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# figuring amperage draw

## figuring amperage draw

#1
08-08-04, 09:45 AM
jwroblesk
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figuring amperage draw

Trying to figure out toal amperage draw for a fluorescent fixture as I have several I want to put on one circuit. The T-8 ballast says .85 amps and there is two 32 watt bulbs. Is the total draw .85 amps or do I have to add the bulb wattage. Joe

#2
08-08-04, 11:10 AM
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Join Date: Jul 2004
Location: Chester, IL
Posts: 270
i know the formula is: watts/voltage = amps, however I'm not sure if the ballast draws some PLUS the bulbs, or if the 2 - 32 watt bulbs is the total draw and the 0.85 ballast is the max for that ballast.

But either way I get, 0.58 amps for the bulbs...and IF you have to add the 0.85 for the ballast thats 1.43amps per fixture MAX. At that rate you could put 13 fixtures on one 20amp circuit, or 10 on a 15amp circuit, and have a little to spare either way, but I THINK(don't quote me I'm not an electrician, and don't keep up on code) you can only put 8 devices on one circuit anyway

One of the pros I'm sure would know about the draw of the ballast, and whether that's in addition to the bulbs, or total, or what. They will also know code for max # of devices.

hope this helps, post back as needed

#3
08-08-04, 11:51 AM
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0.85 amps is the total.

#4
08-08-04, 06:15 PM
johnnyelec
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you can put a MAX of 14 light fixtures on a 15amp circuit and 18 light fixtures on a 20amp circuit. These counts are MAXIMUM allowed.

#5
08-08-04, 07:30 PM
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johnny, I'd be interested in how you made that calculation. Are you applying the continuous load rule, and if so, why? Do the inspectors in your area enforce that rule on residential lighting circuits?

#6
08-14-04, 02:36 PM
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Join Date: Sep 2003
Location: Central New York State
Posts: 13,246
On a resaidential circuit there is no limit to the number of devices that you can put on a circuit. Of course, if you have too many on a at a time then the breaker will trip.

The 80 percent continuous load rule is not generally applied for residential circuits.