Bob Clukey
Member
If I have an installation which contains 5 conductors in a conduit and the conduit, is in an ambient temperature of 100 degrees F, do I have to adjust the temperature twice?
Derating
- Thread starter Bob Clukey
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Yes, you derate for conductors in the conduit and also for temp.
Adjustment Factor
Adjustment Factor
Bundling 5 conductor adjustments would apply at 80% conductor ampacity along with correction factor for ambient temperature conductor rating. A good reference to online www.copper.org for the inside conduit temperature ASHRAE design conversion data may help.
Adjustment Factor
Bundling 5 conductor adjustments would apply at 80% conductor ampacity along with correction factor for ambient temperature conductor rating. A good reference to online www.copper.org for the inside conduit temperature ASHRAE design conversion data may help.
Barndog
Senior Member
- Location
- Spring Creek Pa
As long as all 5 conductors are considered CCC's. if only three of them are CCC's than no deration for the conductor's.
Google CDA Derating Booklet might be quicker for an overall idea of conduit internal temperatures (on roof locations) by major cities.
dana1028
Senior Member
- Location
- San Francisco Bay area
Ambient temp
Ambient temp
A lot has been discussed in the past about 'ambient' temperature.
The NEC Handbook discusses using this 'ASHRAE 2% Design Temperature' when attempting to determine the inside temperature of a rooftop conduit [when using Table 310.15(B)(2)(c)].
For example: Using an ASHRAE 2% design temp of 94 degrees F with a conduit 1/2" above the roof gives a supposed inside conduit temp of 154 degrees F [using the ASHRAE numbers and the copper site mentioned above for the ASHRAE tables].
However, the maximum summer temps could be in the 105-106 degrees F range....not the 2% design temps.
The ASHRAE 2% design temps are useful for sizing an appropriate air conditioner for HVAC mechanics because you don't want to size an AC system based on the very hottest days ....you want to design a system for 'most' of the days.
However, I argue this [ASHRAE 2%] is not applicable when derating your conductors for actual operating conditions [those conditions being the actual 105-106 degrees F during some summer days - I'm using the ASHRAE table for Birmingham, AL].
Even though the NEC Handbook uses the ASHRAE 2% design when giving us an example for derating, there is nothing in the NEC itself that tells us to ignore actual tempertures and instead use 'average' temperatures for the months June-Aug [interestingly, September is often hotter than August and this month is not used for the 'average' ASHRAE design].
Comments please. This has come up repeatly in staff meetings [inspector] and among fellow inspectors in my region. We cannot understand why the handbook would use an HVAC mechanics AC design criteria for determining actual temperatures on the roof!?
Ambient temp
A lot has been discussed in the past about 'ambient' temperature.
The NEC Handbook discusses using this 'ASHRAE 2% Design Temperature' when attempting to determine the inside temperature of a rooftop conduit [when using Table 310.15(B)(2)(c)].
For example: Using an ASHRAE 2% design temp of 94 degrees F with a conduit 1/2" above the roof gives a supposed inside conduit temp of 154 degrees F [using the ASHRAE numbers and the copper site mentioned above for the ASHRAE tables].
However, the maximum summer temps could be in the 105-106 degrees F range....not the 2% design temps.
The ASHRAE 2% design temps are useful for sizing an appropriate air conditioner for HVAC mechanics because you don't want to size an AC system based on the very hottest days ....you want to design a system for 'most' of the days.
However, I argue this [ASHRAE 2%] is not applicable when derating your conductors for actual operating conditions [those conditions being the actual 105-106 degrees F during some summer days - I'm using the ASHRAE table for Birmingham, AL].
Even though the NEC Handbook uses the ASHRAE 2% design when giving us an example for derating, there is nothing in the NEC itself that tells us to ignore actual tempertures and instead use 'average' temperatures for the months June-Aug [interestingly, September is often hotter than August and this month is not used for the 'average' ASHRAE design].
Comments please. This has come up repeatly in staff meetings [inspector] and among fellow inspectors in my region. We cannot understand why the handbook would use an HVAC mechanics AC design criteria for determining actual temperatures on the roof!?
- Status