Service upgrade and addition

[benmcgraw]

Currently I have a 200-amp service through an automatic transfer switch (ATS)/20 KW generator system. I will be adding an addition to the house that will enclose the current meter and the ATS/Generator system, so they will have to be moved. I will need power to the current panel during construction, and I would rather go with a permanent service than a temporary one. I will be upgrading to a 400-amp service and placing the new 200-amp panel on the ATS/generator system.

My proposal is to have an outside pedestal (6x6 treated posts with 2x6 treated wall boards) to mount a new 320-amp (400) meter base, two 200-amp disconnects, and the ATS. The two connected grounding rods will be at the pedestal. I will request AEP (the power company) to disconnect and reconnect to the new meter base. I will power the current panel with one of the 200-amp disconnects during construction and after. Once construction is completed I will power the new panel through the ATS/generator system through the other 200-amp disconnect. Does this sound feasible?

A concrete slab floor will be between the current panel and the new outside pedestal. I propose running a 2” sched 40 PVC conduit approximately 24 inches deep under the floor. My questions are what do I pull? The distance under the floor is 24 feet, another 7 to the pedestal and another 7 up, and another 7 up to the old panel (total of 45 ft). To be conservative I plan on two #4/0 Al for power. #4/0 is good for 200 amps between 46 and 70 ft. Can I go to the smaller #3/0 for the ground and neutral wires? or do I need to pull four 4/0 wires (max number of 4/0 for 2" conduit)? The current bare grounding wire and rod (only one) to the existing panel will be under the floor. Do I need to reroute the grounding wire and drive two new rods somewhere free of the new floor?

 

[Mustang51js]

I would talk to power co to see if they will let you do that with the wood,to me that really wouldn't be a permanent surface to mount but maybe it's acceptable for them. The transfer switch your going to have to pic a panel, I don't think you can do both panels unless the transfer switch is made for it,like two sets of lugs.

 

[benmcgraw]

I would talk to power co to see if they will let you do that with the wood,to me that really wouldn't be a permanent surface to mount but maybe it's acceptable for them. The transfer switch your going to have to pic a panel, I don't think you can do both panels unless the transfer switch is made for it,like two sets of lugs.

The ATS/generator will be disconnected from the old panel and will only supply the new panel. What about the cables to pull?

 

[wyliesdiesels]

4/0 AL cannot be protected by a 200a breaker when used as a branch feeder! 200a would only be allowed for 4/0 al if it was being used as service entrance conductor between service drop and meter and the disconnect and panelboard that supplies the entire load of a dwelling. The 90* c column is for derating purposes only!

 

[benmcgraw]

Does that mean I need to go with #250 from the meter to the 200 amp disconnect and from the disconnect to the current 200 amp panel. Do I need to pull four #250 thus going to a 2 1/2" conduit or can I pull two #250 and two #4/0? Are there any other options?

 

[wyliesdiesels]

Does that mean I need to go with #250 from the meter to the 200 amp disconnect and from the disconnect to the current 200 amp panel. Do I need to pull four #250 thus going to a 2 1/2" conduit or can I pull two #250 and two #4/0? Are there any other options?

I just went back and read everything that you will be doing. First off, does your ATS and generator have automatic load shedding? Generators with ATSs are usually required to be able to handle the full load of the system unless they have load shedding capabilities.....I will have to look up the code...

Next, NEC art. 310.15(b)7 and corresponding table says that the wire sizes listed in the table are allowed when feeding ALL the loads of the dwelling unit. Since you will have 2 panels, that will both be feeding loads in the house, you would not be allowed to use those sizes. So yes, you would need the larger size- 250-250-250-4(EGC) if using AL. However, you only need 3-wire(no EGC) between meter lugs and disconnects.

As far as being able to use a reduced neutral, you would have to meet the requirements of several code sections and calculate your unbalanced load. Also, because of harmonics, it is possible to overheat a neutral. I wouldnt bother reducing the neutral. You may regret it later....

 

[Charles (in GA)]

Local code people may require the meter to be mounted on the building, not on a support in the yard. If you go for something in the yard, do a permanent support, not wood that will eventually rot away.

