4/0-4/0-2/0-4 large enough?

[kert]

I'm getting upgrading to 400A and moving my meter from the house to the new barn (closer to transformer) and will be feeding the house from a 200A off the meter. The distance from the disconnect to the main panel in the house is about 110'. I had originally planned to use 4/0-4/0-2/0-4 Al MHF, but now I'm wondering if the voltage drop would be a problem.

Looking at the existing overhead feed, the wires look to be smaller than the 4/0 conductors that go into the weatherhead, so since the total run is about the same length I don't think there is really an issue with voltage being low, but now that voltage drop (which really is power dissipated in the wire) is on my side of the meter.

What do the experts say?

 

[wakeboarder311]

yeah you will have no problem with that.

 

[wyliesdiesels]

You should be fine! VD will be just under 4v, which is about 1.7%. NEC recommends but does not require a 3% vd!

Also, overhead/'freeair' service drops have different ampacities so the wire overhead will be smaller!

 

[pattenp]

Since it's a feeder after a disconnect, I say it needs to be #250.

 

[kert]

You should be fine! VD will be just under 4v, which is about 1.7%. NEC recommends but does not require a 3% vd!

Also, overhead/'freeair' service drops have different ampacities so the wire overhead will be smaller!

OK Good. For some reason the calculators I was finding seemed to indicate a bigger drop hence my concern.

 

[kert]

Since it's a feeder after a disconnect, I say it needs to be #250.

Why does it make a difference that it is after a disconnect?

 

[pattenp]

Are you burying this? You mentioned MHF.

 

[wyliesdiesels]

Since it's a feeder after a disconnect, I say it needs to be #250.

Why is that? It's feeding his house....

 

[pattenp]

Why does it make a difference that it is after a disconnect?

After a disconnect it is not considered a service and the wire size needs to be calculated as a branch/feeder using NEC 310.15(B)(16) Table.

 

[kert]

Are you burying this? You mentioned MHF.

Yes. It will be buried in PVC conduit.

 

[pattenp]

Yes. It will be buried in PVC conduit.

Then it needs to be #250 Al. #4/0 Al is only good to 180A.

The dwelling service feeder only needs to be a 3 conductor and will go from the meter base to the first means of disconnection. In this use the size is determined from 310.15(B)(7) and #4/0 Al is good for 200A.

 

[Aceman]

Then it needs to be #250 Al. #4/0 Al is only good to 180A.

The dwelling service feeder only needs to be a 3 conductor and will go from the meter base to the first means of disconnection. In this use the size is determined from 310.15(B)(7) and #4/0 Al is good for 200A.

Patten you need to reread 310.15(B)7.

4/0 AL is perfectly fine to go from the disconnect at the barn to the home.

 

[pattenp]

Patten you need to reread 310.15(B)7.

4/0 AL is perfectly fine to go from the disconnect at the barn to the home.

Okay, I reread and I stand corrected. Not what I was taught and the verbiage doesn't agree with the diagram in 230.1 for services.

Edit: It just dawned on me that the use of service and feeder in section 310.15(B)(7) are two different things. I was comparing apples to oranges.

 

[Aceman]

Okay, I reread and I stand corrected. Not what I was taught and the verbiage doesn't agree with the diagram in 230.1 for services.

Since this isn't a service, but a feeder, I wouldn't be looking in 230 at all. I only looked in 310...

 

[pattenp]

Since this isn't a service, but a feeder, I wouldn't be looking in 230 at all. I only looked in 310...

I agree. I added an edit as you were apparently typing.

kert, I apologize for taking you on a wild goose chase. The #4/0 is fine as Aceman has pointed out.

*

 

[kert]

Thanks everyone.

No worries pattenp, I learned something and that's never a bad thing.

 

[wyliesdiesels]

@pattenp- as u know I don't have an NEC book but I'm curious about this and trying to learn. So a feed to a house after a disconnect is considered a service right? In what way would a feeder, feeding a house after a disconnect, not be considered a service?

 

[pattenp]

I'll try to say this as I understand and try not to get too convoluted about it. It boils down to the feeder or service is supplying the main power to the dwelling. The service is the wire serving from the meterbase to the first means of disconnection. A feeder can be between the first point of disconnection and the load center that serves the dwelling. So it's a matter of placement within the system and that it serves as the main power feed. So to me a feeder in this use is an extension of the service. See... the more I say the worse it gets. I guess the simple answer would be that a feeder feeding all the power to the dwelling is in sense a service. I'll stop at that and wait for Aceman to correct me.

 

[wyliesdiesels]

Ok, so in the OP's situation, it is considered a service since it supplies the whole load of the house regardless that it's after a disconnect in the meter main?

 

[pattenp]

Ok, so in the OP's situation, it is considered a service since it supplies the whole load of the house regardless that it's after a disconnect in the meter main?

This is where terms get intermingled. I think it's considered a feeder but is sized buy the rules used for services. Look at 310.15(B)(7) when you get your book.

 

[sberry]

V drop is calculated at 200A, how likely will this ever be to fully loaded?

 

[Aceman]

Service is from the point where the utility connects to the first disconnecting means. Everything after that is a feeder or branch circuit.

 

[kert]

This is where terms get intermingled. I think it's considered a feeder but is sized buy the rules used for services. Look at 310.15(B)(7) when you get your book.

So the note here on 310.15(B)(7) says "These are permitted ratings for Dwelling Unit service and feeder conductors which carry the total load of the dwelling." Since the MHF cable is supplying the entire dwelling, it would be subject to this rating.

Now maybe I'm showing my ignorance, but the ampacity table above that shows 4/0 Al at 90°C rating at 205A. The cable in question is rated USE-2/RHW-2, which is rated for 90°C, so I should be good either way. As far as derating in conduit, I wouldn't think this would be in issue since there are only 3 "current carrying conductors;" ground not being considered a current carrying conductor.

 

[pattenp]

Even though MHF has insulation rated at 90C, the 90C column is used only when derating. The 75C column is used for sizing. That's where I said way back that 180A was it for 4/0. The table 310.15(B)(7) is what you use and it shows 200A for 4/0 Al. If you used the 4/0 as a feeder to a sub-panel then it would be 180A.

 

[wyliesdiesels]

This is where terms get intermingled. I think it's considered a feeder but is sized buy the rules used for services. Look at 310.15(B)(7) when you get your book.

Ok, will do! Thx!

 

[wyliesdiesels]

Even though MHF has insulation rated at 90C, the 90C column is used only when derating. The 75C column is used for sizing. That's where I said way back that 180A was it for 4/0. The table 310.15(B)(7) is what you use and it shows 200A for 4/0 Al. If you used the 4/0 as a feeder to a sub-panel then it would be 180A.

Not to mention that I dont think there are 90c deg rated breakers! Kert, if your termination point is rated @ 75c deg or 60c deg then the wire ampacity is the corresponding rating!

 

[parkiski01]

I think you have now problem on that and no need to reconnect

 

[theoldwizard1]

V drop is calculated at 200A, how likely will this ever be to fully loaded?

There ya go again. Applying "logic" to a situation where illogical humans have written "The Book" !

 

[Aceman]

There ya go again. Applying "logic" to a situation where illogical humans have written "The Book" !

If the "book" is the "NEC", it doesn't require voltage drop calcs.....?

 

[wyliesdiesels]

Yeah, really!!!.....