Contactors

[dochisholm]

hi doing some lights in a commercial unit and want to switch them on contacters question is need to obviously have overcurrent protection how do you people get around this. I was thinking supply the contactors in a seperate unit from mcbs in the 3 phase board. please help

 

[telectrix]

could you not supply contactors from a suitably rated fuse, and fit overloads to the load side of the contactors?

 

[SirKit Breaker]

Fit overloads between the busbars and the contactors usually. If you supply them from MCB's you may have a problem with them tripping with the in rush current when you switch them on, this of course depends on the type and load of the lighting you are installing.

 

[Deleted member 9648]

The mcb's in the DB will provide overlcurrent protection,the contactor is just a switch, break the live of each circuit through 1 pole of the contactor.Use a type C or D (disconnection times allowing) to prevent inrush current problems.Supply the control circuit via a separate 6a mcb.
If you are switching fluorescent lighting make sure your contactor contacts are rated higher than the load,for a 6a or 10a circuit a 20a contactor will suffice.
If you have more than one contactor in the enclosure ensure adequate air space around each one,as they will be energised for long periods the coils will overheat if they are butted up together.

Not sure why it has been suggested to fit overloads to the contactors,these are intended for motor protection,for a lighting circuit a bs60898 mcb of the correct rating for the circuit regardless of type will provide overload protection. 433.1.2

 

[Darkwood]

May i disagree with previous posts as to choosing contactors and mcbs, first establish what make of mcb you are using then get a copy of their distribution boards catalogue (with technical advice in the back normally) if it lacks technical advice then ring them with type and wattage and no' lights per circuit, you will find what size and type of mcb and contactors you need for any given type and no' of lights in table form, if you do it by guess work or pick next rating /size up you will only set yourself up for premature failure of contactors and nuisance tripping, contactors should be rated for the switching of high inductive loads specifically inductive lighting , just buying any main stream contactor will again only lead to problems, all this must be worked out before hand as it may need 16amp mcb's and 2.5mm wiring to compensate for inrush , Square D books have an excellent section at back to help you identify the correct mcb for given job and associated contactors you will need and as mentioned before the spacing needed between contactors is also calculated for you.
Designing this type of supply needs to be done ahead so you dont fall foul of nuisance tripping and not been able to upgrade mcb due to cable size to small, ive followed many rule of thumb companies and explained to customers why their lighting trips or their contactors only last a year or two, finding the correct mcb and contactors using the correct research will supprise you just how far out you can be if just doing a load calc to work it out, also different brands can have different tolerances and thus results may differ.
Also as mentioned by other post feed you contactor load channels via mcb's then have seperate mcb fed control circuit via switches to energise contactors, no overload protection required on contactors as your mcb's already do this.

 

[dochisholm]

Thanks could I fit them inside three phase board on din rail or is that considered wrong

 

[Darkwood]

Thanks could I fit them inside three phase board on din rail or is that considered wrong

Whats the make of board, most new boards can expand with dinrail mount enclosures boxes ideal for this situe.
P.s. read my previous post as you may have missed it as you wrote yours and posted at same time...

 

[dochisholm]

Wager three phase board

 

[Deleted member 9648]

May i disagree with previous posts as to choosing contactors and mcbs, first establish what make of mcb you are using then get a copy of their distribution boards catalogue (with technical advice in the back normally) if it lacks technical advice then ring them with type and wattage and no' lights per circuit, you will find what size and type of mcb and contactors you need for any given type and no' of lights in table form, if you do it by guess work or pick next rating /size up you will only set yourself up for premature failure of contactors and nuisance tripping, contactors should be rated for the switching of high inductive loads specifically inductive lighting , just buying any main stream contactor will again only lead to problems, all this must be worked out before hand as it may need 16amp mcb's and 2.5mm wiring to compensate for inrush , Square D books have an excellent section at back to help you identify the correct mcb for given job and associated contactors you will need and as mentioned before the spacing needed between contactors is also calculated for you.
Designing this type of supply needs to be done ahead so you dont fall foul of nuisance tripping and not been able to upgrade mcb due to cable size to small, ive followed many rule of thumb companies and explained to customers why their lighting trips or their contactors only last a year or two, finding the correct mcb and contactors using the correct research will supprise you just how far out you can be if just doing a load calc to work it out, also different brands can have different tolerances and thus results may differ.
Also as mentioned by other post feed you contactor load channels via mcb's then have seperate mcb fed control circuit via switches to energise contactors, no overload protection required on contactors as your mcb's already do this.

