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Fuse or ground one leg of 230VAC???
- Thread starter nwong16
- Start date
davidbeach
Electrical
The NEC would have you ground the center tap of the 230 so that you do not have a phase conductor more than 150V to ground. You would then need to fuse both phase conductors.
If physically not possible to ground such that you limit voltage to ground to 150V or less, such as if there is no center tap connection, then you would ground one leg and fuse the other.
If physically not possible to ground such that you limit voltage to ground to 150V or less, such as if there is no center tap connection, then you would ground one leg and fuse the other.
- Thread starter
- #3
Is this a single phase 2-winding transformer?
If so, you can ground any one of the ends of the 230V side and it can be treated as a grounded conductor (as if it were a grounded neutral) and you do not have to fuse it. Fuse the ungrounded leg.
Look up NEC 450 for more information on transformers. It is self explanatory.
If so, you can ground any one of the ends of the 230V side and it can be treated as a grounded conductor (as if it were a grounded neutral) and you do not have to fuse it. Fuse the ungrounded leg.
Look up NEC 450 for more information on transformers. It is self explanatory.
- Thread starter
- #5
Skogsgurra
Electrical
Agree with davidbeach and rbulsara. Ground one leg and fuse the other. Why complicate things? If there is a debate in your company, it probably is because your collegues do not "know how". Finding out is a lot better than discuss matters that do not need to be discussed.
Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
The key is to understand the difference bewteen a neutral and a "grounded" conductor. Also understant the differenc between a "grounded conductor" and a "grounding" or "ground" condcutor. Again, read up NEC 250.
In theory any one and only one of the conductors of a power system (source) can be grounded. When a neutral is available, it is a preferred conductor to be grounded, but it does not have to be so. Also not all systems have a neutral.
All single phase system have two phases as hot until one of them is grounded. The grounded one then is loosely referred to as a neutral.
In theory any one and only one of the conductors of a power system (source) can be grounded. When a neutral is available, it is a preferred conductor to be grounded, but it does not have to be so. Also not all systems have a neutral.
All single phase system have two phases as hot until one of them is grounded. The grounded one then is loosely referred to as a neutral.
dgbpeakpwr
Electrical
nwong16
"There seems to be so much debate about grounding a hot leg here at my company. Does anyone else have additional input regarding groudning the hot leg of a 230VAC secondary of a tranformer."
I think the problem is that there is no “Hot leg” or “Neutral leg” until one leg is connected (referenced) to ground. Once that is done the other leg is the “Hot leg” and should be fused.
Your not actually grounding a hot leg.
"There seems to be so much debate about grounding a hot leg here at my company. Does anyone else have additional input regarding groudning the hot leg of a 230VAC secondary of a tranformer."
I think the problem is that there is no “Hot leg” or “Neutral leg” until one leg is connected (referenced) to ground. Once that is done the other leg is the “Hot leg” and should be fused.
Your not actually grounding a hot leg.
dgbpeakpwr
Electrical
That was not the greatest explanation, as I could see someone reading a potential on both legs and thinking they were both “hot” legs.
All there is before connection is an unreferenced difference in potential. How this appears on a meter, (measured to ground)if the primary side is connected would depend on how or where the system is grounded on the primary side. There will be 230 volts between them, however, the voltage from each leg to ground could (and probably will) be different.
You decide which leg is neutral, however, it is usually selected based on the grounding of the primary side. This is to keep the phasing the same. If it is reversed the phasing is 180 deg out. Most of the time it is only important if paralleling or using alternate sources to feed a load.
All there is before connection is an unreferenced difference in potential. How this appears on a meter, (measured to ground)if the primary side is connected would depend on how or where the system is grounded on the primary side. There will be 230 volts between them, however, the voltage from each leg to ground could (and probably will) be different.
You decide which leg is neutral, however, it is usually selected based on the grounding of the primary side. This is to keep the phasing the same. If it is reversed the phasing is 180 deg out. Most of the time it is only important if paralleling or using alternate sources to feed a load.
In fact the term "hot" is not a Code recognised term, the correct term is "ungrounded". NEC requires all ungrounded condcutors to contain overcurrent protection and disconnecting means. Grounded conductors should not have overcurrent protection or a disconnecting means.
So if someone decides to keep the 230V side of a single phase transformer ungrounded, then both legs will require fuses/breakers.
dgb: The primary side grounding has nothing to do with secondary side grounding for transformers with electrically isolated primary and secondary windings.
So if someone decides to keep the 230V side of a single phase transformer ungrounded, then both legs will require fuses/breakers.
dgb: The primary side grounding has nothing to do with secondary side grounding for transformers with electrically isolated primary and secondary windings.
davidbeach
Electrical
rbulsara, Your comment "Grounded conductors should not have overcurrent protection or a disconnecting means." is somewhat misleading. The grounded conductor certainly should not have any independent overcurrent protection or disconnecting means, but there is no prohibition in using multi-pole circuit breakers as overcurrent protection or multi-pole switches as disconnecting means as long as these multi-pole devices open all ungrounded conductors along with the grounded conductor.
