system. The problem would arise in a situation where the equipment where the fault is located is not properly grounded. In this case there could be a voltage potential between the machine and any grounded surface nearby.


I don't see how the location of the accidental bond changes anything in regards to safety.


----------



## varmit

Yes an ungrounded, or a resistance grounded system SHOULD have ground fault indicators, but many don't.

At several plants, where I do jobs, I have informed the plant folks about existing ground faults and the need to schedule a time to find and fix them. I usually get a response something like- "Everything is running, why spend money." My reply is usually something like "Fix it now to same money later."

At one plant where I have done work off and on for 6 years, there has been a ground fault on the power distribution as long as I have done work there. 
This place has also blown up twice(chem. plant) in the last 25 years. There are still places where safety is ignored.


----------



## piperunner

sparks134 said:


> Just wondering if anyone has worked on a grounded B phase service! I ve heard of it but never worked on one!:001_huh:



Just a few they dont use this much anymore on new stuff i think its dew to testing equipment for the use manufactures dont need the cost to do .

We dont work on them they last for ever !

Actually B phase is the grounded phase but you could ground any phase its just standard practice to do B.

Its solid /grounding tap to B or resistive tap a series resistive for industrial work due to factory needs to run in a fault not shut down the plant so the limiting resistor used on grounded B helps limit the current to a lower level back to transformer and keeps stuff running during problem times .

3 phase 3 wire A&C are ungrounded and protected no overcurrent on B ever unless all phase can be open at same time then its ok .

Any two pole breaker must be rated for corner grounded delta like it must be 1 phase 3 phase marked on breaker label .

This old system is still the king of stabilized voltage to ground but has other issues lots of them in disadvantage so no one uses this anymore only in large projects which need it .

Anything more just ask ill try and answer you questions to the best of what little i know .


----------



## SpliceMan

RIVETER said:


> That would be scary,but if the disconnect was built in recent years, the line side of the copper should have been separated from the line voltage just as the fuses would be.


ive seen this alot in steel plants and any kind of warehouse..its a sh*tty thing lazy workers did 10 15 years ago and still do to this day when they find out that they could use a single phase 120v motor rather then a 3 phase 208 motor to save money ypu see it most common in garadge door openers ,exahuast fan motors,hydrolic pumps,air commpressors added after the the fact..they would plug the b phase with a bar and run 2 or more diconnects off the one for 120v motors .. stupid people kill people.


----------



## Grounded-B

Originally Posted by pjmurph2002 
Be careful. 

When I was an apprentice, we were hired to come in on a Saturday and clean transformers and check connections for a facility. The JW I was with shut the line side disconnect off, and went to the bathroom. I figured I would start without him. Prior to starting, I checked the terminals inside the transformer. There was voltage present. At that point the JW returned, and I showed him. We opened the disconnect to find that "B" phase was not fused, in had a copper link in place of the fuse.

This is just something that has stayed with me over the years.



RIVETER said:


> That would be scary,but if the disconnect was built in recent years, the line side of the copper should have been separated from the line voltage just as the fuses would be.


Perfectly legal and required by the NEC for grounded delta systems. You cannot fuse a grounded conductor - the "B" phase.

Most people think "neutral" when they hear "grounded conductor" but it can be one of the phase conductors.


----------



## Grounded-B

knowshorts said:


> How about a "grounded B phase" system, where the B phase is actually the Neutral (grounded)? Anyone see one. Saw it on a WWII Nave vessel.


There is no "neutral" in a grounded B phase delta system. There is a "white" colored conductor, but it's not a "neutral" A "neutral" carries the unbalanced load, the white conductor in a grounded B phase system is a phase conductor - it carries the same load as the other 2 phase conductors.

Remember - the neutral is always white or grey, but a white or grey conductor is not always the neutral. It is however, always grounded (that is, at a 0V potential to ground)


----------



## brian john

Grounded-B said:


> Originally Posted by pjmurph2002
> Be careful.
> 
> When I was an apprentice, we were hired to come in on a Saturday and clean transformers and check connections for a facility. The JW I was with shut the line side disconnect off, and went to the bathroom. I figured I would start without him. Prior to starting, I checked the terminals inside the transformer. There was voltage present. At that point the JW returned, and I showed him. We opened the disconnect to find that "B" phase was not fused, in had a copper link in place of the fuse.
> 
> .



If he turned off the disconnect, solid link or not the power should be off and the service you did that day should have been to check the disconnects.

