Help in understanding proper sizing of conductor in a high ambient environment. SRML

[re-evaluating]

Specifically I am working on a UL Listed stainless steel Chef's counters (with load center). I am required to use SRML 150*c wire per UL (SRML I am using is tin coated copper) to supply power to inductive food warmers. During testing we see temperatures in the 75*c range as a constant operating temperature of shelf that houses the wireway. Wireways typically 8" to 12" wide by 2" to 2 1/2" deep, and can house 6 to 30 conductors. I realize the temperature above isn't exactly the temp of the air in the raceway but if I assume the worst it should give some safety margin I would think (please correct if I am wrong). I have looked all over 310 but don't see any thing that really helps me determine what ampacity my 12 gauge (or 10 gauge) SRML is at my ambient temperature. I want to make sure I am quoting and supplying the proper size for safety sake. I have been searching and reading all kinds of information but still don't have a confidence level to know I am bidding these correctly. Thank you all for your time.
Dave

 

[MTW]

You won't find SRML wire in the code, because it an appliance wiring material. You need to look to your suppliers cut sheet specifications.

Have a look here, but consult your actual supplier.

http://catalog.standard-wire.com/viewitems/appliance-fixture-apparatus-and-motor-lead-wire/srml?

MTW

 

[Jraef]

As MTW said, this is not an NEC issue. That type of wire is UL listed as hook-up wire, i.e. intended on being used INSIDE of UL listed equipment. If you are working for the equipment mfr, you need to follow the UL procedures for the equipment design. If not, then the listed equipment would use the hook-up wire to run out to a terminal box for the installing electrician to then run standard BUILDING wire per the NEC.

If you are the installing electrician, and the equipment mfr is directing you to use hook-up wire in the field, that is outside of the purview of the NEC and is something between you and the equipment mfr. But I can't imagine UL letting them get away with that, so I'd tread carefully there. You might be taking on responsibility and liability that your insurance would not cover.

 

[Julius Right]

The problem is more complicated since it is about 30 wires in this wireway at ambient air of 75oC.
The Manufacturer catalogue shows the ampacity for one single cable in 30oC ambient air.
A single cable in 75oC the ampacity will be only 23 A and for 3 same cables will be only 15.7 A.
For 30 [same cables] as per NEC the ampacity will be 23*.45=10.35 A.

 

[Jraef]

The problem is more complicated since it is about 30 wires in this wireway at ambient air of 75oC.
The Manufacturer catalogue shows the ampacity for one single cable in 30oC ambient air.
A single cable in 75oC the ampacity will be only 23 A and for 3 same cables will be only 15.7 A.
For 30 [same cables] as per NEC the ampacity will be 23*.45=10.35 A.

Again, you are applying NEC rules for field installation to something that would need to follow UL rules for manufacturing. Although UL and the NEC generally agree, it’s not 100%.

 

[re-evaluating]

Thank you for the responses. Yes I agree it is not really an NEC issue at all however the information and experience I have read and learned here is extremely helpful. I also don't want to not just blindly underwire (bid) a project because there isn't good information on the spec sheet. The mfr list 12 gauge wire at 43 amps @ 40*c and to me as an estimator tells me absolutely nothing in a 75*c environment. I will reach out to the mfr and see if they can give me actual information to calculate with. My only concern is that I am bidding and purchasing the correct wire size for the load on the circuit. Safety is my uttermost concern here. This is all internal wiring connected to a load center within a UL Listed counter. Thank you all again for sharing your knowledge.

As MTW said, this is not an NEC issue. That type of wire is UL listed as hook-up wire, i.e. intended on being used INSIDE of UL listed equipment. If you are working for the equipment mfr, you need to follow the UL procedures for the equipment design. If not, then the listed equipment would use the hook-up wire to run out to a terminal box for the installing electrician to then run standard BUILDING wire per the NEC.

If you are the installing electrician, and the equipment mfr is directing you to use hook-up wire in the field, that is outside of the purview of the NEC and is something between you and the equipment mfr. But I can't imagine UL letting them get away with that, so I'd tread carefully there. You might be taking on responsibility and liability that your insurance would not cover.

 

[Jraef]

Hmmm... I can’t think of a scenario in which 12ga wire is ever rated for 43A. You are wise to be questioning this issue.

 

[Julius Right]

It is difficult to know the actual thickness of the silicon insulation and of the glass sheath.
For the SRML wire as per MTW link-see the sketch-[it seems to me it is not your cable].
However, in my opinion, the conductor temperature-which was taken into consideration for ampacity calculation-it was only 120oC and it was for 3 wires in trefoil formation.
So, recalculating the ampacity in this conditions the ampacity of one wire of 3 wires assembly at 75oC air it could be 37 A but for 30 wires 16.5 A.
Note: the 45% derating for 30 wires per wireway it is according to NEC, indeed.

 

[re-evaluating]

Hmmm... I can’t think of a scenario in which 12ga wire is ever rated for 43A. You are wise to be questioning this issue.

Here is what I am looking at seems crazy to me. I am not trying to use for a 43A load (normally 11-18A) but want to know what the limits are before I go to 10 gauge. If it is only good for 17A at 75*c I need to know. Thanks again for the response.

 

[Julius Right]

The wire type Z in the NEC Table 310.15(B)(18) (formerly Table 310.18) it is a Tefzel insulated wire of 0.122 inches overall diameter. NEC declares the wire rated temperature is 150oC but 43A is for 90oC only [on my calculation was 44 A]. That means you could use it up to 150oC but it is not recommended.
A correct ampacity for a similar cable as yours you'll find in the following link:
https://cableusallc.com/wp-content/uploads/documents/srml.pdf
Here the manufacturer takes 150oC as limit for his 68 A[single wire in open air]. Your manufacturer use the maximum 112 oC for his 50 A.[3 cables].
In any case if you don't intend to pass through this wireway more than 3 wires at 75oC ambient a 33.6 A will not produce more than 112 oC of the conductor.
For up to 30 same wires you have to reduce the ampacity as per NEC-in my opinion.

 

[MTW]

You'll want to pay as close of attention to your terminations, as you do for the wire temp ratings. That is the normal failure point in many types of food equipment. Terminals for hi temp are a different composition than that of standard connectors. SRML is fine stranded and may not be approved for the breaker terminals without a crimp on connector.

MTW

 

[re-evaluating]

You'll want to pay as close of attention to your terminations, as you do for the wire temp ratings. That is the normal failure point in many types of food equipment. Terminals for hi temp are a different composition than that of standard connectors. SRML is fine stranded and may not be approved for the breaker terminals without a crimp on connector.

MTW

Very good point I had thought of inner connecting terminals but not at the breaker, I will look into that. Thank you!