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Fuse or ground one leg of 230VAC???

Fuse or ground one leg of 230VAC???

Fuse or ground one leg of 230VAC???

(OP)
If i had a standard 460 to 230VAC 60hz transformer, do i need to fuse both legs of the secondary 230VAC or am i suppose to just fuse one leg and ground the other.  What does NEC specify?  

RE: Fuse or ground one leg of 230VAC???

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.

RE: Fuse or ground one leg of 230VAC???

(OP)
thank you for the response.  Since this is on a secondary of a transformer, there is no cetertap and it is strictly just 2 legs.  so i guess my answer would be to ground one leg and fuse the other.  correct??

RE: Fuse or ground one leg of 230VAC???

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.

RE: Fuse or ground one leg of 230VAC???

(OP)
thank you for your input rbulsara.  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.

RE: Fuse or ground one leg of 230VAC???

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
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Fuse or ground one leg of 230VAC???

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.

RE: Fuse or ground one leg of 230VAC???

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.

RE: Fuse or ground one leg of 230VAC???

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.

RE: Fuse or ground one leg of 230VAC???

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.

RE: Fuse or ground one leg of 230VAC???

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.

RE: Fuse or ground one leg of 230VAC???

(OP)
stevenal, would this not be applicable to me if i chose to ground one of the conductors in my 230VAC.

RE: Fuse or ground one leg of 230VAC???

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.

RE: Fuse or ground one leg of 230VAC???

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

RE: Fuse or ground one leg of 230VAC???

(OP)
i agree with you waross.  but heres the question...is one option more correct than the other?  

RE: Fuse or ground one leg of 230VAC???

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.

RE: Fuse or ground one leg of 230VAC???

"...is one option more correct than the other?"

Yes.

Oh, did you want us to decide? No can do with the limited information you've provided. Besides, that's why you make the big bucks.

RE: Fuse or ground one leg of 230VAC???

(OP)
Thank you for everyone's responses!!!

RE: Fuse or ground one leg of 230VAC???

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

RE: Fuse or ground one leg of 230VAC???

i agree with waross..

and davidbeach..to the extent that a disconnect in a grounded conductor is not prohibited ( i said should not), but I would not have it unless required otherwise for some reason ( a trasfer switch between two separate grounded sources would be one..).

We can go on and on this subject. It is very simple for the people who understand grounding and can be very confusing to one who do not. I think, OP got more than adequate answers. If this is still not sufficient for the task at hand, I have nothing to add.

If safety is foremost in my priorities, I would choose a grounded system over ungrounded. This again can be a topic of debate for some, but not for me.

RE: Fuse or ground one leg of 230VAC???

Where'd you get that transformer?  I can't find anything like it in the catalogs.  All they show is 120x240-volt secondary.

Care to share the manufacturer & model number?

Are you absolutely sure you can't pull a center-tap neutral out of your transformer?

RE: Fuse or ground one leg of 230VAC???

Hi peebee;
230/460 was a common transformer voltage years ago. it is interchangable with a 240/480 volt transformer.
It may be from the UK or EU.
Pulling a center-tap out of a transformer that does not have one will void the approvals unless done by a shop with the authority to issue approvals on rebuilt equipment. For a small transformer that would probably cost more than a new transformer, particularly if it is potted.
Also, older  electricians and engineers sometimes habitually refer to 120/240/480 systems as 115/230/460. That may have been the standard voltage when they recieved their training, or it may have been the voltage current when their mentors were trained. Unless there is a particular reason to know the exact voltage, I regard references to 220V, 230V, and 240V as equal.
If the exact voltage is important, measure it. It is seldom exactly 240 Volts, and if it is 240 volts at lunch time it will probably not be 240 volts at supper time.
respectfully

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