334 NM cable temp rating

[lielec11]

Part I

310.15(A)(3) dictates that the temperature rating of my cables are limited by the terminals of the equipment. It also says that most terminals are built for 60/75 DEG.

Early in my entire career I was taught to design for 75 DEG but specify 90 DEG on my drawings. Reading through this seems incorrect as most equipment isn't built for 90 DEG terminals. Is this correct, should I really be designing around 60 and specifying 75? Most other engineers seem to use the 75 DEG column as well, am I overthinking this?


Part II

338.80 limits the use of NM cable to the 60 degree column of Table 310.15(B)(16).

a) If I am specifying THHN or THWN cables in EMT am I beholden to the 60 DEG column or can I use the 75 DEG column?
b) What is stopping a contractor from using type NM (as long as it applies) in lieu of my specified THHN in EMT?
c) If that happens wouldn't the wire be undersized based on 338.80?

 

[infinity]

For all NM installations you size the conductors at 60° C. For pipe and wire you can use the 75° ampacity if all of the circuit components are rated for 75° C.

 

[MasterTheNEC]

Part I

310.15(A)(3) dictates that the temperature rating of my cables are limited by the terminals of the equipment. It also says that most terminals are built for 60/75 DEG.

Early in my entire career I was taught to design for 75 DEG but specify 90 DEG on my drawings. Reading through this seems incorrect as most equipment isn't built for 90 DEG terminals. Is this correct, should I really be designing around 60 and specifying 75? Most other engineers seem to use the 75 DEG column as well, am I overthinking this?


Part II

338.80 limits the use of NM cable to the 60 degree column of Table 310.15(B)(16).

a) If I am specifying THHN or THWN cables in EMT am I beholden to the 60 DEG column or can I use the 75 DEG column?
b) What is stopping a contractor from using type NM (as long as it applies) in lieu of my specified THHN in EMT?
c) If that happens wouldn't the wire be undersized based on 338.80?

To kinda piggyback on what Rob stated - The most important aspect (in my opinion) is that contained within 334.80, which says " The allowable ampacity shall not exceed that of a 60°C (140°F) rated conductor. The 90°C (194°F) rating shall be permitted to be used for ampacity adjustment and correction calculations, provided the final calculated ampacity does not exceed that of a 60°C (140°F) rated conductor."

As for your specific questions, a) read 110.14(C) and your answer will become clear (gotta make you read something), b) Well some of that may be limited to specification details, code limitations due to construction types and quite frankly the aspects given in 110.14(C) and 334.80 tend to be more restrictive under normal conditions (my opinions) and c) well you have to size the conductors based on the loads and the terminals limitations so if you are sizing everything based on the 60C column then you may be fine but with THHN/THWN-2 which is rated 90C (wet or dry) when adjustments and corrections are needed you will more than likely end up in the 75C column and the use of Type NM-B as a replacement would forever land you in the 60C column ultimately.

Hope this is helpful.....

 

[lielec11]

Thank you both...as a follow up:

110.14(C) has two subsets, one for <100A and another for >100A. Based on 110.14(C)(1) for a 100A panel I am required to use the 60 DEG column?

Can I specify terminations of my safety switches, panel boards, etc. to be minimum 75 DEG? I've never got into this level of detail (or I've never read it) in any of specs I've worked on but this seems like the best place to dictate this.

 

[Dennis Alwon]

Almost all electricians will be using wire rated 90C however 110.14(C) will limit the temp rating to 75C in most cases and definitely in any new designs.

If you design the job for emt and the electrician uses nm cable then he will need to redo the work as the plans rule. Now as an engineer you and the client need to decide if nm is wanted to save money as long as it is compliant in the building type construction -- 334.10

 

[lielec11]

Almost all electricians will be using wire rated 90C however 110.14(C) will limit the temp rating to 75C in most cases and definitely in any new designs.

If you design the job for emt and the electrician uses nm cable then he will need to redo the work as the plans rule. Now as an engineer you and the client need to decide if nm is wanted to save money as long as it is compliant in the building type construction -- 334.10

Very concise and to the point, just what I needed... thank you sir!

