I am going to be attaching my gear in this order: 20 amp outlet => Surge Protector => PDU => servers.

My current PDU says in the manual "does not provide surge or line noise protection". I have been doing research but am a bit confused on the joule rating for some products.

For example, this consumer-grade product advertises up to 4000 joules of protection, but this business/enterprise-grade Tripp-Lite unit, only advertises a 1440-joule rating.

Why is there such a large discrepancy in the joule rating between the two units? The Belkin doesn't mention EMI/RFI filtering or clamping voltage so the price would be low. Any idea why the Tripp-Lite has such a low joule rating compared to a consumer product?

*PS: plugging the PDU with all servers connected to it (16 A) into a single receptacle on the surge protector sounds dangerous no?

  • 1
    Surge protection is achieved using an electronic component called varistor. Depending on how "big" they are, they can absorb more or less of the surge before going up in smoke, therefore the ratings.
    – Dan
    Commented Feb 13, 2015 at 9:54

1 Answer 1


First, that power strip cannot connect to a 20 amp receptacle. It is mechanically shaped to only connect to 15 amp receptacles. A 15 amp receptacle is significant power. Does not matter how many devices are powered. Relevant is the total current drawn that should not exceed 13 amps.

Second, both a 1440 (actually 960 joules) and 4000 (actually 2700 joules) are similar in size. Somehow they must absorb destructive surges that are hundreds of thousands of joules. Those items only claim to protect from another type of surge that rarely cause damage.

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