B4T
Senior Member
- Location
- Long Island, N.Y.
Ever wonder why ???
- Thread starter goldstar
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kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
No.. more luck than anything else.. IMO..
Well they are definately not afraid to operate things at a higher temperature than we do indoors. And with things being in free air most of the time the ratings are not the same as they are indoors anyway.
Take a look at differences in ampacities between T310.16 and T310.17. 2008 NEC. 310.17 is for conductors in free air - they are rated for higher ampacity than similar conductors in 310.16 - but not to extent you sometimes see POCO allowing them to be loaded.
B4T
Senior Member
- Location
- Long Island, N.Y.
What about voltage drop when you have 1/0 AL connected to 500kcm CU. and a 75' run.. they will go up to 125' before a second pole is installed..
PetrosA
Senior Member
- Location
- Lancaster, Pennsylvania
Nah, it's beautiful in a "techno" kind of way, just like conduit
Do you have any photos of aerial services from your neck of the woods? I've seen them in Poland many times but they're very different from what we do here - They use a cable with outer sheath, loop it at a hook at the building, then run it in smurf tube under the stucco to the meter/disconnect. Much cleaner looking.
goldstar
Senior Member
- Location
- New Jersey
- Occupation
- Electrical Contractor
You make a very good point. I don't know what the size of the conductors are in the quad-plex shown in the photo but if we assume (conservatively) that they are 1/0, the 90 degree column of 310.17 says they're good for 205 amps. The quad-plex is connected to (6) 3-phase 120/208 services that are protected at the least 100 amps each. One store is a Snap Fitness (6 arc trainers, 8 tread mills, 4 bikes, all have TV's attached, 1 tanning bead. There's also a hair salon, Chinese restaurant, dry cleaners, vitamin store and 1 currently vacant space. All have A/C units. Not sure what the max draw is during the summer but I'd bet they're pushing the envelope at 205 amps.
T
T.M.Haja Sahib
Guest
One real problem due to above is the lack of co-ordination in the operation of protective devices installed by the POCO with those inside a building.The protective devices of a building designed in accordance with NEC are invariably of higher rating than those of POCO with the result that the POCO's protective devices operate faster than those in any of the buildings whenever there is a fault inside and this may cause considerable inconvenience.
goldstar
Senior Member
- Location
- New Jersey
- Occupation
- Electrical Contractor
I have. This is a piece of tri-plex I cut away from a drop that burnt. It was attached to (2) residences and a sewer pumping station. One of the crimps corroded and failed, began to arc and melted the insulation.Their biggest drop is 1/0 AL for any overhead size service.. but to be fair.. I have not seen one of their drops melt..
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I have. This is a piece of tri-plex I cut away from a drop that burnt. It was attached to (2) residences and a sewer pumping station. One of the crimps corroded and failed, began to arc and melted the insulation.
But that happened at a failed connection. Have you ever seen the insulation melted away from connections purely from heat from overloaded conductor?
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I have very seldom run into this problem. If anything I have seen POCO transformers fail because of overloading and any overcurrent protection provided was not low enough to protect the transformer. Putting in a fuse with 1 amp higher rating on a 7.2kV line makes a big difference in how much current can flow on a 120/240 secondary without opening the fuse.
POCO often does not protect equipment to same levels as we do for indoor installations - to help keep calls for service down.
If the transformer burns up on a pole or in a padmount can it is not as much of a threat to property as is would be within a building.
NO.
Well once. On a welder temp. I hooked up some 60' from it's original location. I came in on a Monday morning and I don't know who did what.......but the insulation on the entire
length of the insulated ground was gone.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Sounds like someone did not put the work clamp for welding very close to the work and majority of welding current followed the EGC you mentioned.
T
T.M.Haja Sahib
Guest
I think the protective devices co-ordination problem arises in indoor HV installations of consumers at connection points with POCO'S or upstream.
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kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Many of those cases could be solved by having site engineers and POCO engineers work together instead of just thinking they know more than the other guy.
renosteinke
Senior Member
- Location
- NE Arkansas
The PoCo operates under different rules for two main reasons:
1) They generally are more competent to make technical decisions than anyone else; and,
2) There are many factors that enter their decisions that do not enter ours.
There's something to be said for competent installation practices. The PoCo isn't able to blame anyone but themselves when something goes wrong - and they have a century of experience telling them what works and what does not.
Let me think back to one 'PoCo failure.' The job was converting an office building (one storey) into a restaurant. Calculated load went from about 100 amps to 330 amps. Now, this was something that should have set off bells at the PoCo, but did not.
The linesman was the first one to catch the significance .... over 320 amps calculated load, a whole new type of metering gear was needed, a type using a control transformer. The PoCo foreman first took me to task, until I established that I had, indeed, gone through their engineering department on this job. PoCo ran new wires, put in new metering equipment, etc.
Then the summer came. I started getting low voltage at the meter. Well, the restaurant shared transformers with a grocery store. Over time, the grocer had added all manner of refrigeration to the store. While the PoCo knew this - the monthly billing told them of the increase in load - it did not draw anyone's attention.
Until, that is, the restaurant opened next door. Now the combined loads were more than the transformer(s) could supply. Ever wonder what happens when you overload a transformer?
