3-Phase residential....is this a problem, or not

[rain252]

I have a friend who seems to have a 3 phase residential service on a 1968 house. The overhead service drop has a bare neutral, and 3 inulated conductors. At the weatherhead, 2 of the hot conductors are spliced to large conductors entering the weatherhead, as does the neutral. But the 3rd hot leg is spliced to a small insulated conductor about the size of your little finger, and it goes into the WH also. I could not locate the emergence of this wire in the panel....packed in tight. The meter is electronic (no wheel) and has 3 little icons in the corner of the display A, B, C.

The main panel is separate, a Bryant mounted next to the meter enclosure. The main labeling is missing, except for a small label that says Bryant, 120-240v. Does not specify phase. It looks like split-bus, main lug panel with no main breaker (6 Bkr rule?), with a 2-pole bkr feeding the lower section. I do not see a 3rd busbar. The upper right corner has a crowded grd/neutral bar arrangement.

The only 3-phase load at the house is a large gas-pack A/C unit. The name plate says it indeed has a 3 Ph. compressor, rated for 208-230V.

Here's where it looks goofy to me. There is a 3-pole breaker in the panel feeding the A/C unit, but one of the terminals shows 0 volts with no conductor on it's terminal, while the other two show 120 volts on each. The homeowner's electrician, who is apparently good and has lots of commercial experience, told her the "Delta" leg is blown. The breaker is obscure and hard to find, so pending later resolution and to keep her A/C running, he has a terminal that is in the open space under the breaker and snugged up to the bad section on the bottom of it. It looks to me like maybe it is internal leftover of what may have been a part of that 3-pole breaker in the 4th space.....maybe whats left of the "Delta" leg? That terminal has 2 wires.....one to the A/C unit, and another larger one that I can't track where from/to. Kind of looked like it may head into the nipple to the meter. But 208V on one leg from the meter???

Here is what I don't get......I measured about 208 volts to grd/neutral from that terminal. I confirmed at the A/C unit, the 3 hot legs are 120v, 120v, and 208v to gnd at the hot side of the fuse block.

So that terminal is supplying one leg of the unit with 208 volts. What the??
I thought 208 would be across two phases, and 120 phase to neutral/gnd?
Is all this ok, or does this sound goofy? What is "Delta" phase??



Can anyone educate me a little on this?

[sloooo]

You have to remember that an un-energized load is a wire. Chances are, the only load that would cause this is the transformer since it will always be hot without the unit running. So, with only 1 of the 2 hot legs energized, your getting feed back through the transformer making you think you have 208 on one leg to ground. Once you get the power issue resolved, everything should bounce right back into place.

[frenchelectrican]

the only way you can verify is look at the transformer connections.

the hint is that if you see pole mounted transformer if the center one have all 3 wires [ 2 hot and netrual on secondary side ] and other two tranformer cans have only two wires hook up that is what we called delta connection system but if look diffrent by see the transformers all are same size and each one only have two wire connected to each transformer that is wye connection there.

now back to the main point you say 208 volt from line to netural or line to ground that is a wild leg you have to be carefull with this one.

for old delta breaeker style this is pretty old one and almost complety history nowdays if you know what brand name of the breaker maybe there is a electrical supply or two may still have it on the self otherwise it will be not cheap to find one or other way you can do is change that to modern subfeed 3 phase box with one 3 pole breaker for the A/C itself.

way back mid 60-early 70's it was pretty common to bring 3 phase for A/C but later on the time the poco system getting better they drop the 3 phase system so that why it kinda pretty rare to see the 3 phase still exsting there the only time useally we see the 3 phase is very large home with hevey load demand.

back to baisic real quick

wye connection L1 - L2 = 208V L2-L3= 208V L3-L1 = 208v L1-N = 120v, L2-N =120 V L3-N=120v

Delta connection L1-L2= 240V , L2-L3 =240v, L3-L1= 240v L1-N=120V,L3-N=120v but becarefull this one L2-N = 208 V

all the L1, L2,L3 is read clockwise rotation starting L1 on bottom left and go clockwork


Merci , Marc

[rain252]

well that's interesting. Then this must be a delta system with that wild leg at 208 volts. I wonder if the A/C compressor likes having 2 legs supplied at 120v and the 3rd one at 208? That's how it is running right now.
It also explains why when I measured across the 2 hot busbars in the panel, it was 240 volts.

[junkcollector]

This is really interesting!

