# single phase 400Amp overhead service for a duplex



## powersolutions (Feb 7, 2010)

I am starting on my first duplex rough-in next week, and was wondering if anyone could suggest what size my service-entrance conductors and riser conduit size should be. Our local utility company provides us with a dual socket meter center, and each duplex shall be supplied with a 200Amp single-phase loadcenter (the builder likes to install electric instant water heaters, all electric HVAC and cooking equipment). Unfortunately, the supplied meter equipment will not have built-in disconnecting means, so I will have to provide a couple 200Amp outdoor disconnects adjacent to the metering equipment, and plan on installing 200Amp SE cable from the outdoor disconnects to the panel locations within the dwelling.


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## JohnJ0906 (Jan 22, 2007)

powersolutions said:


> I am starting on my first duplex rough-in next week, and was wondering if anyone could suggest what size my service-entrance conductors...


Table 310-16



> and riser conduit size should be.


Tables 1,4, &5 from chapter 9

If the riser supports the POCO drop, also check their specs - they will have a minimum size


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## jwjrw (Jan 14, 2010)

powersolutions said:


> I am starting on my first duplex rough-in next week, and was wondering if anyone could suggest what size my service-entrance conductors and riser conduit size should be. Our local utility company provides us with a dual socket meter center, and each duplex shall be supplied with a 200Amp single-phase loadcenter (the builder likes to install electric instant water heaters, all electric HVAC and cooking equipment). Unfortunately, the supplied meter equipment will not have built-in disconnecting means, so I will have to provide a couple 200Amp outdoor disconnects adjacent to the metering equipment, and plan on installing 200Amp SE cable from the outdoor disconnects to the panel locations within the dwelling.


Not enough information. Electric instant hot systems pull alot of amps. You need to know what is being installed.


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## electures (Oct 23, 2008)

powersolutions said:


> I am starting on my first duplex rough-in next week, *and was wondering if anyone could suggest what size my service-entrance conductors* and riser conduit size should be. Our local utility company provides us with a dual socket meter center, and each duplex shall be supplied with a 200Amp single-phase loadcenter (the builder likes to install electric instant water heaters, all electric HVAC and cooking equipment). Unfortunately, the supplied meter equipment will not have built-in disconnecting means, so I will have to provide a couple 200Amp outdoor disconnects adjacent to the metering equipment, and plan on installing 200Amp *SE cable* from the outdoor disconnects to the panel locations *within the dwelling*.


1. Do a service calculation.
2. Did you mean SER cable.
3. Are you an electrician?


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## MDShunk (Jan 7, 2007)

Post your load calculations and you can get an exact answer.

If, by electric instant water heater, you mean an electric on demand water heater, I seriously doubt your 400 amp service will have enough capacity. Most of them take something on the order of 150 amps, each.

If, by electric instant water heater, you mean the insty-hot things you put under the sink to draw water to make a cup of tea, you're probably okay.


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## jwjrw (Jan 14, 2010)

MDShunk said:


> Post your load calculations and you can get an exact answer.
> 
> If, by electric instant water heater, you mean an electric on demand water heater, I seriously doubt your 400 amp service will have enough capacity. Most of them take something on the order of 150 amps, each.
> 
> If, by electric instant water heater, you mean the insty-hot things you put under the sink to draw water to make a cup of tea, you're probably okay.


 
Yep I did one that required 180 amps. Homeowner almost swallowed his tounge when I told him he had to upgrade his service...:laughing:


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## MDShunk (Jan 7, 2007)

jwjrw said:


> Yep I did one that required 180 amps. Homeowner almost swallowed his tounge when I told him he had to upgrade his service...:laughing:


Yeah. All the one's I've ever done took five 30's (150 amps) or three 60's (180 amps).


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## NolaTigaBait (Oct 19, 2008)

jwjrw said:


> Yep I did one that required 180 amps. Homeowner almost swallowed his tounge when I told him he had to upgrade his service...:laughing:


The last one I did required 3 ...40 amp circuits. I don't see the appeal to this thing. It seems like the cost to upgrade the service and to purchase it won't pay for it self for years.


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## JackBoot (Feb 14, 2010)

Why do they break it up into multiple breakers?


