PDU Help for a Novice

[AndyJ]

Hi

I need to buy a PDU for a computer rack and I'm confused about the different ones you can get. Some are for HV and have the big socket type plug (16A) and some have a plain old 13AMP fuse.

To determine which one I need is it as simple as adding up the Ampage draw from all the devices in the rack?

I thought a PDU was passive and wouldn't care less and would just distribute power.

Anyone care to set me straight here.

Cheers

AJ

[Andy Burns]

Most have IEC320 outlets, usually the 10A variety, commonly though of as "kettle leads" (even though there are differences) and sometimes the 16A variety as well/instead. See

just have square 13A sockets, but these tend to eat precious space in a rack quickly and are less popular.

Also the inputs vary from 13A to IEC to "commando plug" to hardwired.

with suitable allowance for startup surge and future expansion.

Nowadays they can be intelligent, you connect to PDU to your LAN and can remotely power off/on individual ports, and measure current drawn either individually or overall.

For example

the "zero U" versions are becoming more popular as they mount vertically in the side of racks rather than tackign up more precious space by eating a "U" themselves.

HTH.

[AndyJ]

Thanks for this.

Here is what I think I need:

I will have a max of 8 servers and each server is drawing approx 1.25 amps which makes a total of 10 amps.

Will a PDU that has an input from a 13 AMP plug from the mains (240V) and an output of 240v for each server be enough for this setup? I'm assuming it will as it will not exceed the 13AMP fuse rating in the plug for the PDU.

So if I were to plug other servers into the PDU which drew over the

13AMP Fuse rating I would blow the fuse.

In this case what are my options if I needed to add more servers?

Thanks for your help, I'm struggling a bit with this one!!!

AJ

Andy Burns wrote:

[Andy Burns]

One feature the "intelligent" ones have, which helps high startup current, is to stagger the startup of each socket, so that you don't get all servers powering up and in turn powering up all their hard drives at once. Also can help to make sure e.g switches, domain controllers and DNS servers are up, before email and file servers come online.

Sounds like 13A should be fine for you, but just remember servers have been getting greedier for years, unless you overspec, you might have to replace the PDU when you upgrade servers.

Also the PDU becomes a single point of failure, unless the servers have dual power supplies, but then you need two PDUs, feeding the PSUs in left and right banks, that's how my biggest customer sites now run.

[AndyJ]

Thanks again.

So if I only wanted one PDU and wanted to support say 16AMP could I just pop a 16AMP fuse in a normal plug and buy a 16AMP rated PDU? or do all the 16AMP PDU come with other input connections requiring you to hardwire or the commando style socket plugs?

If I were to go the hardwire route (seperate radial circuit from the CU) and wired into a junction box would the MCB provide protection for my servers or is there a fuse in the PDU itself? I wouldn't be doing this leccy work myself of course!!!

Cheers

AJ

Andy Burns wrote:

[AndyJ]

Thanks again.

So if I only wanted one PDU and wanted to support say 16AMP could I just pop a 16AMP fuse in a normal plug and buy a 16AMP rated PDU? or do all the 16AMP PDU come with other input connections requiring you to hardwire or the commando style socket plugs?

If I were to go the hardwire route (seperate radial circuit from the CU) and wired into a junction box would the MCB provide protection for my servers or is there a fuse in the PDU itself? I wouldn't be doing this leccy work myself of course!!!

Cheers

AJ

Andy Burns wrote:

[AndyJ]

Thanks again.

So if I only wanted one PDU and wanted to support say 16AMP could I just pop a 16AMP fuse in a normal plug and buy a 16AMP rated PDU? or do all the 16AMP PDU come with other input connections requiring you to hardwire or the commando style socket plugs?

If I were to go the hardwire route (seperate radial circuit from the CU) and wired into a junction box would the MCB provide protection for my servers or is there a fuse in the PDU itself? I wouldn't be doing this leccy work myself of course!!!

Cheers

AJ

Andy Burns wrote:

[Andy Burns]

Wel,, no, you should never have a 13A plus with more than a 13A fuse in it, if you need e.g. 15A then a commando be your easiest option, but presumably would require a dedicated radial, rather than being fed from a ring circuit, we're getting out of DIY territory at this point, especially if this is an office environment ....

for 16A either commando, or the larger IEC connector, for 30A either the bigger commando, or hardwire.

Some of them have fuses, not sure if all, probably best to ask someone else about what protection you need vs what the PDU provides, obviously there is none between the PDU and server as IEC leads are not fused.

Actually when I was thinking of hardwired, that wasn't direct to the PDU, the UPS was hardwired in 3-phase with a rotary lockable isolator, then 16A large IEC connectors to the PDUs, then small IEC connectors to the servers.

[AndyJ]

Great that's it I am all straightened out now. I never realised that a plug was only rated at 13AMP but must admit to never seeing anything higher than a 13AMP fuse in one so this is what made me think!

Thanks for all your help.

Now I'm going to blow myself up! just kidding of course :)

Cheers

AJ

Andy Burns wrote: