Converting NEMA L5-30P to NEMA 5-15P

[BillP]

I'm looking at a 3U or 4U SmartUPS to go in my rack to replace the several 2Us I have.  I'm not sure exactly which model but the ones I've looked at all have one thing in common: a NEMA L5-30P plug.  I unfortunately do not have a 30A line in my apartment (maybe when I get a house, I'll run one but for the time being, I have no say in the matter).  I was looking at a L5-30R to 5-15P adapter that have were sold through various outlets online but I have serious reservations about going this route.  I think of it like this: the system (UPS) was designed to pull up to 30A.  That's why it has that cable gauge/plug selected.  If you decide you want to choke the current down to 15A with that adapter, you could blow a breaker or worse if the current spikes over 15A.  I found this article from APC posted:

https://www.apc.com/us/en/faqs/index?page=content&id=FA156517&actp=search&viewlocale=en_US

At the end it said it would effectively change the unit from a 3000VA to a 1500VA (example).  I suppose my questions are:
-How safe really is this to do?  I'd like to know the technical reasons behind it.
-Would I be able to utilize the full capacity of the battery?  What I mean is I have all my server components plugged into one outlet, so obviously it's less than 15A.  (I'm not home right now, I forgot but can find out and update later).  The battery capacity on a 4U is going to be much higher than one on a 2U UPS.  Would I be able to utilize that capacity if I were to switch to a 15A plug or would the batteries not charge all the way and not be able to utilize their full capacity? 

Thanks!

[Brad_C · Accepted solution]

I have an SU2200 and SUA3000 here. Both have IEC C19 sockets on them (15A and real volts). Our sockets are generally 10A.

I measured the peak consumption of the UPS while charging batteries (a couple of hundred watts) and sized my load at ~700W. On a 2400W outlet I never get close even with full load and charging batteries, so I made an appropriate lead up.

The UPS will still manage full load on batteries, but if I was stupid enough to load it to rated capacity, it'd certainly pop the breaker when under load and charging the battery.

If you have a socket big enough to manage your full load plus a couple of hundred watts to charge the batteries then you'll probably be ok. If you have the right gear you can measure your load and UPS overhead (while charging completely depleted batteries) and do the maths.

The supply input won't limit your on-battery capacity. It might smoke the cable to the socket if you don't do the maths properly  though.