residential service wire size

[melissa]

Hello everyone. My name is Melissa Slate and I am a new electrical contractor. Im bidding a job that will be a home converted to a church. They currently have one 200 amp panel. I need to up grade this service to a 400 amp split into two 200 amp panels. The distance will be 80 feet from the meter. I intend to use 4/0 AL wire for the 200 amp panels. Will I need to use 250mcm due to voltage drop? Also what wire size will I need from the top of the meter to the weather head? prelimenary calculations say 900 mcm AL. This seems to large for residential. Thanks

 

[LarryFine]

Melissa, welcome to the forum! Where in the world are you?

They currently have one 200 amp panel. I need to up grade this service to a 400 amp split into two 200 amp panels.

Obvious solution is to replace the meter base and run a new feeder and panel, presuming the existing panel and loads can remain.

The distance will be 80 feet from the meter. I intend to use 4/0 AL wire for the 200 amp panels. Will I need to use 250mcm due to voltage drop?

Probably not, and probably so. Not likely for 80 feet, but likely for 200a, depending on which code cycle you're operating under.

Also what wire size will I need from the top of the meter to the weather head? prelimenary calculations say 900 mcm AL. This seems to large for residential.

Well, if this was still residential, you wouldn't be asking these quesstions, so don't consider it residential anymore.

We'd have to know your calculations to say what size you need, but that's a rather thick wire. I would look into parallel conductors.

 

[augie47]

Sorry. Theres a whole lot of that confusing me.
We seem to be getting the cart before the horse. First you need to deternmine the total load, this will determine your service requirement, then you need to determine the load on each panel and select the appropriate feeder.
As far as 4/0 AL the ampacity will depend greatly on what type conductor you will be using (XHHW, SE cable, etc. ?? )

 

[melissa]

Thanks for the quick response. Larry, Im Acworth Georgia. This home is out of town in a Rural area. Will i need to treat this as commercial, 3 phase? Augie, Im using XHHW run in conduit around the building. The current 200 amp conductors are lateral and in to small of a pathway to upgrade to a 4/wire service ( it is currently 3/wire). There will be another a/c system added to this buliding. the current panel is maxed out so we were going to add another 200 amp panel and split the loads. This way the church will have expansion room.The calculation charts i use are a little confusing and I want to make sure i have all the wire sizes right.

 

[LarryFine]

Melissa, as is often the case, your responses triggered more questions, especially since you now mention 3ph, and up from 1ph if I read that right. You may have to replace everything, or just have to add on.

First of all, 1ph vs 3ph is not the same thing as residential vs commercial. There are plenty of both kinds in both places. So, make sure you will require, and the POCO (power company) can and will supply it.

Is the POCO going to convert your existing 1ph service to a high-leg Delta (by adding one transformer to the existing), or are they going to supply you with a Wye service (by replacing the one with three)? 240v vs 208v.

We would need to see your present- and new-load calcs, separate for 1ph and 3ph. For a few 3ph loads, the third phase may be enough to let you keep the existing service, and just install a 3ph feeder and one panel.

The bottom line is that you can either over- or under-estimate your load when you just guess. You may need all-new, and you may not. You don't want to replace it twice, or even once if you don't have to.

Again, what code are you under, '05 or '08? What will be your feeder type, cable or conduit? And, the other guys' questions.

 

[augie47]

Another big question that may have a major effect on the job.
Do you know the occupancy of the building, especially the sanctuary (# of people)

 

[mcclary's electrical]

Hello everyone. My name is Melissa Slate and I am a new electrical contractor. Im bidding a job that will be a home converted to a church. They currently have one 200 amp panel. I need to up grade this service to a 400 amp split into two 200 amp panels. The distance will be 80 feet from the meter. I intend to use 4/0 AL wire for the 200 amp panels. Will I need to use 250mcm due to voltage drop? Also what wire size will I need from the top of the meter to the weather head? prelimenary calculations say 900 mcm AL. This seems to large for residential. Thanks

