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Posted By: aland Mcb's used as functional switches? - 08/29/05 08:27 PM
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.
Posted By: gideonr Re: Mcb's used as functional switches? - 08/29/05 08:42 PM
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.
Posted By: Trumpy Re: Mcb's used as functional switches? - 08/30/05 01:14 AM
Alan!,
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
Posted By: britspark Re: Mcb's used as functional switches? - 08/30/05 11:11 AM
aland,
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.

Britspark
Posted By: aland Re: Mcb's used as functional switches? - 08/30/05 11:50 PM
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.
Posted By: aussie240 Re: Mcb's used as functional switches? - 09/01/05 01:41 AM
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.
Posted By: kiwi Re: Mcb's used as functional switches? - 09/01/05 09:18 AM
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.
Posted By: Trumpy Re: Mcb's used as functional switches? - 09/02/05 06:40 AM
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.
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.
Posted By: mxslick Re: Mcb's used as functional switches? - 09/02/05 09:20 PM
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?
Posted By: aland Re: Mcb's used as functional switches? - 09/02/05 10:20 PM
Mxslick, these sound a lot like our type D breakers the tripping charecteristic is something like 20-25 times In for instant tripping hence they withstand the initial surge of a heavy load switching on. Dont think the mechanics of the breaker are any differennt though; so ausies point about the switching endurance probably still has to be considered. Thanks to everyone for the comments. Aland
Don't think so. There are dedicated switches that look like MCBs though.
Posted By: aland Re: Mcb's used as functional switches? - 09/03/05 02:13 PM
Texas_Ranger, I stand corrected never seen anything like that, do they still have all the electrical and mechanical charecteristics of a normal Mcb then? Who makes them? Aland.
I agree with the comments about Emergency Lighting. I have done a PIR where MCBs are used as functional switching and, although I think its not good practice, have considered that it does not contravene the Wiring Regulations.

I looked at Merlin Gerin data sheets and they say that their MCBs are good for 20000 operations on load.

PS
133-01-01 States "Good workmanhip and proper materials shall be used." So could you say using a MCB as a functional switch is not good workmanship?

[This message has been edited by TeesdaleSparkUK (edited 09-04-2005).]

[This message has been edited by TeesdaleSparkUK (edited 09-04-2005).]

[This message has been edited by TeesdaleSparkUK (edited 09-04-2005).]
Posted By: aland Re: Mcb's used as functional switches? - 09/04/05 03:12 PM
TeesdaleSparkUK, Hi, and welcome to ECN, thanks for the info. Good points you raise, never thought of looking up the number of operations recomended by manufacturers. This seemed to be a popular practice in pubs and clubs a few years back apparently. I see the bigest problem as the fact that the E-lighting is on seperate circuit and is not going to operate unless a complete failure of the mains occures. That and many other things were the reasons for the unsatisfactory status on the P.I.R. Thanks again aland
Posted By: britspark Re: Mcb's used as functional switches? - 09/04/05 03:47 PM
Trumpy,
within the building/environmental codes and the local fire officer,

emergency lighting must be fed via the local lighting circuit, not on it own MCB.

if the lighting fails within an area the emergency lighting must be available for egress from that part of the property.

scenario;
power fails to general (local) lighting in the main bar area, emergency lighting is emergised via its own back up batteries, (for Single Point Units only.
if the feeder for the emergency lighting is fed from another breaker it will still be energised and not running on its own batteries.

but thinking on this;
if the fittings are Maintained, IE, lamps lit at all material times, then that would probably be ok.

but with the cost of a Non Maintained fitting being about £14.00 and the cost of a MAintained fitting being about £21.00 most of the clients that i know would go for a Non Maintained fitting all the time, Due to them being tight.!

i personallay prefer MAintained fittings every were, due to the fact if the lamp aint lit its usualy faulty!!

Emergency lighting facts: supply on.
Non Maintained, lamp off battery charging
Maintained, lamp on battery charging

supply off
Non Maintained, lamp on
Maintained, lamp on

this is for single point units only.

Central Battery Systems are totaly different!!

Britspark
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do they still have all the electrical and mechanical charecteristics of a normal Mcb then? Who makes them?
No, they're just ordinary switches, without any tripping mechanism, only built for DIN rail mounting.
I think most breaker manufacturers also do switches, I've found them at the ABB web site, without any specific model # though. They're listed under 'modular DIN rail components'.
I never used them personally, but I've seen some old Austrian F&G brand and I read a rather hefty discussion at a German board which concluded using MCBs as switches is _not_ up to code since the frequent operation _might_ wear it out to a point where it wouldn't trip on faults any more. From personal experience I can say nuisance tripping is much more likely.
Posted By: aland Re: Mcb's used as functional switches? - 09/05/05 12:05 AM
Texas, if these devices do not have any charecteristics of a circuit breaker you still need a fuse or mcb in line with them. Cant quite see the advantage over a normal switch. other than they are din rail mounted. Thanks for the info though. aland
Posted By: Spock Re: Mcb's used as functional switches? - 09/06/05 02:23 AM
Master switch is common in many large common areas, have seen them particularly in teaching labs and classrooms. Usually i have wired them as a switch or mushroom button feeding a contactor on the load side of the c/b.

I would suggest that use of a c/b as a switch may lead to contact welding, dependant on load or more likely internal failure causing an open circuit.
Quote
Texas, if these devices do not have any charecteristics of a circuit breaker you still need a fuse or mcb in line with them. Cant quite see the advantage over a normal switch. other than they are din rail mounted.
That's the problem! The only advantage is you can fit them inside the panel and don't need extra switches. Might be easier to handle all the wires for larger switching asse,blies in a DIN rail panel instead of usual switch boxes. Of course you need an MCB in line.
At some hotels I've seen electricians put in sigle row or even two row panels with switches next to the door in bigger rooms because it's easier to install than let's say 10 individual light switches.
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