NEC says this?

[electricalist]

The meter is only a wide point in the service conductors for the poco to measure usage,
The service begins at the location of the service point, where poco wire meets customer wire.

 

[don_resqcapt19]

sure, ok, i guess. why even give the possibility? just make wire size "no smaller than the main OCD of service panel". all that crazy verbiage alleviated in one simple statement.

So submit a "public input" (proposal) with your technical substantiation for a change. You have until the first Friday in November 2017 to submit your "public input" for 2020 NEC change.

 

[ADub]

so wait, someone said up to the meter is "service" and would be poco, and then said poco doesnt go by NEC, so why then would the NEC address "service conductors" ??? i am not following the intent of the verbiage.

You are clearly a little confused. Try reading through article 100 for definitions to service, service conductors, and feeders. What is your real problem with 310.15(b)(7)? Electricians have been getting by with it just fine for a while. You're the only one here making it complicated


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[kwired]

sure, ok, i guess. why even give the possibility? just make wire size "no smaller than the main OCD of service panel". all that crazy verbiage alleviated in one simple statement.

This section permits you to use smaller conductors then usual if all conditions are met. You certainly are welcome to not use this permission and install "full sized" conductors if you wish and there is no code violations, but if you plan to bid in a competitive market, you probably will be taking advantage of the permissions here as much as possible.

The changes in 2014 gives you same final conductor size for the most part as the tables in 2011 did - before any ampacity adjustments come to play.

You are clearly a little confused. Try reading through article 100 for definitions to service, service conductors, and feeders. What is your real problem with 310.15(b)(7)? Electricians have been getting by with it just fine for a while. You're the only one here making it complicated


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"For a while" has been many decades. Section with this material may have moved or had minor changes over the years but is definitely not a new concept.

 

[FionaZuppa]

You are clearly a little confused. Try reading through article 100 for definitions to service, service conductors, and feeders. What is your real problem with 310.15(b)(7)? Electricians have been getting by with it just fine for a while. You're the only one here making it complicated


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let me say this. regardless if it was allowed or not, competitive bidding has no relevance because in either case the NEC code (as it may be written) would apply, thus all bids would be based on the same restrictions/allowances. the cost difference would be paid for by the customer no matter what bid was accepted, etc.

all i am saying is, if there is a simple table for ampacity (based on NEC view of wire types and sizes) why did they write in "exceptions" that goes against the ampacity table? just doesnt make sense to me.

 

[ActionDave]

.....all i am saying is, if there is a simple table for ampacity (based on NEC view of wire types and sizes) why did they write in "exceptions" that goes against the ampacity table? just doesnt make sense to me.

310.15 has seen many changes in recent code cycles. From what I can tell none of the changes are based on anything bad happening in the real world.

Just doesn't make sense to me either.

I'm not the type to tilt at windmills. If you are, please do so.

 

[Dennis Alwon]

l
all i am saying is, if there is a simple table for ampacity (based on NEC view of wire types and sizes) why did they write in "exceptions" that goes against the ampacity table? just doesnt make sense to me.

It would definitely eliminate a lot of trouble if they did not give the exception for dwellings but years of experience of the loads on a home show that these ampacities work fine for a dwelling where the loads are rarely continuous. It is all about diversity of the load that is why the entire dwelling must be fed from a feeder in order to use the dwelling table.

Commercial jobs do not have the diversity that there is in dwellings simply because of the type of loads that you find in a home. Take a 200 amp service and I bet 95% of the time the loads won't go over 100 amps. Electric furnaces or a/c units are the only reason they may reach 100 amps.

 

[kwired]

let me say this. regardless if it was allowed or not, competitive bidding has no relevance because in either case the NEC code (as it may be written) would apply, thus all bids would be based on the same restrictions/allowances. the cost difference would be paid for by the customer no matter what bid was accepted, etc.

all i am saying is, if there is a simple table for ampacity (based on NEC view of wire types and sizes) why did they write in "exceptions" that goes against the ampacity table? just doesnt make sense to me.

When it comes to competitive bidding you are correct that code still applies, and this particular section has specific allowances for specific condions. There are other areas of code that have specific allowances for specific conditions as well.

When it comes to wiring dwellings, one could run RMC to everything instead of NM cable and still meet code. It generally will cost more though, and if you are competing mostly for the lower price - you use NM cable because it is allowed, why is this any different when it comes to competitive bidding?

 

[FionaZuppa]

When it comes to wiring dwellings, one could run RMC to everything instead of NM cable and still meet code. It generally will cost more though, and if you are competing mostly for the lower price - you use NM cable because it is allowed, why is this any different when it comes to competitive bidding?

sorry, this is bad example. if NEC says you wire dwelling feeder to main panel using the ampacity chart where OCD is no greater than wire ampacity for the connection type (lets say the end-to-end is 75C column regardless if the wire is 90C), why would anyone choose another wire type or larger size if it costs more? answer is, they wouldnt. you might have 1 out of 10 bidders going unnecessarily bigger, but that is their fault and NEC is not to blame, etc.

It would definitely eliminate a lot of trouble if they did not give the exception for dwellings but years of experience of the loads on a home show that these ampacities work fine for a dwelling where the loads are rarely continuous. It is all about diversity of the load that is why the entire dwelling must be fed from a feeder in order to use the dwelling table.

Commercial jobs do not have the diversity that there is in dwellings simply because of the type of loads that you find in a home. Take a 200 amp service and I bet 95% of the time the loads won't go over 100 amps. Electric furnaces or a/c units are the only reason they may reach 100 amps.

and this NEC reasoning doesnt follow across to say a branch circuit because why?

