# Complex electronic circuit design

Discussion in 'General Electronics Discussion' started by Aivaras Kazakevičius, Sep 1, 2015.

1. ### Aivaras Kazakevičius

2
0
Sep 1, 2015
Hello people,

I have an assignment to create an electronic circuit but I'm not an electronics specialist. Therefore i'm looking for some help.

First of all - here's some information: the electronic circuit I have to design should consist of 4 terminal blocks that are connect to main power supply from local electric network via 16 A circuit breakers. Then I have a set of devices that should be connected to the terminal blocks via their separate power supplies, controllers, and circuit breakers.

The problems arise when I need to choose and put circuit breakers into my scheme. The key problem is that I simply have no idea how to choose them. Most of the devices I need to connect into those 4 smaller circuits have labels on them stating only VAC supply,but the only circuit breaker amperage determination i know is to dived the maximum power of a device by the maximum VAC value on the label and multiply by 1.25. Is there another way to find out the amperage of a circuit breaker I need?

Anyway that's only the first of my problems, but I think solving this would really get me going further.

Sorry if my English is hard to follow, I'm not really a native speaker.

2. ### Alec_t

2,970
805
Jul 7, 2015
Your calculation above will give you the load current for a purely resistive load. Is your 1.25 multiplier to allow for some margin, or for the power factor of the load? Bear in mind that many power ratings assume a steady state and don't allow for startup surges and inrush current (such as occurs in motors etc).

3. ### Aivaras Kazakevičius

2
0
Sep 1, 2015
Thank you Alec_t. The 1.25 multiplier is required by the National Electrical Code of USA and some other countries in central America. I got this info from a simple guide on determining the amperage of circuit breakers. I probably should look for European-like regulations. Anyway, this equation gives me the amperage that should be close to the exact value. And if some current spikes would occur, the current breaker should simply switch off right? My problem is that most of devices I'm about to use do not present maximum power value... And since I can't find it in datasheets, I can't apply the equation. So maybe there is another way to determine the amperage?

4. ### Alec_t

2,970
805
Jul 7, 2015
Use an Ammeter? Or a current transformer plus meter?