3-phase disconnect - 2 fuses

[hardworker]

Why does a 3-phase disconnect have only 2 fuse cartridges protecting only 2 conductors?

 

[zbang]

Corner-grounded system?

 

[raider1]

Corner-grounded system?

Or a single phase circuit run through a 3 phase disconnect?

Chris

 

[hardworker]

It is a 3-phase system that is from the early 1900's used for an elevator. It comes in from the street to a meter and then to the main disconnect. The disconnect with the two fuses is tapped from the main. The 3rd leg line conductor is attached to a isolated bar. The load for this 3rd leg is also attached to this bar. I heard one "ole-timer" refer to this system as "Chicago 3 leg" or "Delta 3 leg". I am not sure about the accuracy of these names.

 

[roger]

It is a corner grounded delta and the grounded phase can not be fused.

Roger

 

[hardworker]

So, if I pull the 2 fuses, the 3rd legg is also dead?

 

[augie47]

So, if I pull the 2 fuses, the 3rd legg is also dead?

I do a little voltmeter testing first
From either fuse to ground you should get a reading (hopefully 240v or 480v), from the 3rd leg to ground you should read "0", thus the name "corner (one phase) grounded"

 

[raider1]

So, if I pull the 2 fuses, the 3rd legg is also dead?

The 3rd leg would be grounded and act like a grounded conductor in a 3 phase 4 wire grounded system.

Chris

 

[hardworker]

Ok, thanks for the info.

 

[LarryFine]

So, if I pull the 2 fuses, the 3rd legg is also dead?

It behaves just like a grounded conductor in a 1ph supply.

Added: Or, as Chris said.