Fluorescent calculated amp

[n84jrnation]

I am in need of how to calculate fluorescent lights. One fixture has six 32 watt t5 bulbs on 277 volt.

 

[dkidd]

You really need to get the ballast information from the manufacturer.

 

[iwire]

I am in need of how to calculate fluorescent lights. One fixture has six 32 watt t5 bulbs on 277 volt.

Read it off the ballast, if you don't have the ballast you could look one up on line

 

[kwired]

I am in need of how to calculate fluorescent lights. One fixture has six 32 watt t5 bulbs on 277 volt.

32 watts is typical for T8 lamps, 54 watts is typical for T5 lamps - might want to verify you have that right. Otherwise as mentioned lamp watts and input amps on the ballast do not normally match up to one another as there is some losses and power factor in there but they are closer with electronic ballasts then they were with magnetic ballasts.

 

[iwire]

Relevant

220.14(D) Luminaires. An outlet supplying luminaire(s) shall be
calculated based on the maximum volt-ampere rating of the
equipment and lamps for which the luminaire(s) is rated.

 

[kwired]

Relevant

I take that to mean if the ballast can drive a 28 watt or a 32 watt lamp(s) then you must use the 32 watt lamp as the basis for your load calculations.

 

[iwire]

I take that to mean if the ballast can drive a 28 watt or a 32 watt lamp(s) then you must use the 32 watt lamp as the basis for your load calculations.

Assuming the fixture is capable of holding the lamp I agree.

 

[kwired]

Assuming the fixture is capable of holding the lamp I agree.

I accept your added information here.

 

[iwire]

I accept your added information here.

It seems if the fixture is a 3 footer we can ignore the current ratings for 4 foot lamps.

 

[kwired]

It seems if the fixture is a 3 footer we can ignore the current ratings for 4 foot lamps.

I kind of figured that was what you were getting at. Electronic ballasts have more lamps they can drive as a general rule then the magnetic ones used to.

 

[n84jrnation]

I found the wattage on a bulb from another fixture. It is 54. 54 times six equals 324. 324 divided by 277 equals 1.169. Which is what my amp meter read. Don't know if I was lucky but the numbers matched. Thanks guys

 

[kwired]

I found the wattage on a bulb from another fixture. It is 54. 54 times six equals 324. 324 divided by 277 equals 1.169. Which is what my amp meter read. Don't know if I was lucky but the numbers matched. Thanks guys

There is little or no (significant) loss in the ballast as well as high power factor is why it comes out that way.

 

[Little Bill]

Don't remember where I got it but here is the formula I use on T8. I am fairly certain it was from one of the lamp mfg sites.

for a 32W T8

32 x # of lamps x 1.5/120

example for a 4-lamp 32W

32x4=128
128x1.5=192
192/120=1.60A

If continuous load x 125%

 

[delectric123]

According to this code article you should really use the amps listed on the ballast. But it would probably sum up very similarly.

220.18(B) Inductive and LED Lighting Loads.
For circuits supplying lighting units that have ballasts, transformers, autotransformers,
or LED drivers, the calculated load shall be based on the total ampere ratings of such units and not on
the total watts of the lamps.

 

[GoldDigger]

According to this code article you should really use the amps listed on the ballast. But it would probably sum up very similarly.

One potential factor is that one could, for example, add lamps to a ballast which is rated for a range of lamp numbers and/or wattages and so change the consumption of the fixture without changing the ballast.