If the B phase is grounded this phase is SAFE (relatively) to touch in reference to ground.

I am not sure what you are saying?


----------



## BBQ

Year old thread


----------



## TOOL_5150

BBQ said:


> Year old thread


HAHAH youre catching them all....


~Matt


----------



## BBQ

TOOL_5150 said:


> HAHAH youre catching them all....
> 
> 
> ~Matt


Same guy digging them up ....


----------



## bruce6670

Still interesting though.


----------



## acro

Yes, it is.

I am working on a grounded leg delta now and doing some research.

I do have a question about the grounded leg situations. It seems to me that it would be 33% safer than a "normal" 3 phase installation where one of the phases was not grounded. This is due to the fact that only 2 out of the 3 phases have voltage in reference to ground.

Why is it considered more dangerous? It is just different.

Heck, when I check for voltage before servicing, I check all the phases, not just one.


----------



## Grounded-B

It is 33% safer. That is one of the reasons it is used. It also is cheaper to install, because you are allowed ( and required by the NEC ) to use 2 pole fusible disconnects. Also, 2 main buss pnaleboards with 2pole H rated breakers. This is why people think it's dangerous - because they see what looks like a typical 120/240V single phase panel filled with 2pole breakers. But if you measure hot to ground, you'll read 240V.


----------



## BBQ

Grounded-B said:


> It is 33% safer.


Than what?





> It also is cheaper to install,


I think that is the primary reason.



> because you are allowed ( and required by the NEC ) to use 2 pole fusible disconnects.


Not required, you may use 3 pole, you just cannot fuse the grounded conductor, Buss makes a 'dummy' fuse for this.


----------



## Dennis Alwon

BBQ said:


> Buss makes a 'dummy' fuse for this.


Like putting a penny in the fuse only a piece of pipe instead.


----------



## acro

If you did not take advantage of the "cheaper to install" and used conventional 3 phase disconnects throughout, why in the heck would it be used?

Prevailing convention at the time?


----------



## RePhase277

acro said:


> If you did not take advantage of the "cheaper to install" and used conventional 3 phase disconnects throughout, why in the heck would it be used?
> 
> Prevailing convention at the time?


Delta connected transformers share the current between all three windings, putting less stress on them for high current motor starts, so a delta service is ideal for places with alot of motor load. But grounding a delta service is tricky because there is no neutral point.

It is generally agreed that a grounded service is safer than an ungrounded one, so if you like delta services and you like grounding, you have very few options. Corner grounded systems offer a sensible and effective solution.


----------



## micromind

InPhase277 said:


> Delta connected transformers share the current between all three windings, putting less stress on them for high current motor starts, so a delta service is ideal for places with alot of motor load. But grounding a delta service is tricky because there is no neutral point.
> 
> It is generally agreed that a grounded service is safer than an ungrounded one, so if you like delta services and you like grounding, you have very few options. Corner grounded systems offer a sensible and effective solution.


Plus, a closed delta system will tend to balance voltages better than a wye.


----------



## acro

10-4
Makes sense to me.


----------



## Daddymac

*Grounded B-Phase*

I used to work at an old plant that had grounded B-phase power throughout.
The switch boxes were 3 phase...2 fuses and one copper tube. The old timers said they also used grounded B-phase on trolly and streetcar tracks. I can see why that would save money with the installation, and be safe for pedestrians. Art. 430.85 covers grounded conductors in the NEC.


----------



## Electrifyinit

A lot of the info on this thread is correct but as I skimmed through it quickly I didn’t notice anyone posting one fact about ungrounded systems. I may have missed a post or two as I was just looking for links to ground detector manufacturers.
I believe I got this from the IEEE Buff book. An ungrounded system that develops a ground fault on one phase, especially if it’s intermittent such as a particular motor starting, etc., can experience voltage transients 6 – 8 times the normal L – L voltage which in time can punch holes in the winding insulation of motors, especially small motors, conductors, etc. And of course there is the damage, possibly major depending on the proximity of the faults that can be caused by a phase to ground to phase fault.
I had a costumer that tracked the cost of replacing motors, etc. and after we upgraded their ungrounded Delta with a solid grounded Wye service they did see a huge savings in equipment replacement cost, down time, etc.


