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Metered Rack PDU near @ 22.7 amps on failover.....is that too high?

APC UPS Data Center & Enterprise Solutions Forum

Schneider Electric support forum for our Data Center and Business Power UPS, UPS Accessories, Software, Services, and associated commercial products designed to share knowledge, installation, and configuration.

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jengels_apc
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Metered Rack PDU near @ 22.7 amps on failover.....is that too high?

This was originally posted on APC forums on 5/21/2013


Hey guys,

I am new to this whole power thing but am slowly learning.  We have a rack at a Colo and they are bringing the A Side power down for an entire week.  This leaves each rack running on B side power only.  One of our racks (the SAN and blade server rack) is now at 22.7 amps.  My question is this:  This PDU is on a 32 AMP circuit but the threshold of the PDU itself is 24 amps.  What does or should that mean to me?  Am I too close to tripping a breaker for comfort or am I okay?

The other issue is if we spin up more VM's (20 more to be exact) it will push the amps up closer to 24 amps.

Looking for someone to educate me on the risk of being this close.  The model PDU we are using is: AP8841

1172_pastedImage_0.png


Accepted Solutions
BillP
Administrator Administrator
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298

Re: Metered Rack PDU near @ 22.7 amps on failover.....is that too high?

This reply was originally posted by Angela on APC forums on 5/21/2013


AP8841 PDU is a 30A PDU. Per National Electrical Code here in the US, a circuit is not supposed to use more than 80% of its rating meaning this PDU is de-rated to 24A which is 80% of 30A.

So, your overload threshold is at 24A for the entire PDU because of that 80% rating.

Then each PDU bank (or groups of outlets) is 16A (de-rated 80% from a 20A circuit cause they have 20A breakers) on there I believe so between the two banks, you shouldn't go over 24A and each bank or group of outlets you shouldn't go over 16A.

The breakers actually trip at either 30A (at your panel) or 20A for each bank. It should technically have a 30A breaker and not 32A.

Am I making sense? embarassed

See Answer In Context

5 Replies 5
BillP
Administrator Administrator
Administrator
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299

Re: Metered Rack PDU near @ 22.7 amps on failover.....is that too high?

This reply was originally posted by Angela on APC forums on 5/21/2013


AP8841 PDU is a 30A PDU. Per National Electrical Code here in the US, a circuit is not supposed to use more than 80% of its rating meaning this PDU is de-rated to 24A which is 80% of 30A.

So, your overload threshold is at 24A for the entire PDU because of that 80% rating.

Then each PDU bank (or groups of outlets) is 16A (de-rated 80% from a 20A circuit cause they have 20A breakers) on there I believe so between the two banks, you shouldn't go over 24A and each bank or group of outlets you shouldn't go over 16A.

The breakers actually trip at either 30A (at your panel) or 20A for each bank. It should technically have a 30A breaker and not 32A.

Am I making sense? embarassed

jengels_apc
Cadet
0 Likes
0
298

Metered Rack PDU near @ 22.7 amps on failover.....is that too high?

This was originally posted on APC forums on 5/21/2013


Hey guys,

I am new to this whole power thing but am slowly learning.  We have a rack at a Colo and they are bringing the A Side power down for an entire week.  This leaves each rack running on B side power only.  One of our racks (the SAN and blade server rack) is now at 22.7 amps.  My question is this:  This PDU is on a 32 AMP circuit but the threshold of the PDU itself is 24 amps.  What does or should that mean to me?  Am I too close to tripping a breaker for comfort or am I okay?

The other issue is if we spin up more VM's (20 more to be exact) it will push the amps up closer to 24 amps.

Looking for someone to educate me on the risk of being this close.  The model PDU we are using is: AP8841

1172_pastedImage_0.png

jengels_apc
Cadet
0 Likes
0
298

Re: Metered Rack PDU near @ 22.7 amps on failover.....is that too high?

This was originally posted on APC forums on 5/21/2013


yes.  you are correct on the 30 amp.  My mistake smile  .  I am also managing each bank as you stated above keeping each below 16 Amps.

So if I am understanding you correctly:  Right now I am at 21.6amps total balanced across the two 16 amp banks.  In theory, If I were to run at, let's say .... 25 amps total for a short period (less than 8 hours), (16 amps on one bank and 9 amps on the other) .. how much risk am a I looking at in tripping a breaker? 

BillP
Administrator Administrator
Administrator
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298

Re: Metered Rack PDU near @ 22.7 amps on failover.....is that too high?

This reply was originally posted by Angela on APC forums on 5/21/2013


You're within 5 amps of tripping your upstream breaker which brings the whole PDU down tongue-out

So I would make sure there is no fluctuation and expect the PDU to constantly be alarming you (so you might want to tone down your notification settings during this period).

BillP
Administrator Administrator
Administrator
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298

Re: Metered Rack PDU near @ 22.7 amps on failover.....is that too high?

This reply was originally posted by Angela on APC forums on 5/21/2013


Glad to hear!