The same points would apply whatever switching device is used,circuit legnths,cable size mcb rating and type, and rating of switch contacts will have to be established.....it's no different whether or not a contactor is used as a switching device.

 

[SirKit Breaker]

The mcb's in the DB will provide overlcurrent protection,the contactor is just a switch, break the live of each circuit through 1 pole of the contactor.Use a type C or D (disconnection times allowing) to prevent inrush current problems.Supply the control circuit via a separate 6a mcb.
If you are switching fluorescent lighting make sure your contactor contacts are rated higher than the load,for a 6a or 10a circuit a 20a contactor will suffice.
If you have more than one contactor in the enclosure ensure adequate air space around each one,as they will be energised for long periods the coils will overheat if they are butted up together.

Not sure why it has been suggested to fit overloads to the contactors,these are intended for motor protection,for a lighting circuit a bs60898 mcb of the correct rating for the circuit regardless of type will provide overload protection. 433.1.2

yeah, sorry mate you are right with the overloads, i was thinking 3ph motor circuits........sausage

 

[Darkwood]

The same points would apply whatever switching device is used,circuit legnths,cable size mcb rating and type, and rating of switch contacts will have to be established.....it's no different whether or not a contactor is used as a switching device.

Yes agree but not the point i was making, after doing all the sums and finding your design load i was making him aware that it isnt as choosing a mcb and type to match the rating or contactor, you need to get technical charts or contact makers to confirm they are fit for purpose and as ive found out many times you tend to be supprised that you need mcb's sometimes twice the rating to you calcs hence so many sparkies just do standard cable calcs and this is ok well its not metal hallide, mercury vapour, flourescents all have different inductive effects and inrushes which throw all your college learning out the window.

 

[Deleted member 9648]

Ok mate

 

[mogga]

One same lines a darkwoody there along the contactors butted together bit IMO id try and leave at least 1 modual space between if its abank of contactors and use a large enclosure to assist with heat disipation Been to way to many call outs with no lights only to find contactors overheated out their nuts due to lack of forethought afterall size does matter as her Indoors allways says

 

[Marvo]

If you work out the startup current of all you lights on a circuit and find a contactor with an 'ac3' rating which is higher than this you should be on the right track.

 

[John Bunning]

i have fitted merlin gerin contactors for years on factory lighting circuits ,never had any issues with merlin stuff [bomb proof ]

 

[i=p/u]

Just put less lights on the circuit 1.8 times less, forget contractors.....

Imstarting to get nosey around contactors out in field but still can't work it out quick enough , by time other guy has done what he had to do. Futures bright

 

[johnboy6083]

As far as I'm aware (I'm happy to be re-educated though) this is why we use the 1.8 factor when calculating Ib for fluorescent lights. This means that the cables and switchgear are then sized to account for pf, harmonics and the inductance on the circuits. As Marvo has mentioned, AC3 contactors should be used.

 

[i=p/u]

Say a standard 10A mcb and 58w 5ft tubes you could switch over 20 lamps per per 10A breaker .

i also used contactor once to power 3 x 250 metal halide fittings and my boss said fit contactor but were the only lights on the 10A mcb, which I thought didn't even need it.

 

[i=p/u]

Does the contactor take away inrush by being at correct voltage

 

[infinity]

No the contactor allows the load to be switched by a lower rated switching device

 

[infinity]

Old thread!!!!!

 

[i=p/u]

In my case i used a 3kw 24 hr heating timer to switch contactor

would you of used contactor? Do you think was needed

 

[i=p/u]

Old thread I know, just reading bits

 

[Knobhead]

If you want to read old crap do so. Just don’t regurgitate it for everyone to see.

 

[Darkwood]

LOL ... so forgot i even replied to this be reading it i was still on form 3 yrs ago :rolleyes2: lol... i think we are just geting old ......

Drunk .com at the mo!

 

[i=p/u]

spring chicken with 40 years left to do electrical work, now dont be sick,, and tell me me lots about contactors to give me better understanding of their uses and where and when to apply.. do as your told tony for once ya skitter

im getting their

 

[Silly Sausage]

i=p/u,
check this out...
Eaton - Wiring Manual

There are loads of examples of contactor applications within.
You can get the actual book for free as well, you'll have to find that yourself.

 

[Silly Sausage]

The above being originally courtesy of Tony! Cheers Cock.

I got a hard copy, pity it isn't A4 size.

 

[Knobhead]

Just put less lights on the circuit 1.8 times less, forget contractors.....

Imstarting to get nosey around contactors out in field but still can't work it out quick enough , by time other guy has done what he had to do. Futures bright

1.8 less would be the inverse = 0.55