VA rating for fluorescent light fixtures

[pwhittle]

I want to replace the manual switch with a motion activated one in my garage.

I have 3 fixtures each with 4x4' tubes rated at 40W. That makes 480W.

I see the switches are rated in VA. How do,I determine the VA rating? Is it different from the Watts of all the tubes?

Paul

 

[rockwithjason]

The baalast in the fixture has the va rating printed on it

 

[nehog]

Realize that a 40 watt tube will draw more than 40 watts from the power line due to inefficiencies in the ballast (new solid state electronic ballasts are better than the older magnetic ones) and other inefficiencies.

Your best bet is to use a clamp on meter and measure the current draw from a single fixture and see what you are drawing. Then there is no guess work. Also if they are solid state electronic ballasts you can probably ignore the power factor and just use watts (volts times amps...)

 

[MTW]

I suggest that you check the fine print on the sensor that you want to purchase and make sure that it's compatible with the type of lighting that you have.

Your fixtures could have the older magnetic ballasts or newer electronic type. Either way you need to make sure the the sensor is compatible first. Usually there is a different wattage rating depending on the load type.

The ballast will list the operating current in amps, there may be 2 in each fixture. Multiply the amps by 120V to get the wattage rating, then by the number of ballasts.

Magnetic ballasts are inductive loads and the sensor should be approved for this. Incandescent ratings are usually higher than inductive ones. If it's listed as suitable for it, get the highest rated one you can find, it will last much longer before it burns out.

 

[nehog]

...
Your fixtures could have the older magnetic ballasts or newer electronic type. Either way you need to make sure the the sensor is compatible first. Usually there is a different wattage rating depending on the load type.
...

What is in there is of less importance: there is nothing to suggest that at some point in the future either the ballasts or the fixtures will be updated/replaced/repaired, and that whoever does that work almost certainly won't bother to check to make sure that the controlling device (photocell) will handle the new work!

Best choice is to go with a unit that is 'universal' and will work with any type of lighting, or to use a contactor/relay to control the lights indirectly.

 

[pwhittle]

I opened up one if the three fixtures and it had two of these ballasts in it. I assume the others are the same.

No mention of a VA rating, but I have four F40T12's in each fixture, two per ballast.

It currently has a single switch and ground is available at the switch.



Paul

 

[nehog]

No mention of a VA rating, but I have four F40T12's in each fixture, two per ballast.

Yes it does! The two F40T12 configuration is .75 amp, at 120 volts for a VA of 90 times two give a total VA of 180 for each fixture. The fact that these are high power factor ballasts goes to your advantage--they are going to be more efficient.

 

[pwhittle]

Thanks nehog!

I'll look for an occupancy switch of greater then 540VA.

Paul

 

[Stuart in MN]

This is a link to a pdf file published by my local electric utility, Xcel Energy: http://www.xcelenergy.com/staticfiles/xe/Marketing/MN-Bus-Lighting-Input-Wattage-Guide.pdf It's a list of light fixture input watts they use for calculating rebates for efficient lighting.

T8 lamps start on the third page; for a typical 4 foot fixture with two 32 watt T8 lamps and an electronic ballast they figure 58 watts.

 

[MTW]

Paul, like I said in my earlier post, make sure the motion sensor you buy will have the rating you need and must be that rating for inductive loads. That is the type of ballasts you have, old school magnetic ballasts.

If you want it to last get the one with the highest rating you can find. As a general rule when sizing electrical components, most things should be oversized by 25% minimum for long life. Running components at their maximum rating usually leads to very short life.

 

[pwhittle]

I went with an Leviton ODS10-IDW. 1200VA @ 120V.

http://www.leviton.com/OA_HTML/ProductDetail.jsp?partnumber=ODS10-IDW&section=38557

Paul