Minimum supply to a residential occupancy

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Smart $ said:
It applies to any dwelling unit. Read the first sentence of 310.15(B)(7)...
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Than what is the definition of a dwelling? That means that even a building with 100 apartments can take 310.15 (B) (7)?

Not doubting you, on the contrary Im doubting my self. I guess I always assumed 310.15 (B) (7) applied only to 1 and 2 families per building.
 
mbrooke said:
Than what is the definition of a dwelling? That means that even a building with 100 apartments can take 310.15 (B) (7)?

Not doubting you, on the contrary Im doubting my self. I guess I always assumed 310.15 (B) (7) applied only to 1 and 2 families per building.
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See definitions in Article 100... four of 'em... each starting with the term Dwelling.
 
mbrooke said:
So the dwelling table applies to all of them? :dunce:
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That is correct...

For individual dwelling units of one-family,
two-family, and multifamily dwellings, conductors,
as listed in Table 310.15(B)(7), 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. .....
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It does not apply to service or feeder conductors which serve more than one dwelling unit, or those which do not supply all the power relevant to an individual dwelling unit.
 
Smart $ said:
That is correct...



It does not apply to service or feeder conductors which serve more than one dwelling unit, or those which do not supply all the power relevant to an individual dwelling unit.
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I never knew that even though it was obvious all along. :eek: I guess always assumed that it applied to services rather than the individual feeders to a dwelling unit outside of say an exterior disconnect. When they said muilti dwelling I was assuming a condo each with its own separate service and meter... guess I was wrong then.
 
Smart $ said:
Q1: If you have a multifamily dwelling with separate service disconnecting means for each, does 230.79(C) apply to those disconnects?

Q2: If you have a multifamily dwelling with single service disconnecting means, then supply meters and outside disconnects for each unit, does 225.39(C) apply to those disconnects?
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225 part II is titled buildings or other structures supplied by a feeder(s) or branch circuit(s). 225.39 is within Part II.

If the feeders are on the same building as the service - but are routed on the exterior of the building - they are outside - but not under the scope of part II, and for the most part can be sized just like an indoor feeder. Now a feeder tap routed outdoors can be unlimited in length, but that is kind of veering off topic a little.

I was going to get to it but it has been brought up that 310.15(B)(7) only applies to one-family dwellings and the individual dwelling units of two-family and multifamily dwellings. This comes directly from first sentence of the section in 2014 - has been modified though not sure what it said previously, but the whole section was changed and the table removed, but for most part practical installation hasn't really changed much other then it is now more clear how or when to adjust ampacity of these conductors.
 
kwired said:
225 part II is titled buildings or other structures supplied by a feeder(s) or branch circuit(s). 225.39 is within Part II.

If the feeders are on the same building as the service - but are routed on the exterior of the building - they are outside - but not under the scope of part II, and for the most part can be sized just like an indoor feeder. ...
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Congratulations, you're the only one that caught that... :thumbsup:

While it doesn't change the answer, in that 225.39(C) does not apply, you are correct in that 225.39(D) does not apply either. However, is anybody in their right mind going to install a 30A disconnect for a typical dwelling unit? Yes, it is possible compliantly... but it's going to be something like a super low-budget efficiency apartment. Remember, we're just talking about the disconnect rating here, not the OCPD rating or the feeder ampacity thereafter.
 
Smart $ said:
Congratulations, you're the only one that caught that... :thumbsup:

While it doesn't change the answer, in that 225.39(C) does not apply, you are correct in that 225.39(D) does not apply either. However, is anybody in their right mind going to install a 30A disconnect for a typical dwelling unit? Yes, it is possible compliantly... but it's going to be something like a super low-budget efficiency apartment. Remember, we're just talking about the disconnect rating here, not the OCPD rating or the feeder ampacity thereafter.
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A very tiny dwelling unit that only has 2 SABC's, a bathroom circuit and one other general lighting circuit may not be a "typical dwelling unit"
 
mbrooke said:
But still a dwelling unit, correct? This is exactly my situation with the studios.
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If it fits the art 100 definition, yes.
Dwelling Unit.
A single unit, providing complete and independent living facilities for one or more persons, including permanent provisions for living, sleeping, cooking, and sanitation.
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kwired said:
If it fits the art 100 definition, yes.
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So I could have a studio with:


2 20amp SABC

1 20 amp bath circuit

1 15 amp lights and plugs

1 20 amp Dishwasher & disposal

Use a 50amp OCPD to the subpanel and apply an 83% reduction in the feeders to the dwelling subpanel?
 
mbrooke said:
So I could have a studio with:


2 20amp SABC

1 20 amp bath circuit

1 15 amp lights and plugs

1 20 amp Dishwasher & disposal

Use a 50amp OCPD to the subpanel and apply an 83% reduction in the feeders to the dwelling subpanel?
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Yes to all except the 83% reduction of conductor ampacity.

310.15(B)(7)(2) starts with "For a feeder rated 100 through 400 A..."
 
mbrooke said:
So I could have a studio with:


2 20amp SABC

1 20 amp bath circuit

1 15 amp lights and plugs

1 20 amp Dishwasher & disposal

Use a 50amp OCPD to the subpanel and apply an 83% reduction in the feeders to the dwelling subpanel?
Click to expand...

kwired said:
Yes to all except the 83% reduction of conductor ampacity.

310.15(B)(7)(2) starts with "For a feeder rated 100 through 400 A..."
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Agree.

However, he is not exactly doing a standard load calculation there. Could be he only requires a 40A OCPD and feeder. For example, the 2 - 20A SABC's are only calculated at 3000VA, not 4800VA; the lighting, GP receptacles, and bath loads are all determined at 3VA/ft?.
 
Smart $ said:
Agree.

However, he is not exactly doing a standard load calculation there. Could be he only requires a 40A OCPD and feeder. For example, the 2 - 20A SABC's are only calculated at 3000VA, not 4800VA; the lighting, GP receptacles, and bath loads are all determined at 3VA/ft?.
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Doing the load calc it looks like a 40amp OCPD could do it, but to be safe a 50amp. I am omitting the 20amp laundry circuit as well as the dryer since those are provided by an onsite laundry room with its own 225 amp 120/240 subpanel. Same for HVAC as a central gas boiler is involved for heat and hot water. The Kitchen stove is gas as well, so in short my load calcs are far from a typical dwelling.


So with that said, a 50amp OCPD is ok by the looks of it.

Out of curiosity, is anything restricting me from using NM-B to these dwelling subpanels or does it have to be SER? Specs will probably ask for conduit but just want to know my options.
 
mbrooke said:
Doing the load calc it looks like a 40amp OCPD could do it, but to be safe a 50amp. I am omitting the 20amp laundry circuit as well as the dryer since those are provided by an onsite laundry room with its own 225 amp 120/240 subpanel. Same for HVAC as a central gas boiler is involved for heat and hot water. The Kitchen stove is gas as well, so in short my load calcs are far from a typical dwelling.


So with that said, a 50amp OCPD is ok by the looks of it.

Out of curiosity, is anything restricting me from using NM-B to these dwelling subpanels or does it have to be SER? Specs will probably ask for conduit but just want to know my options.
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334.12
 
mbrooke said:
All that's restricting it is if the building is outside of a type 3, 4 or 5.
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Well there's more than that in 334.12... so are you saying the building is not of a Type III, IV, or V construction? If yes, then you can't use it.
 
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