Ever wonder why ???

[kwired]

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?

On the lines of what I have been saying throughout this thread - how many lives have been lost due to so called undersized POCO transformers or service drops? Compare that to how many have been lost due to undersized equipment or conductors within a building.

Only problem I run into much with small drops is voltage drop. Ampacity wise you can load them pretty good and they remain intact. Usually voltage drop becomes a big enough issue that something is done about that before it gets to the point of melting down the drop.

 

[goldstar]

Wires in free air have a MUCH larger ampacity than in conduit.

This was really the answer I was looking for (as was mentioned by kwired and several others). It was never my intention to bash POCO's (although some are deserving) and I'm sorry that this thread took that route in some cases.

Part of what started me thinking about this was why we have to de-rate internal wiring and POCO's don't do so with external, open air wiring. I was thinking specifically about SER cable. If you are feeding the entire load of say a residence with SER you don't have to de-rate the cable. Yet, if you run SER for a sub-panel you have to de-rate the cable. Does the jacket of the SER give its individual conductors the same characteristics as if they were run in conduit ?

 

[ritelec]

I was thinking specifically about SER cable. If you are feeding the entire load of say a residence with SER you don't have to de-rate the cable. Yet, if you run SER for a sub-panel you have to de-rate the cable. Does the jacket of the SER give its individual conductors the same characteristics as if they were run in conduit ?

Could be wrong here goldstar.........but I don't think it's that your derating it as a feeder after the service, but rather using it for what it's rated for. Compared to being able to use it for higher amperage than it's rated when used as service entrance.

 

[ritelec]

I didn't say that right..sorry.

It's treated as service entrance cable before your first panel board (Allowed to use it for amperage higher than it's rated). After the panelboard, it's ampacity is what it's rated for.


Still didn't say it right but....

 

[T.M.Haja Sahib]

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.

My point is not about the protection of life and property.It is about the mismatch in the co-ordination between POCO's protective devices and a building protective devices,resulting in nuisance tripping.This issue can not be solved by cooperation between field POCO engineer and site engineer.

 

[iwire]

My point is not about the protection of life and property.It is about the mismatch in the co-ordination between POCO's protective devices and a building protective devices,resulting in nuisance tripping.This issue can not be solved by cooperation between field POCO engineer and site engineer.

There are no power company protective devices to worry about, again you are offering suggestion that make no sense and demonstrate your lack of familiarity with US services.

 

[T.M.Haja Sahib]

There are no power company protective devices to worry about, again you are offering suggestion that make no sense and demonstrate your lack of familiarity with US services.

Conductor sizes provided in an indoor HV installation per NEC are of higher sizes and so protected by fuses or circuit breakers of higher ratings compared to that of upstream POCO's devices because they use lower size supply cables.If this is not the case,it is well and good.But do they?

 

[ActionDave]

Making sense is not a prerequisite for offering a suggestion. The value of that suggestion is the opposite.
Most prefer to make suggestions that are of value; others just like to seem valuable.

 

[iwire]

Conductor sizes provided in an indoor HV installation per NEC are of higher sizes and so protected by fuses or circuit breakers of higher ratings compared to that of upstream POCO's devices because they use lower size supply cables.If this is not the case,it is well and good.But do they?

TM let's stay on the topic of this thread and the service pictured in the OPs picture.


There is nothing that could happen to those conductors that would cause a power company overcurrent device to open. They simply do not put overcurrent devices in the secondary side of the transformers and the overcurrent device on the primary side is sized far to large to provide secondary protection. There will be no nuisance tripping of power company OCPDs

 

[T.M.Haja Sahib]

TM let's stay on the topic of this thread and the service pictured in the OPs picture.

Topic of this thread is also about wire sizes of POCO ............

There is nothing that could happen to those conductors that would cause a power company overcurrent device to open. They simply do not put overcurrent devices in the secondary side of the transformers and the overcurrent device on the primary side is sized far to large to provide secondary protection. There will be no nuisance tripping of power company OCPDs

I mentioned about HV indoor electrical installation of a consumer and not about POCO's power supply arrangement to a residence.See

Conductor sizes provided in an indoor HV installation per NEC are of higher sizes and so protected by fuses or circuit breakers of higher ratings compared to that of upstream POCO's devices because they use lower size supply cables.If this is not the case,it is well and good.But do they?

