Residential Shore Power - Service Calculation

[Npstewart]

According to the optional method for dwelling units (220.82), there are only a couple of load types that everything gets categorized into:


HVAC: 65% of heat + 100% of fan/compressor etc.

General Loads: First 10 kVA @ 100% + 40% of ALL other loads.


In the case where you have shore power for a large boat, with a shore power panel equipped with a 50A, 240v receptacle, would it be permissible to categorize this into the "General Loads" category? I dont see why this wouldn't be acceptable but I have a local plans examiner/inspector that thinks otherwise.

Alternatively this load of 12 kW would be added directly on to the service as he claims is required. My problem with this is that this chapter is labled "Marinas & Boatyards". In fact, in 555.1, it actually says "Private, noncommercial docking facilities....are not covered by this article".

All references are to the NEC 2011.

Thanks.

 

[charlie b]

My problem with this is that this chapter is labled "Marinas & Boatyards". In fact, in 555.1, it actually says "Private, noncommercial docking facilities....are not covered by this article".

That just means that you don't have to follow the wiring methods in that article. You also don't get to apply the demand factors from that article, but that doesn't matter since you only have one receptacle for boats.

General Loads: First 10 kVA @ 100% + 40% of ALL other loads.

I am going to invoke "Charlie's Rule" at this point (author's privilege). The code does not say "ALL other loads." Rather, it says ". . . the remainder of the following loads." Your boat receptacle does not appear to fit into any of the 4 sub paragraphs that follow. Specifically, it is not a "general-use receptacle," and none of the other listed items comes close to matching. I have to agree with your plans examiner. That boat could be plugged in and drawing load completely independently of what is happening at the residence.

 

[Npstewart]

That just means that you don't have to follow the wiring methods in that article. You also don't get to apply the demand factors from that article, but that doesn't matter since you only have one receptacle for boats.
I am going to invoke "Charlie's Rule" at this point (author's privilege). The code does not say "ALL other loads." Rather, it says ". . . the remainder of the following loads." Your boat receptacle does not appear to fit into any of the 4 sub paragraphs that follow. Specifically, it is not a "general-use receptacle," and none of the other listed items comes close to matching. I have to agree with your plans examiner. That boat could be plugged in and drawing load completely independently of what is happening at the residence.

The way I read it, it is either one category, or the other.

I cant think of any case or example where they add any load directly on to the bottom line of the service? I will scan the Annex examples real quick.


Just out of curiosity, has anyone done any electrical charging receptacles in dwelling units?

 

[Npstewart]

The way I read it, it is either one category, or the other.

I cant think of any case or example where they add any load directly on to the bottom line of the service? I will scan the Annex examples real quick.


Just out of curiosity, has anyone done any electrical charging receptacles in dwelling units?

I meant to say for electric car charging purposes...

 

[charlie b]

I cant think of any case or example where they add any load directly on to the bottom line of the service?

Neither can I. But we always have the option of calculating a service as the sum total of all connected load. What article 220 does for us is to recognize that not everything will be operated at full load at the same time. That is the essence of "demand factors."

Just out of curiosity, has anyone done any electrical charging receptacles in dwelling units?

We have done a few high rise condo buildings in a city that now requires charging stations be included. What is your question?

 

[Npstewart]

Neither can I. But we always have the option of calculating a service as the sum total of all connected load. What article 220 does for us is to recognize that not everything will be operated at full load at the same time. That is the essence of "demand factors."
We have done a few high rise condo buildings in a city that now requires charging stations be included. What is your question?

I was in a big hurry on Friday so I hope to clarify my question on the Car charging question.

Has anyone done a residential load calculation on a house with car charging receptacles in the garage? If so, did you classify the car charging receptacle load in the "General" column, or add it right on to the entire service demand load? I ask because this is closely resembles the boat charging receptacle. Many of the car charging receptacle loads are actually much higher than the boat charging, some that i've seen have been as high as 80A, 240v. If 80 demand amps were added directly to the service, many homes equipped with 200A service would likely be under-sized because that would only leave 120 demand amps for the rest of the house.


Thanks

 

[charlie b]

I am in a bit of a rush this morning, so I will just mention, (1) I don't know how much power a car charging station uses, nor for how long it is on before the car is fully charged, but (2) It is not a "boat charging receptacle." The boat is a load, and it is on all the time. How much load depends on whether the boat's A/C system is running, or whether they are using the stove, etc. That is the key difference between a car and a boat.

 

[mgookin]

If that homeowner has a boat that draws 50A 240V he's got the money to upsize the service. And if you don't upsize that service, he's going to be all over you when he's getting 190V at that outlet and burning things up.

Set your codes aside and ask "Will it work?"

 

[Npstewart]

If that homeowner has a boat that draws 50A 240V he's got the money to upsize the service.

Not sure that is the best way to go about designing something.

And if you don't upsize that service, he's going to be all over you when he's getting 190V at that outlet and burning things up.

Im not sure I see the connection between the service size and 190v . The original post was really in regards to the overall service calculation using the optional method per 220.82.



I think im going to submit an interpretation request to NFPA. They usually take a couple weeks. Probably wont help me out in this situation but i'd be curious to see their interpretation. I post the reply when this comes in!

Thanks all.

 

[Npstewart]

As promised, I wanted to post my response from NFPA on this particular issue.

MY QUESTION:

In the case where there is a 50A/240v dock receptacle which would be used to power/charge a large boat, would it be permissible to classify this as a “General Load” which would essentially allow them to be calculated at 40% at the service level, after the first 10 kVA?. Article 555 explicitly says dwelling units are not included in this scope and therefore cannot be used to answer this question.




NFPA RESPONSE:

No, based on 220.82(B)(1) and not covered by any of the other listed loads. Where a feeder or service load is going to include loads outside the dwelling unit such loads must be calculated in accordance with Part III of Article 220.