Question: I have a brand new acceleration/giro sensor evaluation board which I want to interface with ESP32 via SPI bus. After spending few days trying to make it work, I have discovered that sensors SS(CSB) and MISO pins are permanently HIGH (3.3V). In my code I'm implementing the required power up sequence described in the datasheet on page 23. But Chip Select and MISO of the sensor stay always HIGH, even when it is only connected to DVDD and GND.

I have contacted the technical support. But I wonder maybe there is something I'm not aware of. What could cause such an issue?

[Datasheet of Murata SCC2230 sensor](https://www.murata.com/~/media/webrenewal/products/sensor/pdf/datasheet/datasheet_scc2230-e02.ashx?la=en)

[Datasheet of evaluation board](https://www.murata.com/~/media/webrenewal/products/sensor/pdf/specification/pcbspec_scc2000.ashx?la=en)

Answer: 
> 
> if each individual current enters via Phases R, Y and B, where does
>  the sum of the three currents (that is Ia+Ib+Ic) flow after meeting at
>  the common point of the three phases?
> 
> 
> 

The "sum" current has to be zero because it can't flow anywhere.

> 
> if I were to keep an ammeter, I can individually measure the value of
>  the three currents right? So how exactly does it become zero?
> 
> 
> 

Your ammeter doesn't account for the fact that the three currents have a phase relationship that means they cancel out. Individually they can be measured but I\_red = -(I\_yellow + I\_blue)

Or, I\_red + I\_yellow + I\_blue = 0
[![enter image description here](https://i.stack.imgur.com/PQAe3.png)](https://i.stack.imgur.com/PQAe3.png)

*Figure 1. Three-phase currents sum to zero.*

1. Here we can see that the black and blue phases are at 0.5 of max current and positive. Meanwhile, red is at -1 of max current. They sum to zero.
2. Here we see that black is at +1 while red and blue are at -0.5. They sum to zero.
3. Here we see that blue is at zero. Red is at \$ +\frac{\sqrt 3}{2} \$ max current while black is at \$ -\frac{\sqrt 3}{2} \$. They sum to zero.

The sum to zero will apply at any point along the time axis if you care to do the calculations.

---

From the comments:

> 
> Ok so if the sum of the currents is zero at the meeting point, how does one draw current from this system to power their load?
> 
> 
> 

There is nothing in your question to indicate whether the circuit represents a generator or a load other than the current direction which suggests that the device is consuming current. In any case, it doesn't matter.

Current flows in a circuit. Current in or out of any branch must find its return through the other two. That's what my Figure 1 is demonstrating.

> 
> Moreover, is the sum of currents = 0 only at the neutral/ common point of the three phases?
> 
> 
> 

There is no other point in your circuit where the currents are summed.

If, however, you run the three conductors through a current clamp meter you will have a reading of zero as the currents in one direction must balance those in the opposite direction.

![schematic](https://i.stack.imgur.com/SnAVK.png)

[simulate this circuit](/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fSnAVK.png) – Schematic created using [CircuitLab](https://www.circuitlab.com/)

*Figure 2. Typical three-phase inverter setup.*

Power flows from the battery, to the inverter where it is converted to three-phase AC and from there to the three-phase load.