Fluorescent tube light help

[Delboy247]

Hi there went a job today to supply a light box for a shop today, it has 30 fluorescent tubes inside it done the cable calc 30 x 58watts = 1740
1740/240=7.25
So I fitted a 10amp rype b mcb and it tripped so I clamped the load going out it was reading 10.8amps and on start up it was hitting 11-12 Amps.
Now I'm thinking of fitting a 10amp type c mcb will this do it
Has anyone come across this??

 

[Strima]

C type should be OK but you need to check your Zs is suitable for the MCB.

What do the manufacturers recommend?

 

[egginyourface]

multiply 7.25 amps by 1.5.

 

[Jimmy Boy]

Firstly can I ask if you are electrically competent and/or qualified to carry out this work ?, I ask because I would like to know if you have established the cable sizes and protective device characteristics required for this load.
J

 

[snowhead]

going out it was reading 10.8amps and on start up it was hitting 11-12 Amps.

I'm thinking of fitting a 10amp type c mcb will this do it

There's a clue there.

 

[egginyourface]

Test your zs at the last light. maximum zs for 10 amp ctype is 1.84 ohms

 

[Bobster]

Has this been a new install?

 

[Plonker 3]

Test your zs at the last light. maximum zs for 10 amp ctype is 1.84 ohms

Should be tested at every point on a new install.

 

[Jimmy Boy]

Has this been a new install?

Well this what I am driving at ! Is someone lobbing a huge light box on the end of some random existing cable ? for all we know it might be a bit of .5 flex lol !. If the OP can give us the supply cable size 1.0 or 1.5 this will help us determine stuff.
J

 

[egginyourface]

but to determine your highest reding u need to find the last point

 

[Plonker 3]

but to determine your highest reding u need to find the last point

Not always a bad connection could cause a bad reading half way along a circuit.

 

[egginyourface]

thats what the r1 + r2 test is for

 

[Jimmy Boy]

Should be tested at every point on a new install.

Zs should be determined at the furthest point of each circuit, on a radial at last point, on a ring with spurs at the spurs with the highest reading.
J

 

[plugsandsparks]

Depending on the type of light you need to take into account the load of the ballast, if appropriate or the HF unit. Also the power factor will also conspire to increase the current above the basic calc of adding up the tubes and dividing by the voltage.

With a tube load of what you have described i would have put it on a C16 on 2.5sqmm cable, depending on cable length.

 

[Delboy247]

The box is pre wired in 1.5mm t + e, I run in a 1.5mm fp cable 10 metre run to the first connection done r1 + r2 at the furthest point all good turned it stuck a clamp metre on the load side with it reaching 10.8 amps.

 

[Delboy247]

Is there a formula for flourescent lighting??

 

[egginyourface]

this is what i think delboy needs to do.

Find out how many lights this circuit is supplying.
determine the cable size and length
do a r1 r2 test on the circuit. every point.
last point will be the highest
If it higher somewhere in the middle then yes u may have a loose connection
do a live test ze at the board
do a live zs test at the last point
This will give you ur zs
if its below 1.84ohms then bang a 10 amp type c

jobs a good'un

 

[Plonker 3]

thats what the r1 + r2 test is for

What about if you use the R2 method?

Zs should be determined at the furthest point of each circuit, on a radial at last point, on a ring with spurs at the spurs with the highest reading.
J

I always record the highest reading.

 

[spark 68]

Is there a formula for flourescent lighting??

It was to apply a factor of 1.8 (multiplied by), for the switch gear, but I cannot see this at the moment in the BGB

 

[plugsandsparks]

There are two main types: switch start and HF, their supply characteristics are different. Also i have noticed that as switched start ones get older they pull more current, so leave plenty of overhead.

 

[Delboy247]

Egg mentioned 1.5

 

[Delboy247]

They hf ballasts

 

[plugsandsparks]

HFs vary alot in efficiency, manufacturers data will help but if its running 10.8 you have little choice but to go C16, 1.5 might work if the runs are not too long

 

[Delboy247]

HFs vary alot in efficiency, manufacturers data will help but if its running 10.8 you have little choice but to go C16, 1.5 might work if the runs are not too long

The run is 10 metres mate what do you think I can easily change the wiring to 2.5mm for a c16 or change the mcb to a c10.

