Power 101: Maintenance Bypass modules

So I haven’t had time to put together a Power 102 article to follow-up from the popular Power 101 article I did, but I thought I would share a little more in terms of what options you have when designing your power protection plan.

When designing a smaller closet one of the things that is often considered is how do you maintain reliable power in the event of a component failure. You basically have 3 options:

  • You could buy two of everything; 2 equal sized UPS’s, 2 PDU’s, etc – this allows you to lose an entire side of power (meaning 1 UPS and 1 PDU) without taking down the load; this is the most costly of the options
  • You could buy 1 UPS and 2 PDU’s; then maybe wire one PDU in to house power and take your chances with surges and brown outs on that one side; while the cheapest this one also is the most risky
  • You could buy 1 UPS and 2 PDU’s and 1 maintenance bypass module; this is sort of the best of both worlds let’s see why

If you don’t know what a maintenance bypass module is that’s ok… you will by the end of this post. Basically a maintenance bypass module allows you to save on the cost of a second UPS system while still providing the ability to lose the UPS without affecting the load.

At a 10,000ft view a bypass module is just a switch that can change positions very quickly; quick enough that power is not interrupted long enough to effect the load. Pretty much every UPS vendor has bypass modules, and they can range in price depending on the size of the load they are designed to carry, but they are generally cheaper than purchasing an entire second UPS system.

How they work

Eaton has a pretty simple little video that explains how a bypass works, so instead of typing it all out, check out this video:


While a dual UPS system is the best option, they can sometimes be out of budget, the next best thing is a maintenance bypass module. So when designing out a remote office or closet that is not as critical as a datacenter consider looking into your UPS vendors maintenance bypass offerings. It cost more than just wiring things into house power, but will save you money if a power issue ever comes up.

Have a question or need more info? Let me know.

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