Cable Insulation 1

[antony09]

I have the following doubt. A office Bldg. have a XTRM (utility owner) that feed a MDP, i understand that the service entrace conductor need to be XHHW (wet location) inside conduit. But what happened between the MDP and the Meter Module, which type of cable I need to specify, each Meter Module will be located in each floor and feed with 500 MCM Aluminum conductor Serie-8000. I can use THHN or I need to specify XHHW, The riser conduit travel through a shaft in the bldg.

 

[davidbeach]

What does the electrical engineer on the project have to say about this, or is he too busy designing the HVAC system?

 

[wareagle]

antony posted "A office Bldg. have a XTRM (utility owner) that feed a MDP, i understand that the service entrance conductor need to be XHHW (wet location) inside conduit."
No true. If the conduit is underground then a "W" rating is required. If this is inside the building, any of the conductor type listed in table 310.16 under the 75C col would be ok. You need someone to assist you with an electrical knowledge and familiar with the NEC.

 

[antony09]

Wareagle, thank for your response, I verified this column and i only found conductor with "W" rating. The reason of my question is that the owner want to use cable THHN this cable is less expensive that XHHW. I think that the riser is dry location so the "W" rating is not necesary. Please clarify

 

[resqcapt19]

I have never seen "THHN" that was not also marked "THWN". It may exist, but I have never found any.
Don

 

[wareagle]

antony
I think you will find cable marked now as THHN/THWN as Don
has said. It is shown in the 90C Col but you can not use that rating. You use the 75C Col rating. I'm not sure why
its not shown in the 75C Col.

 

[rcw retired EE]

THHN = 90 C dry (as indicated by the two "H" and no "W")

THWN = 75 C Wet (as indicated by one "H" and "W")

THHN insulated wires are limited to their 75 C ampacity when connecting to breakers or other devices to avoid over temperature of the connection. But the 90 C rating can still be used as the starting ampacity in derating calculations. In other words, the middle of the wire can operate at 90C as long as the ends stay at or below 75C.

 

[resqcapt19]

A lot of the currently available THHN/THWN is marked THHN/THWN-2 which will permit the use of the 90 C rating even in wet locations.
Don