Center Tap Delta?

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JPRIB 8654

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To make a long story short I am dealing with a 3 Phase 240 Volt center tap Delta service. My understanding per 240.22 I am not allowed to fuse B phase (or the grounded phase). This project involves an elevator renovation that requires a three phase fusable disconnect to meet NEC requirements also. Through an RFI the engineer has informed me to install a three phase fusable disconnect. I know 240.22 (1) allows all three legs to be fused for a motor load but in this case I am feeding a Elevator Control Panel that does alot more than feed a motor. I am not saying this guy is wrong but would appreciate your feedback.
 
Welcome to the forum.:)

First off if this is a single voltage 3 phase delta system it would be a corner grounded system and not a center tapped delta.

A center tapped delta system would be a 120/240 with a high leg.

240.22 would not permit a fuse in the grounded conductor of a corner grounded system unless you meet 240.22(1) or (2).

240.22(1) does not apply to fuses

240.22(2) only permits fuses for overload protection at a motor this would not allow fuses that are used for short circuit or ground fault protection to be installed in the grounded conductor.

Chris
 
Chris here is exactly what I am looking at. The building service is three phase 240 Volt but also has a Neutral to operate a Single Phase Panel (120 Volt Loads). Center Tap or Corner Ground?

A-G 120V
B-G 240V
C-G 120V

A-B 240
B-C 240
C-A 240
 
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JPRIB 8654 said:
Chris here is exactly what I am looking at. The building service is three phase 240 Volt but also has a Neutral to operate a Single Phase Panel (120 Volot Loads). Center Tap or Corner Ground?

A-G 120V
B-G 240V
C-G 120V

A-B 240
B-C 240
C-A 240
Click to expand...

What you have is a center tapped delta 120/240 volt 3 phase system. Not a corner grounded delta.

The grounded conductor will be the neutral connected to the center tap of one of the windings.

The B phase is a high leg not a grounded conductor so 240.22 does not apply to the B phase of a center tapped 120/240 volt delta system.

Chris
 
Chris do you have diagram on how this service is wired. I am not questioning you, I would like it for my own records. Chances are i'll never run into this again but if I do what is the best way to distinguish between a Center tap and a corner ground Delta?
 
JPRIB 8654 said:
Anybody got a wiring diagram for a three phase 240 Volt center tap delta?
Click to expand...

ED's4Wdelta2.JPG


Roger
 
Just to reiterate:
raider1 said:
The B phase is a high leg not a grounded conductor . . .
Click to expand...
And, the voltage to the neutral is 208v, considered unusable as a 1ph source.

The A-N-C portion of the Delta is exactly the same as a 120/240v 1p source with respect to 1ph 120 and 240v loads.

The A-B-C portion is exactly the same as a typical 240v Delta source, except for the voltage of each line to the neutral.
 
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