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daniel-feist avatar image
daniel-feist asked

EM530 vs EM540

I'm planning a residential 3-phase ESS install using 3 x 5kva Multiplus II.

Looking at the meter requirements I purchased a EM530 assuming I needed to use CTs given I have a 3x100A supply (EM540 is max 65A). But, now I've looked at my expected max current I'm only going to have a max of 50-55A on any given phase, even with two 11kW car chargers and all appliances on the go.

So, the question is: Should I use the EM530 I have, but select a 60A CT, or is it really best to send back the EM530 and get the EM540?

Aside from the fact that the installation of the EM540 is simpler, the only difference seems to be "active power" accuracy and minimum current.

EM530 (assuming 5:60 CT):
- Accuracy: 0.5% (>3A), 1% (0.6-3A) (+ 0.5% from CTs so 1-1.5% overall?)
- Min current 0.6A

EM540:
- Accuracy: 1% (>1A), 1.5% (0.5-1A)
- Min current: 0.25A

Looks like it's probably a good idea to switch to EM540 given this. Make sense or am I interpreting things incorrectly? Any thoughts?

ESSEnergy Meter3 phase
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tim-hickman avatar image
tim-hickman answered ·

You could use either if your design current is going to remain <65A/phase. However I might be inclined to stick with the EM530 on CTs as this allows for any changes in the future and the installation of the directly wired meter is not massively simpler.

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daniel-feist avatar image daniel-feist commented ·

I was initially thinking the same as you. But I eventually decided to order the EM540 and send the EM530 back.

Reasons:
- Simpler install, and don't need MCB for voltage connection.
- Install is more resilient to potential issues.
- The direct connect meter (EM540) will be more accurate at lower currents than the EM530, even if I used 5:60A Class 0.5 CTs (and low power accuracy is good for ESS).

This document explains how to think about the total accuracy of meter/CT combinations: https://www.satec-global.com/sites/default/files/Application-note_Accuracy-Class_July2018.pdf

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Sven Bluege avatar image
Sven Bluege answered ·

@Daniel Feist Where did you get the accuracy values from? 0.6A and 230V means, I need at least 138W per phase to get valid readings?

I installed an EM530 + 50/5A clamps today, but get strange readings, especially if there is only the standby power consumption of the house around 70W/phase.

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