3 phase wiring question

[Smart $]

One issue is that ballast reliability can be compromised with improper grounding.

A ballast maybe rated for 240v across terminals, but it may not be designed to have 240v across its casing and any of the terminals.

I suppose this could be true... but in my experience, and IMO, it is not.

 

[acrwc10]

Voltage doesn't build up, nor does it exceed source voltage. Where there is only one line to ground fault, the respective line's voltage is reduced to or near zero using the GES as a reference and current is typically minimal. Only on a second line to ground fault does it potentially become dangerous. If to the same line as the first, parallel current paths are established for operating circuits, while the circuits' ocpd's may not trip. If second line to ground fault is of another line, the system functions similar to an intentionally grounded system.

Then I guess, third generation harmonics can not exist either.
To say that an un-grounded system with out ground detection "is safe" is foolish. If they are safe why are they not allowed? except in very limited installations ?

 

[acrwc10]

Capacitance is the wrong term, I should have said Over voltage. Ungrounded systems are only safer then the shutting down a process that shut down would be a greater hazard.

(Copied material)
Ungrounded systems operate without a grounded conductor. In other words, none of the circuit conductors of the electrical system are intentionally grounded to an earth ground such as metal water pipe, or building steel. The same network of equipment grounding conductors is provided for ungrounded systems as for solidly grounded electrical systems. However,equipment grounding conductors (EGCs) are used only to locate phase-to-ground faults and sound some type of alarm. Therefore, a single sustained line-to-ground fault does not result in an automatic trip of the over current protection device. This is a major benefit if electrical system reliability is required or if it would result in the shutdown of a continuous process. However, if an accidental ground fault occurs and is allowed to flow for a substantial time, over voltages can develop in the associated phase conductors. Such an over voltage situation can lead to conductor insulation damage, and while a ground fault remains on one phase of an ungrounded system, personnel contacting one of the other phases and ground are subjected to 1.732 times the voltage they would experience on a solidly neutral grounded system.

 

[hurk27]

One issue is that ballast reliability can be compromised with improper grounding.

A ballast maybe rated for 240v across terminals, but it may not be designed to have 240v across its casing and any of the terminals.

so a 240 volt ballast could not be used on a 240 volt corner grounded delta?

Even using a multi-tap ballast on 120 volts will have 240 volts between the casing and the 240 volt tap, as it would when the 277 volt tap is used.

The primary side of any multi tap ballast is nothing but a auto transformer, so any time you apply a voltage to one of the taps the other taps will be at there corresponding voltage, the reason we must cap the unused taps.

 

[hurk27]

Capacitance is the wrong term, I should have said Over voltage. Ungrounded systems are only safer then the shutting down a process that shut down would be a greater hazard.

(Copied material)
Ungrounded systems operate without a grounded conductor. In other words, none of the circuit conductors of the electrical system are intentionally grounded to an earth ground such as metal water pipe, or building steel. The same network of equipment grounding conductors is provided for ungrounded systems as for solidly grounded electrical systems. However,equipment grounding conductors (EGCs) are used only to locate phase-to-ground faults and sound some type of alarm. Therefore, a single sustained line-to-ground fault does not result in an automatic trip of the over current protection device. This is a major benefit if electrical system reliability is required or if it would result in the shutdown of a continuous process. However, if an accidental ground fault occurs and is allowed to flow for a substantial time, over voltages can develop in the associated phase conductors. Such an over voltage situation can lead to conductor insulation damage, and while a ground fault remains on one phase of an ungrounded system, personnel contacting one of the other phases and ground are subjected to 1.732 times the voltage they would experience on a solidly neutral grounded system.

I'm not sure where you got that from, but it is totally false.

If a phase were to go to ground in a ungrounded system you would only have the voltage that would be phase to phase, such as 240 volt system would be 240 volts, there is no way it would be 1.732 higher, or you could never have a corner grounded delta, because that is what happens in a ungrounded system, it becomes a corner grounded delta!

there are many of the old school who will tell you that an ungrounded system is a much safer system, and even pool requirements in article 680 show this on LV pool lights where we are not to ground the output of the transformer, if you don't have a reference to ground you don't have a current path to be shocked from, but in a large facility with long wire runs you will have capacitive coupling that will cause varying voltage to appear between the ungrounded conductors and Earth but have very little available current, most wiggy type meters will pull this very weak voltage down to nothing, but it still poses a hazard, but never higher then the system voltage, most of the ungrounded systems I have worked on were 480 volts, which I would expect to see with a high impedance DVM anywhere around 0 volts to 480 volts, but never higher then the system voltage.

Like I said ungrounded systems have been around for a long time, and it has only bee recently that they were required to have monitoring on them, about the "80"s and if you treat them as a grounded system you are no more likely to be shocked then a grounded system, as far as the higher voltage being said in the material you posted that is false.

