Removing lamps from 2 or 3 lamp fixtures.

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steve66

Senior Member
Location
Illinois
Occupation
Engineer
Probably none, as long as it works.

I believe some ballasts run lamps in pairs, in series. If one lamp is removed, the other won't light. So it might work if you remove the right lamp from a 3 lamp fixture. Its less likely to work with a 2 lamp fixture.

A 2 lamp fixture will probalby look funny with only one lamp.
Steve
 

jeremysterling

Senior Member
Location
Austin, TX
For me personally, the adverse effect is when a facility manager says to replace all the lamps that are not working, only to discover office workers have rolled them out of the sockets to reduce light output. Awkward.

On the plus side, you will probably save on your electric bill.

The downside is decreased production from sleeping workers.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Look for "1 or 2 (or 3) ... " in front of the tube types on the ballast label, and heed the "cap unused wires" warning.
 

Electric-Light

Senior Member
The ballast label is not complete. Just because its not listed on there doesn't mean its not permissible. The spec sheet often gives you a more comprehensive combination.

GE UltraMax supports N-2 operation at the time the publication I was reading was published. Same model # ballasts can have different capabilities from revision to revision, so if it's a large scale thing, its important to consult the manufacture with the date code and model # to see if what you're doing is permissible.

GE UltraMax doesn't sigificantly change in ballast factor from all slots used or partially delamped. Most ballasts cause the remaining lamps to operate at higher output.
 

GlennG

Member
Location
Hicksville, NY
I was always under the impression that if you have a lamp out in a fixture than it is creating more of a strain on the ballast, or a greater strain on the other lamps that are still working. Is this true or am I making this up on my head?
 

Electric-Light

Senior Member
I was always under the impression that if you have a lamp out in a fixture than it is creating more of a strain on the ballast, or a greater strain on the other lamps that are still working. Is this true or am I making this up on my head?

Strain on lamp, yes and no. ballast, not usually.

Almost all standard T8 ballasts operates the lamps at 85-88% light output.

If you remove a lamp on a 4 lamp ballast, the remaining 3 lamps operate around 100%. (BF 1.0)

3 x 1.0 = 3
0.87 x 4 = 3.5
Suppose you're running 3 lamps (its permitted by ballast manufacturer in this case), but one of the lamp fails. Now, the remaining two lamps will probably operate 1.0+ BF.
Usually the lamp manufacturers permit up to 1.2 BF for high output application, but anything beyond voids lamp warranty.

Or total output is about 85%, not the hopeful 25% reduction, because some, but not all power gets allocated to remaining lamps.

If ballast maintains the same efficiency, you'll be getting 15% reduction in output. The reduction in power maybe greater or lesser than 15% depending on design.

You should specify PARALLEL lamp operations whenever you can. Programmed start is usually series, but parallel is available. Series means that if one lamp goes out, a string goes out.

The probability of one going out is greater than all three going out separately, so if one goes out whole string goes out. As such, series design significantly shortens group re-lamp interval.

As I mentioned, GE UltraMAX sells on holding same lamp ballast factor even when one or more lamp fails preventing lamp stress and improve the ability to fine tune by de-lamping.
 

GlennG

Member
Location
Hicksville, NY
Strain on lamp, yes and no. ballast, not usually.

Almost all standard T8 ballasts operates the lamps at 85-88% light output.

If you remove a lamp on a 4 lamp ballast, the remaining 3 lamps operate around 100%. (BF 1.0)

3 x 1.0 = 3
0.87 x 4 = 3.5
Suppose you're running 3 lamps (its permitted by ballast manufacturer in this case), but one of the lamp fails. Now, the remaining two lamps will probably operate 1.0+ BF.
Usually the lamp manufacturers permit up to 1.2 BF for high output application, but anything beyond voids lamp warranty.

Or total output is about 85%, not the hopeful 25% reduction, because some, but not all power gets allocated to remaining lamps.

If ballast maintains the same efficiency, you'll be getting 15% reduction in output. The reduction in power maybe greater or lesser than 15% depending on design.

You should specify PARALLEL lamp operations whenever you can. Programmed start is usually series, but parallel is available. Series means that if one lamp goes out, a string goes out.

The probability of one going out is greater than all three going out separately, so if one goes out whole string goes out. As such, series design significantly shortens group re-lamp interval.

As I mentioned, GE UltraMAX sells on holding same lamp ballast factor even when one or more lamp fails preventing lamp stress and improve the ability to fine tune by de-lamping.

great info, thanks for clearing that up.
 

cadpoint

Senior Member
Location
Durham, NC
“OR” is one of those very tricky words.

Ballasts are sold to be installed as per the required lamp count not as a reflection of 2 or 3 lamps burning in a fixture at any one time, or one burning out.

