Question regaurding Overload/Max Amps

[Anonymous user]

Hi there,

First i wanted to say thanks. This forum has always provided me with good information.. so good work 🙂

On to the issue at hand. In regarding to PDU AP 7932, and 7930. We have some confusion amongst people here regarding what the acceptable load for these units are. They are either advertised as 20a or 30a PDUs, but the problem is people seem to think this is the max continuous load these guys can handle. I know otherwise, and know the default 16a Overload is set that way by APC for a reason. I read that you want it to be less the 80% capacity. I just lack the ability to explain why we shouldnt ever go above 16a.

We have some units running at 19amp loads on a 7932. What im looking for is a simple "plain English" explanation as to why this is bad. Or if its not bad, why its not bad, so i can relay the information and clear up confusions.

Thanks!!

Message was edited by: kungfu1

Message was edited by: kungfu1

[Anonymous user]

Thanks for the reply.

So in the case of say, a AP7932, its 30a but is split into 2, 20a circuits from what I understand? So even though its 30a, its still unsafe to run, for example, a 19a load (10amp on bank a, 9amp on bank b) continuously on that unit?

thanks!

Message was edited by: kungfu1

[BillP]

per National Electrical Code, a circuit should not exceed more than 80% of its breaker size.

thus, PDUs and UPSs, etc will have a 15 amp plug and be rated for 12 amps or have a 30 amp plug and only be rated at 24 amps. it is important to note that the breaker would trip at its actual rating - meaning the 15 amp plug would be plugged into a 15 amp breaker and trip when it hits 15 or the 30 amp circuit would actually trip at 30 amps.

[take a look at this article for further info too|http://nam-en.apc.com/cgi-bin/nam_en.cfg/php/enduser/std_adp.php?p_faqid=1123]

let us know if you need anything else!

[BillP]

i'll double check tomorrow but you probably mean this has two separate banks on the rPDU. without checking, I am not sure what they are rated at but it should be 80% of whatever the breaker size is on the top of the rPDU.

you should basically distribute the power amongst the banks evenly.

the entire rPDU itself though should not exceed 24 amps, since it has a 30 amp plug on it.

i'll double check tomorrow on what i mentioned here about the banks but i am pretty sure i got that right 🙂

[Anonymous user]

Great, thanks. Im just a little confused since APC's default setting for Overload is 16a on that unit. I wasnt sure if you shouldnt exceed 16a since theres two 20 amp banks and 80% of 20 is 16. We just had a situation where a PDU died entirely, totally dead and it was under a 19a load, it was a 7932 and im wondering if that load fried the thing over time, or if it was just a bad unit. And again, why the default overload is 16a.

thanks

[Anonymous user]

Gonna reply to myself here as some late-night poking around has yielded the results I was looking for.

I hope others find this useful as well.

Using the AP7932 as an example -

This is a 30a PDU. This model has two banks. Each bank has a 20a breaker, there for you want to balance things evenly between the two banks. If one bank gets overloaded, the breaker will pop, but you only lose half your stuff. Thats a big advantage obviously.

Regardless of the 20a breakers for each bank, this PDU is still a 30a (TOTAL) PDU, but derated to 24a (TOTAL) (30 -80% for electrical code). There for, the overload setting on this PDU should be 24a.

The reason why, in the rPDU web interface/config, even with this model the default setting for overload is 16a, which didnt make sense, is because the rpdu version is model agnostic. It doesnt care what model you have, it just assumes you have a 20a PDU, which 16a overload would be correct for. So if you have a 30a guy, you need to set that to 24a.

Thanks for your replies, feel free to verify what I stated here.

One last question - Does this model (or any model) do staggering by default (power sequencing)? I know the power-on delay can be set through the configs, but ive noticed its set to 0 by default which leads me to believe that by default if the PDU does a cold start, all outlets turn on at the same time and there is no staggering by default. Is this true? If this is true, then to solve that problem id just have to go in and select some/all of the ports and configure them with a power-on delay, correct?

Thanks again and I hope any information i provided here is helpful to others as well.

Message was edited by: kungfu1

[BillP]

>

One last question - Does this model (or any model) do staggering by default (power sequencing)? I know the power-on delay can be set through the configs, but ive noticed its set to 0 by default which leads me to believe that by default if the PDU does a cold start, all outlets turn on at the same time and there is no staggering by default. Is this true? If this is true, then to solve that problem id just have to go in and select some/all of the ports and configure them with a power-on delay, correct?

Message was edited by: kungfu1>

To answer this question, no by default they will all be set to 0 (or instant power on). The reason being is that we try to make no assumptions about what a customer may need for time delays (as they could potentially vary wildly depending on what a customer is using). As a result, so that we do not create any conflicts from unusably timed staggers, we set them to instantly power on by default. If you wish to, or need to stagger, you would as you mention simply go into the port and configure whatever power-on delay is required by your setup.

[Anonymous user · Accepted solution]

Thanks guys!

Youre always very helpful in answering questions.