The output voltage drops. A lot. What read 211V at sunrise reads 182 at lunchtime ... noontime sun, air conditioner going full-bore, kitchen cooking like mad. Now we're frying motors and kicking overloads. We're not melting wires because those transformers are not providing enough power to do so.
In retrospect, the PoCo missed several cues that there was trouble brewing. Still, damage was limited by the impedence of the transformers.
I submit that transformer capacity is one factor we do not consider in our service calculations. For the PoCo, though ... the transformer's capacity is one check on the system. If there's a problem, they count on the customer having some measurable symptom, and contacting them. We are not in a position to do that.
1) They generally are more competent to make technical decisions than anyone else; and,
2) There are many factors that enter their decisions that do not enter ours.
There's something to be said for competent installation practices. The PoCo isn't able to blame anyone but themselves when something goes wrong - and they have a century of experience telling them what works and what does not.
Let me think back to one 'PoCo failure.' The job was converting an office building (one storey) into a restaurant. Calculated load went from about 100 amps to 330 amps. Now, this was something that should have set off bells at the PoCo, but did not.
The linesman was the first one to catch the significance .... over 320 amps calculated load, a whole new type of metering gear was needed, a type using a control transformer. The PoCo foreman first took me to task, until I established that I had, indeed, gone through their engineering department on this job. PoCo ran new wires, put in new metering equipment, etc.
Then the summer came. I started getting low voltage at the meter. Well, the restaurant shared transformers with a grocery store. Over time, the grocer had added all manner of refrigeration to the store. While the PoCo knew this - the monthly billing told them of the increase in load - it did not draw anyone's attention.
Until, that is, the restaurant opened next door. Now the combined loads were more than the transformer(s) could supply. Ever wonder what happens when you overload a transformer?
The output voltage drops. A lot. What read 211V at sunrise reads 182 at lunchtime ... noontime sun, air conditioner going full-bore, kitchen cooking like mad. Now we're frying motors and kicking overloads. We're not melting wires because those transformers are not providing enough power to do so.
In retrospect, the PoCo missed several cues that there was trouble brewing. Still, damage was limited by the impedence of the transformers.
I submit that transformer capacity is one factor we do not consider in our service calculations. For the PoCo, though ... the transformer's capacity is one check on the system. If there's a problem, they count on the customer having some measurable symptom, and contacting them. We are not in a position to do that.
T
T.M.Haja Sahib
Guest
It is more a case of NEC and NESC to work together.............
T
T.M.Haja Sahib
Guest
The POCO can't get away with overloading their transformers:those transformers will fail prematurely.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
It is done all the time. Sometimes they do fail.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
No it is not. You can have one install comply with both and no problems. You can have an install across the street that also complies with both and have voltage drop issues. Both codes are minimum codes for the protection of life and property. Chosen designs can certainly exceed these minimums, for either code and that is up to the designer/installers.
goldstar
Senior Member
- Location
- New Jersey
- Occupation
- Electrical Contractor
Not in this case but yes, I have seen a triplex burn up. I occasionally do work at a day camp that runs hot (electrically speaking) in the summer. I've been there on at least 2 occasions where the triplex they had running to a kitchen facility building burnt. Something in the kitchen probably started the issue. When I got there I pulled the meter and one of the lugs in the meter enclosure was blue it was so hot. We suspected it was a feed to another building where they had a kiln that was used for ceramics. Checked all connections inside the breaker panel. All were good. Put the meter back and a week later the triplex burnt. Was it one of the crimps ? Maybe but not sure. POCO came and replaced it with the same size triplex but the issue never resurfaced because they moved the kiln and the ceramics activities to another building.
Few things to consider:
1: Wires in free air have a MUCH larger ampacity than in conduit.
2: The demand for multiple occupancies (damn the spell checker, shows me "occupancies" as not a valid word, but MW list it as a valid plural for "occupancy") is MUCH smaller than for one. In fact, 20 some apartments may give you a smaller demand than 3-4 taken at single value.
3: How many fires did you hear about from a POCO perspective? I've heard of a few from the internal wiring.
4: Do you REALLY want POCO to adhere by the NEC rules? I can see our electric bills triple (if not quadruple) if that was the case.
So the question is: "can we make it better?".
Sure, but at what cost?
Keep in mind money is a limited resource.
I know you can't put a price on a life, but here's the deal: do we spend a trillion dollars to save ONE LIFE? while that trillion dollars can save thousands of lives by different methods?
1: Wires in free air have a MUCH larger ampacity than in conduit.
2: The demand for multiple occupancies (damn the spell checker, shows me "occupancies" as not a valid word, but MW list it as a valid plural for "occupancy") is MUCH smaller than for one. In fact, 20 some apartments may give you a smaller demand than 3-4 taken at single value.
3: How many fires did you hear about from a POCO perspective? I've heard of a few from the internal wiring.
4: Do you REALLY want POCO to adhere by the NEC rules? I can see our electric bills triple (if not quadruple) if that was the case.
So the question is: "can we make it better?".
Sure, but at what cost?
Keep in mind money is a limited resource.
I know you can't put a price on a life, but here's the deal: do we spend a trillion dollars to save ONE LIFE? while that trillion dollars can save thousands of lives by different methods?
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