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## MDShunk (Jan 7, 2007)

JackBoot said:


> Why do they break it up into multiple breakers?


Seems to me that there's something in the NEC, in the water heater section, that limits the max size of the branch circuit that can serve the water heater. You can look it up. I suppose they get around that by running multiple branch circuits.


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## jwjrw (Jan 14, 2010)

JackBoot said:


> Why do they break it up into multiple breakers?


 
Because you cant have more that I think 48 amps per circuit
Per heating circuit sorry


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## MDShunk (Jan 7, 2007)

jwjrw said:


> Because you cant have more that I think 48 amps per circuit
> Per heating circuit sorry


Yeah, curiosity got the better of me, so I had to look it up. It's in 420-something or other. Each element (or group of elements) can't total more than 48 amps, and the breaker for each group can't be more than 60 amps.


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## Mike Guile (Jan 14, 2010)

*?*

Why can you run a 100 amp line to resistive furnace block then??? I just ran 3x40's yesterday to an on demand water heater and was thinking the same thing.


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## jwjrw (Jan 14, 2010)

MDShunk said:


> Yeah, curiosity got the better of me, so I had to look it up. It's in 420-something or other. Each element (or group of elements) can't total more than 48 amps, and the breaker for each group can't be more than 60 amps.


 
First hvac unit I ever wired was a 15kw and when I saw it split up I asked my dad and he told me no more than 48a. Probally the only thing he told me that I've never forgot:whistling2::laughing:


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## Shockdoc (Mar 4, 2010)

powersolutions said:


> I am starting on my first duplex rough-in next week, and was wondering if anyone could suggest what size my service-entrance conductors and riser conduit size should be. Our local utility company provides us with a dual socket meter center, and each duplex shall be supplied with a 200Amp single-phase loadcenter (the builder likes to install electric instant water heaters, all electric HVAC and cooking equipment). Unfortunately, the supplied meter equipment will not have built-in disconnecting means, so I will have to provide a couple 200Amp outdoor disconnects adjacent to the metering equipment, and plan on installing 200Amp SE cable from the outdoor disconnects to the panel locations within the dwelling.


SER between the disconnect and panels, we derate 80% of 200 amps . For two services you will rate at 350 amps you might be able to get away with 500 mcm al , if not it will be 600mcm al or 500 mcm cu. You can derate your nuetral conductor to 350 al/ 250 cu depending on your utility companies requirements.


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## MerriamElectric (Oct 16, 2013)

*too much muchness...?*



Shockdoc said:


> SER between the disconnect and panels, we derate 80% of 200 amps . For two services you will rate at 350 amps you might be able to get away with 500 mcm al , if not it will be 600mcm al or 500 mcm cu. You can derate your nuetral conductor to 350 al/ 250 cu depending on your utility companies requirements.


shockdoc.....fueled by anger, i like it!
in my locale, we normally would parallel the service conductors larger than 4/0 copper on residential services......much cheaper, and since you need 4/0, 4/0, 4/0, 2/0 SER for the feeder wire anyway...........
that size is already on site. i would just double it up (200Ax2), and mark 2 red, 2 white, and 2 (black). the meter base that handles 400 amps will accept 2 wires, in a double lug terminal......


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## Control Freak (Mar 8, 2008)

MDShunk said:


> Yeah, curiosity got the better of me, so I had to look it up. It's in 420-something or other. Each element (or group of elements) can't total more than 48 amps, and the breaker for each group can't be more than 60 amps.


Is this for Residential only?


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## boora2 (Jan 28, 2012)

MDShunk said:


> Post your load calculations and you can get an exact answer.
> 
> If, by electric instant water heater, you mean an electric on demand water heater, I seriously doubt your 400 amp service will have enough capacity. Most of them take something on the order of 150 amps, each.
> 
> If, by electric instant water heater, you mean the insty-hot things you put under the sink to draw water to make a cup of tea, you're probably okay.


 Has this guy ever heard of 3 phase,in Australia the standard size for an instant hot water has gone up from 13 to 22kW,36kW units not uncommon and at 415v current is quite easily handled by a 10mm 5 or 4 core orange romex cable.


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