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I am trying to find a 6-port version of this: https://czh-labs.com/products/czh-labs-din-rail-mount-ac-dc-532v-10-position-power-distribution-fuse-module-board-p0445

I found something close (https://czh-labs.com/products/din-rail-mount-6-position-dc-power-fuse-distribution-strip-module), except it is rated at 32VDC and I need 24VAC support (which transformer actually seems to be outputting 33VAC).

I contacted the manufacturer and they said it will work with up to 22VAC, which seems strange to me since I was under the impression that DC was harder to interrupt than AC, so a given circuit can typically handle the same or more AC voltage than DC.

To double-check their reply, I searched and found a product with a similar specification (https://hkxyautomation.sell.everychina.com/p-108997010-mtl-surge-protector-250a-32vdc-22vac-mtl-sd32x-surge-protector-sd-series-data-line-3-outlets-36-v-with-best-price.html), so now I'm really confused. Why would a 32VDC circuit not support anything more than 22VAC?

Bonus points: I'd love to just find the product I need and get that, but I can't find it :)

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2 Answers 2

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DC is more difficult to interrupt than AC.

However, note that 24VAC (rms) has peaks of 31V. So I'm guessing they copied treated the DC rating to a peak value, then converted that peak value to an RMS value to come up with the AC rating. In that case, I would expect the true AC interruption capability to be higher than what is written.

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  • \$\begingroup\$ Making such assumptions will backfire if you're dealing with any kind of regulated fields. AC also has more stringent safety requirements, i.e. 48VDC is considered safe (for consumers) just like 48VAC is not. \$\endgroup\$
    – Barleyman
    Oct 25, 2021 at 17:22
  • \$\begingroup\$ @Barleyman When it comes to regulatory stuff though, it almost doesn't matter what the physics are. It just matters what is written in the code because that's what the inspector is going by. \$\endgroup\$
    – DKNguyen
    Oct 25, 2021 at 18:02
  • \$\begingroup\$ As far as safety is considered, AC is more dangerous than DC and it is reflected in the voltage levels that are allowed on various types of devices. \$\endgroup\$
    – Barleyman
    Oct 25, 2021 at 18:50
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If they have rated the fuse to voltage of 32V for some technical or approval reason, then it would be 32VDC or 22VAC, as 22VAC has a peak voltage of 31.1 V.

It looks like the board uses automotive type blade fuses, and they are rated up to 32V DC.

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