Tuesday, January 18, 2011
A Few New Code Changes
The new 2011 NEC is out. Hopefully everyone ran out and purchased one for themselves. This year they came with a free .PDF version that can be downloaded at their website, www.2011NECOFFER.ORG. As everyone knows, the code is released every 3 years and it always has tons of changes. I thought I would discuss some of these. I will do more each week so as not to make this one long boring read.
I want to start off with Section 110.11. The new requirement is to protect equipment identified for indoor use, dry locations, or damp locations from damage DURING construction. So don't be hanging panel boxes before the building is dried in unless you have some way to protect it.
110.24 (A) Field Marking. Service equipment in other than dwelling units shall be legibly marked in the field with the maximum fault current. The field marking shall include the date the fault current calculation was performed and be of sufficient durability to withstand the environment involved.
220.5 (B) Fractions of an Ampere. Calculations shall be permitted to be rounded to the nearest whole ampere, with decimal fractions smaller than 0.5 dropped.
Doesn't seem like that big a deal, until you get an inspector that argues you have exceeded the amperage limits. Suppose you calculate 16.4 amps for a 20A circuit, now you can drop the .4 and use the 20A circuit.
250.24(C)(3) Delta-Connected Service. The grounded conductor of a 3-phase 3-wire delta service shall have an ampacity not less than that of the ungrounded conductors.
You may not derate in this situation.
250.30 (A)(2) Supply-Side Bonding Jumper. If the source of a separately derived system and the first disconnecting means are located in separate enclosures, a supply-side bonding jumper shall be installed with the circuit conductors from the source enclosure to the first disconnecting means. A supply-side bonding jumper shall not be required to be larger than the derived ungrounded conductors. The supply-side bonding jumper shall be permitted to be of nonflexible metal raceway type or of the wire or bus type as follows:
So if you install a transformer in a building and the disconnecting means is not located in the transformer enclosure then you must install a supply-side bonding jumper along with your ungrounded and grounded (neutral) conductor. Do not forget the rest of the requirements in Article 250 regarding separately derived systems.
More to come.....
Posted by Norman W at 2:13 PM