Practical Preparation.

[Mr Curnow]

In the practical preparation which I have on monday next week, do I write down the tools that I will be needing aswell or just the equipment?

I posted a thread before on this but no one really said anything about tools.
But I am not sure if they told us to improve on the stuff I had already wrote down which is here.

If someone could just talk me through it for a few minutes then that would be great.

 

[Mr Curnow]

I don't need to do continuity of final ring circuit conductors because I don't have a ring, it's radial.

 

[Adam_glover18]

Your test must differ from the one I did pal

 

[Mr Curnow]

I need to answer why the 20A and the 6A protective device is satisfactory for the circuits. Also why is the KA rating of the device satisfactory? It is a 6KA protective short circuit protective device.

 

[Mr Curnow]

Also what are the function tests that you have to do?

 

[Mr Curnow]

I have to resit the practical, I want to know:

Why is the B type MCB suitable for the installation?
Why is the current rating of the MCB suitable?
Why is the KA rating of the MCB suitable?
What are the functional tests?

 

[malcolmsanford]

1. To be honest not knowing the circuit hard to advise, but I would assume all loads are resistive.

2. Same as above but I would assume than In is greater than Ib but less than Iz

3. This would depend on your PFC and the value of it, what is this

4. making sure the mechanics side of the circuit is working, switches, MCBs RCDs etc etc.

But to be honest sir what level are you at to need ot ask these.

 

[Mr Curnow]

The circuit has lights and sockets so it is resistive.

 

[malcolmsanford]

So why is a B type breaker used for such a load. ??

 

[Mr Curnow]

Are you asking me to give an explanation or do you think that I shouldn't be using it?

 

[malcolmsanford]

I'm asking you why do you think you would use a B trype MCB for an resistive load

 

[Mr Curnow]

The type B MCB is used for a resistive circuit, that's what you said.

But I was told from a mate at college that a type B was used for lower startup currents.

Sorry but I don't know these things because my practical teacher can't teach for his life, that's why half my classed failed the exam.

 

[malcolmsanford]

Then it is time to change colleges son to be honest.

Your mate is right you would use the B type MCB for lights, providing they are just normal house type lights and sockets, as there is little chance of the breaker tripping due to inrush currents that you would get on Inductive loads such as motor and HF lighting.

So the 2nd answer I gave can you explain what I did and why the breaker in your scenario was suitable??

 

[Mr Curnow]

You would choose an MCB which would trip before the current carrying capacity of the cable is reached, a 20A mcb would be used for a circuit containing sockets to stop the current reaching 32A, therefore protecting the cable from damage.

Oh and if I pass this years course then I am going to look for an apprenticeship, much better way into the trade, what do you think?

 

[malcolmsanford]

Yes you have the general gist of it, the protection device is there to protect the cable not any type of appliance.

I could write a whole script on circuit design and to be honest without going over it with you in person it would be pointless. There are a load of books out there by Brian Scadden, Chris Kitcher. John Whitfield that will help and appendix 4 page 255 section no 3 of the regs is also a guide.

Yes try and get yourself into the industry via an apprenticeship if you can, IMO it is the best route you can take.

I do feel sorry for you if your experience at college is not giving you what you need, and by the looks of things it isn't. This is a good place to come for help and advice, but I'm afraid it is no substitute for actually teaching you the trade.

 

[Mr Curnow]

Well you got that right, no way is it a substitute for practical experience at college. Next year at college I don't get any practical, the reason why I am going to look for an apprenticeship.

The KA rating is the rating the protective device will continue to function correctly in case of fault currents. Is that right?