When Is SIS Wire Required Vs Allowed

[yesterlectric]

When is it okay when adding components to relay racks, switchgear, large switchboards, or similar equipment, to use the more readily available THWN-2 to run between components in the equipment instead of needing to use the SIS wire that usually ships fro the factory?

Per 300.3A, conductors in table 300.4A (including THWN-2 and SIS) should only be installed in a chapter 3 raceway. However 300.2B clarifies that article 300 is not intended to regulate internal wiring of equipment (no mention of if that exclusion is for field wiring or only factory wiring).

I'm wondering if this is a UL product standard (there goes $5,000 more in book fees) thing instead of an NEC thing?

"Talk to the manufacturer and follow their instructions" may be a response, but they likely won't answer and it's likely a generic requirement applying to a lot of applications.

 

[rbalex]

See Table 310.4(1).

Type SIS is extremely flexible - and soft. As such, it is only appropriate to be “laid in” rather than pulled. It is especially useful where wiring transitions across hinges.

Type THWN-2 is not expressly prohibited for switchboard wiring.

 

[yesterlectric]

See Table 310.4(1).

Type SIS is extremely flexible - and soft. As such, it is only appropriate to be “laid in” rather than pulled. It is especially useful where wiring transitions across hinges.

Type THWN-2 is not expressly prohibited for switchboard wiring.

Yes I’m aware that the NEC at least doesn’t expressly prohibit use of XHHW-2 or THWN-2 in switchgear and switchboards. However sometimes things like this are buried in a product standard. There’s a lot of NEC rules that exist because there’s something in a product standard that electricians don’t read, that they need to know.

Not all SIS wire is extremely flexible as you can get SIS wire in solid and also course stranding if you want it. A lot of SIS wire is dual rated to UL 3173 which is listed at 125°C.

 

[Macbeth]

The NEC is primary the field installers guide. Since panelboards are Factory Constructed under the Factory “Label” they do not use NEC they use other standards such as UL891. Good example is Control panel builders are UL508A. We apply for a “Label” we go through a training program take a test, if we pass, we are awarded a UL File number and the ability to purchase “UL Labels” and put them on our panels. So yes, the answer you are looking for is in another “Standard”. Look on the panelboard manufactures name plate it might show what standard it was built to. Technically when you modify a panel, you violate and void the factory applied label. You are supposed to remove/cover label, have panel reevaluated by UL or another agency. Even if the factory people modify it in the field. I have only seem this done once..

 

[Jraef]

SIS not “required” anywhere unless by specification (the Army Corps of Engineers and the Bureau of Reclamation seem to like it a lot). In days gone by it was used in switchboards and control panels because it was extra flexible and the wire was tinned, so it provided some corrosion protection. But SIS** is only rated for dry locations so its use is limited.

** A lot of SIS is now dual listed as XHHW-2, because it is basically the same thing with tinned conductors, in which case it can be used for either application.

THWN-2 has fewer strands so would be less flexible, which for internal factory wiring is less desirable. But for field connections, if you want to use it there is nothing stopping you, unless, as mentioned, there’s a spec demanding that you use SIS.

 

[yesterlectric]

The NEC is primary the field installers guide. Since panelboards are Factory Constructed under the Factory “Label” they do not use NEC they use other standards such as UL891. Good example is Control panel builders are UL508A. We apply for a “Label” we go through a training program take a test, if we pass, we are awarded a UL File number and the ability to purchase “UL Labels” and put them on our panels. So yes, the answer you are looking for is in another “Standard”. Look on the panelboard manufactures name plate it might show what standard it was built to. Technically when you modify a panel, you violate and void the factory applied label. You are supposed to remove/cover label, have panel reevaluated by UL or another agency. Even if the factory people modify it in the field. I have only seem this done once..

Yes I know you’re technically right. Larger switchboards and switchgear that’s made to have all sorts of relays, ethernet switches, and a whole bunch of other gizmos is inevitably going to have things added to it. What’s the difference between snapping a breaker into a panel board and snapping another breaker on a piece of existing dinrail, mounting a piece of dinrail onto an existing backer plate, or adding a little fiber converter that needs a 24v power source?