sizing sub panel

[GlennG]

I recently got a new job, its a second floor addition that is going to be an apartment for the parents. Someone else did the rough on this job and then got thrown off. I didnt like the idea of picking up a halfway done job to begin with but i figured i can make a few bucks while i help these people out. Anyway the apartment has a full kitchen, living room, bedroom and bathroom. The electrician that did the rough installed a 60 amp sub panel, I dont feel that this was the right move but i am not sure of any references that would prevent this or if i am just looking into this to much. Between the free standing range, fridge, micro, etc. i feel like it wouldnt take much to have a problem. I am tryinh to convince the home owner to let me replace it with a 90 amp sub panel instead. Any input would help, just trying to get some other opinions, and if possible any references. thanks.

 

[Ohms law]

What is the main panel OCPD size?

 

[Sierrasparky]

What size is the Feeder,
Around here the minimum Size service to a apartment unit is 100 amps unless it is a hotel. I suppose the theory is it may go condo. Hotel different story.

 

[Ohms law]

What size is the Feeder,
Around here the minimum Size service to a apartment unit is 100 amps unless it is a hotel. I suppose the theory is it may go condo. Hotel different story.

Agree.

 

[ptonsparky]

Do a load calc on it. There are a lot of homes out there with 60 amp services.

 

[GlennG]

Main ocpd is 200amp. sub panel is fed with 6/3 on a 60 amp breaker. I was looking to use #4 SER on a 90 amp breaker. Is having the minimum 100 amp sub panel for an apartment a local amendment?

 

[suemarkp]

Code requires a 100A disconnect for a separate (detached) dwelling unit. But if this addition is part of the main dwelling, then I don't think any particular rule applies except the panel and feeder must be large enough to accommodate the calculated load. So do a load calc just like you would for a house -- 3VA per square foot of that addition, 2 kitchen appliance circuits, the range, perhaps a laundry circuit or other dedicated appliance or HVAC circuits on that feeder. If no laundry on that feeder, it may fit.

#4 SER may not work either, as it is limited to 60C (if in thermal insulation??). Is the SER copper or aluminum? NM is only good for 55A, so the load calc needs to come in under that with 6-3 NM.

 

[Ohms law]

Code requires a 100A disconnect for a separate (detached) dwelling unit. But if this addition is part of the main dwelling, then I don't think any particular rule applies except the panel and feeder must be large enough to accommodate the calculated load. So do a load calc just like you would for a house -- 3VA per square foot of that addition, 2 kitchen appliance circuits, the range, perhaps a laundry circuit or other dedicated appliance or HVAC circuits on that feeder. If no laundry on that feeder, it may fit.

#4 SER may not work either, as it is limited to 60C (if in thermal insulation??). Is the SER copper or aluminum? NM is only good for 55A, so the load calc needs to come in under that with 6-3 NM.

Read 230.79 (A-D)
Obviously if you where to go with a 60 amp disconnect, make sure it is adequate size.

 

[roger]

Read 230.79 (A-D)

This is not a service supplying this attached apartment, so 230.79 would not be applicable. A calculkation based on part IV of article 220 would be all that is needed.

Roger

 

[Smart $]

IMO, what has the most bearing is separation of loads. That is, the set up may be as an apartment... living wise ...but the electric will likely be more like a large household. For example, the HVAC load may be entirely on the main panel, as may be the water heater... of course some is going to depend whether gas or electric is used.

Edit to add: Forget to mentiion, I agree with doing a load calc... simplest way to determine for certain... and it is the only compliant way!!!

 

[kwired]

What size is the Feeder,
Around here the minimum Size service to a apartment unit is 100 amps unless it is a hotel. I suppose the theory is it may go condo. Hotel different story.

May be a local rule, is not an NEC requirement.

IMO, what has the most bearing is separation of loads. That is, the set up may be as an apartment... living wise ...but the electric will likely be more like a large household. For example, the HVAC load may be entirely on the main panel, as may be the water heater... of course some is going to depend whether gas or electric is used.

Edit to add: Forget to mentiion, I agree with doing a load calc... simplest way to determine for certain... and it is the only compliant way!!!

Likely the situation, you have the kitchen and some likely minimal general lighting, but otherwise probably do not have HVAC, water heating, maybe even don't have any laundry in this area. 60 amps may be plenty of capacity for what is there.