One housing, 400amp meter socket and places to install two 200 amp main breakers

JC0404L1400RLM

 

[benmcgraw]

The ATS does have automatic load shedding, but whenever the generator has been in use it has not had to implement it.

 

[benmcgraw]

Going with three 450 that is the max for 2" conduit. Would I be better off with 2 1\2" conduit?

 

[wyliesdiesels]

Going with three 450 that is the max for 2" conduit. Would I be better off with 2 1\2" conduit?

U mean 250mcm? Yes i would definitely use 2 1/2" as u need the egc!! Even bigger conduit would make it slightly easier. How many bends are u going to have? Make sure to use conduit snot!!

 

[benmcgraw]

I am retyping this, because apparently my last response did not take. There will be two sweep els. I do mean 250 kcmil. Can anyone tell me how we get MCM (mcm is smaller than oughts) from kcmil? As an engineer going from kilo to mega for the same measure makes no sense to me. Back to my problem. I have no problem going with a 3" conduit. However, what size is needed for the EGC for the three 250 kcmil 200amp run? Can it be 4/0 or even smaller. Does it need to be insulated or can it be bare?

 

[justsam]

. Can anyone tell me how we get MCM (mcm is smaller than oughts) from kcmil? As an engineer going from kilo to mega for the same measure makes no sense to me. QUOTE]

MCM is an older term. It takes the first "M" from the Roman numerals, where "M" is 1000. The rest is of course Circular mils, equal to the area of a circle whose diameter is 0.001 inch.

Kcmil is a more logical term, but I dare say that MCM is so entrenched that most know it as that.

 

[bill in in]

Just a couple of questions. Do have have a 400A load? Does/will the power company have 400A available to you? 400A usually means 8-10,000 sq. ft. an elevator and more in my experience. Maybe you should look at different strategies- an example might be going from electric resistance to geothermal heat.

 

[benmcgraw]

For some reason it does nor appear that my first posts are being posted. When I submit I get logged off of the site. So here it goes again. The current size is 2000 sq. ft. The new addition will add another 2000 sq. ft. My current 200 amp panel is completely full. The new panel will have on it a 5 ton heat pump, an 80 gal water heater, a dryer, a sewage pump, a kitchen (when I wire my kitchens all receptacles are single 20 amp circuits for as many waffle irons at one time as needed), two side by side refrigerators, a freezer, two dishwashers, and eventually a garage with a table saw, radial arm saw. a chop miter saw, and an upright compressor, etc. All this plus normal circuits for five bedrooms, two baths, etc.

What size is needed for the EGC for the three 250 kcmil 200amp run? Can it be 4/0 or even smaller. Does it need to be insulated or can it be bare?

 

[wyliesdiesels]

For some reason it does nor appear that my first posts are being posted. When I submit I get logged off of the site. So here it goes again. The current size is 2000 sq. ft. The new addition will add another 2000 sq. ft. My current 200 amp panel is completely full. The new panel will have on it a 5 ton heat pump, an 80 gal water heater, a dryer, a sewage pump, a kitchen (when I wire my kitchens all receptacles are single 20 amp circuits for as many waffle irons at one time as needed), two side by side refrigerators, a freezer, two dishwashers, and eventually a garage with a table saw, radial arm saw. a chop miter saw, and an upright compressor, etc. All this plus normal circuits for five bedrooms, two baths, etc.

What size is needed for the EGC for the three 250 kcmil 200amp run? Can it be 4/0 or even smaller. Does it need to be insulated or can it be bare?

I answered your question about the EGC above in #6 but I guess u missed it. The EGC can be #4(see NEC T250.122 or link below)....No NOT 4/0....and yes it can be bare but if youre going underground i would DEFINITELY use an insulated ground due to water and corrosion issues!

EGC size is based on breaker size. However if u upsize the ungrounded conductors then the EGC needs to be proportionatly upsized as well...

http://www.safecoelectric.com/images/resources_pdf/NEC2008 Table 250.122.pdf