480 delta to 120/208 Y

[domnic]

On a 480 v corner grounded to transformer 120/208 Y is the grounded leg of 480 v delta always bonded to the frame of the transformer.

 

[templdl]

On a 480 v corner grounded to transformer 120/208 Y is the grounded leg of 480 v delta always bonded to the frame of the transformer.

The manufacturing plant that I worked for always bonded the X0 of a 480v delta -208y/120 to the frame but as I understand it not all manufactures do this I picked up upon when using one as a step up transformer when it is imperative to assure that the X0 was un bonded to the frame and left ungrounded.

 

[ggunn]

On a 480 v corner grounded to transformer 120/208 Y is the grounded leg of 480 v delta always bonded to the frame of the transformer.

I don't know but I wouldn't think so. The grounded phase of the 480 is grounded elsewhere and is essentially a neutral, isn't it? It seems to me that bonding it to the frame of the transformer would be establishing a second neutral to ground bond.

 

[iwire]

No, you never rebond a grounded conductor

 

[augie47]

No, you never rebond a grounded conductor

That would be my answer also {250.24(A)(5)}. The fact that it's a corner grounded system does not relieve you of the requirement to provide an equipment grounding conductor as defined in 250.188 for equipment noted in Art 250 Part VI

 

[domnic]

480 to 120/208

480 to 120/208

So the grounded leg on a delta 480 v to 120/208 v is always bonded to the transformer ?

 

[iwire]

So the grounded leg on a delta 480 v to 120/208 v is always bonded to the transformer ?

No.

If you have a corner grounded supply to any transformer you do not bond the grounded supply conductor again. It is already bonded at its source.

 

[domnic]

delta

delta

No.

If you have a corner grounded supply to any transformer you do not bond the grounded supply conductor again. It is already bonded at its source.

What about a EGC from the source to the transformer housing ?

 

[don_resqcapt19]

What about a EGC from the source to the transformer housing ?

There is a difference between a grounded conductor and an EGC. The grounded conductor is only connected to the grounding conductor at one point....at the main bonding jumper for a service or at the system bonding jumper for a separately derived system.

The primary EGC must be connected to the transformer non-current carrying parts, but that is not the same as connecting the primary grounded conductor to the transformer non-current carrying parts.

Note, for transformers fed by more than two wires, the case of the transformer being supplied from a corner grounded system. is one of the very few cases where you bring a grounded conductor to the primary terminals of a transformer.

 

[domnic]

480 v

480 v

There is a difference between a grounded conductor and an EGC. The grounded conductor is only connected to the grounding conductor at one point....at the main bonding jumper for a service or at the system bonding jumper for a separately derived system.

The primary EGC must be connected to the transformer non-current carrying parts, but that is not the same as connecting the primary grounded conductor to the transformer non-current carrying parts.

Note, for transformers fed by more than two wires, the case of the transformer being supplied from a corner grounded system. is one of the very few cases where you bring a grounded conductor to the primary terminals of a transformer.

Is a neutral a grounded conductor.

 

[templdl]

There is a difference between a grounded conductor and an EGC. The grounded conductor is only connected to the grounding conductor at one point....at the main bonding jumper for a service or at the system bonding jumper for a separately derived system.

The primary EGC must be connected to the transformer non-current carrying parts, but that is not the same as connecting the primary grounded conductor to the transformer non-current carrying parts.

Note, for transformers fed by more than two wires, the case of the transformer being supplied from a corner grounded system. is one of the very few cases where you bring a grounded conductor to the primary terminals of a transformer.

This is the way that I have always looked at it:
It seems like corner grounded Delta's are often foreign to most because a phase is being grounded contrary to our thinking unlike a wye where the X0 is grounded.
I often explain that even though you are corner grounding the Delta you treat that grounded conductor similar to the grounded neutral, that even though it is a phase conductor it is never grounded again. That you must also run an egc which originates from the corner of the Delta that has been grounded similar to the EGC which originates from the grounded X0 of a wye. It is that EGC that is terminated to the transformer enclosure. The grounded phase. Conductor is terminated on on of the 'H' high voltage terminals.
The thing that plays with most minds is that with a corner grounded delta you are grounding a phase conductor unlike a wye.
Does that make sense?

 

[electrofelon]

The thing that plays with most minds is that with a corner grounded delta you are grounding a phase conductor

I have never hooked a corner grounded service or sds, but I have heard people say half jokingly that the first time you throw that switch after "grounding out a phase" is a bit intimidating

 

[Smart $]

Is a neutral a grounded conductor.

In most cases, yes.

 

[MD84]

Is a neutral a grounded conductor.

The simple answer is yes. It is very common to refer to the grounded conductor as the nuetral.

Technically I would say that a nuetral is always a grounded conductor but a grounded conductor is not always a real nuetral.

 

[GoldDigger]

The simple answer is yes. It is very common to refer to the grounded conductor as the nuetral.

Technically I would say that a nuetral is always a grounded conductor but a grounded conductor is not always a real nuetral.

Technically a neutral does not have to be a grounded conductor. It is defined in terms of its voltage relationship to the rest of the circuit conductors.
But with very few exceptions the NEC requires that if a neutral exists it must be grounded.

 

[petersonra]

Technically a neutral does not have to be a grounded conductor. It is defined in terms of its voltage relationship to the rest of the circuit conductors.
But with very few exceptions the NEC requires that if a neutral exists it must be grounded.

Where does it say that? While it is common to ground the neutral of a 480/277 system, I dont recall it being required like it is required on a 208/120 system.

 

[MD84]

Where does it say that? While it is common to ground the neutral of a 480/277 system, I dont recall it being required like it is required on a 208/120 system.

250.20(B)(2)

 

[augie47]

Technically a neutral does not have to be a grounded conductor. It is defined in terms of its voltage relationship to the rest of the circuit conductors.
But with very few exceptions the NEC requires that if a neutral exists it must be grounded.

250.26 appears to contradict that statement.

 

[Smart $]

250.26 appears to contradict that statement.

250.26 applies to systems that are to be grounded, i.e. if the system is to be grounded, it shall be the neutral that is grounded.

Under 250.20(B)(1)&(2) In the case of 480Y/277V 3Ø 3W, the neutral is not required to be grounded because grounding would not result in any 150 volts or less to ground and the neutral is not used as a circuit conductor, so this system can be ungrounded, but can it be corner grounded if so desired? I should note that 250.26 uses the term "neutral conductor" not just "neutral" or "neutral point".

 

[domnic]

480 delta

480 delta

On a 480 v corner grounded to transformer 120/208 Y is the grounded leg of 480 v delta always bonded to the frame of the transformer.

Article 100 definitions BONDED - CONNECTED TO ESTABLISH ELECTRICAL CONTINUITY AND CONDUCTIVITY so the grounded leg of a corner grounded delta must be bonded to case of transformer in a grounded system.