VAV Box Grounding

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amsco

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A 3-phase 3-wire 480V feeder was specified for connecting a VAV box?s electric heat coils. A 50VA control transformer was supplied with the box to create 24Vac for a control board (tied to relays for the heating coils).

The control transformer was mistakenly specified at 277V primary, and includes a fuse link on the secondary side. Since no neutral has been provided but the current is very small, can the primary side be safely grounded to ?create? 277V?
 
R

R Bob

Senior Member
Location
Chantilly, VA
amsco said:
A 3-phase 3-wire 480V feeder was specified for connecting a VAV box?s electric heat coils. A 50VA control transformer was supplied with the box to create 24Vac for a control board (tied to relays for the heating coils).

The control transformer was mistakenly specified at 277V primary, and includes a fuse link on the secondary side. Since no neutral has been provided but the current is very small, can the primary side be safely grounded to ?create? 277V?
Click to expand...


Am I understanding you correctly, that you are proposing to connect one phase of the branch circuit to the xfmr primary and connect/bond the remaining primary terminal to the enclosure (the EGC) as a substitute for the missing neutral/grounded conductor?
 
C

chevyx92

Senior Member
Location
VA BCH, VA
amsco said:
A 3-phase 3-wire 480V feeder was specified for connecting a VAV box?s electric heat coils. A 50VA control transformer was supplied with the box to create 24Vac for a control board (tied to relays for the heating coils).

The control transformer was mistakenly specified at 277V primary, and includes a fuse link on the secondary side. Since no neutral has been provided but the current is very small, can the primary side be safely grounded to ?create? 277V?
Click to expand...

Short answer, NO!
 
J

jeremysterling

Senior Member
Location
Austin, TX
R Bob said:
Am I understanding you correctly, that you are proposing to connect one phase of the branch circuit to the xfmr primary and connect/bond the remaining primary terminal to the enclosure (the EGC) as a substitute for the missing neutral/grounded conductor?
Click to expand...

You don't even have to say it like R Bob to realize the answer is no. If this is a Y, pull a grounded conductor(neutral). If this a 480 delta, you will have to do something different like buy a new control XFMR.
 
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