3 Phase Resi?

[LarryFine]

It was common in the Phoenix area to have 3Ø for a air conditioner & single phase for everything else.

A friend of mine grew up in a house with the typical separate-three-wire service drop, plus a small fourth conductor that supplied only the A/C compressor.

 

[Little Bill]

I worked in a residence a while back putting in a hot tub. It had a 600A 208/120 3ø. I was told by someone at the POCO that the 3ø was there to balance the loads on POCO equipment in the area. This was an old house that once was the "rich" neighborhood. The garage used to be a carriage barn. They just drove the horse and buggy right in.

 

[kwired]

I worked in a residence a while back putting in a hot tub. It had a 600A 208/120 3ø. I was told by someone at the POCO that the 3ø was there to balance the loads on POCO equipment in the area. This was an old house that once was the "rich" neighborhood. The garage used to be a carriage barn. They just drove the horse and buggy right in.

That was back when they used to plug those horses in overnight to recharge them, they had a pretty high current draw when charging and probably was better when local grid wasn't as developed to balance that load over all three phases.

 

[ggunn]

A friend of mine grew up in a house with the typical separate-three-wire service drop, plus a small fourth conductor that supplied only the A/C compressor.

Most likely 240/120V high leg with open delta xfmrs.

 

[jmellc]

In the hot weather areas, it was not uncommon, many years ago, to find 3 phase high leg service with a delta breaker feeding a dwelling unit with air conditioning. However a new installation of 3 phase for a dwelling would be rare.

Here is some info about that use from an home inspection blog.


Here is some info on this use from a Square D document.

Don't think I ever saw one of these or heard of it. This field is indeed deep and wide. I discover every day how much more that I don't know.

 

[kwired]

408.36(C) prohibits use of delta breakers. My understanding is NEC prohibited this since the 1978 edition.

A major reason being if you turned off the main breaker in the panel, the high leg could still backfeed through the three phase load and energize one or both the other lines if the delta breaker was still closed.

Here is an old thread with what is a delta breaker being main topic

 

[Seven-Delta-FortyOne]

408.36(C) prohibits use of delta breakers. My understanding is NEC prohibited this since the 1978 edition.

A major reason being if you turned off the main breaker in the panel, the high leg could still backfeed through the three phase load and energize one or both the other lines if the delta breaker was still closed.

Here is an old thread with what is a delta breaker being main topic

I can start a new thread about this if the Mods would prefer it.

In that link to the old thread, they are talking about adding a third phase to a single phase panel.

Is this a single phase panel derived from 3 phase, or a single phase 120/240 from a transformer?

Because if it’s the latter, you wouldnt end up with 3 phases 120 degrees apart.

And if it was the former, why not just pull the third phase at the start, and run all you single phase loads off that?

 

[kwired]

I can start a new thread about this if the Mods would prefer it.

In that link to the old thread, they are talking about adding a third phase to a single phase panel.

Is this a single phase panel derived from 3 phase, or a single phase 120/240 from a transformer?

Because if it’s the latter, you wouldnt end up with 3 phases 120 degrees apart.

And if it was the former, why not just pull the third phase at the start, and run all you single phase loads off that?

You must not be understanding what a "delta breaker" is. And that is understandable because of them being pretty rare and only would be in older existing installations as well.

You don't convert a panel to three phase with said breaker nor do you create a third phase, it just is a breaker with two poles that connect to each bus of a single phase panel and a third pole with lug for input and lug for output of the third phase. Generally only were used for when you had one three phase load and all other loads were single phase. Such situation today you would either need to use a three phase panel and have a lot of unused spaces for high leg or put in a single phase panel and at very least a separate service disconnect for the single three phase load.

 

[Seven-Delta-FortyOne]

No I've never worked on/with these. Before my time.

You don't convert a panel to three phase with said breaker nor do you create a third phase, it just is a breaker with two poles that connect to each bus of a single phase panel and a third pole with lug for input and lug for output of the third phase.

I understand this part, but if you install it on a standard single phase panel, two phases are 180 degrees apart, not 120.

 

[Hv&Lv]

No I've never worked on/with these. Before my time.



I understand this part, but if you install it on a standard single phase panel, two phases are 180 degrees apart, not 120.

This is what the metering phasor looks like.

 

[LarryFine]

I understand this part, but if you install it on a standard single phase panel, two phases are 180 degrees apart, not 120.

If you understand how a high-leg delta works, then you should understand that. The center-tapped secondary is identical to a 1ph secondary, with the delta superimposed on it.

Between any two lines of a 240v delta, the voltage is 240v 1ph. It has to be, because the secondary (as well as the primary) is wound onto a single transformer core.

The three phases take turn developing their full 1ph voltage, 120 degrees apart, but the output of each pair of secondary conductors is indistinguishable from a 1ph source.

The delta breaker was developed as part of modifications to existing 1ph services, where new pieces of 3ph equipment were needed, and high-leg open deltas were economical.

 

[ActionDave]

...I understand this part, but if you install it on a standard single phase panel, two phases are 180 degrees apart, not 120.

