UPS Surge Protection

[Anonymous user]

I often read people on forums asking if the surge protection of a UPS is enough. Everyone says it's enough.

Everyone advises that you should choose the lowest clamping voltage as possible and that the ideal clamping voltage is 330V.

Well, being a curious person as I am I've opened my Back-UPS BE600-LM 120V sold in Latin America / Brazil and found out that the MOVs used on these units are far from havign a 330V clamping/let through voltage. The MOVs are installed this way and as per the catalog available on the GNR website:

- One Phase to Neutral MOV: GNR14D471K:

Working RMS Voltage: 300VAC.
Clamping voltage: 775V (!)
10/1000us Energy: 125Joules

- Two Phase to Ground MOVs: the same specs above

- One Neutral to Ground MOV: 14D241K:

Working RMS Voltage: 150VAC
Clamping voltage: 395V
10/1000us energy: 63 Joules

Well, how come an 120V UPS have a 300Volt MOV with 775V as it's clamping voltage?! I have a feeling that this is working to protect my computer against surges, it's only protecting the UPS eletronics itself and I have my doubts about that as well.

Can anyone explain me why APC put 300V MOVs on an UPS made to output 120V? I also have an APC Surge Protector and it's got many 130V MOVs Phase-Neutral, Neutral-ground and Phase-Ground and also one rated at 300Volts for Phase-Neutral, but the 130Volts ones are there! I now feel safer connecting my UPS to the surge protector and don't come tell me this is not safe! I'm still waiting good technical explanations for those who say it's not safe. If you don't overload the surge protector, this is safe at least for most cases.

Thank you!

Message was edited by: The Notorious K.M.P.

[Anonymous user]

I have just found this out:

http://www.eeel.nist.gov/817/pubs/spd-anthology/files/Lower%20not%20better.pdf

so I think it clears this matter a bit for me, but I still think for 120Volt the best choice would be a 230VAC MOV maximum for a longer life and 130VAC for the best protection, but a lower lifetime.

[Anonymous user]

Hi, cm33414!

The main purpose of my message was not to say pluging a UPS to a surge protector is a safe thing or it's not a safe thing to do, but instead to ask if a 300VAC MOV would do something to protect equipments. At a first glance, the 300VAC MOV wouldn't do anything to protect against surges because it wouldn't do anything until 400 or something volts, the point where this specific MOV starts conducting excess voltage to neutral (which is "grounded") or to the protection ground wire, and would only "clamp" both wires, to make the fuse or breaker trip, only at 775Volts! How could your equipament be protected if the MOV would allow 400volts or more to reach the equipament? That was my first thought.

Well, first off, an MOV wasn't made to protect equipments against "swells" or momentary overvoltage. It can do at some cases, but this is not its main job. Let's say there is a 5 second swell and the voltage goes from 120V to 250V. On an 130VAC MOV, the ones usually found on good surge protectors and those made by APC, the initial conducting state would begin at 180 to 190Volts or even lower, and that would reduce the voltage reaching the equipment, and if the voltage reached 330Volts, the mov would clamp, making the fuse blow or the circuit breaker trip. But as I said, this is not the main purpose of an MOV. MOVs are made to protect equipments against high and fast rising surges - those caused by lightning strikes which are very high in energy and has a fast peak rising with a fast return to it's initial state. Most equipments can survive peaks like 700volts or more energy for a few nanoseconds or so, time an MOV takes to react agains this fast rising peak, even those equipments made for an 120V outlet. Of course, it's better to have the lowest clamping voltage as possible, the lowest residual voltage or let-through voltage as they call it as possible, but if this number is too low, it means the working RMS voltage rating for that MOV has to be lower and lower voltage means lower lifetime. Why? Because it means the varistor will heat itself on every small swell that happens naturally or not on the utility. MOV are not made to work this way, they degrade themselves very fast if constantly hit by these swells which has a much slower rising voltage than an actual surge cause by a lightning strike or something else. So, that's why I say this is not their job to do.

Some high end surge protectors, like some made by Panamax and other brands, come with a feature that when the voltage goes beyond a certain threshold, it disconnects power via a relay or something like that. It would be the same thing done by an UPS, but the UPS would transfer to battery, keeping the equipment on and this is a much more desired feature. Imagine a relay disconnecting the power everytime there is a 5 to 10 seconds swell. That'd wouldn't be nice and many power supplies now a days can work with anything from 80 to 270Volts!