 

[Ohms law]

This is not a service supplying this attached apartment, so 230.79 would not be applicable. A calculkation based on part IV of article 220 would be all that is needed.

Roger

230.79, states minimum size service disconnecting means. I know you still need to do a calc.

 

[kwired]

230.79, states minimum size service disconnecting means. I know you still need to do a calc.

I did not even read 230.79, but the fact is anything in 230 applies to service equipment, the OP's installation is not service equipment.

The circuit in the OP is a feeder and if you can find anything in 215 that is similar to what is in 230.79 please tell us where it is.

 

[Ohms law]

A sub-panel is a sub-service is it not? What article would you use to install a sub-panel? Is it not considered a remote panel? I know you size the service conductors according to 310.17(b)(7) for the service as a whole. But for a sub-panel you would use the 310.15(b)(16).
I'm not trying to argue, more than anything i want a understanding. So, I like to have input from others.

 

[Smart $]

A sub-panel is a sub-service is it not? What article would you use to install a sub-panel? Is it not considered a remote panel? I know you size the service conductors according to 310.17(b)(7) for the service as a whole. But for a sub-panel you would use the 310.15(b)(16).
I'm not trying to argue, more than anything i want a understanding. So, I like to have input from others.

Supplied by is not the same as service equipment. Service equipment (used loosely to include conductors) as covered by NEC is between POCO connection and the service disconnecting means (or OCPD if not integral with disconnecting means). All equipment on the load side of that does not fall under Article 230 purview.

 

[roger]

A sub-panel is a sub-service is it not?

No, it is not.

What article would you use to install a sub-panel?

215, 220, 225 if applicable, and 310.

Is it not considered a remote panel?

Yes it is but it is not part of the service equipment. It is actually not much different than an enclosed breaker for a piece of equipment.

I know you size the service conductors according to 310.17(b)(7) for the service as a whole. But for a sub-panel you would use the 310.15(b)(16).

You are correct but I think you meant 310.15(B)(7)

I'm not trying to argue, more than anything i want a understanding. So, I like to have input from others.

See the artcle 100 defintion of "Service Equipment"


Roger

 

[Ohms law]

No, it is not. 215, 220, 225 if applicable, and 310. Yes it is but it is not part of the service equipment. It is actually not much different than an enclosed breaker for a piece of equipment. You are correct but I think you meant 310.15(B)(7)
See the artcle 100 defintion of "Service Equipment"


Roger

Thanks for all that! When I read the definition originally "or an otherwise designated area, intended to constitute the main control and cutoff of the supply."
I was thinking supply to the branch circuits of the sub-panel. Sometimes I think to hard about something and I confuse myself?

 

[Sierrasparky]

May be a local rule, is not an NEC requirement.

I thought he was speaking of a service feed to a sub.

Also around these parts you cannot have a sperate apt. attached to a dwelling without having a seperate meter. POCO does not allow an idividual person to charge for the electrical to the sub tennant. So a seperate meter is usually installed and thus a 100 amp min is usually provided.

 

[kwired]

I thought he was speaking of a service feed to a sub.

Also around these parts you cannot have a sperate apt. attached to a dwelling without having a seperate meter. POCO does not allow an idividual person to charge for the electrical to the sub tennant. So a seperate meter is usually installed and thus a 100 amp min is usually provided.

No such thing as a service feed to a sub. See last few posts and some definitions in Art 100. Service equipment is from utility to the service disconnecting means. Anything beyond that point is a feeder or a branch circuit.

Some exceptions are situations where more than one service is permitted to a building or structure, but they generally must be grouped in one location, or if multiple occupancies and separate services are permited there must usually be fire rated construction between the occupancies effectively making them separate structures from fire codes point of view.

Many places it is illegal to sell power to a tenant, there is nothing wrong with having an apartment or sub unit within another structure if not selling power to the occupant. In OP's situation I believe it was a sub unit for the elderly parents to live in. Chances are it is all under 1 meter and nobody is selling power except for the POCO. If it were to be metered separately, it can be done with two service disonnects grouped together and at least one dwelling or the other will have a feeder run to it, or both service/branch circuit panels are in same location and both occupants have access to them.