fluorescent lighting

[soulman]

what is the maximum wattage fluorescent tube that can be switched with a standard light switch? when would you have to use a contactor and how are these wired into the circuit?

cheers

 

[jameseye12]

The max wattage for a light switch depends entirely on what that particular switch is rated at. For example the switches I use are rated at 10amps

Contactors are quite often used in large Commercial or Industrial environments to switch large numbers of lights at once. A 6A circuit is usually used to control the contactor via a standard light switch. Lighting on a contactor will be spread over 3 phases and so will need to be 4 pole

Example of one i came across recently:

2 x Contactors fed from 'maintained' CU

Each contactor was controlled by a standard light switch

These 3 phase contactors then each fed a separate 'non maintained' CU

These CUs were fitted with single pole breakers each supplying a section of lighting (it was in a shop so there were circuits for various display lights as well as the main lighting which was divides up into sections)

Hope this Helps

James

 

[soulman]

thanx mate thats great i didn't realise contactors for lighting were just 3 phase cheers for that

 

[jameseye12]

No probs dude

As I said I've only seen it in large commercial and industrial environments and you really should balance everything across the phases if you are using that much lighting

so it would obviously need to be 3 phase. I suppose you could use a single phase one if you really wanted to. Depends on the situation I guess

I cannot honestly imagine a domestic situation needing a contactor as a domestic lighting circuit rarely exceeds 6 amps. At the most 10 amps and most switches are rated a 10amps

 

[steptoe]

single phase contactors are widely available,

and used often,

design of the circuit comes into play a lot.

but almost any configuration of either single phase or 3ph lighting can be switched via contactors etc.

cable lengths/volt drop/ and Zs etc all still need to be taken into account though.

 

[SPECIAL LOCATION]

Most bog standard light switches are either 6A or 10A rated.

 

[steptoe]

remember too that PIRs etc do not act like normal light switches,

 

[Sidewinder]

Also remember that IF you have a 3 phase supply feeding 1 phase lighting, say at 20A per phase on all 3 phases, with a single light switch controlling the lot via a contactor, what will the N current be...

 

[Riggy]

Also remember that IF you have a 3 phase supply feeding 1 phase lighting, say at 20A per phase on all 3 phases, with a single light switch controlling the lot via a contactor, what will the N current be...

Nowt (ish)

 

[steptoe]

Nowt (ish)

and you get that how?

headbang

 

[Riggy]

and you get that how? headbang

Balanced three phase load?

 

[steptoe]

the point was made if it was supplying single phase lighting.

needs a neutral, and not all lighting phases on at once,

so no balance anyway,

but you still need a neutral to carry all those amps, but only a line to carry 20.

you cant really balance single phase loads on 3ph, you can only try and equalise them.

 

[Riggy]

the point was made if it was supplying single phase lighting.needs a neutral through the contactor

I understood that Sidewinder's point was "you have a 3 phase supply feeding 1 phase lighting, say at 20A per phase on all 3 phases" this is a a balanced three phase load is it not?

 

[steptoe]

not if its single phase loading.

sorry, thats why I had to EDIT

 

[Riggy]

Steptoe, you edited your post, glad I quoted the original!

 

[steptoe]

it doesnt matter riggy, the point is still the same,

the neutral can be carrying 40A, but the line is only rated at 20A, so you have to have a contactor rated accordingly, ie 60A in this instance.

 

[Riggy]

not if its single phase loading.sorry, thats why I had to EDIT

As I understood what Sidewinder was saying it isn't single phase loading, 20A on each phase is a balanced load, no current in neutral (until a lamp goes of course). I rather think we just read his post differently?

 

[steptoe]

read SW post again,

it states 20A per phase on single phase loading from a 3ph supply, do you know of a normal light switch that can handle 20A,

IMO that is why he stated 20 as opposed to 10, a normal sw can handle 10.

if it were all on a balanced load then it would be 3ph loading,

 

[Sidewinder]

Guys you are all a little off, but generally on the right lines!

However, I may not have described it the best way.

A single 1ph lighting load of 20A on a single ph of a 3ph supply will have an N current of 20A.

If you switch this via a contactor no bother.

Now add another 1ph identical load.

You can't balance this cross the 2ph as it is a 1ph load, thus you have a ph & N on each bank.

next ad another now you have 3 off 20A 1ph loads each on an individual ph & N.

The N is common at the contactor as they are all fed from the same one.

Now what is the N current?

It can't be balanced load side as each phase is seeing a 1ph load, back at the DNO trans it will be seen as a balanced 3ph load, but inbetween...

Unless you have 400V lighting which was not my intention, lets say its 20A of filament lamps, per phase, to avoid inrush issues!

 

[Riggy]

How many poles is your contactor?

The way I see it, if it's a 4 pole contactor (which I'd assumed) the neutrals of your 3 x 1ph loads are connected downstream of the contactor, i.e. your contactor is switching a star connected 3ph load, so as long as the phases are balanced the neutral current through the contactor is zero. Yes?