So, when I said the document I had found cleared things out was because it proved to me that MOVs up to 300Volts or more, can protect electronics or most of them against power surges or power peaks, even having a 775 volts let-through voltage. This paper states that the UL 330V rating, the lowest rating allowed for surge protectors in US are made to protect equipments working at 50Volts, not 120V! Which means for an 120V equipment, the 330V rating offers much more protection than it acctually needs! But yes, an 130VAC MOV (which has a 330V let-through voltage) would offer much more protection against swells as well, even this not being the main purpose of an MOV and it would also protect equipments working at lower voltage at the same time.

But getting back to the UPS plugged to the Surge Protector now. How would you tell you're not overloading the surge protector? Well, there are some ways!

Most if not all surge protectors come with a label on the bottom that shows you how many Amperes can be put on it or drawn of it. Surge protectors come with a fuse or a circuit breaker that will blow or trip when the it's overloaded. Let's say you draw 20amps from and 15A surge protector. Few seconds later it's overloading protection will cut the power, ie: the circuit breaker.

15A means your surge protector is capable of hadling 1800Watts at 120V which is a lot! You'd have to plug a lot of stuff to overloading the surge protector. Even with two UPSes plugued to the surge protector it wouldn't be easy to reach it's limit since the UPS draws very little power for itself.

Some surge protectors come with an overload LED, which lits up before the maximum load alowed by the surge protector is reached.

You can also do some math and calculate how much power your equipment draws, so as not to overload the "poor" surge protector or buy an APC UPS cos it shows how many watts your gear is pulling out from it and consequently from the surge protector! The UPS itself protects againt overloads! There is an overloading protection on every UPS! How would you overload a 15A surge protector if an 1500VA UPS can only supply at the best case 1500W or 980W at the worst case??

See, there are many ways for knowing this and there is also one more line of protection. The circuit breaker of your house, usually 15A for the outlet circut, is also protecting against overloads.

I hope you understand my message. English is not my first tongue, so I apologize of any mistake or confusion I made with the words. 🙂

The IEEE even has a document titled: How to protect your home and your equipments from lightning strikes that recomends connecting everything to a multiport surge protector, even the UPS!!

Thank you and if you don't understand something I said, I can try to write in a different way. 😉

[Anonymous user · Accepted solution]

I apologise for bringing up this topic again, but I think things are still a bit unclear to me.

I see people saying that you don't need a surge protector if you own an UPS with surge protection built-in, and if you have a whole house surge protector, good for you!

Well, it's been two days that I'm using a new APC UPS, a brazilian/latin american version, the Back-UPS ES BR600 and to my surpprise, it comes with 385VAC MOVs with its clamping voltage being 1025Volts! WTF!

This is a bi-volt unit which means it can work off a 120V or 220V outlet. The out put of this unit is ~115Volts for any of these two input voltages, which means everything will be running at ~115V no matter what input voltage is being fed to the unit.

So, how can a 1025V let-through voltage protect my equipment? Why use a 385VAC MOV when a 175VAC one or 150VAC one could be used and would offer a much better protecion agaist spikes?

I understand that the 330V let-through voltage level is more than what 120V electronics needs to be protected, but 1025Volts let-through voltage?? I don't think so!

I would love to have a chat with an APC engineer or something like that so he/she could clarify things out on this subject. I still have my doubts that an MOV rated to be working on a 385Volt circuit is protecting my equipment, even the 300VAC MOV that comes inside my other mono-volt 120V APC UPS.

Why APC Surge Protectors come with 130VAC MOVs inside or a 275V MOVs for the 230V international models and the UPS units come with an over rated MOV? I know the unit becomes much more reliable in terms of longevity, the MOV longevity, but at what cost??

[Anonymous user]

I apologise you guys for insisting on this so I'm gonna make one simple question, I've done it before but I tend to write too much:

Why APC has chosen to use 300VAC MOVs on a 120V in 120 out UPS (BE600-LM) and 385VAC MOVs on a 120/220V in 120V out (BE600-BR)?

I know that only an engineer who made this choice can explain me that, but I'm still hopeful someone will give me an answer.

Thank you!

[Anonymous user]

First, here is the IEEE Paper:

http://www.lightningsafety.com/nlsi_lhm/IEEE_Guide.pdf

My setup is very simple.

I have a relatively old and simple PC with a one year old 20" Samsung LCD, printer, scanner... I plan to upgrade this PC until the end of the year...

It consumes about 120-180Watts with the printer and everything, it never go past 200 watts with everything on.

