A quick mcb calc for the newbies on here.

[Darkwood]

I just want to see if colleges are teaching correct methods for woking out what mcb would be needed in a certain senerio.

Please dont answer if your experienced in circuit design or if you can see what im curious about.


1. I want to choose a MCB to protect 1 x 400w high pressure sodium fitting, for this reply its 20m clipped direct T&E and no other influences (so for this question dont worry about working the cable size out)- set up with a switch direct to an adjacent C.U. what mcb minimum mcb rating and type should i use?

Note! The running current of a 400w fitting is 2.2amps in this example this takes into account the control gear and losses.

2. I now want to add another 400w high pressure sodium to the circuit ... will the mcb chosen for question 1 be large enough?

 

[danzor]

How would you work it out?

 

[telectrix]

with a pencil. like the constipated mathematician.

 

[Darkwood]

The idea here is to give me your answer, i design commercial and industrial lighting schemes regular ... my ability to work it out isn't in question ive 25yrs exp' but what i have noticed is what i believe is the colleges are not teaches students correctly and leaving them to fall foul of their own calcs when they venture away from domestic to larger installs.

If i show my working out which i will do later it will influence the whole thread, im asking for mcb size not the calcs that got them there as i already know how they are taught to calculate it.

 

[Chr!s]

What Type of Ballest is being used?

 

[Darkwood]

No trick in the question its just standard ballast kit

 

[telectrix]

root through the box of bits till i find one that stays in. LOL.

 

[Chr!s]

No trick in the question its just standard ballast kit

No, but the number of lights per MCB will vary with the type of Ballast.

 

[Darkwood]

Answer first part then 1 standard ballast high pressure sodium 400w... fitting running current 2.2 amps... i want a answer for the loweat rated mcb where nuisance tripping on start-up wont be and issue so type b's out of the equation then

 

[wade88]

D type 63 amp, triple pole.... to allow for future additions and heavy surging..... :30:

 

[telectrix]

D type 63 amp, triple pole.... to allow for future additions and heavy surging..... :30:

and what relevance do your bedroom antics have to do with the thread?????

 

[wade88]

Past experience has just taught me to err on the side of caution when faced with potentially large loads...

 

[staggie65]

Is there a spike on start up?

 

[Darkwood]

Id love to see wade connect his 16mm cable to a light fitting ....

Ive give the initial loads as 400w ....its a high pressure sodium so you should be able to tell me if it will have an inrush without asking ...im not asking about future expansion etc just the smallest mcb's and type for my 2 questions.... its not a trick question i want you to answer as you were taught.

 

[wade88]

I have never had any trouble squeezing into tight spaces in the past my friend.