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#143734 - 08/29/05 03:27 PM Mcb's used as functional switches?  
aland  Offline
Joined: May 2004
Posts: 186
United Kingdom
Hi Guys, been out of circulation for a while, trust that your all in good health.
Anyone got any thoughts on the use of Mcb's as functional switch's? Just done a periodic inspection on a pub, noticed that the dis board was behind the bar and the mcb's are being used to switch the lights on and off, no light switch's anywhere. Anyone know if BS7671 accomodates this? Imput apreciated Regards AlanD.

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#143735 - 08/29/05 03:42 PM Re: Mcb's used as functional switches?  
gideonr  Offline
Joined: Dec 2004
Posts: 161
Edinburgh, Scotland, UK
Hmmmm, should be rated for the job, though not sure how many operations they'll cope with.

There might be building regs violations in that light switches should be accessable to disabled employees, accessable for safety reasons, and accessable for energy saving reasons.

#143736 - 08/29/05 08:14 PM Re: Mcb's used as functional switches?  
Trumpy  Offline

Joined: Jul 2002
Posts: 8,223
SI,New Zealand
Long time no see mate, welcome back. [Linked Image]
I don't have a problem with it myself, just as long as there is more than one circuit for the lights in that particular area.
Just going to throw this link into the ring again:
TLC Direct Electrician's Guide Contents Page

#143737 - 08/30/05 06:11 AM Re: Mcb's used as functional switches?  
britspark  Offline
Joined: May 2005
Posts: 54
southampton united kingdom
hi mate, in regard to using MCB`s as switches, well personally i would not do this and would advise that the installation is fitted with loght switches to turn the lights on or off,

are there emergency lighting fittings on the same lighting circuit?

as the local authority will require that the emergency lighting is connected to the local lighting supply, by switching out the MCB the supply is lost to the emergency lighting,

not a good idea in my book, and we specialise in the license trade.


#143738 - 08/30/05 06:50 PM Re: Mcb's used as functional switches?  
aland  Offline
Joined: May 2004
Posts: 186
United Kingdom
gideonr, Mike,britspark thanks for the info, like you mike in some rspects I dont have a problem with it in theory; but as britspark pointed out the e-lighting has to be on a seperate breaker so is only active when total failure occures, marked it as all unsatisfactory anyway. Yet another disgruntled customer! Thanks again gents. aland.

#143739 - 08/31/05 08:41 PM Re: Mcb's used as functional switches?  
aussie240  Offline
Joined: Jul 2005
Posts: 223
Blue Mountains, NSW, Australia
One objection in using MCB's as a conventional switch is that mechanically they aren't designed for the purpose, having a lesser number of on/off cycles as compared to a proper switch. A few years ago I was shown the insides of a Westinghouse Quicklag breaker used as a switch and observed that the copper braid to the moving contact wasn't in very good shape from the continuous flexing.
This particular breaker was being used as a main switch for a laboratory; rather than turn off all the equipment individually at the end of the day, the main circuit breaker was just used to turn off the whole lot instead.
Having said that, other MCB's might fare better. The problem was solved simply by fitting a 45A 3phase switch at the bottom of the breaker panel for the staff to use instead.

#143740 - 09/01/05 04:18 AM Re: Mcb's used as functional switches?  
kiwi  Offline
Joined: Dec 2004
Posts: 354
christchurch new zealand
Aussie240 is right. MCBs have only a fraction of the switching endurance of a light switch.

MCBs are only required by AS/NZS approvals testing to perform 1000 switching operations at full load, whereas light switches are required to do tens of thousands.

MCBs were never intended for control of a load, only isolation for servicing and overcurrent disconnection.

#143741 - 09/02/05 01:40 AM Re: Mcb's used as functional switches?  
Trumpy  Offline

Joined: Jul 2002
Posts: 8,223
SI,New Zealand
Some good comments here.
What I would be thinking of in terms of using MCB's as the isolation point in the circuit, with the continued switching of the MCB cause it's primary function to be lessened?.
It is switching under the full load of the circuit, where as a functional switch usually only switches a portion of the load on that particular MCB.
As far as E-lighting goes, it is supposed to be fed from it's own MCB that is taken straight off of the Main Switch and is it's own dedicated circuit.
Mind you, the number of times I've inspected the E-lights at Commercial premises (pubs mainly) and found the Batteries flat because the MCB had tripped and no-one ever noticed it would suggest that a lot of owners have little knowledge or just don't care about those that use thier facilities.
We had a fire in a 3-Phase pillar box here outside a pub about 3 years ago.
The E-lighting never even attempted to start, mainly because some upon investigation, some idiot had replaced the MCB for the circuit, but had installed it upside down and had left it OFF, basic testing would have found that fault.
But what a bloody panic that was, getting 200 drunken kids out of a dark pub at 2 in the morning.
Those that didn't want to have a fight with us FF's, were trying to find thier way out, with little success.

#143742 - 09/02/05 02:47 PM Re: Mcb's used as functional switches?  
Texas_Ranger  Offline
Joined: Dec 2001
Posts: 2,405
Vienna, Austria
At school the laboratory benches are controlled by breakers that are operated quite often. Most of them don't hold up too well any more (sometimes can't switch them on), so I don't think it's such a good idea.

#143743 - 09/02/05 04:20 PM Re: Mcb's used as functional switches?  
mxslick  Offline
Joined: Oct 2004
Posts: 803
Atomic City, ID USA
Here in the US you can get some brands of breaker with a "SWD" marking. (Switch duty, usually for large banks of discharge lighting.)

There is also HACR ("hacker") rated breakers for the loads imposed by heating and air conditioning equipment.

Is there any such standard for MCB's overseas?

Stupid should be painful.

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