Type B or C MCB

[philipbg]

Can anyone help. At the moment I’m working on a library with about 11 power circuits for SSO & a CCTV/security system & 10 lighting circuits which are mostly track mounted LED spots & 2 fluorescent fittings all wired in T&E & MICC fed from a 125A TPN board. The spec calls for 10ka C type MCB or RCBO for fluorescent lighting & 10ka B type MCB or RCBO for power circuits. The problem is the make of dist board I have do not have in the country any B type RCBO so would it matter if I used C type RCBO which are off the shelf at any wholesaler. Plus do I really need RCBO for a library my understanding is if the area is supervised you can get away with MCB & RCBO are just for a house.

Thanks

 

[paulj76]

If the spec calls for type B then type B it has to be although all you seemed to be asking if you needed to use type B for the LED lights which is yes you can use as there is no surge as with fluorescent lights. Nevertheless, if you have the choose of RCBO or MCB go for MCB it is a library for god sake you will not get some nugget hammering in nails all over theplace. If a spark turns up to do any work on the site would have to be a proper spark not some part P house basher who has never seen pyro since the day they left college. The list below may help to confirm any doubts you may have about the use of RCBOs.
Requirements for RCD protection
30 mA
■All socket outlets rated at not more than 20 A and for unsupervised general use
■Mobile equipment rated at not more than 32 A for use outdoors
■All circuits in a bath/shower room
■Preferred for all circuits in a TT system
■All cables installed less than 50 mm from the surface of a wall orpartition (in the safe zones) if the installation is unsupervised, and also at any depth if the construction of the wall or partition includes metallic parts
■In zones 0, 1 and 2 of swimming pool locations
■All circuits in a location containing saunas, etc.
■Socket outlet final circuits not exceeding 32 A in agricultural locations
■Circuits supplying Class II equipment in restrictive conductive locations
■Each socket outlet in caravan parks and marinas and final circuitfor houseboats
■All socket outlet circuits rated not more than 32 A for show stands,etc.
■All socket outlet circuits rated not more than 32 A for construction sites (where reduced low voltage, etc. is not used)
■All socket outlets supplying equipment outside mobile or transportable units
■All circuits in caravans
■All circuits in circuses, etc.
■A circuit supplying Class II heating equipment for floor and ceiling heating systems.

I doubt the council will not have any cows on site nor will it have a sauna so if none of the above applies, use type B MCBs it is in the 17[SUP]th[/SUP] soit cannot be wrong.
If the consultants has been slung off the job for what ever reason maybe there spec is a pile of c**p they can not of been that good or they would still be there.

 

[GLENNSPARK]

this all centres around final circuits intended to be used by unskilled/uninstructed person/s not under supervision....i mean...whats not clear about that?

 

[paulj76]

Not under the supervision of a skilled or instructed person may seem to extend the requirement to include many commercial premises (offices, shops and warehouses) and industrial premises (factories, workshops) and gives the impression that exemptions only apply to installations that are under the supervision of an electrical engineer. This is not the case.
BS 7671:2008 PART 2 DEFINITIONS:
Skilled person.
A person with technical knowledge or sufficient experience to enable him/her to avoid dangers that electricity may create.
Instructed person.
A person adequately advised or supervised by skilled persons to enable him/her to avoid dangers which electricity may create.

 

[Engineer54]

It really doesn't matter what you think or don't think. There is a contractual Specification in place on this project!! Either you, or your employer signed your contract with that specification in place. There really is no ifs or buts about it, you follow the spec's of the job, end of!!

Unless this specification has been taken out of your contractual requirements (And you would have definitly been so informed officially if it had) then you MUST follow them!! Remember the job has been priced and accepted according to those specifications!! Contractual law, is something you really don't want to get into, ..it's a mine field and a costly one for those that crosses that law.

But you don't seem to want to listen, and you obviously know best, so do whatever you want to do...

 

[Knobhead]

Why can’t you accept you are tied in to a contract? It’s not open to discussion on the internet, it’s the rules you will abide by or pay for the consequences.

You have been given a remit, now follow it!

If in the future there are problems you can turn around and say “I told you so”, for now your balls are in a sling!

 

[philipbg]

Thanks to paul76, the only person who came up withanything practical for the information & as I suspected this type ofcommercial building does not require RCBOs. We have never been asked to installthem in any other project nor has any other engineer on the company in acommercial building. We have even spoken to the council’s engineer who is morethan happy to use MCBs on this project & agrees this is classed as acommercial building so not requiring them. However, I have been able to source RCBO from anotherwholesaler so problem solved. As for the spec, the client has told us it is acommon spec they had used on all premises including housing & consultants was anidiot (their words) & only part of it that had any reference to this jobwas the description of the site the rest was just cut & pasted this was thereason they got slung off.

 

[Engineer54]

You still don't get it, do you!! ... Doesn't matter how daft, or how much the specification isn't related to your project, the specification STANDS!! It doesn't matter what has been said by the Council Engineer to you or your company, unless he backs up what has been discussed in writing then nothing has changed!! As i said before your companies contract with the client predisposes that your company has priced and won this project based on the requirements of the contract specification!!!

One more thing, this is a Public Building, which the general public will be using on a daily basis. Public Buildings tend to have a higher specification than a general commercial buildings often to the point where product manufactures or preferred manufactures are specified.


I'm dealing with contractual and specification matters on almost a daily basis, i can assure you it's one area you don't want to mess with, it bites and bites hard too!!!

 

[D80]

I agree with E54, although I don't have as vast an experience.

If spec asked for 10mA RCD protection on sockets and I'd signed up to it that's what they'd have. My arse is covered.

If you're making any changes to spec get it writing! Changing from RCBO down to MCB is quite a big measure and could entail other changes too. A full DB change down, even if adding RCD's could be a nice big cost saver. Will the client see the saving?

 

[philipbg]

The spec calls for 10ka C type MCB or RCBO forfluorescent lighting & 10ka B type MCB or RCBO for powercircuits. So leaving the option open to use either which we are now going to doRCBO in the public areas & MCB on all other circuits back of house. Now Ihave been able to source 10ka B type RCBO this is no longer a problem.