The center tap winding of a three phase delta system is the same as a single phase so line A to line B to line C are still 120 degrees apart.

 

[Hv&Lv]

We still have several of the old duplex 5/10 transformers in service. They were an open delta in one transformer for the purposes we are discussing.
Now they are for very small kids like old air compressors or saws, etc..
I believe all our residences now that used to have these are removed and are basic single phase service.

 

[kwired]

No I've never worked on/with these. Before my time.



I understand this part, but if you install it on a standard single phase panel, two phases are 180 degrees apart, not 120.

The supply is still three phase high leg delta- most cases probably open delta with a smaller transformer for the high leg since it will have limited load on it.

The 120/240 side of the delta is the same thing as 120/240 single phase and supplies a typical 120/240 single phase panel. The high leg only goes to the input side of the 3rd pole of the delta breaker and of course there is only the one load wire on the load side of that pole of the delta breaker. Other two phases go through poles that receive their supply from being plugged onto the buses in the panel like all the other breakers in that panel.

Like I said it does not create a "three phase panel" nor does it create a third phase. it is just a passive item other than providing overcurrent protection that all three phases pass through in one way or another. If there is only one delta breaker in said panel, then high leg is only present on that one pole of the delta breaker that does not directly connect to a panel bus.


Is somewhat pointless to have used this breaker on a wye system, because you can directly utilize all three lines of a wye where with a high leg delta you can't, especially with your 120 volt loads.

The danger is if the single phase main breaker is open but the delta breaker is closed, there potentially can be backfeed voltage from the high leg through the three phase load and back through the other poles of the delta breaker and onto the panel buses. If any other breakers are also closed, that will feed that voltage onto those circuits as well, even though the main is "off".

 

[Jraef]

I haven't heard this question in a long time but I think I am right in saying that most power companies will not supply 3 phase power to a residence. Am I correct on this?

The main issue is that most urban and suburban residential streets do NOT have 3 phases down the entire street, they tap off an some central location and distribute as single phase. So when a residential customer wants 3 phase, they make them pay for the cost to run that 3rd wire back to that central point, sometimes all the way back to the nearest substation. The last one I was asked to investigate for someone was over a mile of cable, they wanted $20k just for running that wire (and the extra transformer). If however you happen to live in a place where 3 phase is already running down your street, because for example there is a commercial installation or a large apartment complex that uses 3 phase, it can be significantly cheaper. They still usually make the user pay for the extra transformer though.

The other side of that however is that by rule, "demand charges" are not assessed to residential users (they are, but are baked into the rates instead of separately). Once you go 3 phase, many utilities will assume it is for commercial endeavors and also slap on a demand meter and assess Peak Demand penalties, which can be a rude awakening for a former residential user.

 

[chris kennedy]

I got a call around a year ago from one of our resi guys. He couldn't figure out how to install a rain shield on a transformer.
Wasn't faraway so I headed to a very exclusive residential neighborhood in Fort Lauderdale called 7 Isles.

It was a 480V-208y/120V tranny. Turns out it was for a mega yacht docked out back.

I have also recently heard talk at the shop about on going talks with FPL (poco) about a 3 phase service to another dwelling unit in the same area.

 

[rambojoe]

I now have 2 friends w/cnc machines (3p) in the garage. And naturally, i have custom, very necessary stuff on my racebikes All they ask in return is some race coaching, with which ill share with yall-
- Go that way really really fast and when its time to turn...turn.
- Keep on the gas until you hear your mom's annoying voice saying "those things are dangerous"...thx ma..
- No more lessons until i get my bored throttle body and billet cases..
I think the good phoenix question is, which was the main reason for delta drops, the electrical rural farm equipment or bad azz low draw a/c units...i gotta guess ag equipment.

 

[Hv&Lv]

View attachment 2559320 I now have 2 friends w/cnc machines (3p) in the garage. And naturally, i have custom, very necessary stuff on my racebikes All they ask in return is some race coaching, with which ill share with yall-
- Go that way really really fast and when its time to turn...turn.
- Keep on the gas until you hear your mom's annoying voice saying "those things are dangerous"...thx ma..
- No more lessons until i get my bored throttle body and billet cases..
I think the good phoenix question is, which was the main reason for delta drops, the electrical rural farm equipment or bad azz low draw a/c units...i gotta guess ag equipment.

Ag equipment for sure.
Cooperatives mainly. To expensive to run that third wire but the farmers need the delta for the new motors they were getting to do more by machine and less by hand

 

[rambojoe]

Keep in mind that these are normal single fam dwells in the heart of dwntwn phoenix, not exactly "farms" just fyi. So its still odd, even if only a few families on the street had livestock...i think in this part of town it was incubators, heaters and fans. Ill dig a bit deeper and see what i can find. Alot of homes still have a delta service.

 

[ggunn]

The center tap winding of a three phase delta system is the same as a single phase so line A to line B to line C are still 120 degrees apart.

It depends on where you take your measurement. For a high leg service when you measure the voltage of the A and C phases relative to the center tap neutral, they are120V 180 degrees apart.