Hi,I am an electrician that has done mostly residential work up to 200A service.I have a job that will require 400Amp service.Seeing I have never done one I am seeking any advise that you could give me.I have read that most of the time 2 200A panels are used.This project is a garage and I would like to use just 1 main panel.Is this impractical? Just looking for some guidance. Thanks in advance.

If you use a single 400 amp panel in place of two 200s you will pay more money and have half the circuit space when it's done.

The last 400 home service I did I used a single 400 only because I had not yet seen a double 200 set up. If it comes up again I am going with double 200s.

I use either a 320A metermain with (2)200A breakers installed to feed (2)200A 40ct ML panels or if they can be back to back with a 320A meterbase I use (2) 200A 40ct MB panels. I am currently upgrading a 320A service at a house to an 800A due to a 6500 sq.ft. addition. The PoCo is hitting my CT cabinet at the addition where it will feed a 800A ML panelboard with (1)400A CB to feed the old service and (2) 200A CBs to feed (2) 200A 42ct ML panels in the new addition. Houses around here keep getting bigger and stupider.

I always wonder how much of that 400a actually gets used. What are these people's electric bills? Average 60a 24/7 is over $1000 a month here.

Generally speaking, in many places 400A service is the next step up if the load calc exceeds 200A. And, of course, the load calc is interested in making sure that the probable sustained peaks are covered; it's not about the average draw. So one might need a 400A service when the current draw averaged over the course of a month is only a few dozen amps or less.

So it looks like I need a 1/O GEC for 400A service based on 600 kcml conductors. Do you normally parallel them with smaller conductors? Any help on the conductor size please. Also do they make a rebar clamp for the 1.5" rebar for the 1/O conductor size?

4 AWG CU is the largest conductor you ever have to run to a concrete encased electrode.

Thanks Iwire. How about help with the service conductor sizing.If 600 kcml is required what 2 sizes do I need to parallel to make up this size?

Just a reminder to pay extra attention to your load calcs. If the calculated load is over 320 amps, then a different type of service - one with a current transformer- will be needed.

Reno- I believe that would be true if the 320a. were a continious load. He stated that this was a residential installation and residential is not continious. He could do the calc and come up with 400a. and if the equipment were rated for 400a. he's good to go.

I recently did a service that someone else started where I had to relocate the service head. I used 250 kcmil from POCO service drop to a 320 amp rated meter. From out of the meter there were two sets of feeders, each going to 200 amp main breaker panels fed with 2/0 copper. So this is considered a 300 amp service based on the size of the feeders going to the POCO drop. Correct?

Could someone tell me what article permits using (2) 200 MB panels for a 300 amp service?

#2 copper was run to H20 meter and #4 copper was run for the Ufer. Also, #2 jumper was installed to bond both ground busses in either panel.

Just want to clear up that I have done mostly residential,not that the garage is residential. It is non-residential. Thanks

Services are popularily sized per the combined ratings of the service disconnects, despite 250.66 requiring the GEC based on the size of the SEC.
230.23(A) sizes the SDL, 230.42(A) sizes the service entrance conductors, 230.71(A) allows up to six service disconnects, and 230.90(A) requires the OC device to be rated no greater than the ampacity of the service entrance conductors.

Schockme, I wouldn't call your service 300 amps, unless you installed two 150 amp mains.
2/0 copper is good for 200 amps per 310.15(B)(6) for residential services, you have two 200 amp mains and panels, for a combined 400 amps of capacity. I'd call that a 400 amp service.

230.90(A) exception #3 allows the sum of the ratings of the 2-6 circuit breakers to exceed the ampacity of the service conductors, provided the calculated load does not exceed the ampacity of the service conductors.

George, you may be correct as to the calculated load not being continuous.

Services are an area where the NEC changes places with the local PoCo rules. It is the practice of our PoCo to treat the calculated load as if it were continuous, and change over to a CT type meter at that point.