I might add that that skinnier wire that you mention going into the weatherhead is the 208 volt high leg. (you probably figured that out by now...) The wierd thing is is that triple pole breakers have to be specially designed for the delta system. The trip coil inside the breaker is actually smaller because less current passes through the 208 v leg than the other two. Standard triple poles have all of the coils the same, so if such a breaker is used on this system, the high leg would be overloaded. Fuses are (were) used almost exclusively in this type of service because it is easier and less expensive to use one smaller fuse for that leg. Also, is this by any chance this house is in a more commercial /industrial area? Did you take a look at the connections at the transformers on the pole? There could be two connected open delta, (one large one and one small one.) Or there could be three connected with the closed delta. In this case, one transformer is larger than the other two. I might add that this is extremely uncommon to have a residential service like this.

keep us posted...

[rain252]

No, its not in a commerical zone....just a residential area from the 1960's. There are some neighborhoods here in the Phoenix area that still have resi 3 phase service. I didnt look at the transformers, but will again next time I get back over there. I hear the POCO tries to snatch your 3-ph power from you if they get the chance, as in any big change to your service. But the homeowner has pretty new A/C equipment that is 3-ph.....don't know how they could swap it to 1-phase and expect her to buy all new A/C equipment.

I read the whole nameplate on the A/C unit, and I didn't see anything except that the compressor wants 3 ph. 208-230 volts, and the smaller blower/fan loads are 1-phase. I gotta wonder if that compressor motor is designed to run with one leg at 208v. It was running along just fine, so I know it works, but is it a bad way to supply it, I don't know.

So based on the info learned here, I also believe the main panel is a single phase 120/240 panel, with just that one special 3 pole breaker there for the A/C that had blown the high leg 208 pole. The breaker had one handle and it was closed, with about 118v on 2 terminals and zero on the 3rd one, hence the special solid wiring of the terminal where the 208 leg attached to the big breaker. The homeowner and electrician are discussing whether to add a small subpanel beneath the main as it is crowded and no more room. And the part I didn't add earlier is that the big 3 pole breaker actually was tapped for a smaller 3-ph. A/C unit in another part of the house. Adding the subpanel would give enough room for each unit to have its own breaker. The other discussion has been about whether to change out the whole panel since the Bryant panel is old, crowded, and not raintight.

I also noticed the neutral bracket screwed into the house wood was mounted vertically so the service drop is pulling sideways on it instead of straight away as it was designed to, so the mount wire is cutting through the porcelain, and it looked about to give way. Looks like it had been mounted that way because in that day, the weatherhead was allowed to be lower and it didn't allow enough room for a neutral clamp right on the riser. That will be addressed.

[suemarkp]

The AC should be seeing 240V between each leg (phase) of its circuit. You shouldn't be using these as phase to neutral except perhaps one of them to run electronics and/or a 120V fan. You're not supposed to use the 208V leg in a phase to neutral mode -- phase to phase only where it appears as 240V.

This is what makes 240V delta panels so tricky and why that "wild leg" is supposed to be colored orange. No single pole breakers off that orange legged bus! And you need to know where that orange leg is going on that AC unit, as putting it where it may expect 120V to ground is going to burn something up.

[rain252]

The pullout fuse block at the unit has 3 fuses (at the hot terminals when the block is removed) which measure 120v, 120v, and 208v to Gnd (a screw on the metal fuse block box). I didn't measure hot to hot at the fuse block. Wish I had.

Apparently the electrician has hard-wired the 208 wild leg on a single pole directly to one of the 3 legs feeding the A/C units just to keep them running until a better fix can be done.

There is 240v from one of the 120 legs to the other 120 leg (as measured at the main panel busbars). That big 3 pole breaker in the panel looks to be getting 2 sources of 120v power from the two hot busses in the panel, and then the 3rd feed was a direct wire of 208v. There was definately no third vertical hot busbar in the panel.

So what do you suppose would be voltage from the 208 leg to either of the 120 legs ??? I wish I had checked that, but I didn't. If I get a chance to, I will see what it is.
The unit runs along like that, but I can't imagine American Standard (the mfr) would think it is a great idea. Nothing I saw on the nameplate indicated that would be an approved supply to it.

I'll try to go tomorrow to get better measurements and scope it out more as far as what goes where. I'll take my camera and get some photos.

[suemarkp]

They should be 240 between each leg. Perhaps you haev a disconnect or panel somewhere where all three of these phases exist. Separating one out from the other is bad with metallic wiring methods and for EMF.