Remember we are talking about circuits run in a facility inside of a grounded to Earth raceway, not conductors run in open air where static voltages can be developed, which can exceed much higher voltages like that with power lines.

These two are not the same.

If we were talking about free air conductors then your (Copied material) would be true, well not about the 1.732 part

 

[hurk27]

Ok I had to re-read it before it hit me:

if an accidental ground fault occurs and is allowed to flow for a substantial time, over voltages can develop in the associated phase conductors. Such an over voltage situation can lead to conductor insulation damage,

ok this part I do not accept, as most of the conductors use will have an insulator voltage rating higher then the system voltage that there used on.

and while a ground fault remains on one phase of an ungrounded system, personnel contacting one of the other phases and ground are subjected to 1.732 times the voltage they would experience on a solidly neutral grounded system.

yes in a Y system you would have 1.732 volts less to ground than in a delta, grounded or not, but the NEC allows both and there is no restrictions on a corner grounded delta other then everything has to be rated for the system voltage to ground, Ie... wire must be rated for more then 240 volts, breakers have to be rated for 240 volts, switches have to be rated for 240 volts, 480 for a 480 volt system, and this is for both ungrounded and corner grounded systems.

this is like saying we can't use a delta service?

 

[Smart $]

Then I guess, third generation harmonics can not exist either.
To say that an un-grounded system with out ground detection "is safe" is foolish. If they are safe why are they not allowed? except in very limited installations ?

My comments mentioned nothing about [the degree of] safety (or danger). Even with a compliant electrical system there are various levels of potential danger present, and with each, one or more counterposed measures of safety. One issue of non-compliance doesn't change the system from safe to unsafe, but rather increases the potential danger and defeats at least one measure of safety.

If you want an ultimately safe system, remove it.

 

[Electric-Light]

so a 240 volt ballast could not be used on a 240 volt corner grounded delta?

Even using a multi-tap ballast on 120 volts will have 240 volts between the casing and the 240 volt tap, as it would when the 277 volt tap is used.

The primary side of any multi tap ballast is nothing but a auto transformer, so any time you apply a voltage to one of the taps the other taps will be at there corresponding voltage, the reason we must cap the unused taps.

Long time reliability can over a large sample can still be affected adversely. A 277v ballast is designed for 480Y/277 with 277v with respect to ground, but 208 or 240v components are usually designed with 120v with respect to ground.

480v ballasts for example, are not designed to have anything floating over 277v over ground

 

[don_resqcapt19]

While I don't have the background or knowledge to explain it, there can be cases of extreme over voltage on an ungrounded system where there is a fault with inductive reactance to ground on an ungrounded system. Beeman, in "Industrial Power Systems Handbook" says in extreme cases the voltage can rise to 10 times system voltage. He gives the example of a ground fault on a control wire to a coil in a starter as being able to provide the inductive reactance that can cause this overvoltage. Another example is a ground fault on a transformer lead where the fuse between the power circuit is open and the fault is on the transformer side of the fuse.

 

[Electric-Light]

While I don't have the background or knowledge to explain it, there can be cases of extreme over voltage on an ungrounded system where there is a fault with inductive reactance to ground on an ungrounded system. Beeman, in "Industrial Power Systems Handbook" says in extreme cases the voltage can rise to 10 times system voltage. He gives the example of a ground fault on a control wire to a coil in a starter as being able to provide the inductive reactance that can cause this overvoltage. Another example is a ground fault on a transformer lead where the fuse between the power circuit is open and the fault is on the transformer side of the fuse.

Electronic ballasts are particularly sensitive to transients. When they experience failure, its not necessarily that they're prone to failure.

Just as you can drop a plastic cup without breaking many times while you get one shot with a glass. It's not that glass is lower quality for proper use. It's just not as tolerant of abusive conditions.

 

[acrwc10]

While I don't have the background or knowledge to explain it, there can be cases of extreme over voltage on an ungrounded system where there is a fault with inductive reactance to ground on an ungrounded system. Beeman, in "Industrial Power Systems Handbook" says in extreme cases the voltage can rise to 10 times system voltage. He gives the example of a ground fault on a control wire to a coil in a starter as being able to provide the inductive reactance that can cause this overvoltage. Another example is a ground fault on a transformer lead where the fuse between the power circuit is open and the fault is on the transformer side of the fuse.

Thank You.
I could not remember where I had read it so I could not quote the source.

