Most likely Electrical fault for this situation?

[Leroy Grant]

Hello everyone, I am currently doing a level 3 Electrical Installation course and I am doing one of my assignments. I was just wondering if I could get any views on this question I've been posed.

What is the most likely electrical fault for this Symptom?

A fault has occurred on a lighting circuit in the glasshouse area, so that when it is switched on RCBO protecting the circuit operates?

Thank you.

 

[peppers]

Earth fault causing imbalance between L-N on RCBO output side

 

[DPG]

What are your thoughts? Remember with an RCBO there are two separate types of fault that could cause it to trip - think of the two types of protection it is providing. Daz

 

[Leroy Grant]

Just spoke to my lecturer and he has confirmed what you said pepper, thank you both very much.

 

[peppers]

I knew those 4 years at college would come in handy one day.

 

[Richard Burns]

It is normally good practice to post what your ideas on the answer are before asking for homework help, this allows you to learn rather than just copying information.

Think about why an RCD will trip and what sort of fault causes this.
Think about why an MCB will trip and what sort of fault causes this.

The fault occurs as the circuit is switched on so the fault is present all the time and will be likely to be a fault in the wiring.

How would you test for either fault?
As you have a both an MCB and RCD in the one RCBO unit you would need to differentiate between the two types of fault to find the cause.
The likelihood of a fault is difficult to specify, but one of them occurs at a much lower current so may be considered more likely to occur especially considering the location.

 

[telectrix]

could even be an obcure fault like cat pi$$ in the light switch now that we're mounting then so ridiculously low down.

 

[peppers]

Now that leroy's got the answer he might decide to find out why it is what it is (hopefully), if not, he's probably decided to struggle through college by blagging his way through untill he comes to the conclusion it's not for him. Either way I don't like to see people squirm.