Ungrounded single phase systems not only require overcurrent protection on both legs, but require ground detection as well. As suggested, read the code.
- Thread starter
- #13
I see two possible interpretations of 250.20(B)(1) in this circumstance, (assuming this is premises wiring so B applies)
1. Impossible to ground the existing 230 V transformer to meet the 150V rule.
2. Anything is possible given enough time and money. Replace transformer with one that has a center tap.
Modification of above advice: Read code and speak to inspector.
1. Impossible to ground the existing 230 V transformer to meet the 150V rule.
2. Anything is possible given enough time and money. Replace transformer with one that has a center tap.
Modification of above advice: Read code and speak to inspector.
- Moderator
- #15
hi friends;
I read it this way;
The 150 volt rule does not require grounding. Grounding is optional.
Option #1, Ground one line.
Switches and breakers are only required in the ungrounded leg.
No fuses are allowed in the grounded line.
Switches and/or breakers may be single pole however two pole switches and/or breakers must open both lines simultaneously, not only in the circuit protection but in any attached devices.
Option #2, leave the circuit ungrounded.
Both lines must be protected by fuses or breakers.
Switches and/or breakers must open both lines simultaneously.
Switches and or breakers must be two poles.
Ground detection must be provided.
I would choose to ground one line.
respectfully
I read it this way;
The 150 volt rule does not require grounding. Grounding is optional.
Option #1, Ground one line.
Switches and breakers are only required in the ungrounded leg.
No fuses are allowed in the grounded line.
Switches and/or breakers may be single pole however two pole switches and/or breakers must open both lines simultaneously, not only in the circuit protection but in any attached devices.
Option #2, leave the circuit ungrounded.
Both lines must be protected by fuses or breakers.
Switches and/or breakers must open both lines simultaneously.
Switches and or breakers must be two poles.
Ground detection must be provided.
I would choose to ground one line.
respectfully
- Thread starter
- #16
dgbpeakpwr
Electrical
If the use falls under the definition of “Premises” wiring I would say that 250.20 (b) (1) would prohibit the use of transformer. If not then 250.21 applies and grounding is optional.
If choosing to go the ungrounded route, I believe that fuses are out of the picture as they operate independently.
rbulsara: You are right phasing is rarely an issue in the single phase low voltage world.
If choosing to go the ungrounded route, I believe that fuses are out of the picture as they operate independently.
rbulsara: You are right phasing is rarely an issue in the single phase low voltage world.
- Thread starter
- #19
- Moderator
- #20
Is one option more correct than the other?
There is a general answer to this, however there are some important exceptions.
If this is a contest as to who is right and who is wrong, then the person who says that there is only one option may be wrong.
Grounded: I prefer grounded.
The component count and cost is less.
Trouble shooting is much easier. Many years ago I had experience trouble shooting control circuits in large sawmills. With grounded control circuits a signal could be followed by checking with a voltmeter to ground. When you passed the open device the voltage to ground would drop to zero. I spent some time in a large mill with ungrounded control circuits. Almost every terminal in the system was at 55 volts to ground. The fastest way to trouble shoot was to add a temporary ground.
Ungrounded: An ungrounded circuit is sometimes selected to reduce shock hazards.
Exceptions: In the US and Canada there are special circumstances where an isolating transformer is used for extreme safety. These circuits are usually 120 volts.
A common instance will be some 120 volt circuits in an operating theatre. The allowable leakage current and the resulting possible shock hazard is much less normal installations. The insulation resistance must be very high and the circuit capacitance to ground must be very low.
This is not so much a question of which option is better as it is a question of which way does the boss want it.
respectfully
There is a general answer to this, however there are some important exceptions.
If this is a contest as to who is right and who is wrong, then the person who says that there is only one option may be wrong.
Grounded: I prefer grounded.
The component count and cost is less.
Trouble shooting is much easier. Many years ago I had experience trouble shooting control circuits in large sawmills. With grounded control circuits a signal could be followed by checking with a voltmeter to ground. When you passed the open device the voltage to ground would drop to zero. I spent some time in a large mill with ungrounded control circuits. Almost every terminal in the system was at 55 volts to ground. The fastest way to trouble shoot was to add a temporary ground.
Ungrounded: An ungrounded circuit is sometimes selected to reduce shock hazards.
Exceptions: In the US and Canada there are special circumstances where an isolating transformer is used for extreme safety. These circuits are usually 120 volts.
A common instance will be some 120 volt circuits in an operating theatre. The allowable leakage current and the resulting possible shock hazard is much less normal installations. The insulation resistance must be very high and the circuit capacitance to ground must be very low.
This is not so much a question of which option is better as it is a question of which way does the boss want it.
respectfully
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