Plugging in a server rack with UPSes into a room that has its own UPS backup issues

Thank you everyone who's responded. There's been a common theme in some of the responses that I wanted to clarify since I wasn't clear in my original post. This is an upgrade that will replace their current hardware as part of our standard upgrade cycle. We aren't installing this in a data center; it's local hardware meant to run just that site. It's a net negative in heat generation compared to what they currently have and we still hook into the EPO lines, so they have full control of shutdown in an emergency. Despite this clarification, I think the responses have been on point and it's given me enough to come up with some options we can work with.

I'm installing a server rack at a client site that has two APC SMARTUPS 6K UPSs in the bottom of it. I'm getting pushback from the facilities manager at that local site. This person is claiming that since the server room I'm going to install in has its own room UPS, I will cause damage to the components when I plug my UPSes into the room. When asked for details, they are claiming that plugging in a UPS to a room with a built-in UPS will cause damage due to power harmonics.

My knee-jerk reaction is of course that won't happen. However, I'd like to be able to speak intelligently about this and if I'm off base then I'd like to know too. I tried to do some research into the topic myself and went down the rabbit hole pretty quick into electrical design that's beyond my knowledge.

What may this person be talking about? Are they accurate and is it something I need to worry about?

Your typical UPS (i.e., excluding a double-conversion UPS), including all APC SmartUPS that I've worked with in the past, does nothing to the power except when running on batteries. It will draw a little extra power in regular use. When power is restored after an outage, it will draw extra power to charge the batteries. During a power outage they will just monitor the incoming power and wait until it is stable and back in range (e.g., 105V - 125V) before switching from battery to line power. If there is a room/building UPS, your own UPS will never switch to battery power. (Two exceptions: if everything is totally out (in which case, in my opinion, it doesn't matter much because you have no internet connection) or if you have a separate non-UPS power source - i.e., the data center provides both backed up and non-backed up power to your rack. That last possibility seems a bit odd to me, but based on comments it could be a thing in some places.)

So the end result is that from a practical standpoint - energy usage, interference, etc. your UPS is effectively dead-weight if there is a room/building UPS (which itself is hopefully backup by a generator for long-term outages). The only real advantage to your own UPS is that you can setup monitoring (APC has this as a standard feature) to do an orderly shutdown, but that will only apply if the room/building UPS stops working.

However, safety is an important thing. The big red shutdown button (or equivalent) for use in a true emergency - e.g., fire or flood - will shutdown power to everything else but not to your computers. Which means if your rack is part of a fire then you have a serious problem, because power will keep going. Or if everything is getting flooded, you are now pumping power into the rising waters when everything else has been safely shut off.

Plus, unlike your own office where the rack might contain your router, fiber/cable modem, etc., in a data center you are dependent on the provided network connections. If power goes out to everything else, continuing to run your computer might save some data corruption but won't actually keep your web server accessible.

So follow their directions - even though their stated reasons are meaningless.

Every data center/server room I've ever been in and worked in, that had its own UPS system, has prohibited customers, clients, etc. from using their own UPS systems. I can't speak to power harmonics, or any other reason they gave you, but they are correct. You should not install your own UPS systems.

Why would you need your own UPS system if backup power is already provided for you?

Additionally, think of yourself as a "guest". It's not your house; it's their house. Abide by their rules and respect their wishes.

See the accepted answer to this question:

What are the pros and cons of having your own UPS attached to your own server hosted in a data center?