a shove in the right direction please ! 2365 design project Q3

[lankyone]

Hi guys , hoping someone can help
I was due to finish the 2365 course in April this year but with 2 weeks to go some virus came along ( you might have heard about it ? )
just back into the training centre and got the last science exam finished off with merit so quite a relief .

unfortunately with not being in for so long we have only just got the projects returned with feedback ( and there was lots !! )

I've pushed through and am pretty happy with the work I've produced but just a little stuck on question 3 which is

select with aid of manufacturers data , a suitable range of circuit protective devices for this contract , your selection should be based on the following
prospective short circuit currents
requirements for additional protection and special locations

the answer I had submitted was the following
For this installation I shall be using mainly RCBOs as combined RCD and MCB protection for earth leakage fault , short circuit and overload protection , this will be used to protect all circuits ( at a rating appropriate to each individual circuit that will be specified in a table for Q4 ) apart from the two fridge circuits near the kitchen when will have the RCD element omitted and MCBs used instead to avoid unwanted tripping. A separate risk assessment has shown that as not in public areas and only operated by staff this is acceptable.

All breakers must be rated at 6Ka to ensure they can take the maximum 5Ka prospective short circuit current .

which i was told was outdated and requires additional support anyone have an idea what more they might be looking for and if you've answered this question recently how much did you put into it ?

 

[Mark Wright]

Probably can only be exempt from RCD protection in very rare circumstances, let us know the outcome.

 

[Lister1987]

It is asking you to look at manufacturers data as well so I suspect just stating rcbo or MCB won't suffice. They'll be looking for (not exhaustive list);

• Brand and reasoning behind it
• Device Type (MCB/rcbo)
• Device characteristics (Type A, Type B, Type AC)
• Calculation to support choose of device.

I would imagine simply putting PSCC and PFC values won't be enough, they want information from trip curves.

'I chose X brand device with a y tripping characteristic due to xyz equipment being in use.

A y type device will achieve ADS in X time because.....

You get the idea? The clue is what the question is asking of you, you just have to think why am I being asked to use manufacturers data rather than OSG/7671

 

[lankyone]

thanks guys, so i broke down the reasons for the protective devices , went to manufacturers spec page and copied all of the details with pics etc and all ok thanks for the poiinters

and RE the rcd ommited for the fridges , that was stipulated in the question so just mentioned that and selected appropriate mcb rather than rcbo

thanks again