While the GE UltraMAX seems to sell that point in the literature, I don’t believe that it’s the intent to drop a lamp as the OP is asking. Point being is that there are only 3 models of 15 ballasts in this line that that only have the 2 or 3 lamp application.
This is stated in the ordering guide, in the product “letters” below it states, one, two, three, and four lamps.

Frankly it’s my general understanding that all fluorescent ballast are wired in Series.
Series wiring is not mentioned on the GE UltraMAX, it does say parallel but this is also based on other “selling - or a smarter aspect” of this product line. One can almost think through what would be required for a ballast so sense or to be programmed for the difference.

So from my reading, it is that the GE UltraMAX is or remains smart till burnt out and never is burnt into a set requirements or any sequencing other than it can adapt for constant level light.

Frankly my interest was sparked by the fact that the levels of the ballast factor of this new product was so low.

References:
GE UltraMAX

Advance

Where did the OP say these were fluorescent fixtures? Did I miss something?

Thanks for the reminder, I am now...

"Scotty.... I need those shields now" :)
 
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Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
Everybody inferred it is for fluorescents and they are almost certainly right. If this were a DIY site this assumption might have less foundation.

I wasn't saying that it wasn't fluorescent I just didn't see where the OP said for sure nor did I see any reply from him. I have assumed before and been wrong. I would think fluorescent too since he said "lamp" but wasn't sure.
 

Electric-Light

Senior Member
“OR” is one of those very tricky words.

Ballasts are sold to be installed as per the required lamp count not as a reflection of 2 or 3 lamps burning in a fixture at any one time, or one burning out.
Many ballasts support more than one lamp count configurations as per the official specifications, but the label on the ballasts don't necessarily tell you every possible approved usage.

Frankly it’s my general understanding that all fluorescent ballast are wired in Series.

Almost all T8 instant start ballasts are parallel wired, which has the largest market share now.

Almost all T12 and T8 rapid start magnetic and programmed rapid start electronic are series. There are a few programmed rapid start ballasts using parallel configuration, which is superior, because a failure of one lamp doesn't turn off other lamps.

Frankly my interest was sparked by the fact that the levels of the ballast factor of this new product was so low.

Standard output T8s by major brands are 0.87 or 0.88. I'm not sure why those values were chosen, but that's just the way it is.

Now most manufacturers offer three choices, low (0.75 to 0.77 range), standard, standard + (1.00, GE), or high (1.15 to 1.25) to give contractors and lighting professionals more choice.

Given a common 4 lamp T8 ballast,lamps are driven at 0.88 or so ( meaning that they're pushing 88% of published lumens). Most 4 lamp T8 ballasts allow 3 lamp operation, but they'll operate around 1.0. So you have 1.0 x 3 vs 0.88 x 4, so you have 15% reduction in output.

Biggest downfall is that it's an eyesore, because to the occupant, it will look like there is a burnt lamp and missing lamp can affect the light distribution adversely.

Other options are changing ballast to low ballast factor 0.77 units and keep the same number of lamps, but this is a substantial work.

Easier solution is to use the same number of lamps as currently in use, but use 25W, 28W or 30W energy saver lamps, climate permitting. The energy saver lamps work good in offices, but they do not work well below 60F. They will provide reduction in power use as well as light output without producing "burnt bulb" appearance.

I am only discussing commercial grade stuff. Junk residential grade things are all over the place and they are generally not friendly to lamps and many do not meet ANSI specs.

I'm not kidding about EYESORE thing, so I don't recommend de-lamping.
 
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z1bill

New member
The manufacture of a fixture I installed told me that if I run one lamp in this two lamp fixture if could catch on fire. The fixture has two 13watt CFL's.

Can that be right?
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
The manufacture of a fixture I installed told me that if I run one lamp in this two lamp fixture if could catch on fire. The fixture has two 13watt CFL's.

Can that be right?
Z1, welcome to the forum! :)

If it's true, a broken or burned-out tube presents the same danger.

Anything's possible, but unlikely that a ballast can't withstand that.
 

Electric-Light

Senior Member
The manufacture of a fixture I installed told me that if I run one lamp in this two lamp fixture if could catch on fire. The fixture has two 13watt CFL's.

Can that be right?

No. Inevitably one lamp will fail before the other.

Screw in 13W? Take it out and its no issue. pin based? It might not light up, or the lamp/ballast may fail early, but not a fire hazard.

Some are parallel wired. Some are series (Most programmed rapid start). Series wired ballasts often support one or two lamp operation, but you need to rewire it if you're going to make it one lamp.

If it's a series wired system, it won't light up when you pull one lamp.
 
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