----------



## varmit

Electrifyinit said:


> A lot of the info on this thread is correct but as I skimmed through it quickly I didn’t notice anyone posting one fact about ungrounded systems. I may have missed a post or two as I was just looking for links to ground detector manufacturers.
> I believe I got this from the IEEE Buff book. An ungrounded system that develops a ground fault on one phase, especially if it’s intermittent such as a particular motor starting, etc., can experience voltage transients 6 – 8 times the normal L – L voltage which in time can punch holes in the winding insulation of motors, especially small motors, conductors, etc. And of course there is the damage, possibly major depending on the proximity of the faults that can be caused by a phase to ground to phase fault.
> I had a costumer that tracked the cost of replacing motors, etc. and after we upgraded their ungrounded Delta with a solid grounded Wye service they did see a huge savings in equipment replacement cost, down time, etc.


That would seem logical as an ungrounded system can have extremely high, long duration fault currents due to the lack of a return path to open the overcurrent device on a ground fault. On an ungrounded system, the only way for fuses to blow or breakers to trip is from a current overload.


----------



## Bad Electrician

Electrifyinit said:


> I had a costumer that tracked the cost of replacing motors, etc. and after we upgraded their ungrounded Delta with a solid grounded Wye service they did see a huge savings in equipment replacement cost, down time, etc.


If the reason for the ungrounded system was continuity of service, such as a manufacturing facility where a single fault could damage the manufacture processing a better alternative is to install a impedance grounded system.


----------



## LGLS

Bad Electrician said:


> If the reason for the ungrounded system was continuity of service, such as a manufacturing facility where a single fault could damage the manufacture processing a better alternative is to install a impedance grounded system.


Don't utilities sometimes run high tension lines that are ungrounded systems?


----------



## Bad Electrician

IslandGuy said:


> Don't utilities sometimes run high tension lines that are ungrounded systems?


I am not sure but if the system was ungrounded and one phase fell to ground the chance of serious damage to humans could be a major problem.

But I could be wrong


----------



## freeagnt54

varmit said:


> That would seem logical as an ungrounded system can have extremely high, long duration fault currents due to the lack of a return path to open the overcurrent device on a ground fault. On an ungrounded system, the only way for fuses to blow or breakers to trip is from a current overload.


How can you have ground fault currents on an ungrounded system?


----------



## varmit

freeagnt54 said:


> How can you have ground fault currents on an ungrounded system?


You can have a ground fault on any system. The difference would be how the over current devices react to the fault.


----------



## Bad Electrician

freeagnt54 said:


> How can you have ground fault currents on an ungrounded system?


It is a fault, cable failure or insulator failure, the ground is now energized in relation to the other phases. If it is an impedance ground system then you are passing current, though limited.


----------



## freeagnt54

Bad Electrician said:


> It is a fault, cable failure or insulator failure, the ground is now energized in relation to the other phases. If it is an impedance ground system then you are passing current, though limited.


This is true, but irrelevant to my post.

Re-read his post and my post, then try again.


Edit: I'll help you.


varmit said:


> That would seem logical as *an ungrounded system can have extremely high, long duration fault currents due to the lack of a return path* to open the overcurrent device on a ground fault. On an ungrounded system, the only way for fuses to blow or breakers to trip is from a current overload.


----------



## Switched

We still have a few industrial buildings around here like that. I was dumbfounded the first time I worked on one.


----------



## Meadow

2 year old thread :whistling2:


----------



## Bad Electrician

meadow said:


> 2 year old thread :whistling2:


Electricity in it's modern use is well over a 100 years old and we still discuss it.


----------



## Meadow

IslandGuy said:


> Don't utilities sometimes run high tension lines that are ungrounded systems?



They do in some cases, but depends on what you mean by high tension. It is exceptionally rare to run systems above 69kv as ungrounded or even impedance grounded. Often these systems are so large and interconnected that the capacitive reactance to ground alone will produce current values to high (hundreds if not thousands of amps) to keep the system running. Impossible with even short under ground cables since capacitive reactance is so high. Insulating large towers and all equipment phase to phase at that level is very, very expensive. Phase to ground distances go up taking more space. Relaying gets to complex. And generally, in systems like this faults tend to be to infrequent and permanent when they do happen. The cost isn't worth the benefits in transmission above 60kv, assuming it can be done to start with. However, in systems at or below 46kv which tend to be small and radial it can be done, has been and still can be, though in such cases impedance grounding is preferred for newer installations. 

