Installing a UPS on a UPS
Installing a UPS on a UPS
(OP)
I'm maintaining a data center here in Texas, we have a Liebert UPS (4 750KVA modules per UPS with redundancy). In talking with building engineers, Leibert Techs, other electricians, i have learned you are not supposed to install a UPS on a UPS. My question is why. The only answer i get is "you just don't". The reason I'm asking is there are a number of cabinets, same make, with three UPS's in each one that give us quite a bit of grief. The owners of the cabinets insist on having the UPS's. They are not very reliable, and they drag our power factor way down, less than 70% in cases where they are the only equipment on a Power Distribution Unit. The owners want to blame our power supply, but they get the same protected power as anyone else on the floor yet they are the only one with problems. So if you shouldn't put a UPS on a UPS any body know why?






RE: Installing a UPS on a UPS
Have you put your UPS's in series--so that if one fails, nothing gets through (do you have a single-line?)?
I have not heard of a UPS that causes a bad power factor.
RE: Installing a UPS on a UPS
Also as ykee sez you can end up with one taking both out.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Installing a UPS on a UPS
RE: Installing a UPS on a UPS
RE: Installing a UPS on a UPS
Bear in mind, that those rack-mount UPS will add additional charge current after an outage, so if you do lose the lieberts and they come back up, those little UPS are going to go into recharge simultaneously, and you'll see a big current spike.
RE: Installing a UPS on a UPS
RE: Installing a UPS on a UPS
In the case that is mentioned by du1dug, I'd be getting rid of the small UPSs. As others have mentioned the reliability of the system will be less than the large UPS system alone.
As for the small UPS manufacturer claiming that the input power to their small units is causing problems, it sounds to me as if they are trying to shift responsibility. A 3kVA unit running off a 3MVA large UPS should have absolutely no problems. Have someone throw a scope on the PDU unit to have a look at the waveform and check the voltage THD to make sure that there is no weird reasonance issues. Present the figures to the manufacturer and tell them to get their **** together.
RE: Installing a UPS on a UPS
RE: Installing a UPS on a UPS
RE: Installing a UPS on a UPS
If they say that and the user pulls his UPSs and then you fail to provide continuous power,(and it happens), then you get all the blame. If the customer has his own UPSs and anything at all goes wrong you get to point at his UPSs.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Installing a UPS on a UPS
Integral UPS units in a rack can cause issues with the supply and you have to be really careful as you could cause problems with other kit on site.
1. Id let them know that your UPS network is proven and there has never been an outage on your site. Explain if you do have an outage how does that affect the infra structure on site like cooling and comms to the racks ? No good having a unit protected if it cant interact.
2. Is it for controlled shut down ? Some servers do have this fitted so that if there is a power outage then the server can detect the utility failure and then shut down safely.
3. emergency power off buttons - these dont link with the kit should a power down be initiated then the rack will ramin live until the batteries run down. Not good if you have the hall EPO system that doesnt kill all the power.
4. Introducing batteries into a hall - electrical supplies are protected and fused. Put a large battery into the hall and you have a power source that can not be isolated.
5. Did I say batteries ? If you have a leak of the electrolite that wrecks the underfloor infrastructure.
6. Did I say batteries ? If you have a fire in the data hall you have a risk present from a battery.
7. Id ask him for a full risk assesment for having batteries in his equipment and then ask him for reassurance that his kit will not have an effect on your kit. Id also see about setting up a standard specification for equipment within the hall. Only kit that is to your specification is allowed in the hall - a bar being placed on non conforming equipment. That way you can keep control.
If your UPS and system is properyl designed then there is no need for a UPS to be within the hall.
Rugged
RE: Installing a UPS on a UPS
If this is in an "Information Technology Equipment Room" per NEC Article 645...
...645.11(2) limits the size of a UPS in the room to 750VA
RE: Installing a UPS on a UPS
RE: Installing a UPS on a UPS
davidbeach is indeed right - I stand corrected.
By the time the customer pays for the reconfiguration of the EPO System, additional rack space, and a cooling surcharge to accommodate there unnecessary heat load they could possibly have a change of heart.
RE: Installing a UPS on a UPS
Good thing is these units are passive and dont require batteries. 2nd supply has to be seperate from the primary source say another UPS else where?