Likewise, and service upgrade 200 amps or larger must be approved by their planning department. Again, they need to know what loads theit transformer will be facing.

SInce local PoCo rules vary greatly, I really have to stress the need to talk to them when a job like this one comes around.

Thanks Earl.

Earl IMO To determine the ampacity of a service requires more than adding up the combined rating of the service disconnects.

If you do that you stand a good chance of overloading the service conductors.

230.90(A)Ex. 3

Here is a common example of using Ex.3 This is a service a buddy of mine did.



Notice the size of the riser, it has a capacity of about 200 amps. If you add up the six main breakers inside you would get 600 amps.

This is not a 600 amp service, this is an approximately 200 amp service with six 100 amp service disconnects.



[This message has been edited by iwire (edited 01-01-2007).]

So those are sill plates, I always wondered what the were used for, pictured where the SE enters the building. Is that last meter allowed. I know that on some 2-gang meter sockets there is a label stating that the other set of lugs are not meant for feed thru.

[This message has been edited by HCE727 (edited 01-01-2007).]

[This message has been edited by HCE727 (edited 01-01-2007).]

iwire, where are the disconnects for those meters? And is that se at the bottom of each meter? Don't you have to protect wire from physical damage? Sorry for all the questions.

[This message has been edited by texassparky (edited 01-01-2007).]

HCE727, My buddy could have bought a gang socket but the units only needed 100 amp sockets and the power company requires a 200 amp socket for the landlord panel even if it is a 100 amp panel.

So you see a 5 gang 100 amp socket with a single 200 added on the end.

And yeah those are sill plates, kind of hard to use and not exceed the bend radius of cables. But that is an accepted practice in this area.

Bob

The Panels are all main breaker type located on the inside of the wall behind the sockets in the basement. The longest SE inside is about 5'


Yes.


That is up to the AHJ if they feel they are subject to damage.

These are not on a driveway so SE is generally accepted. If this was the driveway side the inspector would likely want PVC 80 or RMC.

This service as you can see is new, but I could drive down any multifamily street in most any city and town in MA, RI, CT, NH etc and take pictures of thousands of identical services.

As matter of fact here is the service he was replacing.





Notice the original services had no mains.


No problem, that is what this place is about.

We all do things differently, I know that all this SE is surprising to electricians in many areas.

Here is how we do it

320A Meter Base
3" conduit
2 parallel sets of 4/0 aluminum URD to the transformer
Meter base is grounded to groud rods with 2/0 copper

2 parallel sets of 4/0 aluminium SEU to each 200A Panel

each panel has 4ga copper cold water ground

I have found that parallel aluminum is alot cheaper than non parallel copper

Why?

6 CU or 4 AL is the largest conductor the NEC requires to run to a ground rod regardless of service size.

why 2/0 to ground rod? .....

thanks for pointing that max 4ga out. I always just looked at the grounding conductor size chart in NEC Table 250-94 and based it on the largest equivalent service entrance conductor size like the notes say.

Where do you find in NEC the 4ga max? and how does it relate to 250-94. This will save me some money.

Try 250.66
(A) Connections to Rod, Pipe, or Plate Electrodes. Where the grounding electrode conductor is connected to rod, pipe, or plate electrodes as permitted in 250.52(A)(5) or 250.52(A)(6), that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum wire.
(B) Connections to Concrete-Encased Electrodes. Where the grounding electrode conductor is connected to a concrete-encased electrode as permitted in 250.52(A)(3), that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than 4 AWG copper wire.

Iwire, what I was refering to was the 5-gang meter socket has 3 termination points for the line side, with one set of lugs that can be moved, depending where you enter the meter socket. If I am not mistaken there is a label on the meter socket stating that the other two termination points are not for feed thru. Why would the POCO require a 200a meter socket, even if there is only a 100-a panel.

I misspoke, remember this was not my service.

The power company requires a lever bypass which results in a 200 socket.

Thanks gfretwell,

I see that is an exception to 250-94. My mistake. From now on #6 copper.