 

[iwire]

Topic of this thread is also about wire sizes of POCO ............

Yes it is.

I mentioned about HV indoor electrical installation of a consumer and not about POCO's power supply arrangement to a residence.See

That is not the topic and if you wish to discuss 'HV indoor electrical installation of a consumer' start your own thread to do so.

Do not take this one off topic, if you do your posts will be removed.

 

[T.M.Haja Sahib]

The wire sizes provided by POCO either for supplying power to an indoor HV installation or a residence of a consumer is invariably of lower size and so their protective devices,if they provide any, are of lower size than corresponding protective devices provided by the consumer per NEC and this may result in protective device co-ordination problem in addition to other problems mentioned in this thread due to adoption of lower size conductors by the POCO.

 

[kwired]

My point is not about the protection of life and property.It is about the mismatch in the co-ordination between POCO's protective devices and a building protective devices,resulting in nuisance tripping.This issue can not be solved by cooperation between field POCO engineer and site engineer.

Just who is going to resolve the issue - the accounting department:?


Having the HV line inside customer facilities is not common except for larger industrial plants. Where this does happen you are not dealing with technicians with limited experience - especially with over 600 volt applications. There often is a plant engineer - may not be a plant employee but there is someone. You can bet these types of customers have a closer relationship with the POCO than the average customer does.

 

[iwire]

I have moved the off topic question to it's own thread.

It can be found here.
[h=3]T.M.Haja Sahib power company thread.[/h]

 

[David Hinton P.E.]

Open air and ease of change. A #2 alum is good for 150 amps continuous. a 4/0 is good for 315 amps.
I have wired up houses myself and had to use 4/0 SE cable, only to come back and install #2 overhead after I received my inspection.
I can't tell you how many times I have been asked about our choice of wire size.

History and experience has led many PoCo's to their choice of wire size. How many houses pull 150 amps continuously? If you get down to it, a #4 Al. is good for 115 amps, how many houses will pull that much at one time? Especially with gas...

Good point Hv&Lv. I changed out my overhead service from 100A 120/240V to 200A 120/240V over a year ago. The City (AHJ) required I use 4/0 AL as SE conductors, whereas at the Service Point, the POCO only used #1 AL as the servcie conductors to connect to the SE cable. When asked, their reasoning was they only size for 80% of the service (i.e. 160 Amps). The NESC applies on the line side of the service point typically whereas the NEC applies on the load side of the servcie point. Their methodology works since I don't hear of service conductor related fires or meltdowns ever.

For grins, when the old meter was temped into the new service with #6 copper, I cranked up all of the current sucking electrical devices in the house (e.g. dryer, HVAC, microwave, garbage disposal, washer, and some lighting) at once at took a current measurement. The reading was around 70 amps on each leg. The NEC is a conservative-based document. It's very doubtful you'll ever use 200A on a 200A service, depending, of course, on what the load study says. Unlikely though.

 

[kwired]

Good point Hv&Lv. I changed out my overhead service from 100A 120/240V to 200A 120/240V over a year ago. The City (AHJ) required I use 4/0 AL as SE conductors, whereas at the Service Point, the POCO only used #1 AL as the servcie conductors to connect to the SE cable. When asked, their reasoning was they only size for 80% of the service (i.e. 160 Amps). The NESC applies on the line side of the service point typically whereas the NEC applies on the load side of the servcie point. Their methodology works since I don't hear of service conductor related fires or meltdowns ever.

For grins, when the old meter was temped into the new service with #6 copper, I cranked up all of the current sucking electrical devices in the house (e.g. dryer, HVAC, microwave, garbage disposal, washer, and some lighting) at once at took a current measurement. The reading was around 70 amps on each leg. The NEC is a conservative-based document. It's very doubtful you'll ever use 200A on a 200A service, depending, of course, on what the load study says. Unlikely though.

That first 100 amps is pretty critical for most dwellings - probably why they want minimum of 100 amp service to a dwelling. After that the diversity of loads starts to really make a difference. If the home has electric heating that may bump that first 100 amps up to at least 150 - 200 depending on how much heat load there actually is.