Also Keep in mind that even though a line is 3 wire it does not automatically mean that the supply transformers is ungrounded on its secondary. In the US most 3 wire lines are usually uni grounded Y, even though people mistakenly assume delta. The supply transformer XO is grounded solidly to the substation ground grid as normal, however since the loads on the lines are always phase to phase connected (typical in sub transmission), its cheaper to just eliminate the ground wire. Faults are detected by setting zero sequence relays (ground pick up values) to a few amps. It actually works out well. 

Older utility distribution lines before the 60s (which almost always ran at 2.4kv and 4.8kv) were ungrounded delta. In fact, when pocos started out 95% of the time distribution and in most cases sub-transmission (typically was 11kv or 22kv back then) was 3 wire and ungrounded delta. The supply transformer for these was delta on the secondary and a ground detector indicating relay was employed. When a line grounded down it would signal in the substation that a ground existed. Beauty was when a tree brushed up against a phase no violent flash over would occur, so auto reclosing feeder breakers was needed less. Most US pocos today however solidly ground everything since cost is lower doing so. 


Some pocos do however build new distribution or even sub transmission lines that are capable of operating with a faulted phase for various reasons (primarily where high reliability is needed). California has a lot of pocos that do it and in some parts of the world (like Eastern Europe, Russia, China, the Netherlands) its the norm rather than an exception. I say operate with a faulted phase because in those cases High resistance grounding or Peterson coil earthing is chosen for new installations over an ungrounded system. You still get all the benefits of ungrounded, minus the arc fault overvolates. Relaying gets easier to with a resistor since it allows enough current through for regular CTs and fault realys to detect it. 


Peterson coil grounding is the most complex yet best since it actually goes as far as reducing the fault current in addition to eliminating destruction from arcing ground faults. The Peterson coil is an automatic reactor which adds a reactive component to the ground system which in turn cancels out most current from capacitive coupling between phase and earth. Literally your are correcting "power factor" between phase and ground. Its physically impossible to cancel it all out but you can literally reduce the majority of the current during a ground fault. A large network where 12 amps might flow current can be reduced to half an amp. The reduced current increases the chance of an arc caused by a temporary fault going out on its own. If the fault is permanent you can either continue operating the system without fear of overvoltage while a ground relay senses the neutral shift voltage between phase and ground alerting headquarters its time to go fault hunting (hospital will still have power even though one phase is faulted on the line feeding it) or for non critical loads you can close a resistor in parallel with the Peterson coil that will allow for current to flow on the ground system so standard zero sequence relaying can pick it up. A resistor that produces a current of say, 20amps will be sensed by standard low cost CTs found in all breakers. Standard off the shelf zero sequence time current curves on the feeder breaker or line recloser will trip out the line there after. If the line is part of a loop or mesh system you can even transfer loads off the faulted line to none faulted feeders while the fault is still happening.:thumbup: After the load is transferred the feeder is then tripped off line. The beauty here is that both clearing temporary faults and locking feeders out on permanent faults produce *zero* thermal and magnetic stress and *zero* voltage dips on all the customer. Nobody even knows a squirrel bridge an insulator or in both scenarios 12,000+ customers sharing a 40MVA substation transformer don't experience up to 4 voltage sags. 2000 customers don't notice loop restoration either which can take up to minutes. A solidly grounded system clears a temporary fault with thousands of amps and locks out after closing into a permanent fault up to 4 times. Really makes a difference where desired :thumbsup: 

Long reply but thought someone might be interested about it. 



Bad Electrician said:


> I am not sure but if the system was ungrounded and one phase fell to ground the chance of serious damage to humans could be a major problem.
> 
> But I could be wrong


Same with solidly grounded systems, especially multi grounded neutral systems. (Because MGNs often contain phase to neutral loads ground pick up values must consider normal neutral current on the grounding system)When POCOs design distribution systems their concern isn't so much human safety, rather keeping the lights on at a low price. Typical fuses protecting laterals can hold dozens if not a few hundred amps continuously, same with reclosers and breakers which can hold hundreds if not thousands of amps for some time if not continuously. And don't forget nearly all automatic relays protecting over head lines will reclose after tripping. Even then, a blown fuse is a single phase device, that means remaining phase (s) can back feed the downed wire through load. 


Usually, time current curves are chosen close to the conductor's damage curve or thermal limits of equipment because it works out better: to allow for customer hot/cold load inrush, lightening withstand (normally applicable to fuses to prevent nuisance blowing) and often the biggest factor being to allow for a myriad of protective devices to coordinate with one another out on the line. The more protective devices the higher the next one up will be set so all will be able to coordinate under fault conditions, which means more chances a downed wire will stay live. (substation breaker> trunk line recloser> midline recloser> sectionalizer> lateral branch fuse> lateral midline fuse> lateral spur fuse> side street tap fuse> transformer fused cutout) 

I posted a thread a while back "Dumbest move ever by Firefighters" which showed downed lines remaining energized. The amount of arcing clearly was from well over a dozen amps with conductors arcing until the poco showed up. 


