MCB Trips


voltage 230 v, 3 CT sensors, Arduino 328p, mysensors ,pimatic

  1. measuring apparent power. so no voltage measure using AC-AC transformer across phases .
  2. CTs are connected after MCB to each phase in 3 phase supply.
  3. getting Irms current reading using CT sensors and arduino atmega 328p.

the setup works for some time ( getting reading) and then main MCB trip. not sure why?

Taking full precaution since playing with high voltage can be dangerous


You are putting yourself and anyone who touches the equipment and anything connected to it in danger of electrocution should you get anything wrong or should a fault develop anywhere on the power network.

Your main MCB trips because you have an overcurrent fault somewhere - unless it is an RCBO in which case you might have excessive earth fault current instead or as well.

In any case, you will still be able to measure active and reactive power (up to a point) even when you use an ac adapter, so your reason for not using it is ill-conceived and dangerous. It is nothing to smile about.

Wow!! I fully understand the danger of working with live current and your point is fully acknowledged.

Now coming back to question…

Why AC-AC adapter is strongly advise. does it has impact on reading only which i know or it can lead to hazardous situation? For voltage, can’t I safely assume constant value ~230v.

Now the point as to why MCB tripped twice. not sure why, but after removing CT sensors tripping stopped. yeah, i know it may be because of over current , earth fault etc.

My hypothesis is that, may be while clamping CT sensors the extra weight of CT sensors on phase wire can lead to MCB trips while testing. But not fully sure. may be need to check my electrical wiring from my main MCB to other circuit breaker for individual room . It may require to further tightening. will call the electrician for that.

If you are not qualified and experienced with electrical installation practice, then, given that you appear to have created a fault on your system, you must have the installation checked by a competent person without delay.

Installing split-core current transformers should normally be safe and should have absolutely no effect on the installation. If adding the few tens of grams weight has created a fault, then there was something very seriously wrong before you started.

From your questions, I don’t believe you do fully understand the dangers that you face. The a.c. adapter isolates your Arduino/emonTx from the mains supply. If you make a direct connection, and the neutral connection breaks outside your house, then everything - your emonTx/emonPi/Arduino and the computer and anything else connected to it becomes live at the full mains voltage - even the cases and connectors that you think only have low voltages will be live. Did you realise that?

You must have the a.c. adapter if you need to measure reactive power. If you assume 230 V, you do not have a voltage against which you can measure the relative phase of the current, so you will have no means to know how the power resolves into real and reactive components.

If you don’t have an c adapter, you can only estimate VA - apparent power - based on the supply voltage you assume. That’s why when you said “no voltage AC-AC transformer is used”, I understood you to mean that you had directly connected to the mains electricity supply and that was the cause of your breaker tripping.

no .no ,

Actually,I am trying to measure 3 phase power usage across home . Using 3 CT sensors for measuring currents across phases . Using Atmel 328p microcontroller to measure the the Irms current reading and using an AC-DC adaptor to get 5v ~1A supply. reading are calibrated and fairly accurate. Not using any AC-AC transformer to measure the voltage across the phases. electrical installation only have MCB installed and don’t have RCB/RCCB installed. Now I think RCB is must for safety.

So you’re trying not to measure reactive power then after all? It would have saved a lot of misunderstanding if you had not used the wrong words.

OK, then what I wrote above about a fault that must be attended to urgently remains the case.