Melissa, you stated 4/0al . Please keep in mind 310.15 (b) (6) does not apply to "other than dwelling units" That doesn't mean you can't have 4/0 in a 200 amp panel, but it does make it alot harder to use 4/0. Under 08' code, your 4/0 is gonna be limited to 150.

under 05' if your load calc comes in at say 176 amps for example, they don't make a 180 amp breaker,so you could go to 200 with 4/0,,,,,,

but only under specific circumstances. And be ready to argue as soon as an inspector see 4/0 in a commercial panel


Also, under 08 code that chart for res. feeders does not apply unless it is carrying the entire load of the house, which is not the case here

 

[erickench]

If the service is 400A then according to NEC Table 310.16 the size of the conductor would be 600 MCM or 500 MCM if you apply NEC 240.4(B). Where did you get 900 MCM from?

 

[kwired]

Melissa, you stated 4/0al . Please keep in mind 310.15 (b) (6) does not apply to "other than dwelling units" That doesn't mean you can't have 4/0 in a 200 amp panel, but it does make it alot harder to use 4/0. Under 08' code, your 4/0 is gonna be limited to 150.

under 05' if your load calc comes in at say 176 amps for example, they don't make a 180 amp breaker,so you could go to 200 with 4/0,,,,,,

but only under specific circumstances. And be ready to argue as soon as an inspector see 4/0 in a commercial panel


Also, under 08 code that chart for res. feeders does not apply unless it is carrying the entire load of the house, which is not the case here

T310.16 did not change in the 08 only the temperature rating of SE cable. If not using SE cable then 4/0 75 degree aluminum is still 180 amp conductor and since 180 is not standard overcurrent device size you can protect it with 200 amp overcurrent device. Been doing this for years and never had inspector question ampacity of 4/0 aluminum.

 

[LarryFine]

If not using SE cable then 4/0 75 degree aluminum is still 180 amp conductor and since 180 is not standard overcurrent device size you can protect it with 200 amp overcurrent device.

As long as your load calcs come in under 180 amps, that is.

 

[mcclary's electrical]

T310.16 did not change in the 08 only the temperature rating of SE cable. If not using SE cable then 4/0 75 degree aluminum is still 180 amp conductor and since 180 is not standard overcurrent device size you can protect it with 200 amp overcurrent device. Been doing this for years and never had inspector question ampacity of 4/0 aluminum.

Good point. she did not say SE

 

[bob]

If the service is 400A then according to NEC Table 310.16 the size of the conductor would be 600 MCM or 500 MCM if you apply NEC 240.4(B). Where did you get 900 MCM from?

I intend to use 4/0 AL wire for the 200 amp panels. Will I need to use 250mcm due to voltage drop? Also what wire size will I need from the top of the meter to the weather head? prelimenary calculations say 900 mcm AL

The OP said that AL will be used.

 

[Smart $]

... The distance will be 80 feet from the meter. ...

Is the meter on/at the main structure or remote from it? Not that this really matters, it is more a question of where the service disconnect(s) are located, which is typically close to the meter but not required.

And I bring this up because if the service disconnect(s) is remote from the main structure, conductors thereafter are feeders, and some jurisdictions interpret the section on other building and structures as applying to the main structure, in that you can only run one feeder. They consider the meter/disconnect location as the first structure and the main structure as an "other" than. FWIW, I do not agree with this interpretation if the meter/disconnect combination supporting means is solely for the electrical equipment... but it is not my interpretation that matters.

 

[kwired]

As long as your load calcs come in under 180 amps, that is.

After I posted that I knew someone would mention this. That is correct.

If I had a 180 amp calculated load I would seriously consider larger service or feeder unless there was little chance of ever adding more load in the future. An installation of a single load or loads of a specific purpose may never have additions but a builing like in the OP always has something added down the road.

