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Running a C7000 using 3 x 4.8KVA PDUs in an N+N configuration

 
chuckk281
Trusted Contributor

Running a C7000 using 3 x 4.8KVA PDUs in an N+N configuration

A power question from Andrew:

 

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This week I have talked wit two accounts wanting to use C7000 with smaller PDUs 208volt @4.8KVA with configurations that are likely to exceed 4.8KVA on a single PDU.

 

Can a N+N – 6 power supply configuration be supported using 3 PDUs.?

 

I have always approached this from a bank “A” and a bank “B” view point…..

 

A – power supply 1, 2, 3

B – power supply 4, 5, 6

 

To ensure N+N redundancy.

 

 

Using 3 x PDUs:

A – power supply 1, 2  

B  – power supply 3, 4

C  – power supply 5, 6

 

In a N+N configuration does it matter which power supplies are providing power and which are not?

 

My understanding is that all power supplies provide power when the dynamic power setting disabled. So does it matter which 2 power supplies are powered down – in a N+N configuration… will support have problems with a 3 x PDU connected to 6 x powers supplies in a N+N configuration?

 

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Input from Monty:

 

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c-Class N+N redundancy assumes that all the power supplies on a side will lose power at the same time – and the facility is wiring the other side to a service that will NOT lose power.

 

You haven’t described the source of power to the third PDU – but if the facility only has two independent feeds – then the third PDU will be connected to one of them.  This will result in enclosure brownout if that feed used for the two PDUs fails – so not N+N redundant.

 

Regardless of the enclosure Power Mode – all power supplies share the enclosure load equally (exception is the power supplies placed in standby by the Dynamic Power Savings feature, if enabled).

 

If the enclosure configuration can be powered up with only four supplies in N+N power mode, then the other two supplies aren’t needed and will result in brownouts if connected to one of the two feeds.

 

If the enclosure configuration requires six power supplies – then each side needs to be connected to a single feed (this could be from different PDUs on that feed – see the c7000 enclosure installation guide for wiring practices) in order to have N+N protection.

 

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