Single phase Existing Dwelling Service Size

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kwired

Electron manager
Location
NE Nebraska
I probably need some caffeine too. It's not really a big issue. Let's take a 200A service as an example.

200A ? 0.83 =166A

No feeder supplied by this service will be required to have an ampacity greater than 166A.
I still don't get what you are after. Right now a service with a 200 amp overcurrent device would be allowed 4/0 aluminum or 2/0 copper after the change, the conductors would still be the same for 200 amps anyway. For applications where this doesn't apply the 4/0 aluminum can still be protected by 200 amp device as long as calculated load is not over 180, but to use the alternate method allowed the load calculation can be right up to 200 amps both now and likely after the change.
 

Smart $

Esteemed Member
Location
Ohio
Okay, I get your point.

What I was referring to was that now you can drop a load or two at a meter/panel disco and use the calc. for a main feeder to the house panel and not get grief/flack over it.
Told you I needed some caffeine...

I still don't get what you are after. Right now a service with a 200 amp overcurrent device would be allowed 4/0 aluminum or 2/0 copper after the change, the conductors would still be the same for 200 amps anyway. For applications where this doesn't apply the 4/0 aluminum can still be protected by 200 amp device as long as calculated load is not over 180, but to use the alternate method allowed the load calculation can be right up to 200 amps both now and likely after the change.
Under current code, permitted reduction in ampacity could be based on feeder rating. As the proposal is worded, it can only be based on service rating. For example, you have a 300A service. You split the service 100A to detached garage an 200A to house. How do you size the wire to house under the proposal? ...under current Code?
 

kwired

Electron manager
Location
NE Nebraska
Told you I needed some caffeine...


Under current code, permitted reduction in ampacity could be based on feeder rating. As the proposal is worded, it can only be based on service rating. For example, you have a 300A service. You split the service 100A to detached garage an 200A to house. How do you size the wire to house under the proposal? ...under current Code?
I see now. They either forgot to include the word feeder or they don't intend to use this for anything but services.
 

jumper

Senior Member
I see now. They either forgot to include the word feeder or they don't intend to use this for anything but services.

Is this what you guys are talking about?


Comment on Affirmative:
CLINE,
S.: This proposal is the result of many, many hours of panel member
time over many code cycles. It is intended to clearly and easily express the
ongoing intent of the panel over these many code cycles of misinterpretation.
This wording gives a simple ?duty cycle? type adjustment which, through a
simple mathematic multiplication, yields a minimum ampacity requirement for
conductor sizing. Hopefully the twelve submitters who also spent their time
trying to resolve the misunderstandings will be satisfied with this result.
It
recognizes the long-known diversity of load for this exact class of load. It
recognizes that conditions of installation may also affect the ampacity of the
conductor. It recognizes that feeders, only if sized in relation to the service
rating, may safely be allowed the same diversity adjustment since they are
either carrying 100% of the diversified load, OR only loads too small to change
the effective diversity have been removed ahead of the feeder, OR large enough
loads have been removed ahead of the feeder to make the 17% adjusted
ampacity a moot point. The concerns about increased dwelling loads in general
is addressed in 230.79 where the service rating amperage itself is determined.
It
should now be clear that while feeders may also use the diversity
adjustment, it must be based on the 230.79 service rating, not the size of the
OCPD for the feeder. If you run a 200 amp feeder from a 200 amp rated
service, you get to use the adjustment, start with a 166 minimum ampacity
conductor, apply any other required adjustments, and choose your conductor. If
you run a 100 amp feeder from a 200 amp rated service, you still get use the
adjustment, but of course the 166 minimum ampacity conductor then required
might not be an advantage over the normal 100 amp conductor. You may not
use 100 amps (the feeder OCPD size) to apply the adjustment to - you must use
the service rating.
 

Smart $

Esteemed Member
Location
Ohio
Is this what you guys are talking about?
Nailed it.

However, I believe he/they overlooked the fact that a feeder may be the "main supply feeder" to the dwelling unit, with no associated loads pulled off the service ahead of the feeder ocpd.
 
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don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Why don't we adjust the load calculations in Article 220 to match the real world and get rid of the rule in 310.15(B)(7)?
 
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