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.
Alan!, Long time no see mate, welcome back. 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
Re: Mcb's used as functional switches? #143737 08/30/0507:11 AM08/30/0507:11 AM
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.
Re: Mcb's used as functional switches? #143739 08/31/0509:41 PM08/31/0509:41 PM
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.
Re: Mcb's used as functional switches? #143740 09/01/0505:18 AM09/01/0505:18 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.
Re: Mcb's used as functional switches? #143742 09/02/0503:47 PM09/02/0503:47 PM
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.
Re: Mcb's used as functional switches? #143743 09/02/0505:20 PM09/02/0505:20 PM