More load center/conduit/NEC questions

[JRobyn]

Hi collective experts,

We are building a new house, about 2500 sqft with typical loads, probably not over 200A (not yet fully calculated out). But I'd like to use two separate load centers, one in the basement near the major loads (heat pump system w/2 10kw heat strips, conventional water heater, buzz box welder, 3-5 HP air compressor) - totalling 200A or less, and another load center on the main floor for everyhting else, also 200A or less.

I have my 400A rated meter base with the necessary multiple load-side lugs, and I know that I cannot run the conductors from the meter base more than 2 ft inside the structure with out a fused disconnect, so I plan for two 200A disconnects just inside the foundation wall underneath the meter base. The meter base as supplied by the local EMC has two knockouts in the bottom, each capable of up to 4" conduit. One of these will be the incoming service lateral (underground) which the EMC specifies must be in 3" sch 80 conduit.

So finally, my question(s) - can I run BOTH sets of conductors to the two disconnects for the two load centers in a SINGLE 3" or 4" conduit, and then TEE the conduit inside the structure to the two disconnects? I assume that for NEC purposes, this is considered to be six conductors, right? I plan to mount the two disconnects right beside each other, and then plan to conduit (2") from each disconnect to it's respective load center. The total wire run from meter base to the disconnects will be about 3-4 ft. What ampacity derating will I need to include when figuring my conductor size?

I will sure appreciate advice and guidance that might save me from buying a bunch of disconnects/parts that won't pass inspection!

- Jay

 

[SPIKER]

Jay:

First off you need to check with youre local code people, many if not most areas now require a disconnect at the meter base, so fire dept can kill power in event of fire. If not then it needs to be within I think 3 feet of the most readily accessible door for the fire dept. I have not looked at code book in a long while, this was the latest 2009 NEC I glanced over like 12 months back. I have not dug into it since then...

If you can run the feeds in separate conduits, if there is only one run the 4" conduit and "T" off with roller pull elbows.

400A Seems like a pretty lot of excess power for normal family home even with the heat pumps and such. Where did you get your figures from?

I'll look around for a better answer to your question and post back if I can find my PDF copy of the NEC 2009, (it is on CD)

Mark

 

[JRobyn]

Thanks Mark,

My local inspector just told me that I need the disconnects, and I told him that I'd like to have them inside to save the cost of two more outdoor-rated disconnect boxes. He agreed to having them inside (no more than 2 ft inside;-), but I bet he did not consider their distance from the nearest exterior door, which would be about 25 ft.

Yeah, 400 is way more than I'll actually need, but the meter bases aren't available in anything in between 200 and 400 (guess some are actually rated at 320, and that's what service I'll request). And anything other than a 320/400 that can be equipped with dual load-side lugs are apparently as rare as hen's teeth.

- Jay

 

[hr3]

Jay,, If you only need 200 amp. just use one 200a. disconnect you don't need to use the whole meters capicity.. We downsize services all the time to make possible "and less expencive" whole house transfer switch installation.. A 400a runs 5 to 6 grand but a 200a is only 2grand.. Sometimes we even drop a 200a. service down to 100a.. But we are in Maine,, not much AC and no electric heat for sure,,

 

[SPIKER]

Here ya go, a bit out of the 2008NEC, here is short answer from the book.

+++
VI. Service Equipment Disconnecting Means
230.70 General. Means shall be provided to disconnect all
conductors in a building or other structure from the service-entrance
conductors.
(A) Location. The service disconnecting means shall be
installed in accordance with 230.70(A)(1), (A)(2), and
(A)(3).
(1) Readily Accessible Location. The service disconnect-ing
means shall be installed at a readily accessible location
either outside of a building or structure or inside nearest the
point of entrance of the service conductors.

(2) Bathrooms. Service disconnecting means shall not be
installed in bathrooms.

(3) Remote Control. Where a remote control device(s) is
used to actuate the service disconnecting means, the service
disconnecting means shall be located in accordance with
230.70(A)(1).
(B) Marking. Each service disconnect shall be perma-nently
marked to identify it as a service disconnect.
(C) Suitable for Use. Each service disconnecting means
shall be suitable for the prevailing conditions. Service
equipment installed in hazardous (classified) locations shall
comply with the requirements of Articles 500 through 517.
intended to provide fire protection, shall be permitted to be
located remote from the other disconnecting means.
+++
Additionally (Which I think is a recent change)
+++
230.205 Disconnecting Means.
(A) Location. The service disconnecting means shall be
located in accordance with 230.70.
For either overhead or underground primary distribution
systems on private property, the service disconnect
shall be permitted to be located in a location that is not
readily accessible.

+++

Looks like you will be OK having the disconnection means in the 2 different locations from the single meter base...

Mark