230 single phase A\C running on 460 3 phase circuit- OK? 6

[jrick]

Is there any reason I should not use 1 leg of the 460 three phase circuit and ground to run a single phase 220 Air condition unit.

Employees at the School maintenance report they do this all the time. If this is true then I connect nothing to the ground on the unit or the same ground I am using with the hot for the 220.

 

[crshears]

Gotcha, Bill, and thanks; in the past I've thrown together concepts using that scheme. It might even be of use on board...?

CR

 

[waross]

For awhile twenty some years ago, three phase lighting transformers at 480:120/208 Volt and in the 25 KVA or 37.5 KVAs range were supplied with two transformers in "T" configuration. I was never able to find out what the advantages were of this connection. I haven't seen a new one for years.
The connection was similar to, but not identical to a Scott connection. The neutral was supplied from a tap on one of the transformers.

Bill
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"Why not the best?"
Jimmy Carter

 

[crshears]

Can't say I recall seeing a beast like that ever...not that I was thinking of doing anything like that; my reference was to if we transition to an actual three-phase supply being brought on board, of which there suddenly is a slight possibility due to an unexpected but positive change in local circumstances...

CR

 

[waross]

Availability depends on the policies of the local utility. The old school solution to the need for a small amount of three phase power in addition to a large amount of single phase power is an open delta connection. The open delta avoids the issues found with a wye:delta bank when the delta is closed.
In jurisdictions where the open delta is used, you may see a 50 KVA or 100 KVA distribution transformer feeding a number of single phase loads at 120:240 Volts. Next to it on the pole will be a 5 KVA transformer in open delta to feed a small three phase service at 240 Volts delta.
One installation that I used to see often was a small machine shop with three phase motors situated in a predominantly residential area.

Bill
--------------------
"Why not the best?"
Jimmy Carter