Choosing between cross-linked polyolefin, PVC and rigid board

The electrical row is not the decision

All three materials clear the electrical duty at the walls they are supplied in. The polyolefin shroud publishes 22 kV/mm, the GBBS board 20 kV/mm and the PVC shroud 16 kV/mm. Six kV/mm across three parts that are each specified by voltage class is a footnote, not a choice.

Tracking does not separate them either. The polyolefin shroud and the GBBS board both record no tracking, erosion or flame failure to 3.25 kV for 20 minutes, and the PVC shroud publishes no tracking figure at all. It is the row buyers reach for to rank the three, and it ranks nothing.

Two rows do decide it. The board holds −45 °C and both polyolefin parts −40 °C while the PVC shroud stops at −20 °C, and there is nothing to choose at the hot end, where all three sit at +105 °C or +115 °C. The second is halogen: both polyolefin parts are listed halogen free, the PVC shroud is not, and an enclosure specification carrying a halogen-free clause has already chosen.

Two hardness scales, three figures

Hardness is the row most often misread. The PVC shroud is quoted on Shore A and the other two on Shore D, so the three numbers do not compare directly. At 65 ± 5 Shore A the PVC shroud is a rubber you can deform between finger and thumb; at 45 ± 10 Shore D the polyolefin shroud sits on the harder scale and will not.

The board then reads 40 ± 5 Shore D, marginally softer than the polyolefin shroud, and is still the rigid part of the three. Rigidity comes from section rather than from the polymer: a flat sheet at 2.0 to 5.0 mm resists bending in a way no 1.8 mm wall moulded round a tee ever will.

Read the row as how a part behaves in the hand while it is being fitted, not as how it performs once fitted. Every test method named on this page is decoded once for this site on the standards page.

Where each one is the wrong choice

The limits are more useful than the properties, and they are the part a datasheet will not print.

• Cross-linked polyolefin sleeve, on anything that has to come apart again. It recovers onto the bar at 125 °C and its published data says nothing about coming back off. The shroud is the part published as installing, removing or replacing in minutes, and the PVC version ships with its fasteners.
• Cross-linked polyolefin sleeve, on a tee or an elbow. The sleeve is published for straight and angled runs. Joints of any shape, tees and elbows included, are the moulded shroud's job.
• Flexible PVC, below −20 °C. Its continuous limit stops there, while both polyolefin parts are qualified at −40 °C for four hours with no cracking.
• Flexible PVC, under a halogen-free clause. A yes-or-no specification question, not a preference to be argued at the design review.
• Flexible PVC, where panel width is the constraint. The penalty runs the length of both tables and is worst at the top: 4.50 mm at 38 kV against 2.5 mm at 36 kV, two different rows and not the same test.
• GBBS board, on the bar itself. It does not shrink and it is not moulded to a connection. It is a flat inter-phase and under-structure barrier, cut and drilled from a 670 mm or 970 mm roll without special equipment.
• GBBS board, above +105 °C. It is the only one of the three that stops short of +115 °C.
• Any of the three, as a mechanical support. These parts insulate a bar; they do not hold one up. That is a different part with a different failure mode.