Digital Timer and Discharge Lighting :(

[councillor]

We have a large floodlight (Discharge) outside our wharehouse. It has a photo cell on it and comes on at night as you would expect. I only want it on when people are working so really I want it to switch off at 7pm. At the moment the floodlight is supplied by a fused spur and I want to add a timer so as to limit the time the light is energised. A timer like this would have been good http://www.tlc-direct.co.uk/Main_Index/Timers_Index/Immersion_Heater_Timers_1/index.html, but it states thy are not to be used with discharge lighting I wondered why is this the case?

As an Alternative I could use this: http://www.tlc-direct.co.uk/Products/TCGP24.html
Any probs here?

 

[Spark123]

You fail to mention what size the floodlight is.
A timer can be used to drive a contactor however it should be noted that as a photocell is powered on it may close for a short period, not the best idea with discharge lighting.
Also - as a place of work I take you are aware of your duties under the Electricity at Work Regulations and HASWA?

 

[bongos]

What is the MCB/fuse rating of the circuit which powers the discharge lighting? Is the FCU on a ring final circuit?

I see no reason why you could not fuse down in the FCU (as you already are anyway) and then add an adjacent box with this timer in it powered from the FCU. This way the timer would be protected by the FCU as well.

>---FCU--->---Timer--->---Light

Can't answer the question as to why the first timer can't support discharge lighting though (I'm sure someone else will be able to help

 

[Spark123]

Put simply the contacts in the timer won't have been designed to cope with the high current start in inductive loads and the arc when the circuit is broken.

 

[councillor]

Spark 123.
I will have to double check the size of the flood and advise later.
You say when the photocell is powered on it may close for a short period, Im not following you here can you elaborate. As for Electrical safety the whole installation has had a recent PIR and is in good condition, Im certainly not going to install anything remotely suspect I would rather raplace the lot.

 

[Spark123]

If you use the timer to power a photocell then when the timer comes on say at 12 noon, the light will power up for about 30 secs whilst the photocell gets it's act together, then it will switch off the power to the light.

I didn't mean wether or not the place has had a PIR - I meant are you aware of your duties under the EAWR and HASWA as it is a place of work, i.e. you must be able to prove that you are "Competent" to prevent danger or injury and the system must be installed, inspected and tested to prevent danger, relevent paperwork in place etc etc.

 

[councillor]

123:

Yeah I see your point about the photo cell should have guessed that one, most security lights with photocell switch themselves on for a short period if you knock the power off and switch them back on again. I guess the bottom line is that discharge lighting as you point have a high current start, and perhaps is better on a timer that can cope with the current, or a contactor. Thats why I thoght this: http://www.tlc-direct.co.uk/Products/TCGP24.html may be good its rated at 2A inductive, that will limit me to a 460W flood but should be enough. Re electrical safety I have 2381 and 2391