It would be interesting if you hcould see you transformer is fed from.
3-phase power to Dwelling Units
- Thread starter nosratrouhani
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It would be interesting if you hcould see you transformer is fed from.
JFletcher
Senior Member
- Location
- Williamsburg, VA
Ill try to snap some pics tomorrow of the disconnects/transformer connections. The overhead lines are 3 wires up top, 1 a bit below, and cable/phone below that. Each pole has just one transformer, tho I imagine if I look closely, each one down the street is probably coming from a different phase.
May one of the lines be a ground to protect the lines from a lightning strike? If the transformer is fed from those line you would as lso think there should be a fused cutout switch that feeds the transformer. Is it a pole mount transformer or padmounted?
JFletcher
Senior Member
- Location
- Williamsburg, VA
All of the transformers for residential in this area are pole mount. I dont think the switches from the overhead (3ph) to the transformers are fused; they look like a straight disconnect. Keep in mind this neighborhood was built in the 50s. Newer construction has pad mound transformers and buried POCO lines. afaik, here, fusing for POCO mains is done fairly far away, maybe at the substations? I know Ive seen a fair share of blown transformers around here in storms; we lose power all of the time.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
151923-0055 EDT
In my neighborhood we have a primary that is three phase delta. There is no overt neutral. At the substation it may very well be a wye with the neutral earthed.
Also on our block there is at least one home with three phase open delta service. On the block across the street from our block on a different primary feed there is at least one home with three phase service. i don't have three phase, but I could easily have it with the addition on one transformer.
Photos of my primary and transfomer are at http://beta-a2.com/misc_TMP_photos.html .
See photo P4 in particular.
.
In my neighborhood we have a primary that is three phase delta. There is no overt neutral. At the substation it may very well be a wye with the neutral earthed.
Also on our block there is at least one home with three phase open delta service. On the block across the street from our block on a different primary feed there is at least one home with three phase service. i don't have three phase, but I could easily have it with the addition on one transformer.
Photos of my primary and transfomer are at http://beta-a2.com/misc_TMP_photos.html .
See photo P4 in particular.
.
- Occupation
- Licensed Electrician
That disconnect you see has a fuse in it I'll bet.
- Location
- Massachusetts
I agree and it is not there to protect the transformer. It's there so if a transformer has a primary side fault it does not take out the over current device upstream.
kwired
Electron manager
- Location
- NE Nebraska
Most all the single phase pole mounts around here have internal overcurrent device, and external operating handle. They do use external fuses on most three phase banks though. There is a lot of 240/480 single phase transformers for irrigation services - those usually do have an external fuse applied.
I think it all depends on what they order for options when they purchase the units, and maybe what is commonly stockedn wherever they order from. Last couple larger padmounts I was involved with had internal disconnect on the primary - most of older units in the system do not have this. Made it convenient for them to kill that transformer so I could pull more conductors for increased need to the service being supplied without having to kill or make a temporary bypass to the "feed thru" primary lines connected to that unit.
kwired
Electron manager
- Location
- NE Nebraska
I must not have been all that clear, if there is three phase primary in the vicinity they still will need to provide a 208/120 transformer, but there is a three phase source available in the area.
In small town USA like I mostly work around, there is three phase in residential neighborhoods, maybe not down every street or alley, but depending on your location that line that passes behind your house possibly feeds the majority of the town, or maybe there is a commercial or other non residential customer that needs three phase somewhere downstream. Electric heating is common around here as well, so residential service loading may average higher then it does in some places, balancing that load across phases will be desirable to the POCO.
In most areas, a single meter for new construction would be a violation of adopted energy codes. People have no reason to conserve electricity if they aren't paying the bill.
kwired
Electron manager
- Location
- NE Nebraska
Some do have a meter and still don't pay the bills (for various reasons) and little incentive to be conservative ...just saying.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
I believe that when air conditioning first came out for dwelling units it was three phase and was supplied by high leg deltas.
1 small transformer and 1 large one that was center tapped for 120V loads was common.
I have seen a few in old homes in VA and my old neighbor here in MD had one at one point. The transformers, unused, are still on the pole, he has a standard underground service now, and the old equipment, unconnected, also was in the basement.
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
Primary looks like 2,400 or 4,800 3 phase 3 wire, probably ungrounded delta (as was common back then). One of the lighting suppressors looks like it had its bottom cap blown off (friendly to call in). FWIW the transformer is at least 60 years from the style. Ditto for the "wido maker" cutouts. Line is definitely seen time but has nice nostalgia.
No necessarily, it depends on the POCO and fault condition. Each have their own intentions regarding fusing and some will factor in more protection some less.
Generally POCOs fuse transformers 2 to 3.5x the full load primary amps. While such fusing will not protect a transformer from a sustained overloading, should a fault occur near the transformer primary current is usually high enough to blow the fuse before the transformer sustains thermal damage. The fuse does indeed protect the transformer about halfway through its damage curve.
There is a youtube vid (will find it) of a short on the secondary clearing the primary fuses within seconds.
From an old thread:
http://forums.mikeholt.com/showthread.php?t=53190&p=477658#post477658
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
Found it
Here is an example where primary fuses blow during a secondary short circuit before the transformer boils over. Im willing to bet the transformer wingdings barely went above lukewarm:https://www.youtube.com/watch?v=1Uq03cvYdVA&index=1&list=PL48840A8215C94018
Iron_Ben
Senior Member
- Location
- Lancaster, PA
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
Single phase panel would have done, but still, I like it
That panel schedule is the most professional Ive seen for a dwelling, in fact most buildings.Iron_Ben
Senior Member
- Location
- Lancaster, PA
Single phase panel would have done, but still, I like it
Agreed on the panel schedule. When I worked for the poco, I saw a lot of new $400k+ homes with blank panel schedules, or incomplete and sloppily filled out schedules. I realize it's kind of a pita to take the time to fill one out neatly but it's part of the job. Reflects poorly on the electrician when it's blank or half-assed. IMO.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Agree and code requires it to be filled out in a "professional" manner.
408.4 Field Identification Required.
(A) Circuit Directory or Circuit Identification. Every
circuit and circuit modification shall be legibly identified as
to its clear, evident, and specific purpose or use. The identification
shall include an approved degree of detail that
allows each circuit to be distinguished from all others.
Spare positions that contain unused overcurrent devices or
switches shall be described accordingly. The identification
shall be included in a circuit directory that is located on the
face or inside of the panel door in the case of a panelboard
and at each switch or circuit breaker in a switchboard or
switchgear. No circuit shall be described in a manner that
depends on transient conditions of occupancy.
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