Doesn't this seem like a bad idea?

[don_resqcapt19]

Don't all UPS systems have battery backup? I thought that was what makes them "uninterruptible power supplies".

No, there are other types such as the ones that store energy in a flywheel.

 

[jdsmith]

Why would they be "synced"? They don't parallel their output with the utility. They close a switch to provide battery power to the loads from the inverter after the sense the loss of utility power. The do not have a "closed" transition back to the utility power after it has been restored.

Any time a consultant is hired to design a UPS system rather than cobble something together there should be some things that are not negotiable: the UPS should be a double conversion true online type, and it should have a maintenance bypass switch so the UPS can be serviced without de-energizing the load. This necessitates a make-before-break type transfer switch, so the UPS output will be connected to the utility for brief periods of time. Keep in mind that this maintenance bypass switch is typically supplied by the UPS manufacturer, included in the UPS O&M manual, and the UPS/bypass switch system is warranted as a unit.

I am amazed that anybody willing to spend money on a UPS and willing to pay somebody to design it would consider buying a static transfer type UPS - even the name is an oximoron!

 

[massfd]

I think I would be asking the Manfacturer how they feel about having a utility source backfeeding the UPS output. I see the potental to let the magic smoke out of the UPS on the first attempt to run it. Would you attempt to backfeed an engine driven generator, you could if you want smoke. Also if the UPS fails with a short in it's output circuits it may blow the utility backbeed breaker and you woud be powerless

My data center has a 10kw Liebert UPS that is double conversion, has both static bypass (to handle overloads and clear faults) and maintenance bypass to allow servicing.

Our answer to allow us to remove the UPS completly without effecting the load is to have the UPS feed an automatic transfer switch (50amp). The UPS feeds the line lugs the Utility feeds the generator lugs and the load lugs feed a sub panel in the data room. If the UPS was to fail the transfer switch moves the load to the generator lugs (feed by the utility). The transfer switch engine start terminals are used for an alarm that tells us the transfer switch line input (UPS) has gone away and it has switched to backup.

 

[Volta]

Does this not back feed one panel from the other and this is not allowed or safe?

215.2(A)(1)

During a utility outage the UPS would back feed into the non UPS panels via the receptacle as well. Which 20 amp breaker trips first?

210.23

They are basically suggesting having one panelboard fed directly from the utility, and one fed from the UPS, then run wire from both and connect them to the same outlet

705.4, 12(D), 40, 42 . . .

Of course, the UPS will supply high voltage when backfeeding utility transformers and can kill lineman working on the lines to restore power.
That's bad.

 

[don_resqcapt19]

Any time a consultant is hired to design a UPS system rather than cobble something together there should be some things that are not negotiable: the UPS should be a double conversion true online type, and it should have a maintenance bypass switch so the UPS can be serviced without de-energizing the load. This necessitates a make-before-break type transfer switch, so the UPS output will be connected to the utility for brief periods of time. Keep in mind that this maintenance bypass switch is typically supplied by the UPS manufacturer, included in the UPS O&M manual, and the UPS/bypass switch system is warranted as a unit.

I am amazed that anybody willing to spend money on a UPS and willing to pay somebody to design it would consider buying a static transfer type UPS - even the name is an oximoron!

First the use of non-dual conversion type UPS is a design issue. There are many applications where they work just fine. I have installed a number of systems of that type that have all of the features that you mentioned above.

Second my question about the UPS being synced to the utility was addressed a statement made by another member that said "all UPS's are synced to the utility. I don't believe that is a correct statement and I am not sure it is even possible given the output type of some of the small plug and play systems that are often used.

 

[dbuckley]

Second my question about the UPS being synced to the utility was addressed a statement made by another member that said "all UPS's are synced to the utility. I don't believe that is a correct statement and I am not sure it is even possible given the output type of some of the small plug and play systems that are often used.

That would be me

Its only double conversion UPSs where one gets the theoretical choice of whether to sync or not sync, as the inverter mechanism is separate and distinct from the incoming supply during normal operation. All other types of UPS dont have the capability to not have the output syncronised tothe input when the input is present. Most serious size UPSs (from a few KVA up) are double conversion.

Smaller UPSs either use a single transformer for both battery charging and inverting, and so that transformer is by definition absolutely in phase with the mains supplying it, and thus the output of the UPS is syncronised tothe mains feed. Another sort uses the big transformer and inverter only when incoming power has failed and normally the incoming power is static switched to the outgoing sockets. There is a smaller transformer for battery charging. Should the supply fail then the inverter starts up in phase with then lost incoming power and takes the outgoing load.

If there are any examples where there are unsyncronised UPSs I'd really like to know about them. My curiosity is piqued!

The only time this type of technology is used with the output unsyncronised to the incoming power is where you have 60Hz in and want 50Hz out and then you dont want a bypass at all! Often this type of "UPS" isn't a UPS at all, it has no batteries, its just used for frequency conversion.

