Surge Protector VPR Rating Comparator

Last updated 2026-08-23

Every surge protector's box has a big joule number on it. What most boxes don't say as loudly is that Joules has no recognised test standard at all — a completely different number, the Voltage Protection Rating (VPR), is the one actually standardized and tested under UL 1449. We fetched five products across two brands' own current pages directly and compared what each one states, for both numbers.

Joules is not standardized. VPR is — and the two don't move together. NEMA's own Surge Protection Institute page states: "There is no clear standard for SPD energy measurement, and manufacturers have been known to use long tail pulses to provide larger results misleading the end users," and that this is exactly why "many of the industry standards (UL) and guidelines (IEEE) do not recommend the comparison of joules." The same page states VPR "is rounded up to one of a standardized table of values" — "330, 400, 500, 600, 700, etc." — which is why it "allows the direct comparison between like SPDs." Every VPR figure below is one of those exact standardized values, fetched from each product's own current page, not a brand's own number.

Same brand, double the joules, identical VPR

CyberPower's own P405UC page states "1500 J" next to "600V (H-N, H-G, N-G)" clamping voltage. CyberPower's own B1206 page states "3000 J" — exactly double — next to the identical "600V (H-N, H-G, N-G)." Same brand, same clamping-voltage test basis, twice the joules, and the standardized protection rating does not move at all. And it isn't just a within-brand coincidence: Panamax's own SP8-AV states the lowest joule figure of the five (1125 J) next to a better VPR (500V) than either CyberPower product's 1500 J or 3000 J. A bigger joule number on the box does not predict a better VPR on the same box, or on a different brand's box.

What this does not do

It does not convert Joules into VPR, or the reverse — no brand's own page states a formula between them, and NEMA's own page gives the reason none exists: Joules has no standard test method to convert from.
It does not certify that any product will clamp at exactly its stated VPR in your own home's wiring — every VPR figure is each brand's own UL 1449 test result on their own page, not an independent lab's re-test.
It covers five specific products across two brands checked directly, not an exhaustive catalog of either brand's lineup.
Where a product states different VPR figures for different line paths (Panamax's MD2-TL: L-N 400V, L-G and N-G both 500V), only the line-neutral (L-N) figure is used, since that's the path a plugged-in device sits on.

Runs entirely in your browser. Nothing you type is sent anywhere. The generator noise level claim comparator found the same "the number brands advertise loudest isn't the one that's actually standardized" shape in a different market, and the blender motor power comparator found it again in peak-vs-continuous wattage claims, and the tripod load capacity comparator found it a third time — an uncertified "Max Payload" number next to a newer, actually standardized one.