 

[Smart $]

...
and this NEC reasoning doesnt follow across to say a branch circuit because why?

As the supply branches out, diversity diminishes.

 

[Dennis Alwon]

Sorry guys this thread accidentally got closed and it took awhile to figure out what happened. It is now re-opened.

 

[FionaZuppa]

Sorry guys this thread accidentally got closed and it took awhile to figure out what happened. It is now re-opened.

hmy:

 

[kwired]

sorry, this is bad example. if NEC says you wire dwelling feeder to main panel using the ampacity chart where OCD is no greater than wire ampacity for the connection type (lets say the end-to-end is 75C column regardless if the wire is 90C), why would anyone choose another wire type or larger size if it costs more? answer is, they wouldnt. you might have 1 out of 10 bidders going unnecessarily bigger, but that is their fault and NEC is not to blame, etc.



and this NEC reasoning doesnt follow across to say a branch circuit because why?

As the supply branches out, diversity diminishes.

Smart $ answer is the short and simple answer.

How many times have you clamped a service/feeder to a average to even fairly large dwelling and read anywhere near 100 amps, unless it had electric heat. You may see higher demand but still a varying demand at certain times outside of the heating/cooling. But you are not as assured of that kind of diversity with most branch circuits. The feeder situation they want the entire dwelling load to be on the feeder or you can not use the reduced conductor sizes. This actually does get some people that don't pay close enough attention to details in the code into trouble as they may think those values apply to all dwelling feeders, but they don't - just a feeder that supplies the entire dwelling unit load.

 

[kwired]

For 200 amp dwelling services or feeders that are using aluminum conductors - most of the time you use 4/0 AWG conductors whether you use the normal selection method or 310.15(B)(7). Only time the normal selection would require bumping up from 4/0 AWG to 250kcmil is if load calculation is over 180 amps.

 

[FionaZuppa]

Smart $ answer is the short and simple answer.

How many times have you clamped a service/feeder to a average to even fairly large dwelling and read anywhere near 100 amps, unless it had electric heat. You may see higher demand but still a varying demand at certain times outside of the heating/cooling. But you are not as assured of that kind of diversity with most branch circuits. The feeder situation they want the entire dwelling load to be on the feeder or you can not use the reduced conductor sizes. This actually does get some people that don't pay close enough attention to details in the code into trouble as they may think those values apply to all dwelling feeders, but they don't - just a feeder that supplies the entire dwelling unit load.

if diversity on service feeder says you can downsize the wire, then is it ok to also downsize the main panel OCD? it is what it is, just not following the logic.

 

[ActionDave]

if diversity on service feeder says you can downsize the wire, then is it ok to also downsize the main panel OCD?

It depends on the load calc.

it is what it is, just not following the logic.

You are looking for logic in a place where the only thing that matters are rules.

 

[kwired]

if diversity on service feeder says you can downsize the wire, then is it ok to also downsize the main panel OCD? it is what it is, just not following the logic.

The idea here is a 100 amp service/feeder to a dwelling unit may pull 100 amps at some time, but load diversity is diverse enough that they have determined an 83 amp conductor can handle it for no more then it would be loaded above 83 amps. How they determined this IDK, and IMO it is still a conservative figure based on my experiences. I don't know I ever measured more then 50-60 amps on a 100 amp dwelling supply - that is one that had a art 220 load of 100A or less anyway. Start getting into electric heating and you have more load but also typically are in the 200+ amps supply being needed. Like I said in a earlier post, unless your load calc is over 180 you are running 4/0 aluminum for 200 amp supply either way, so no difference there.

 

[FionaZuppa]

The idea here is a 100 amp service/feeder to a dwelling unit may pull 100 amps at some time, but load diversity is diverse enough that they have determined an 83 amp conductor can handle it for no more then it would be loaded above 83 amps. How they determined this IDK, and IMO it is still a conservative figure based on my experiences. I don't know I ever measured more then 50-60 amps on a 100 amp dwelling supply - that is one that had a art 220 load of 100A or less anyway. Start getting into electric heating and you have more load but also typically are in the 200+ amps supply being needed. Like I said in a earlier post, unless your load calc is over 180 you are running 4/0 aluminum for 200 amp supply either way, so no difference there.

so are all these 100A services that use undersized wire due to diversity now "we must re-do that" scenarios when diversity decides to change?? it just seems like the NEC is going against themselves in that their rules are typically a tad overkill but do in fact protect things, so why would that same thinking then go out the window on this one?

 

[Dennis Alwon]

The simple fact is that the dwelling unit deduction has been in place for an increible number of years and the reality there have been no issues. Show that is an issue and write a proposal to change this.

I don't know why it was done in the first place but nonetheless it is what it is and I don't have an issue with it

 

[Little Bill]

I don't have a copy of the 2014 so I'm going solely on the pasted section Infinity posted.
I don't see the language that 310.15(B)(6) [2008 code] had concerning the service or feeder serving the entire load. Or as it put it, "serves as the main power feeder"

I guess I'm asking if that language is necessary since if you have a subpanel the 83% could be used but based only on the service size? Or the language may be there and I can't see it because I don't have the actual code to read.

(6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services
and Feeders. For individual dwelling units of onefamily,
two-family, and multifamily dwellings, conductors,
as listed in Table 310.15(B)(6), shall be permitted as
120/240-volt, 3-wire, single-phase service-entrance conductors,
service-lateral conductors, and feeder conductors
that serve as the main power feeder to each dwelling unit
and are installed in raceway or cable with or without an
equipment grounding conductor. For application of this section,
the main power feeder shall be the feeder between the