310.15(B)(1), When to apply adjustment factors for SCIFs with ECUs?

[jorgieee_87]

I'm trying to develop a streamlined method to be able to size conductors properly when designing power distribution systems using the NEC as a foundation. Most of the SCIFs we manufacture have an integrated ECU that supplies air throughout the interior but most, if not all, of the applications would subject the shelters to extreme or high heat environments.

My train of thought is that while the SCIF is in operation, the interior would be kept at a moderate temperature for personnel to work comfortably. Because of this, I don't think I'll need to apply temperature derates for internal cabling since it'll always be around ambient temperature. Our standard method for cable routing is aluminum raceway, so I would have to get my ampacity values from 310.16 and derate per 310.15(C)(1), if needed.

However, for wires that run though enclosures & conduits that are exposed on the outside would need 310.15(B)(1) to be applied in addition to all of the other adjustment factors mentioned above.

My question is if my current way of thinking is the right way to go, and if there are other factors I need to think about when selecting wire (apart from terminal ampacity, conductor ampacity, temperature and current-carrying-conductor adjustment factors).

 

[hbiss]

but most, if not all, of the applications would subject the shelters to extreme or high heat environments.

Where do you drop those things, in the middle of a desert?

-Hal

 

[jorgieee_87]

Where do you drop those things, in the middle of a desert?

-Hal

Most of the time we don't know where the shelters are getting deployed to (due to confidentiality), but we are given an operating temperature range specification requirement when we have our technical interchange meetings. An example of one would be that a shelter has to operate in an external environmental temperature range of -4F to 122F.

 

[augie47]

It might be worth noting 310.15(A)(2)... Not knowing the length of the conductors exposed to the higher temperatures , I don't know if it's applicable but it's worth taking into consideration.

 

[suemarkp]

When doing work for a military application, i dont push things because they do. So margin is good. Id use wire at its 60C ampacity and thermal derate from 75C rating. Maybe use the 90C thermal/bundle derating but only if using a 125F ambient. Whether you win the contract by overbuilding is a different story, but there is so much cost in a SCIF that upsizing wires a size is probably a minor expense.

 

[brother]

What does SCIF and ECU stand for?

 

[suemarkp]

Sensitive Compartmented Information Facility. Assume ECU is environmental control unit which is its hvac system.

A SCIF processes or contains SCI information. This is national security intelligence information. This information is compartmentalized and restricted so you may understand sources and methods in compartment A, but have no idea that compartments B, C, D .... exist.

You can search for Talent Keyhole on wikipedia to learn about one older compartment.

For the electrician, many SCIFs are shielded. So things are excessively grounded, and there are filters on any wire line penetrating the perimeter (e.g. power, data, controls, phones, etc). You have to mount stuff without damaging or putting holes in the shield.