Just a quick question. Is there any time we can actually use the 90 degree column when sizing our wire, or do we always have to go with the 75 degree over 100 amps and the 60 degree under 100 amps. Thanks Steve.....

You can always use the 90C column for sizing wire (if you have 90C insulation).

The problems occur when you want to terminate the wire. You can not connect any wire to a device unless the size is equal to or larger than the size determined by using the 75C (or 60C) column.

Also #10, #12, and #14 are limited to a maximum overcurrent protective device (30A 20A and 15A respectively) unless permitted by specific NEC articles (i.e. motor circuits).

A situation where I might use these data is:
Start at OCPD with 75C wire (i.e. 4-#4)
Go 3' to a junction/splice box
Use 90C wire as needed (i.e. 4-#6)
End at a junction/splice box
Go 3' to device with 65C wire (i.e. 4-#3)

JBD ---

Let me ask question here.

Are most wire connectors rated at 90 degrees? I never looked at the temp rating of connectors before.

I never even considered that issue with can lights that require 90 degree wire.

Yes, most connectors and splice equipment are rated 90C or higher.

Also I should have said use 4' of wire (not 3'), as this is the length UL uses for heat rise testing.
http://www.idealindustries.com/wt/TwistOnWireConnectors.nsf

I have installed larger equipment that has been 90C rated Square D 3000 amp breakers specifically.

Also when you need to do ampacity adjustments for temperature or number of conductors you can start with the 90C column. Once you do your derating you check the derated figure against the column for the temperature of the termination or wire you are using and use the lowest figure.

From this non-electrician...

Wet locations are always limited to the 75° column, correct?

So If I understand it right, there is no place that I can use the 90 degree column to size my wire from the OCPD to the termination device. Looks like the manufactures would be made to make their lugs suitable for the maximum allowable degree of wire So the 90 degree table is no good unless you want to make a bunch of junction boxes??? Don't seem right somehow... Thanks for the input... Steve

TG — Many insulated conductors are 75°C wet and 90°C dry, but two exceptions in (99)NEC table 310-13 are RHW-2 and XHHW-2 that are rated 90°C for both. A common application aside from termination-temperature limitations is as a “starting point” for table 310-16+ ampacity-table temperature adjustments and §31O-15 ‘more than 3 conductors’ adjustment.

sparkync


It is not as bad as that, as I said there is some equipment out there rated 90C.

The real gift of the 90C column is when we have to derate.

Lets say you are running 9 current carrying conductors in a raceway or in a bundle of cables.

310.16 lists 12 AWG at 30 amps in the 90C column which is the figure you can start with for derating.

Table 310.15(B)(2)(a) requires a 70% adjustment for that many conductors.

30 amps x .7 = 21 amps.

So now after derating you can still use these conductors for a 20 amp circuit.

If you did this derating starting at 20 amps

20 x .7 = 14 which would mean you would need to use a 15 amp breaker for these conductors.

240.4(B) is the article that allows the next standard size breaker to be used in most instances.

Bob

Oh I should mention that 14, 12 and 10 AWG are not "rated" 15, 20 and 30 amps, (they are rated higher) the requirement that we use 15, 20 and 30 amp OCPDs on these size wires is 240.4(D) which does not change the rating of the conductors just the OC protection.


[This message has been edited by iwire (edited 07-15-2003).]

ThinkGood,
Wet location wire with a "-2" after the wire type letters is 90°C wet or dry.
don

Most failures in this industry are at the terminations. The manufacturers are aware of this. They are not planning on designing termination to the 90C column for that reason.

Pierre

iwire,

You posted just what I was going to say. You use the 90 deg column all the time. Every time the wires get bundled, go through an attic, or in a boiler room. You need the higher amperage to start with so that by the time you need to derate the wire, you can be right back down at the proper amperage where you need to be.

HE