Yes, it's been almost a year now that my APC Back-UPS ES 600VA is connected to an APC PF11VNT3 Surge Protector - I had to import this surge protector...

A year ago APC would only sell UPSes and voltage regulators in my country and at that time I really wanted to buy a good surge protector. Almost if not all the surge protectors made in my country are a real joke! The're crap but you can find good UPSes from national brands, but not as good as those made by APC. So I decided to import a surge protector to plug my UPS to, giving more protection to the UPS itself and my equipment, the telephone line and protect my computer from surges coming down the network cable.

I also had to plug this surge protector to a step-down transformer which converts 220V to 110Volts. I can tell this is not the best thing to do since you can burn your surge protector if you connect the power transformer in a wrong way, I mean, if you plug the transformer on a wrong polarized wall outlet or if the transformer plug allows you to invert it. Inverting it will cause 220V to be referenced between neutral and ground, and the 130VAC MOVs put between those lines will blow up.

One thing I have to complain about and I have complained about that before is that APC seems to have forgotten that my country is 110-127V and also 220-230V. It's one of the only, if not the only country you can find a mix of voltages, even on the same city! There are cities where you can find 220V Phase-Phase outlets (even being against the code for wall outlets) and 110-127V Phase-Neutral, but most of the cities are 220V Phase-Neutral or 110-127V Phase-Neutral only. Where I live it's 220V Phase-Neutral only. So, APC brings from other countries and make products in their brazilian factory that focuses more on the 110-127V market. APC makes very few products for the 220V market in Brazil and 220V Surge Protectors are not sold by APC here. If you look all Europe, Africa, Middle East, Asia... APC sells 230V Surge Protectos which would work well here, apart the very different power outlet shape found in the part of the world...

You can find 220V UPSes in my country from many brands, including national brands, but most of them come with a built-in step-down transformer since many products we use come from the US, so for most people it's a handy feature, but for me If I had good options, I'd rather power everything at 220V, it's more energy efficient. You can find the biggest variaty of voltage regulators in this part of the world than in any other part, most of them are 220V to 115V transformers as well. Even not being necessary, people still buy it thinking their computer are isolated from every single problem just because of the name the voltage regulator has been given here - it's know as a Stabilizer, people and manufactures call it only a "stabilizer". If you go to a computer store and say "voltage regulator", they won't know what you're talking about. It's funny because most people don't know it regulates the voltage, they only know it "stabilizes" "everything"... 😞 The voltage regulator industry in Brazil is very big and they will never admit most electronics today, with Switched Mode Power Supplies, don't need external voltage regulation to work well, unless for extreme cases where the voltage is too low or too high. If you don't live close to a slum or a very poor neighbohood where people constantly still power, or a rural area, voltage regulators is a thing of the past in my opnion.

Well, I think I have written too much already! 🙂

[Anonymous user]

I've been trying to understand the whole issue about plugging a UPS into a surge protector (to get the additional joules protection) but I have yet to see an answer that makes sense to me/clicks as to why it shouldn't be done.

I keep thinking exactly as you said in your post:

"I'm still waiting good technical explanations for those who say it's not safe. If you don't overload the surge protector, this is safe at least for most cases."

Also, how would I measure/know if I'm overloading the surge protector?

The pdf document you posted didn't help clear anything up for me...so now that you seem to understand it better, can you explain what you came away with?

ETA: based on the search I did on the forums A LOT of people cannot understand why you shouldn't plug a UPS into a surge protector. Same with the whole issue as to why UPS joules ratings are so much lower than surge protectors. I "get" that surge protectors have the MAIN job of protecting against surges, as opposed to what a UPS does...but why not offer UPS units with higher protection? Maybe I'm missing something, but it shouldn't be hard for a layperson to find explanations to these answers that make common sense.

Message was edited by: cm33414

[Anonymous user]

Rau, thank you so much for the very thorough answer.

You put quite a bit of information there, so I had to reread a few times to absorb everything you said. And I think I understand everything.

Thank you also for the tips on how to make sure I'm not overloading the UPS - I haven't purchased one yet - I have that question under a separate post - but this is stuff that is good to understand. It's a big purchase, and I want to understand what I'm buying, and why.

I am definitely going to read the IEEE document you cited, and make my own determination, along with your answer.

What is your setup at home, if you don't mind my asking? Is your UPS plugged in to a surge protector?

[Anonymous user]

Thank you, Rau. I learned a lot through your answers!