 

[hurk27]

While I don't have the background or knowledge to explain it, there can be cases of extreme over voltage on an ungrounded system where there is a fault with inductive reactance to ground on an ungrounded system. Beeman, in "Industrial Power Systems Handbook" says in extreme cases the voltage can rise to 10 times system voltage. He gives the example of a ground fault on a control wire to a coil in a starter as being able to provide the inductive reactance that can cause this overvoltage. Another example is a ground fault on a transformer lead where the fuse between the power circuit is open and the fault is on the transformer side of the fuse.

While the only one I have ever experienced was a transformer 480 primary with a 240 grounded phase (intentionally) secondary, the problem was, who ever hooked up the secondary bonded the X1/X3 connection instead of the X2/X4 and when the 480 volt system went to ground on H4 side of the primary, it caused this transformer to behave like an auto transformer, giving an additive voltage between the H1 on the 480 side and X2/X4 on the secondary side which gave us about 720 volts between the two systems, luckily nothing was effected since no loads sourced both systems, and was caught during a shutdown time, we checked all other control transformers and found five more with the X1/X3 bonded instead of the X2/X4, these were just small control transformers,
but what I can't see is how a inductive reactive circuit would rise the whole system voltage when you still have the transformer windings across the phases which would limit the voltage through its impedance? to me this would have to be in a very local loop isolated to where the inductive fault was placed, its been a while since I done major industrial work, but I cant for the life of me ever remember having a problem like this (other then the one we found above) this sounds like having an inductive kick back that is occurring continuously at 60 hz, which would make sense, but as it says this would be a extremely rare occurrence? Kind of like one of those What if's that code can't be enforced on?

As to the OP it sounds like a plant that has a bottling production line, which could meet the requirements of having an ungrounded system, sounds also like it was wired back before the requirements of ground monitors, yes it would be beneficial to install ground monitors because it will tell them when a phase goes to ground, and allow for a safe proper shutdown, and repair,

but even with the added info from don, this would still not effect a circuit phase going to ground, whether it is a feeder or a branch circuit, a OCPD will not open and everything will keep operating till a second phase were to go to ground, this would be nothing more that having a grounded phase system at this point, which to me would pose no additional threat, but could cause an event of un-necessary shutdown if a second phase went to ground before they repaired the first fault, so yes a ground monitor would benefit the production staying up and running, but to me nothing else. oh and ground/phase monitors don't trip anything, thats what a GFP does, which would not work on a ungrounded system.

 

[hurk27]

After rereading Dons post, I can now see where an inductive reactance can couple with the capacitive coupling on the grounding of a ungrounded system, and cause an oscillation of a much higher voltage to appear between a phase conductor and the grounding, but would this voltage carry any damaging amount of current? to me this would be kind of like hitting a circuit conductor with a Hi-Pot test? just a longer one.:roll:

 

[acrwc10]

While the only one I have ever experienced was a transformer 480 primary with a 240 grounded phase (intentionally) secondary, the problem was, who ever hooked up the secondary bonded the X1/X3 connection instead of the X2/X4 and when the 480 volt system went to ground on H4 side of the primary, it caused this transformer to behave like an auto transformer, giving an additive voltage between the H1 on the 480 side and X2/X4 on the secondary side which gave us about 720 volts between the two systems, luckily nothing was effected since no loads sourced both systems, and was caught during a shutdown time, we checked all other control transformers and found five more with the X1/X3 bonded instead of the X2/X4, these were just small control transformers,
but what I can't see is how a inductive reactive circuit would rise the whole system voltage when you still have the transformer windings across the phases which would limit the voltage through its impedance? to me this would have to be in a very local loop isolated to where the inductive fault was placed, its been a while since I done major industrial work, but I cant for the life of me ever remember having a problem like this (other then the one we found above) this sounds like having an inductive kick back that is occurring continuously at 60 hz, which would make sense, but as it says this would be a extremely rare occurrence? Kind of like one of those What if's that code can't be enforced on?

As to the OP it sounds like a plant that has a bottling production line, which could meet the requirements of having an ungrounded system, sounds also like it was wired back before the requirements of ground monitors, yes it would be beneficial to install ground monitors because it will tell them when a phase goes to ground, and allow for a safe proper shutdown, and repair,

but even with the added info from don, this would still not effect a circuit phase going to ground, whether it is a feeder or a branch circuit, a OCPD will not open and everything will keep operating till a second phase were to go to ground, this would be nothing more that having a grounded phase system at this point, which to me would pose no additional threat, but could cause an event of un-necessary shutdown if a second phase went to ground before they repaired the first fault, so yes a ground monitor would benefit the production staying up and running, but to me nothing else. oh and ground/phase monitors don't trip anything, thats what a GFP does, which would not work on a ungrounded system.

You are assuming that the second phase to "ground" (which is actually not ground because the system is not grounded) is going to be at a point in the system that can carry the full fault current and not burn up. Or the fault is not somehow isolated from the first fault. There are "Burn clear or Burn down" scenarios that could occur. Along with the possibility of a resistance in the path between the two faults that could cause a shock hazard to a person.

