PVC conduit that has not been tested and third-party certified to the requirements of UL 651’s 90°C wire requirements cannot safely be utilized in modern 90°C conductor systems. Ensure the conduit’s print line includes the words “maximum 90°C wire” or “max 90°C wire.”

What is the 90°C requirement?

90°C refers to the insulating rating of a conductor. For modern conductors, a common temperature rating is 90°C. Only PVC conduit that has been specifically tested and certified for 90°C wire according to UL 651 can be safely utilized for 90°C conductor systems. Conduit that is not rated to 90°C can only be used in systems designed and rated for 75°C maximum.

Why does 90°C compliance matter?

Specifying engineers, architects and utilities often specify that conduit meets the 90°C standard to match the 90°C rating on the conductors. If conduit without the correct rating is installed in 90°C specified systems, it is out of compliance and will be rejected by inspectors. When conduit does not comply, conductors must be de-rated to meet the conduit, or the conduit must be replaced with compliant conduit.

If there is no temperature rating listed on the PVC conduit, the installer or AHJ (authority having jurisdiction) will have no way to know what temperature the conduit is rated for. Therefore, they won’t know if the conductors inside will be operating over the temperature rating of the conduit. This is why inspectors look for the 90°C marking and reject any product that does not have it.

If an inspector for a public or private job becomes aware that lower-rated products are being used, they could reject the entire system and require replacement with conforming product. This exposes the contractor and supplier to significant liability for uninstall, re-install and delay damages. For this reason, it’s important to avoid risk by ensuring initial compliance.

Testing procedure

The procedure for determining 90°C compliance is very rigorous. UL 651 outlines the procedure, which takes up to 360 days to determine conformance. Third-party certification agencies such as ETL, UL, CSA or NSF perform this testing in their nationally recognized labs and provide an official listing or certification to the manufacturer.

The 90°C wire testing, detailed in UL 651 Section 6.15, is an accelerated aging test that assures the Schedule 40 or Schedule 80 conduit does not experience a significant decline in properties when subjected to continuous, long-term high temperature exposure. The critical physical property being tracked in the test is impact strength. Up to 12 times over the course of 360 days, multiple conduit samples are removed from an oven and tested for impact strength using a statistically valid average impact calculation.

The majority of electrical installations in the United States are required to comply with the National Electrical Code (NEC). Section 352.6 states that all PVC conduit needs to be listed in order to be in compliance. For conduit to be listed according to the NEC® definition, it must be published on a third-party organization’s list as meeting the product standard and is subject to periodic inspections by the third party to ensure continued compliance with the product standard.

Reducing noncompliance risk

Choose American-made PVC conduit

Imported PVC conduit has a higher likelihood of noncompliance. Many importers of PVC conduit, particularly those manufactured outside of North America, sell their products into the United States without the required 90°C marking.

Therefore, avoiding imports and sourcing conduit made in the USA for 90°C conductor systems helps reduce the risk of noncompliance. For example, Atkore is a leading supplier of PVC conduit and fittings, providing SCH 40 and SCH 80 conduit that is 90°C compliant and marked accordingly. With 10 PVC manufacturing facilities across the United States and an extensive national distribution network, Atkore’s PVC conduit is Build America, Buy America certified.

Check the print

It is not enough for conduit to simply pass the 90°C wire tests. As with most national standards, UL 651 requires that PVC conduit tested and certified to the 90°C wire requirement must include this on the conduit’s factory-applied, permanent print line.

As proof of UL 651 conformance, the repeating print line on every piece of 90°C rated Schedule 40 or Schedule 80 PVC conduit must include the words “maximum 90°C wire” or “max 90°C wire.” If these exact phrases are not included in the print line, the conduit is NOT properly listed or certified.

Checking the print is the best way to know for certain that your conduit is 90°C compliant. Your vigilance in this matter will help avoid putting your project—and your company—at risk.

Interested in learning more? Reach out to Atkore at [email protected] to schedule a training session for you and your team.