How Surge Protective Devices Function

Did you know that inside of a surge protective device (SPD) specially designed components reduce voltage spikes to protect your electrical equipment from being damaged? To learn more, watch this video where Mike and the team explain just how SPDs do what they do!

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[rickmelcher]

Hey Mike, I thought you might like to know, back in the mid to late 1970s I was working for Honeywell and I initially had a problem when I was working at the Federal Reserve Bank in Philadelphia, when the motor operated doors came to the end of their cycle, opening or closing, they caused an inductive kickback spike which would kill our solid-state circuitry. MOV’s, (relatively new at that time, ) seemed like they may be an answer to our problem. So, I tried them and they worked amazingly well! Sometime later we also had some problems with another site that kept getting hit with lightning; MOV’s also proved to be the answer there. I'm glad that the National Electrical Code is starting to finally Implement MOV’s and I look forward to their continued protection on these systems. However, on signal lines, super-fast Bidirectional Zener diodes most likely work better than the MOV’s.

Thanks and keep up the good work.
Rick.

[oldtimefarmboy]

I have a UPS with built in surge protection. I have a surge protector on my computer equipment and peripherals. I have a surge protector for my television and digital recorder and radio and etcetera which also has surge protection for the coaxial cable. I use WIFI to connect my computer to the cable modem.

Lightening once struck inside the apartment complex and took out all the electronics in three buildings except for mine. I immediately went out and bought new surge protectors and replace the old ones.

[ssl]

I always get pumped when I hear the electric guitar on a new Mike Holt video

[yarekk]

I understand that this is designed for general electrician consumption, but Mike's hand-waving explanation illustrates the difference between tradesmen and scientists. Mike may make fun of research engineers that they may call something a "light fixture" instead of a "luminaire", but similarly, I can't help but smile at this explanation.

[moosepasshippie]

I was laughing, just like Eric and Mario, when the panel was in agreement about surge protectors cannot guarantee protection from surges. FYI, I have noticed older power strips with surge protection have been tripping arc-fault breakers when vacuum cleaners are turned on from other circuits.

[delmarmartin]

I would just like to add that Metal Oxide (essentially a metal typed rust) is semi-conductive and not a semiconductor in the sense like the ones that are used by chip manufacturers. It's a metal powder between two plates that has poor conductivity until there's enough voltage to break down the resistance (heating the oxide and converting it back to metal); causing the two plates to "clamp" down and shunt voltage either to ground or a short circuit. Either way, once this occurs, the MOV must be replaced or removed before the circuit can operate again.

[LLAMA-gym]

Interesting theory and explanation behind this. So there’s no guarantees that a surge protector will work after a strike?

[vince]

Very informative. Thank you for sharing your knowledge.

[irarubinson]

Open neutral can create sustained 240V on a receptacle. I've seen this damage all sorts of appliances. MOVs in surge protectors at the outlets will burn up, sacrificing themselves to protect the appliance.. A whole house surge protector may not do anything to alleviate damage from an open neutral on the power company side so, like you said, best to have surge protectors on all appliances. I recommend putting fire proof material, such as a piece of tile, between the surge protector and the carpet because I've seen some surge protectors with their plastic cases melted after an open neutral event.

[logic]

Excellent explanation, thanks🙏 for sharing

[trespire]

CNC machines and data centers, all need surge protection.

[harveypaxton]

As a service Electrician very often I find the breaker feeding/protecting the surge protector is tripped. Even though the indicator LED is off the customer is unaware. The service call is never related to a “surge”.

[allenshepard]

Is there any research on ferrite core chokes vs. MOVs ? Yes frequency is a big factor.
Is there anything in NFPA 70B about checking MOV indicator lights ? Power panels are often in a boiler or mechanical room where they are no checked. As for the home? I doubt people will look at them.

[keystar]

Just took my test again got a 66% I am only on page 131 of the electrical exam preparation. I feel like in connecticut they make the test difficult and tricky because the questions are misleading and lacking absolutism. They could make the test difficult as well as being cut and dry just saying. Will keep at it!

[ronaldkovacs]

Creates a false short circuit during surge conditions, shunts extra current away from load, can even cause OCPD to open to put an end to the problem.

[gerardashton]

Transients are crud that doesn't belong. Nobody will guarantee that it is AC, nor will anyone guarantee it's anything like a sine wave. So the expression "RMS" ought not be applied to transients.