Monitoring Away From Meter

Hi there,

I have a need to monitor the energy consumption of a rack’s worth of IT kit being installed in my basement.

The description of the emonPi implies that it’s designed to be installed in the vicinity of the main incoming supply meter.

For my requirement, I’d be installing it near the equipment rack, and using the CT on the main power feed to the rack (my budget doesn’t stretch to a managed PDU, unfortunately).

Is this a suitable use case for the emonPi, and will it let me track energy consumption over time as various servers, switches & storage arrays are taken on / offline?


In principle, yes.

However, the power consumption of your racks may well be significantly less that the maximum current of 100 A that the emonPi is designed for, therefore you won’t have the accuracy and resolution - especially at low currents, say below 1 A (250 W) - that you might wish for.

I can probably give you a better guide if you give me some numbers - the maximum running current (or power) and the peak inrush current that you expect to see. I assume it’s all on one phase?

Hi Robert,

accurate figures are hard to come by, from the manufactures, especially PF & inrush values, but this is what I’ve been able to find:

2 x “Server type 1” each with 2 x 460W (2.2A, 30 A inrush) PSU
2 x “Server type 2” each with 2 x 1200W (5.5A) PSU
1 x “SAN type 1” with 2 x 840W x (5A) PSU
2 x “FC Switch” each with 1 x 75W (2A, 21.5A inrush) PSU
1 x "GB Switch) with 1 x 65W (0.3A) PSU



I didn’t expect exact numbers, but of course I had no real idea of what you might have either.
So it looks like a running current of around 50 A ?

So I think the standard emonPi, with standard UK a.c. adapter and standard 100 A split-core c.t. should be fine. The c.t. accuracy spec only goes down to 5 A (hence the reason for asking about powers), but we find it’s reasonable down to 1 - 2 A, and accuracy really only gets a problem below that, as I mentioned.