 

[infinity]

Here's something I said in similar thread, maybe Paul will chime in with some NEMA information.

I believe that most receptacles terminals have a 60° rating. I recently installed a 50 amp generator inlet box with #8/3 MC cable that had 60° C terminals so I had to tail off the #8's with #6's to connect to the device. For other equipment like disconnect switches (except for the $12 AC pull out types) I would guess that many would have 75° C terminals.

 

[GoldDigger]

Here's something I said in similar thread, maybe Paul will chime in with some NEMA information.

Based on the UL testing of the terminals with a 6' (?) tail of appropriately sized wire attached, the tails of #6 should probably be at least that long.

 

[infinity]

Based on the UL testing of the terminals with a 6' (?) tail of appropriately sized wire attached, the tails of #6 should probably be at least that long.

That sounds about right from what I've heard, do you have a reference? I was referencing Paul for the terminal information not the tail length.

 

[GoldDigger]

That sounds about right from what I've heard, do you have a reference? I was referencing Paul for the terminal information not the tail length.

No reference immediately to hand. It was a quote from or reference to the UL test spec in another thread. Probably over a year ago.

 

[MasterTheNEC]

Here's something I said in similar thread, maybe Paul will chime in with some NEMA information.

"The terminations of devices intended to be wired to flexible cord are based on the use of flexible cord or cable having copper conductors, in with Article 400 of ANSI/NFPA 70, ‘‘National Electrical Code’’ (NEC). The ampacity of the flexible cord and cable is based on Section 400.5, Tables 400.5(A) and 400.5(B). The conductors are sized as specified on the product or in the manufacturer’s instructions provided with the device.


The terminations are based on the use of 60°C flexible cord or cable. Unless stated otherwise in the individual product categories, the termination provisions of all other devices are based upon the use of 60°C insulated conductors in circuits rated 100 A or less, and the use of 75°C insulated conductors in circuits rated more than 100 A, as specified in Table 310.15(B)(16) of the NEC."

The whitebook goes on to say :
TERMINALS
Terminals of 15 and 20 A receptacles not marked ‘‘CO/ALR’’ are for use with copper and copper-clad aluminum conductors only. Terminals marked ‘‘CO/ALR’’ are for use with aluminum, copper and copper-clad
aluminum conductors. Terminals of receptacles rated 30 A and above not marked ‘‘AL-CU’’ are for use with copper conductors only. Terminals of receptacles rated 30 A and above marked ‘‘AL-CU’’ are for use with aluminum, copper and copper-clad aluminum conductors.


Terminals marked ‘‘75 C’’ may be wired using the ampacities for conductors rated 75°C as well as conductors rated 60°C in Table 310.15(B)(16) of the NEC.


Terminals of the wire-binding screw, setscrew, or screw-actuated backwired clamping types are suitable for use with both solid and stranded building wires.


Terminals of a receptacle are permitted for use with certified field installed crimped-on wire connectors or an assembly, if so identified by the manufacturer.
A receptacle may also be provided with conductor leads with factory installed crimped-on connectors. Such connectors may be either attached to the receptacle terminal or are provided with the receptacle in the smallest unit shipping container and are suitable for use with the terminal of the receptacle.

Now from a NEMA standpoint the manufacturers meet UL 498 so it would be as followed " Maximum continuous 75° C; minimum -40° C (w/o impact).

But the NEMA Rep Mr. Holland may be able to elaborate even more.

 

[Unbridled]

Thank you both...as a follow up:

110.14(C) has two subsets, one for <100A and another for >100A. Based on 110.14(C)(1) for a 100A panel I am required to use the 60 DEG column?

Can I specify terminations of my safety switches, panel boards, etc. to be minimum 75 DEG? I've never got into this level of detail (or I've never read it) in any of specs I've worked on but this seems like the best place to dictate this.

I've always interpreted 110.14(C)(1) that equipment with no rating will require conductors to be sized from the 60 DEG column. However, most equipment is rated at 75 DEG, thus conductor ampacity may be calculated from the 75 DEG column.

 

[infinity]

I've always interpreted 110.14(C)(1) that equipment with no rating will require conductors to be sized from the 60 DEG column. However, most equipment is rated at 75 DEG, thus conductor ampacity may be calculated from the 75 DEG column.

