I didn't say "grounded" i said "grounding" but yes
corner ground delta
- Thread starter craig65
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This system is still strange to me but i know a lot more now that i did yesterday.In my mind it makes me a better electrician. I never stop learning and I do my best to leave nothing to chance...or the next guy. this trade is not what I do it is what am
the first journeyman I worked with told me that when you strap on a tool belt
and do what we do..it is like straping on a gun belt...if you use poor judgement you will kill someone. So be smart, be careful, and be good at it
and I have this forum to thank for a great deal of the being good part
hillbilly1
Senior Member
- Location
- North Georgia mountains
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- Owner/electrical contractor
I didn't say "grounded" i said "grounding" but yes
Just checking, I thought thats what you meant.
Like I said I dont deal alot with delta systems,so I'm not 100% sure of what I'm doin
Like I said I dont deal alot with delta systems,so I'm not 100% sure of what I'm doin
is the lighting system 277V?
Are they connected to the 120/208 neutral?
Does any one see where this is going?
Wye to Delta load.
Like I said I dont deal alot with delta systems,so I'm not 100% sure of what I'm doin
is the lighting system 277V?
Are they connected to the 120/208 neutral?
Does any one see where this is going?
Wye to Delta load.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
the 480 delta windings have no reference to ground until one of the phases is bonded, once bonded this reference is 480 volts to each of the other phases, there is no 277 volt potential anywhere. if there is no bond the voltage to ground is unpredictable for the most part and will vary with every unimaginable change
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
I think the problem is utility's don't use a common core transformer like the OP is, without the common core there is no problem with bonding the X0 point in a Y-Y installation, but in a common core transformer, an imbalance on the secondaries (480v side) will cause a higher imbalance in the Y (208 side) proportional to the ratio of the transformer, this imbalance can over load a single primary winding if the X0 is bonded hence why we float it.
I will add that it is more common to bond the "B" phase of the delta.
I will add that it is more common to bond the "B" phase of the delta.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
If the cause is electrical in nature, and not magnetic, I don't think that is the difference. When transforming between wye and delta, one phase's current on the wye side is split between two on the delta side, and vice versa.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
You must remember current only returns to source, each transformer is an isolating "new" source.
since only the circuits ahead of this transformer have a reference to ground, the secondaries of this transformer will not have a reference to ground, so you could bond any phase to ground and there would be no current until a second phase went to ground. but like I said above and Jim have mention, it is common to bond the "B" phase, and the "B" phase will now have to be white where used as a current carrying conductor. this could be a whole new can of worms to open.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
You might be right as I was told this when I ran into this a long time ago, and like the OP one phase on the Y side had very high current on it, but when we took apart the X0 connection it balanced out, I always thought the utility's did connect the X0 at both points when going from a Y source to a Y transformer, and because they don't use a common core transformer they could?
Also blueheels2, bonding the X0 on the primary side will not provide a fault path for the secondaries because of the current isolating across a transformer.
Guess I'm due to learn somthing new.
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
It's no different than bonding any supply conductor. What's throwing you off is never having OCP on a grounded conductor in most services.
All this is is a conductor installed between a lug on the transformer's (usually) B phase terminal and a lug on the EGC/GEC bus, bar, or bolt.
The reasson you're not creating a 'dead short' is that you're making the connection between the seperately-derived supply and earth.
You're the one that actually assures that contact between another phase conductor and ground would be a short to ground, by grounding one.
See if this post helps any: http://forums.mikeholt.com/showpost.php?p=708650&postcount=4
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
No, when transforming wye to wye, there is no heating issue, and I believe the primary X-0 must be connected to the supply to keep the secondary voltages stable.I always thought the utility's did connect the X0 at both points when going from a Y source to a Y transformer, and because they don't use a common core transformer they could?
It's a wye primary to a delta secondary where the primary X-0 must float. It seems to me that the secndary voltages would not be stable, but it apparently works.
ceb58
Senior Member
- Location
- Raeford, NC
Let me throw this in. On a installation I did with 208 prim. 480 sec. for a crane I installed a fusible disconnect on the 480 side. My B phase was grounded, and I cannot recall the code #,but I installed a "no blow" fuse on B phase in the disconnect.
The article is 240.22 and 230.9(B). If a fused disconnect is used, then a solid insert is required, if a straight rated breaker is used then it needs to open all phase and grounded conductors.
I don't see any reference to requiring the "B" phase to be used. 250.26(4) only says that one phase needs to be grounded. 230.56 and 408.3(E) pertains to the higher voltage to ground.
Rick
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