A common implementation on 240 Delta is a single phase panel that gets the two normal legs and a neutral. This makes it a normal 120/240 panel. But all of this plus the 3rd leg need to be in an enclosure somewhere (maybe not the neutral though, depends, but you've have an equipment ground instead or perhaps in addition to this).

[rain252]

All 3 phases do appear to exist in the main service panel. Two of the hot legs ...the 2 large conductors coming down the mast feed the two hot busbars. A large neutral comes down and feeds the neutral bar. A pink (faded red?) small (maybe 1/4") insulated conductor is spliced to a large 3rd conductor at the weatherhead with a odd-looking white connector. It seems to come down into the panel and land only on that hard wire terminal associated with the big 3-pole breaker that feeds the A/C only.....the breaker with the failed 3rd leg reading 0 volts. Its crowded but I'll see if I can trace it out better tomorrow.


Maybe as the Frenchelectrician said a few posts ago that with Delta configuration..... that leg-to-leg, even with the wild leg 208, there should still be 240v leg-to-leg. And no problemo to the A/C unit.


I will get some photos and measurements of it all tomorrow and post them here.

[rain252]

Well, I went back to my friend's house today and took more voltage measurements. The 208v high leg indeed only feeds the 3-pole breaker via a hard wired terminal. The voltage from that leg from it across each of the other two legs is 240v, or thereabouts. So I guess that means the A/C units are happy. Good deal. I did get photos....to follow.

[rain252]

Transformer(s)...feeding several houses.

[rain252]

(Panel dead front removed before photo)

[rain252]

The room to the right was a room addition done some time ago.

[rain252]

Panel and service drop. Besides the meter enclosure and main service panel, all the other boxes are just tv, phone, water timer, etc. The homeowner is now contemplating having the electrician add a small sub-panel below to give each A/C unit its own breaker for now, until whole changeout later. Or just biting the bullet now and changing out the whole service to new panel with proper height mast, etc. The old Bryant has big gaps all around the cover edges, and the door is obviously a water sponge as well. Check out that GFI recep with no cover also.

[rain252]

That hard-wired terminal is on the left, half way down, with a brass looking shroud around it. The red 208v leg feeds it, with two white feeds going off to the two A/C units, along with the two wires coming off the two poles of the breaker that have wires landed.

[rain252]

Closeup of upper, middle, lower views.

[junkcollector]

Wow!

The connection at the 2 transformers confirms the open delta connection. I see what you mean about the deterioration of the panel. Seems very crowded with lots of potential problems. I see the copper lug you point out. I understand that that is a temporary fix but those white wires do not seem to be fused at and this point one cannot shut off the power to them! I understand that it is fused at the AC disconnect. I think that it is wierd to have such a lug in a panel like this: It makes me wonder if this is some sort of aftermarket part that allows a triple pole breaker like this in a single phase panel. I don't see how that can even fit. It looks like the installer took this lug from another panel and hacked it in. An indoor panel outside? I am starting to wonder if this was professionally installed to start with.

Thanks for sharing the photos!

[rain252]

The "brass" looking part of that lug is not hot....just the terminal below. Up close, it looks to be on metal framework that is part of the whole breaker. The terminal is triple-tapped.....the larger red 208v incoming, and two whites outgoing to the two A/C units. As I understand it, those white wires used to be on that third pole of the breaker before it blew. The electrician was called over recently when the homeowner complained of no A/C, I believe is how it all happened. The hard wired lug was a temp fix to get the A/C up and running again, pending a better resolution later. I wonder if that breaker is made to snap onto a 2-bus panel, and that funny lug is meant as a source for the 3rd pole of the breaker??

Yes, you're right the only protection for the A/C unit on that leg is a fuse at the unit's fuse block.

Back in the day around here (60's and earlier), if a panel was mounted under any overhang at all, they considered it enough protection. Wouldn't fly now, obviously. Around the Phoenix area, it is the norm for a service entry panel to be outside like that.

I'm glad I got to see it. With the info exerybody posted here, I learned a little about 3-phase. Its been interesting. I wanted to post the pics....it 'splains it all better than words.

I just hope the electrician addresses that failing neutral line bracket on the roof before if breaks through.

[suemarkp]

Does this panel have a main breaker, or an upstream disconnect? If not, we're way over the 6-disconnect rule.

Those white wires on the brass lug, in addition to the red wire on it, should all be taped orange. It looks like there was a nice orange jacket coming in, but the color got lost.

Why are there two wires on each pole of the breaker to the AC unit? Are there two of them, or did they parallel undersized conductors?

What a mess....

