3-phase, wye, 3-wire no neutral?

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KasseemF

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I came across an RO plant with is main distribution connected to the secondary side of a transformer that is a wye seconday but the neutral is not connected, only the three phases and equipment grounding conductor. Is this acceptable according to the NEC?

The load is predominantly pumps for the plant but their are a number of 120v circuits for house lighting and control equipment.

In addition to this an upgrade is being done and the electrician is proposing to connect from a breaker in the main distribution panel to a transformer that is primary delta-secondary-wye and then use a neutral to a panel taking care of house load.

Is the wye connection allowed according to NEC without the neutral and are their any hazards to connecting another transformer to this system?
 
A wye secondary winding with no neutral wire cannot directly feed line to neutral loads (120V).
Depending on the voltages of the wye, the center point may have to be grounded, but that wire need not be brought to the location of line to line loads.
You are definitely not allowed to use the EGC to supply line to neutral loads.
If the transformer secondary belongs to a utility, making the wires service wires up to a service point, then it is normal for there to be a grounded conductor without a separate EGC.
 
KasseemF said:
I came across an RO plant with is main distribution connected to the secondary side of a transformer that is a wye seconday but the neutral is not connected, only the three phases and equipment grounding conductor. Is this acceptable according to the NEC?

The load is predominantly pumps for the plant but their are a number of 120v circuits for house lighting and control equipment.

In addition to this an upgrade is being done and the electrician is proposing to connect from a breaker in the main distribution panel to a transformer that is primary delta-secondary-wye and then use a neutral to a panel taking care of house load.

Is the wye connection allowed according to NEC without the neutral and are their any hazards to connecting another transformer to this system?
Click to expand...

We need the rest of the story:

This Wye secondary - Is is 208/120? Or 480/277?

When you say the neutral is not connected:
Is the wye point (neutral) bonded to the transformer steel and not brought to the first disconnect?
Or is the neutral completely open circuited?​

The 120V circuits for house lighting - Are these existing and operatinal?

ice
 
KasseemF said:
I came across an RO plant with is main distribution connected to the secondary side of a transformer that is a wye seconday but the neutral is not connected, only the three phases and equipment grounding conductor. Is this acceptable according to the NEC?

The load is predominantly pumps for the plant but their are a number of 120v circuits for house lighting and control equipment.

In addition to this an upgrade is being done and the electrician is proposing to connect from a breaker in the main distribution panel to a transformer that is primary delta-secondary-wye and then use a neutral to a panel taking care of house load.

Is the wye connection allowed according to NEC without the neutral and are their any hazards to connecting another transformer to this system?
Click to expand...
Ireread your post a number on the times and the secondary. Voltage rating of the transformed appears to be missing.
From the numbers non the subsequent posts one is led to believe that it may be a 208y/120 where the 3 lines are brought out along with a EGC. This I find to be a bit odd for a 208Y/120.
However it is not uncommon to do with a 480Y/277 where it is common to feed an MCC with 480v 3w w/ an EGC where the 277v is not use full.
 
iceworm said:
We need the rest of the story:

This Wye secondary - Is is 208/120? Or 480/277? the utility transformer secondary is 480V

When you say the neutral is not connected:
Is the wye point (neutral) bonded to the transformer steel and not brought to the first disconnect?
Or is the neutral completely open circuited?​
Open circuited, no neutral feed. the GEC is connected to the frame of the frame of the transformer and connected to the EGC which feeds to the main distribution board ground bar.

The 120V circuits for house lighting - Are these existing and operatinal? They were existing and operational but they are being moved to a new distribution board which they intend to feed from another transformer which should be 480/208Y with the 480 feed coming from the MDB.

ice
Click to expand...

i haveve answers to questions in the quote above3
 
KasseemF said:
the utility transformer secondary is 480V

(Neutral) Open circuited, no neutral feed. the GEC is connected to the frame of the frame of the transformer and connected to the EGC which feeds to the main distribution board ground bar.

120V circuits for house lighting: They were existing and operational but they are being moved to a new distribution board which they intend to feed from another transformer which should be 480/208Y with the 480 feed coming from the MDB.
Click to expand...

The system is ungrounded 480V. Grounding or not grounding the 480Y is a design decision. Either will meet the NEC. Grounded is perhaps more normal. Utilities usually don't like to provide ungrounded services.

If you get a chance, I would recommend asking the original designer why they left the 480Y ungrounded. It does not matter too much, but still good to understand.

The only code issue is the ungrounded system requires ground detectors. They can be as simple as three 480V transformered pilot lights, wye connected, with the neutral connected to area ground - say building steel.


Connecting additional transformers for the house loads is fine. Use a 480D primary and a 208Y secondary. Bond the 208Y neutral as normal.

The only curious part is why the original install was ungrounded. Could have been inadvertently left off, or done on purpose. If there are no ground detectors, that makes it look inadvertent. Still, I would not change it with out a thorough study - possibly something you will want to do anyway. Changing this is a new design and you are now the engineer of record.

ice
 
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