In its normal form, rotary (flywheel) UPSs stay syncronised too. But they are a whole different (and facinating) kettle of fish...

 

[don_resqcapt19]

dbuckly,
Sure, the output of non-dual conversion UPS's are synced when on utility power, but the inverter output is never synced with the utility.

 

[dbuckley]

dbuckly,
Sure, the output of non-dual conversion UPS's are synced when on utility power, but the inverter output is never synced with the utility.

Absolutely - on a non-dual conversion UPS, when the inverter is on, the utility has gone

 

[dbuckley]

Time for me to eat a little humble pie - A UPS from a proper manufacturer that supports non-syncronised operation has crossed my path. The Toshiba 1000 series UPS can operate in the normal syncronised manner or:

Output frequency can hard set at 50 or 60 Hz by installing an optional software upgrade. This upgrade enables the user to select a fixed output frequency and simultaneously disables the bypass mode.

So if you need fixed frequency output, and are willing to operate with no bypass then it can be done.

Of course, no bypass means no ability to achive fault clearing for reasons already outlined. But if what you need is a 60Hz to50Hz converter (or vice versa) then this box'll do that n'all.

(Edited to note that many of the Toshiba UPSs appear to offer a "free run" mode without bypass.)

Theres also at least one other manufacturer that offers 60Hz out irrespective of input frequency, but this UPS is intended for home theatre systems, so I'm inclined to think it more of a tool to part an audiophool from his money, along with those $500/m cables...

 

[got_nailed]

I keep reading this and I know I have seen a rack mount 20 amp 120 volt automatic transfer switch made for computer servers. I have been looking for it but can not find it. APC made it and might want to give them a call if you?re still looking at doing something like this.

 

[Smart $]

That works for me.

Additionally, the receptacles had better be rated 40A. Two supplies—each with an ocpd rating 20A—is capable of delivering 40A to and beyond the point where they are tied together... and if the circuit(s) are extended to more than one outlet, rather large wire (#8 Cu) would be required for the continuation.

The receptacle(s) aspect would fall in the 210.21 to 210.24 area, if I'm not mistaken.

 

[mattsilkwood]

to hell with what article it violates it is supplying a rec at 40a thats enough for me.

 

[jrannis]

It is not the best design but I would guess that the load may not be just a duplex receptacle but represents a "load".

This load could be plugged in to two different sources if it was designed to operate that way.
Maybe the designer saw something like that once and was doing his best to describe it to you.
My guess is that it would be something like a double corded server.

 

[doubleE]

I keep reading this and I know I have seen a rack mount 20 amp 120 volt automatic transfer switch made for computer servers. I have been looking for it but can not find it. APC made it and might want to give them a call if you?re still looking at doing something like this.

After talking with client more, it looks like this is the way they're going to go. The two feeds only touch each other at a rack ATS designed for two feeds. I'm not sure if it was a miscommunication by a non-electrically inclined person or if they were really going to feed both to one receptacle but changed their mind now, but I can breathe easier now.

 

[doubleE]

Concurrent maintainability!!! - You can switch off the UPS output to work on the distribution panel without dropping service and without needing to work live. These are big benefits.

This makes the most sense to me. This is a critical facility, so being able to service the UPS panel without killing the service would definitely be beneficial.

 

[got_nailed]

When I read your post I thought of something.

Try playing with this http://www.apc.com/tools/selector/pdu/

You need to play with that but it has some close stuff. APC will costume build what you want if you have the cash.

 

[dbuckley]

For rack level stuff, look at Raritan power management solutions. The data centr ops may already use Raritan KVM switches, and then they can have integrated remote power control.

 

[mileschamb]

Charles - totally agree. Most, though, are missing the point that the UPS will hardly ever be in phase with the utility source - especially if double conversion!!! I'd love to see it when turned on...

Miles from Mountlake Terrace.

 

[wthomas]

DON'T DO IT without an interlock!

DON'T DO IT without an interlock!

Without speaking to the code, this installtion is not safe!

The UPS and the Service will have a common neutral (through the ground). When in operation, the UPS voltage will NOT be in sync with the power system unless special provisions are made to synchronize them. You therefore will have a short circuit between two points at different potentials if both branch circuit breakers are ever turned on at the same time.

This is safe to do IF you interlock the two branch circuit breakers so only one can be on at any given time.

 

[dave__asdf]

ups tech

ups tech

wow, this is a huge post! i'm a ups technician, i see similar setups a lot. i don't think they are going to have the two in parallel normally. if so, it's stupid, but if it's there as a maintenance bypass it's totally normal. under normal conditions the ups is running and the bypass breaker to the recpt is open. to transfer to bypass you would place the UPS on internal bypass then close the bypass breaker, then power down the ups.

that ups will normally be synced to the incomming or bypass power but that wouldnt matter. if there was a parallel backfeed to it when it was operating on inverter the output filter would circulate enough current to put the UPS in overload then transfer to internal bypass automaticall.y.