 

[snowhead]

Is there a formula for flourescent lighting??

Yes, you've got enough information to determine it;

10.8 / 7.25 = 1.49

12 / 7.25 = 1.65

Seems to agree with earlier posts.

 

[Delboy247]

Yes, you've got enough information to determine it;

10.8 / 7.25 = 1.49

12 / 7.25 = 1.65

Seems to agree with earlier posts.

Interesting.

 

[Jimmy Boy]

What about if you use the R2 method?


I always record the highest reading.

Agreed on a ring with spurs, with a Radial how can a higher reading be anywhere except at the end unless you have a fault or an external influence ? If you have done the r1 stuff first, I fail to see how the impedance can be higher mid circuit than end circuit on a Radial ?
J

 

[somersetsparks]

HFs vary alot in efficiency, manufacturers data will help but if its running 10.8 you have little choice but to go C16, 1.5 might work if the runs are not too long

Do the fittings not have to fused to be connected to a 16a mcb? Seem to remember havinbg to install a load of fused fittings when the circuits were 2.5/16A

 

[Guitarist]

You say it is pre-wired? Did it come with any literature/manufacturers instructions? If so, these would probably tell you what overcurrent device you need to fit, and you can install the supply accordingly.

 

[Plonker 3]

Just a personal preference, but checking every point ensures all current using points meet the required Zs rather than relying on a installation being perfect because one other test says all is good.

 

[plugsandsparks]

The run is 10 metres mate what do you think I can easily change the wiring to 2.5mm for a c16 or change the mcb to a c10.

A C16 can run on 1.5 if you can get the right ZS readings for it. Fitting a C10 is high risk if its running 10.8 now, you could well be back after tripping in hot weather assuming it stays in long enough for you to leave the premises.
I cannot say because i dont know you total cable run through the switches and the Zdb.
What i do is (before ordering cable) measure Zdb stride the cable run for an idea of cable length then over a coffee decide how many circuits and how fat a cable to use.
You wont get a definitive answer here because your variables are unknown, but i would be surprised if you cannot make it work on a C16 and 2.5, as you have run the cables, if your ZS at the end of your run is less than 1.16ohms than fit a C16, if its greater then oops,

 

[Guitarist]

Just a personal preference, but checking every point ensures all current using points meet the required Zs rather than relying on a installation being perfect because one other test says all is good.

Agree. Picks up any loose connections that way.

 

[spark 68]

Egg mentioned 1.5

Found it in the OSG Append. A Diversity, see note 2 on page110.

Final circuits for discharge lighting etc...etc. the demand in VA is taken as the rated lamp watts multiplied by not less than 1.8, unless more exact information is available.

 

[spark 68]

I knew it was X 1.8, just wasn't sure where it was listed.

 

[Delboy247]

I knew it was X 1.8, just wasn't sure where it was listed.

That's why these sites are good we can't all know everything it all makes sense now.

 

[plugsandsparks]

1.8 sounds about right for ballasted fittings although i have seen 2.0 times for older ones

 

[steveberry11]

The correct method for calculating the protective device is as follows.

30 x 58 x 1.8 = 3132 W

3132 Divide be 230V = 13.61A

The protective device should be 16A

The normal type this type or lighting should be type C.

Cable calculations should be based on a load of 13.61A

 

[tigerpaul]

As the others have said, check your Zs at the end of line (should be the highest) and just make sure it doesnt exceed the maximum value given for the mcb you require. (in this case a Type C)
If it does exceed that value, how about changing for an rcbo? Or reduce the earth loop impedance by adding supplementary bonding (if practical)

 

[steveberry11]

As the others have said, check your Zs at the end of line (should be the highest) and just make sure it doesnt exceed the maximum value given for the mcb you require. (in this case a Type C)
If it does exceed that value, how about changing for an rcbo? Or reduce the earth loop impedance by adding supplementary bonding (if practical)

Or carry out cable calculations and get it right first time.

 

[steveberry11]

As the others have said, check your Zs at the end of line (should be the highest) and just make sure it doesnt exceed the maximum value given for the mcb you require. (in this case a Type C)
If it does exceed that value, how about changing for an rcbo? Or reduce the earth loop impedance by adding supplementary bonding (if practical)

Why do electricians need to be reminded of this stuff time after time?