3 Phase 4 Wire Supply
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Delta breakers are now obsolete and not allowed in new installations.
There was a time when 3 phase 4 wire 240/120 services were common for small commercial business with one or two three phase loads. Delta breakers were 3 phase breakers which could be installed in a single phase panel and they had a wire stubbed out for the line side of the third phase.
see 408.36(C)
There was a time when 3 phase 4 wire 240/120 services were common for small commercial business with one or two three phase loads. Delta breakers were 3 phase breakers which could be installed in a single phase panel and they had a wire stubbed out for the line side of the third phase.
see 408.36(C)
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
The 120/240v section of a high-leg Delta 3-ph supply is exactly, and I mean exactly the same as a 120/240v 1-ph supply.
In fact, the high-leg Delta began as a 3-ph conversion to existing 1-ph services, simply by adding one more line conductor.
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- Licensed Electrician
This thread has some info and pictures http://forums.mikeholt.com/showthread.php?t=125076&highlight=delta+breaker
They were used just like Larry said. In years past, when you wanted to upgrade to three phase for one or two loads all you needed was an extra hot from the power company and a delta breaker and there you go. No need to upgrade the whole service.
They were used just like Larry said. In years past, when you wanted to upgrade to three phase for one or two loads all you needed was an extra hot from the power company and a delta breaker and there you go. No need to upgrade the whole service.
stevebea
Senior Member
- Location
- Southeastern PA
Are you referring to delta rated breakers meaning a straight 240V vs. a 120/240V slash rated breaker?
No, in this case I am referring to "delta breakers" as referenced in 408.36(C). Three pole breakers with two "stabs" and one wire for line feed.
Like me, dinosaurs.
stevebea
Senior Member
- Location
- Southeastern PA
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Whether there's a high leg depends on which conductor is grounded. If the center of one secondary is grounded, the opposing line is the high leg. That's what I described above.
Otherwise, either any line is grounded, creating a corner-grounded Delta; or no lines are grounded, and you have a floating Delta, which requires ground-detection.
Not for line-to-neutral loads, nor for line-to-line loads that require the neutral. Line-to-line loads that do not use the neutral can use any two lines, even the high leg.
Imagine an existing 120/240v 1-ph service like your home has, and you want to add a 3-ph motor. You have two lines, so the POCO must add one more, either one more transformer and supply an open Delta, or two and supply a full Delta.
The meter can would be swapped out for a 3-ph one, and the additional line added to the service entrance, and run directly to the "in" terminal on a Delta breaker, which has four bodies, like a 3-ph shunt-trip breaker.
The original two poles of the breaker receive power from the stabs as usual, and the third pole is fed via a terminal on the fourth body. The back of the breaker has two stab clips and two empty holes.
So, even though the existing service has only two lines, a 3-ph load could be supplied from the original panel. It probably became illegal because throwing the main did not deenergize the third phase.
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