However, your not entirely wrong. In an ungrounded system a downed line is more likely to appear de-enrgized since the current flow is lower, but regardless of system grounding downed lines remaining energized is very common. 


Long reply, but thought it is good discussion from a safety standpoint 




freeagnt54 said:


> How can you have ground fault currents on an ungrounded system?


Capacitive reactance from each phase to ground. All wires between each other and ground will have a weak captive potential. Its this that will cause current to flow on a ground fault. The larger the system the more current, it may be a few micro amps on a very small system to dozens of amps on a very large system. It is very dangerous to assume ungrounded systems pass no current to ground because in most cases that current is high enough to severally injure or even kill. Generally its only a few amps in a typical 240 or 480 volt industrial system but that is enough to be dangerous. 

Ungrounded systems are not designed to keep ground current below a value safe for people. There is one exception and that being ungrounded systems used in hospital ORs and critical care units. Those are designed small enough to keep currents below 5 milli amps during a single ground fault (person between phase and ground) making them unlikely to injure a normal healthy person. (This is why this system can be substituted for GFCIs where interruption of power is not tolerable in hospitals) But, outside of that forget it. Treat all ungrounded systems as though they are solidly grounded even if you know its not. 













varmit said:


> You can have a ground fault on any system. The difference would be how the over current devices react to the fault.


If one wanted to they can employ relaying sophisticated enough to trip branch circuits / feeders on an impedance or ungrounded system. Difficult and usually not worth the price but I have seen it done on MV systems. 






Bad Electrician said:


> It is a fault, cable failure or insulator failure, the ground is now energized in relation to the other phases. If it is an impedance ground system then you are passing current, though limited.


It rises to the square root of 3 on a solid ground fault, this is why everything must be phase to phase rated insulation wise. Even in an impedance grounded system that rise will exist. The lower the impedance of your ground impedance on your XO the less voltage rise compared to the square root of 3 one will have.


----------



## Meadow

Bad Electrician said:


> Electricity in it's modern use is well over a 100 years old and we still discuss it.


I had a change of heart, see above thread. :whistling2::laughing:


----------



## Bad Electrician

meadow said:


> I had a change of heart, see above thread. :whistling2::laughing:


I know, They need a smiley with a "I am just busting your buns", maybe an electrician bent over and he boss taking...............


----------



## Bad Electrician

freeagnt54 said:


> This is true, but irrelevant to my post.
> 
> Re-read his post and my post, then try again.
> 
> 
> Edit: I'll help you.


1. If what I posted was true why would I repost?
2. Why the snarky attitude, I hurt your feelings?
3. I'll help you. Smile and Hug someone you will feel better.


----------



## Bad Electrician

meadow said:


> If one wanted to they can employ relaying sophisticated enough to trip branch circuits / feeders on an impedance or ungrounded system. Difficult and usually not worth the price but I have seen it done on MV systems.
> .


 But in most cases that would defeat the intention of having the impedance grounded system, correct?

Have you seen cases where ungrounded systems were converted to impedance grounded systems?


----------



## Meadow

Bad Electrician said:


> I know, They need a smiley with a "I am just busting your buns", maybe an electrician bent over and he boss taking...............


They do :laughing:





Bad Electrician said:


> But in most cases that would defeat the intention of having the impedance grounded system, correct?
> 
> Have you seen cases where ungrounded systems were converted to impedance grounded systems?



It would defeat one intention that being service continuity. But from a thermal stress stand point it is a good idea. Same as a safety standpoint since the second fault would be a bang. It all boils down to what one is trying to accomplish. 

I have seen a few cases, and its done to help with arc faults. Basically in simplest terms a resistor is selected that passes more current than the capacitive to ground reactance normally would. This helps prevent arc faults from causing overvoltages above the phase to phase value.


----------



## freeagnt54

Bad Electrician said:


> 1. If what I posted was true why would I repost?
> 2. Why the snarky attitude, I hurt your feelings?
> 3. I'll help you. Smile and Hug someone you will feel better.


Sorry bad electrician. It wasn't my intention to come off snarky.


----------