Add: If I were in a bidding war I would price them the 200 amp service and tell them the situation and give them an optional price for the larger service. Or at least install a 320 or 400 amp meter and allow space to install a second 200 amp disconnect/panel at a later time.

 

[melissa]

residential service.

residential service.

Hello everyone, thanks for the info, I come up with the conductor sizes for the meter to the weatherhead from 310:16 400 amp AL would be as much as 900mcm. The 500 or 600 would be if i used copper. I was trying to save some money by using AL. The church currently has a 200 amp service that is maxed out. they will be adding 2 a/c units and a stage with lighting and sound. The two panels would not add up to over 180 amps after I split the loads. The meter is on sight and will be 80 feet from the 2-200 amp panels. I'm using the 08 code. I spoke to the county inspector and he said I could use parallel conductors out the top of the meter to the weather head which would be 250mcm. I spoke with the county EMC who would hook to the transformer at the pole and they said parallel conductors wasn't standard practice so I would need to use single conductors which would be 500 copper or 900 AL XHHW. Another question was weather this was going to be treated as residential or commerical, eather way its single phase.

 

[mcclary's electrical]

Hello everyone, thanks for the info, I come up with the conductor sizes for the meter to the weatherhead from 310:16 400 amp AL would be as much as 900mcm. The 500 or 600 would be if i used copper. I was trying to save some money by using AL. The church currently has a 200 amp service that is maxed out. they will be adding 2 a/c units and a stage with lighting and sound. The two panels would not add up to over 180 amps after I split the loads. The meter is on sight and will be 80 feet from the 2-200 amp panels. I'm using the 08 code. I spoke to the county inspector and he said I could use parallel conductors out the top of the meter to the weather head which would be 250mcm. I spoke with the county EMC who would hook to the transformer at the pole and they said parallel conductors wasn't standard practice so I would need to use single conductors which would be 500 copper or 900 AL XHHW. Another question was weather this was going to be treated as residential or commerical, eather way its single phase.

I had someone call and ask me if they could parallel as you describe. The first thing I asked was "Where are you gonna get a weatherhead with 8 holes in it?

Secondly, derating would apply.

 

[kwired]

I had someone call and ask me if they could parallel as you describe. The first thing I asked was "Where are you gonna get a weatherhead with 8 holes in it?

Secondly, derating would apply.

two raceways with two weatherheads. Most 320 - 400 meter sockets I have seen are either drill your own KO in top or have two hub openings.

 

[mcclary's electrical]

Hello everyone, thanks for the info, I come up with the conductor sizes for the meter to the weatherhead from 310:16 400 amp AL would be as much as 900mcm. The 500 or 600 would be if i used copper. I was trying to save some money by using AL. The church currently has a 200 amp service that is maxed out. they will be adding 2 a/c units and a stage with lighting and sound. The two panels would not add up to over 180 amps after I split the loads. The meter is on sight and will be 80 feet from the 2-200 amp panels. I'm using the 08 code. I spoke to the county inspector and he said I could use parallel conductors out the top of the meter to the weather head which would be 250mcm. I spoke with the county EMC who would hook to the transformer at the pole and they said parallel conductors wasn't standard practice so I would need to use single conductors which would be 500 copper or 900 AL XHHW. Another question was weather this was going to be treated as residential or commerical, eather way its single phase.

That ain't what I'm reading

 

[erickench]

If the existing service is 120/240 3-wire then you may still be able to use the existing service to feed the two panels. If the panels both have 120 Volt loads you could balance the panels. One ungrounded conductor and common neutral would feed one of the 200 A panels and the other ungrounded conductor and common neutral would feed the other 200 A panel. The existing service would have a 200 A main circuit breaker but each panel would still be able to take 200 A simultaneously when balanced. If one panel CB is open then all 200 A would flow through the neutral instead.

 

[Volta]

... Another question was weather this was going to be treated as residential or commerical, eather way its single phase.

It is being converted from a residence to something else, so it would not be considered a residential occupancy.