Fluorescent startup draw

[slider45]

Hi,

Wondering if anyone can suggest how to calculate what can be fitted to an existing circuit.

Its a 6A B6 MCB running 1.5mm t&E to the light fittings.

How many 1800mm 70w tubes can I expect to run without the MCB popping / overloading the cicuit? I was hoping for up to 10!

Are there calcs for this?
Would a C6 help?

Cheers.

 

[Lectrician]

Typically, as a rule of thrumb..........multiply the lamp wattage by 1.8.

If this comes out "out of favour" with you, contact the manufacturer for more precise characteristics.

Do not be perturbed (spelling in phenetics?) by installing more than one circuit!

 

[slider45]

Typically, as a rule of thrumb..........multiply the lamp wattage by 1.8.

So - ball park:
10 x (70w x 1.8) = 1260 watts

1260 / 230 = 5.4 A

Sounds just within the range of a 6A MCB.
Perhaps changing from a B6 to a C6 might help further.

 

[Lectrician]

No - A C should not be considered due to loading, but to the type of load.

But, your lucky with the guess - A C would be better suited to discharge lighting due to the inductors (chokes)...

I would still split this cct to be honest.

What is the install? Shop, workshop...?

Would it be disruptive if the entire cct failed one day?

 

[slider45]

No - A C should not be considered due to loading, but to the type of load.

But, your lucky with the guess - A C would be better suited to discharge lighting due to the inductors (chokes)...

I would still split this cct to be honest.

What is the install? Shop, workshop...?

Would it be disruptive if the entire cct failed one day?

There'd be no issue - its only a single car garage / workshop!

Only put all the double tubes in because 1) they were free
2) I can then pull starters & select which areas have 1 tube and which have 2 functioning. Would probably never want all 10 running in reality - it might be a bit too bright!

I'd rather not add another circuit as they're already on 3 way switching and thats another whole lot of cabling!

Sorry - but what do you mean by:
A C should not be considered due to loading, but to the type of load.
?

 

[ricicle]

Sorry - but what do you mean by:
A C should not be considered due to loading, but to the type of load.
?

A type C MCB will handle slight inrush currents (currents larger than running currents for a short duration) caused by the likes of Fluorcescent lighting/small motors when they start up.It needs around twice the current to instantly trip it compared to a type B.
However a 6amp type C is still the same as a 6 amp type B with regard to running current.They will both operate eventually when this current is exceeded so you would still be left in the dark.
Due to the above the earth fault loop impedance needs to be lower for a type C than a type B so that the MCB operates in the required time in the event of an earth fault, so tests need to be carried out before swapping breakers for different types.

 

[slider45]

Nice work lads - think I follow.
Cheers for the advice - tis appreciated.

 

[Stoday]

With that number of tubes it sounds like you will be using your garage as a workshop. If so, high frequency ballasts would be better, avoiding stroboscopic effects. Also HF (NOT HPF!) luminaires don't have such a high starting transient.

 

[JohnD]

give then individual switches. Then you will not have them all starting up at the same time.

Beware of using ordinary fluorescents as working lights on rotating or reciprocating tools like lathes, car engine when running, fans, drill, grinders etc.

bah, slow again