Why You Should Never Plug a Surge Protector Into Another Power Strip or UPS
People do this all the time.
Power strip into a power strip.
Surge protector into a UPS.
UPS into a surge protector “just to get a few more outlets.”
It feels harmless. It feels convenient.
It’s also one of the most common causes of electrical failures, damaged equipment, and in worst cases, fires.
Here’s why this setup is unsafe, why manufacturers explicitly forbid it, and what to do instead.
The Warranty Reality Most People Miss
Almost every surge protector and UPS manufacturer includes language like this in their warranty:
All surge protectors must be plugged directly into a wall outlet.
Daisy-chaining surge protectors, power strips, UPS units, or extension cords voids the warranty.
That means if something fails, melts, or takes out your equipment, you are on your own. No replacement. No claim. No argument.
And that’s just the paperwork side of the problem.
1. Surge Protectors Don’t Stack Protection
They Break It
Surge protectors use components called MOVs (metal oxide varistors). Their job is to clamp excess voltage during a surge.
MOVs are not designed to be placed in series.
When you plug one surge protector into another, that’s exactly what you’re doing. Instead of working together, the MOVs interfere with each other. Best case, protection is reduced. Worst case, they fail unpredictably.
You don’t get “extra protection.”
You get undefined behavior.
2. You’re Quietly Overloading the Circuit
Most consumer power strips and surge protectors are rated for 15 amps total, protected by an internal breaker.
Here’s the trap:
Most devices draw between 0.5 and 1.5 amps
Eight outlets filled with normal equipment can already push you near the limit
Plugging another power strip into one outlet concentrates load through a single point
The breaker may not trip immediately. Heat builds up instead. Over time, insulation breaks down, outlets loosen, and failures happen when you least expect them.
This is how “it worked fine for years” turns into “why did it melt.”
3. UPS Units and Surge Protectors Don’t Play Nice
UPS systems already contain surge suppression and filtering. They also monitor incoming power very closely.
When you plug a UPS into a surge protector:
The UPS receives altered, pre-filtered power
MOVs inside both devices end up stacked
The UPS may misread line conditions or behave erratically
This causes unnecessary stress on internal components and defeats the design assumptions of the UPS.
4. Surge Protectors After a UPS Overload the Battery
This one surprises people.
Plugging a surge protector into the output side of a UPS to “add outlets” is not acceptable.
Every device downstream looks like load to the UPS. More outlets invite more devices. More devices drain the battery faster, create excess heat, and shorten battery life dramatically.
If the UPS was sized for five devices and now feeds ten, you’ve already exceeded its design.
5. Extension Cords Are Not Permanent Power
Extension cords are temporary by definition. They are not designed for continuous daily use, especially under load.
Fire departments warn against this for a reason. So do electricians. So do insurance companies.
Using extension cords with power strips or UPS units creates multiple failure points with no monitoring and no protection.
What You Should Do Instead
Plug one surge protector or UPS directly into a wall outlet
Buy devices with the correct number of outlets, not adapters
If you need more capacity, install a properly rated outlet or circuit
Size UPS units based on actual load, not convenience
Replace surge protectors periodically. MOVs wear out silently
The Short Version
If it plugs into the wall, it should plug directly into the wall.
No chains.
No stacks.
No “just this once.”
Electrical safety failures don’t announce themselves. They wait.
More information can be found at:
http://ulstandardsinfonet.ul.com/scopes/1363.html
This was a post I wrote back on Dec 2012
It's well archived on the internet archive. See below:
https://web.archive.org/web/20130525053624/http://www.evolutionelectronics.net/node/37