[rain252]

The upper right corner 2-pole Bkr is the feed to the lower half of the buswork.....the wired go all the way to the bottom to feed onto the bubars there. Ohter large loads (i believe the 100A 2-pole feeds the the small attached parent residence complete with electric range. Besides the electric HVAC equipment, the rest is all electric. Since it is split-bus design, I believe it meets the 6-throw rule.
The double -taps on the 3-pole breaker feeds BOTH A/C units (fix coming soon), thats the reason for double tap......no second breaker availble yet.

No upstream disconn. Mast feeds meter, meter nippled to main panel. There may be a subpanel in the garage....don't know.

Yes, when done, I will be looking for proper tagging.
Tomorrow or Wed, that neutral bracket will get tied to the mast pipe with heavy rope to hold it until good repair.

If the homwowner does opt for a full monty service upgrade to 200 amp, I will post pics to show the progress. Sound good?

[suemarkp]

I don't think it meets the 6 handle rule anymore -- too many separate breakers installed at the top. The top right breaker could be a double pole -- that would reduce one handle. The twin in the upper left is two handles. I'm assuming the top 12 slots are not controlled by the main in the upper right. Making the kitchen breaker also a double pole would get the handle count to six.

I'm not sure if twin breakers are even listed for use in this panel (even though they fit). I don't think they existed at the time the panel was made.

[rain252]

The upper right breakers feed the lower section busbars via conductors that land on those lugs on the bottom.

The whole panel is a mess that will get changed....maybe sooner than later.

[junkcollector]

I'm still wondering how that 3 pole breaker is even working. If installed in a standard single phase panel like this, the third pole of the breaker would be on the same bus as the first pole. The installer must have broken that bus tab off in the panel in order to use that third lug thingy. Does anybody else wonder about this too?



I will post pics to show the progress. Sound good?

Heck yes it sounds good! I love those before, during, and after shots that people do of stuff like this.

[suemarkp]

The upper right breakers feed the lower section busbars via conductors that land on those lugs on the bottom.

The whole panel is a mess that will get changed....maybe sooner than later.

But where does the top bus stop and the lower one begin? Since the upper right breaker is only 40A, there can't be that much load on it. I think the bus containing the 3P breaker is on the top section. I just don't know if the top 8 or 12 slots are in the upper bus.

[rain252]

Yeah, thats a good point about that top right breaker.....40 amps isn't much capacity for the lower part of a split-bus arrangement.

I know, junkcollector, that 3-pole breaker is a funny one. It usre looks like that terminal underneath is part of it, but its new to me. Maybe the electrician did rig something up there. I'll find out if I can.

The homeowner called the POCO at the request of the electrician. The electrician wanted to have them point out who is responsible for exactly what...as in that broken mounting bracket for the service drop. I told the homeowner it is hers downstream of those splics at the weatherhead and including that bracket. Surprised a local electircian would not know that.
So they were supposed to make a hazard trouble call at the house today.....rut-roh! I told her to stand by for a service turnoff pending repair. Apparently the electrician got a rope around the mast to shore up the service drop good enough so they kept the power on.

[Ohm1]

good topic!

I just left a customer who converted a commercial building to a house. She still had a three phase service. She said her refer went out, and a few other things, I just refered her to a commercial electrical contractor. Wasn't up to trying to figure out all the mess, Nor deal with 3-phase! In my eyes, it was still commercial>>>>>>>>>

[junkcollector]

I wonder if the A/C compressor likes having 2 legs supplied at 120v and the 3rd one at 208? That's how it is running right now.
It also explains why when I measured across the 2 hot busbars in the panel, it was 240 volts.

I forgot to mention how that works. You said you measured the voltage between each hot leg in reference to ground. The AC units do not use the grounded wire for their operation. (The frames are presumably bonded to ground for safety.) Therefore the voltage phase to phase between any of the three phase wires is 240 volts. So as long as the AC units say they are for 240 V three phase it will work fine. I attached a photo (may be a bit hard to see.)

[rain252]

Yup it measured 240v phase to phase when I went back and checked it. I was surprised that 208v high leg measures 240v leg to leg. Its been interesting to learn a little about how this works.

The homeowner called the power co and cancelled the hazard call the other day, it turns out. Probably a good ideas since they might have turned it off. Its all tied up with rope now, so it will be good enough until a permanent upgrade/repair. The design guy from the power co is coming Monday to tell her what they will require for a service upgrade. I will be especially interested to see if they will support leaving the 3-phase service there, or try to yank it.
Thanks for the drawing.