I agree when the size is 100 amps or less. Over 100 amps it is required to be listed for use at 75° C.

 

[JFletcher]

Almost all electricians will be using wire rated 90C however 110.14(C) will limit the temp rating to 75C in most cases and definitely in any new designs.

If you design the job for emt and the electrician uses nm cable then he will need to redo the work as the plans rule. Now as an engineer you and the client need to decide if nm is wanted to save money as long as it is compliant in the building type construction -- 334.10

I recall a graphic here a while back for a feeder between 2 panelboards that used 90*C wire at 90*C ampacities. iirc, the feeder ran from panel to gutter/box to a 90*C connector, then used 90*C wire to another gutter/box a few feet away from a panel on the other end. On longer/larger runs of wire and/or where CU is spec'd, it could be quite a money savings to be able to use 90*C 95% of the wire run.

You're right tho, all wire we'd use is rated 90*C - light fixtures alone now require that insulation value even if the circuit is loaded to ampacity ranges that wouldn't come close to taxing the 60* column.

~~~~~~~~~~~~~~~~~~~~~~~~~

NM is rated 90*C insulation but can only be used at the 60*C column even if all other components in the system are 75*C rated.

lielec11, you can specify 75*C equipment - most is anyway, so kind of a moot point. I dont think you'll find items like circuit breakers rated for 90*C terminations, but even if you did, just because the lug temps are rated for 90*C doesnt mean the enclosure or eqpt is:

http://www.schneider-electric.us/en/faqs/FA176152/

 

[lielec11]

Thank you all for helping clear up this somewhat simple topic for me

 

[Unbridled]

Part I

310.15(A)(3) dictates that the temperature rating of my cables are limited by the terminals of the equipment. It also says that most terminals are built for 60/75 DEG.

Early in my entire career I was taught to design for 75 DEG but specify 90 DEG on my drawings. Reading through this seems incorrect as most equipment isn't built for 90 DEG terminals. Is this correct, should I really be designing around 60 and specifying 75? Most other engineers seem to use the 75 DEG column as well, am I over-thinking this?

It's usually up to the electrician to use de-rating of 90 DEG insulated conductors. Occasionally this can effect conduit size.
It is nice however when the EE has done these calcs., and even specified the conduit size!!


Part II

338.80 limits the use of NM cable to the 60 degree column of Table 310.15(B)(16).

a) If I am specifying THHN or THWN cables in EMT am I beholden to the 60 DEG column or can I use the 75 DEG column?
b) What is stopping a contractor from using type NM (as long as it applies) in lieu of my specified THHN in EMT?
c) If that happens wouldn't the wire be undersized based on 338.80?

It's usually up to the electrician to use de-rating of 90 DEG insulated conductors. Occasionally this can effect conduit size.
It is nice however when the EE has done these calcs., and even specified the conduit size!!

 

[kwired]

I recall a graphic here a while back for a feeder between 2 panelboards that used 90*C wire at 90*C ampacities. iirc, the feeder ran from panel to gutter/box to a 90*C connector, then used 90*C wire to another gutter/box a few feet away from a panel on the other end. On longer/larger runs of wire and/or where CU is spec'd, it could be quite a money savings to be able to use 90*C 95% of the wire run.

You're right tho, all wire we'd use is rated 90*C - light fixtures alone now require that insulation value even if the circuit is loaded to ampacity ranges that wouldn't come close to taxing the 60* column.

~~~~~~~~~~~~~~~~~~~~~~~~~

NM is rated 90*C insulation but can only be used at the 60*C column even if all other components in the system are 75*C rated.

lielec11, you can specify 75*C equipment - most is anyway, so kind of a moot point. I dont think you'll find items like circuit breakers rated for 90*C terminations, but even if you did, just because the lug temps are rated for 90*C doesnt mean the enclosure or eqpt is:

http://www.schneider-electric.us/en/faqs/FA176152/

Actual lugs on a breaker could be marked as 90C, but the entire breaker assembly (with the lugs) is still going to be 75C.

I don't do medium voltage work, but I think you do find 90C terminations in that area of the trade.