mstrlucky74
Senior Member
- Location
- NJ
Was watching a Mike Holt video today and he states that when sizing conductors under 100a you use the 60 degree column. Is this true for THHN? That's rated for 90 degree .....that's why I ask. Thanks
Post the video..Was watching a Mike Holt video today and he states that when sizing conductors under 100a you use the 60 degree column. Is this true for THHN? That's rated for 90 degree .....that's why I ask. Thanks
While true for supply-end distribution equipment, one has to be careful regarding load and circuit devices... some wall switches and receptacles, for example, are not marked or are only rated 60?C. Termination limitations apply to both ends of the circuit conductors.As mentioned 60C is the rule if the equipment is not otherwise marked. Most equipment today is marked for 75C and you generally only need to watch out for needing to use 60C if you are dealing with existing older equipment.
While true for supply-end distribution equipment, one has to be careful regarding load and circuit devices... some wall switches and receptacles, for example, are not marked or are only rated 60?C. Termination limitations apply to both ends of the circuit conductors.
The 90? ampacity can be used for ampacity adjustment or correction, but the final ampacity cannot exceed the value in the 60? column if the equipment is rated at 60?C.Was watching a Mike Holt video today and he states that when sizing conductors under 100a you use the 60 degree column. Is this true for THHN? That's rated for 90 degree .....that's why I ask. Thanks
The video in question is not available...it was his live streaming of the production his calculation DVD program. It is not posted anywhere for viewing. The program will be available for purchase after it is completed.
I agree with Gus. If the termination temperature of the lugs or whatever are not known then mike holt is correct but if they are known and are 75C rated then things change. We are limited to the weakest link in the connection.
While true for supply-end distribution equipment, one has to be careful regarding load and circuit devices... some wall switches and receptacles, for example, are not marked or are only rated 60?C. Termination limitations apply to both ends of the circuit conductors.
Was watching a Mike Holt video today and he states that when sizing conductors under 100a you use the 60 degree column. Is this true for THHN? That's rated for 90 degree .....that's why I ask. Thanks
Not much in the below 600 volt world has 90C temp rating. Some lugs have 90C rating but the equipment they are attached to does not have 90C rating so that still puts you back to lower temp. Many neutral and EGC bars in panelboards are 90C but that is about it. We often don't get to use that higher temp rating because the device at the other end of the conductor is not 90C, or in the case of service/feeders, we may actually reduce the conductor size because the neutral only carries imbalanced current, and temp rating kind of just gets lost in those applications though it could apply. The EGC is not sized the same way as other conductors and temp rating just isn't a part of that process.what if the term temp is rated for 90 degre, which many are? Do you use the. 90 degree column? Thanks
Not much in the below 600 volt world has 90C temp rating. Some lugs have 90C rating but the equipment they are attached to does not have 90C rating so that still puts you back to lower temp. Many neutral and EGC bars in panelboards are 90C but that is about it. We often don't get to use that higher temp rating because the device at the other end of the conductor is not 90C, or in the case of service/feeders, we may actually reduce the conductor size because the neutral only carries imbalanced current, and temp rating kind of just gets lost in those applications though it could apply. The EGC is not sized the same way as other conductors and temp rating just isn't a part of that process.
When discussing panelboards, there are none even tested to 90?C under UL certifications. Even 100%-rated assemblies are only tested to 75?C, but instructions require using 90?C-rated conductors. (disclaimer: that I'm aware of)Great info, thanks. So if a dist panel feeds(via. Breaker) another dist panel( to a main breaker) you are saying that usually the breakers won't be rated for 90 degree? Or instead of a MCB say it's a MLO.
FWIW, you can use 90?C conductors at their 90?C rating, but you must use a transition enclosure (aka terminal box) completely separate from the panelboard. General consensus is the transition must be at least 4' of conductor away from the panelboard. The "transition" box must contain all 90?C or greater rated equipment, including wires from the panelboard. In the case of 75?C-rated equipment at both ends of the circuit, a transition would be required at both ends.
Great info, thanks. So if a dist panel feeds(via. Breaker) another dist panel( to a main breaker) you are saying that usually the breakers won't be rated for 90 degree? Or instead of a MCB say it's a MLO.
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