 

[acrwc10]

A fault could also be an "arching fault" that doesn't burn clear or trip the OCP. In a bottling plant you could expect wet (conductive) conditions that could put a person in the path between the two faults. Say one hand on a conduit and the other hand on the faulting equipment. Difference in potential.

 

[hurk27]

You are assuming that the second phase to "ground" (which is actually not ground because the system is not grounded) is going to be at a point in the system that can carry the full fault current and not burn up. Or the fault is not somehow isolated from the first fault. There are "Burn clear or Burn down" scenarios that could occur. Along with the possibility of a resistance in the path between the two faults that could cause a shock hazard to a person.

Why would this be any different from a grounded system? all equipment are required to have EGC's and bonding just like a grounded system, and grounding electrodes at the service, all parts of machinery are required to be bonded, and fault current paths should be intact in a code compliant install. there just wont be a fault path for the first fault back to source on a fault, but on a second fault there would be, as long as you have a code compliant install.

A fault could also be an "arching fault" that doesn't burn clear or trip the OCP. In a bottling plant you could expect wet (conductive) conditions that could put a person in the path between the two faults. Say one hand on a conduit and the other hand on the faulting equipment. Difference in potential.

An "arching fault" can happen in either system, bad grounding practices can happen in either systems, "What If's" can happen in either system?? not sure where your going with this one?

Both systems will have grounding that will bring all parts of equipment to one plane of voltage, both will also have a connection to Earth through a grounding electrode system, just one wont have a path back to source until a second fault happens. that is the only difference between the two systems.

Sort of two strikes your out system instead of a one strike your out system.

I wonder if you would have a problem with Europe's ungrounded systems, of course they use an RCD but the principle is the same. with no fault current path to Earth less electrocutions, less fires.

 

[acrwc10]

Why would this be any different from a grounded system? all equipment are required to have EGC's and bonding just like a grounded system, and grounding electrodes at the service, all parts of machinery are required to be bonded, and fault current paths should be intact in a code compliant install.

And we all know every system is in perfect opperating condition.:-?
Thats a good one. LMAO Like I said if they were inherently safer systems they would not be so restricted in there use.

 

[hurk27]

And we all know every system is in perfect operating condition.:-?
Thats a good one. LMAO Like I said if they were inherently safer systems they would not be so restricted in there use.

I guess after doing some more research into this, the problem of this stray voltage that can occur, is possible, but in my many years or working on these ungrounded systems I have never ran across this problem, at least never identified it as such, back then we didn't have to many electronics that would have been fed from a ungrounded system directly with out its own isolating transformer, soft starts where just coming out, and VFD's were not perfected enough so we didn't see much of them, guess I'm learning too:roll: I can see where MOV's would do a good job between the line conductors and ground on this type of installation though.

but this voltage would only be between L/G and should be shunted L/L also this voltage is described as a ghost voltage and is drained off fairly easily by even the coil of a solenoid type voltage tester, but is has been said it does damage electronics.
What I have read is that this voltage will be present when the grounding is floating, but not when a circuit conductor is grounded

The thing I do read in the NEC is grounding a system that will have a voltage to grounding above 150 volts is a permission in the NEC not a requirement 250.20(B)(1) and (250.21(A). with that in mind, the picture kind of looks different of course this is only for a delta, as both a Y is required to be grounded, and a 4-wire delta where there is a center tap between two phase, better known as a high leg delta.

So why a straight delta is treated differently, I'm not sure?

 

[don_resqcapt19]

After rereading Dons post, I can now see where an inductive reactance can couple with the capacitive coupling on the grounding of a ungrounded system, and cause an oscillation of a much higher voltage to appear between a phase conductor and the grounding, but would this voltage carry any damaging amount of current? to me this would be kind of like hitting a circuit conductor with a Hi-Pot test? just a longer one.:roll:

The book also cites an intermittent arcing ground fault as being able to produce voltages 5 or 6 times normal, with enough current to cause motor failures.

 

[hurk27]

The book also cites an intermittent arcing ground fault as being able to produce voltages 5 or 6 times normal, with enough current to cause motor failures.

I seen this but very perplex with it, thinking out the circuit, I can't see where the current would be from to provide enough current to cause an arc? most of the stray voltages we would measure would be drawn off by a simple load such as a coil of a solenoid type voltage tester, and the few reference I looked at seem to support this, but if this arcing was because of a phase went to ground then you have a corner grounded system and this would apply to that type of a system also, but no where does any reference say it does?

Off subject:
Has anyone had a laugh at what the spell checker want's to change some of our user names too? Don's is Escaped
Mine is Huck:roll: