250 Watt HPS Lamp in a 400 Watt HPS Fixture

[mikezima]

I have opened one light in a parking lot and found ballast that says "use 400 watt S51 bulb" and the bulb was 250 watt and seems to be working normally. Is it OK? Some people say it is wrong, it will shorten life of the bulb... and so on.
My view of this issue is this: the ballast works at 62% of its capacity, the bulb takes as much power as it is rated for, therefore, nothing wrong will happen, except the efficiency of this whole deal is not the best one. Am I correct? Another similar (as I think) example is an engine working at half of its capacity or #10 copper wire delivering 15 amps to the load.
Thanks for looking into my terrible problem.. )

 

[iwire]

the bulb takes as much power as it is rated for, therefore, nothing wrong will happen,

That is incorrect, the entire point of the ballast is to limit it the current drawn by the lamp. A 400 watt ballast is going to allow to much current flow into the lamp shortening its life.

Use only lamps that match the ballast.

 

[GoldDigger]

People not familiar with small or negative resistance in arc lamps may not realize that, like LEDs, the voltage across the element does not increase fast enough (or at a) as current increases. This makes it impossible for the bulb to regulate on its own the power that it consumes at a particular supply voltage.

 

[mbrooke]

Two things:

Either the ballast was changed to a 250 watt version or the bulb is indeed over driven.

An over driven bulb is at risk of arc tube rupture especially if metal halide. The lamp will run for some time but with a greatly reduced life. I would not be surprised if the bulb starts to cycle soon.

 

[Haji]

I have opened one light in a parking lot and found ballast that says "use 400 watt S51 bulb" and the bulb was 250 watt and seems to be working normally. Is it OK?

Check the current from the ballast to lamp with a clamp meter. If the current is per the manufacturer's data, it is okay. A rough calculation for lamp current is 250/260=0.96A. So I think if the current is less than 1A, it is okay for 270V lamps.

 

[iwire]

Check the current from the ballast to lamp with a clamp meter. If the current is per the manufacturer's data, it is okay. A rough calculation for lamp current is 250/260=0.96A. So I think if the current is less than 1A, it is okay for 270V lamps.

Unless the labeling of the lamp and the ballast match it is an NEC violation of 110.3(B) regardless of any measurements taken.

 

[Haji]

Unless the labeling of the lamp and the ballast match it is an NEC violation of 110.3(B) regardless of any measurements taken.

I do not agree with your interpretation because how you are sure the lamp and ballast does not match.
So listing of the lamp and ballast is to be checked and who would do that apart from empty argument?

 

[iwire]

I do not agree with your interpretation because how you are sure the lamp and ballast does not match.

By the labeling. The ballast and lamp both have labels and must match

So listing of the lamp and ballast is to be checked and who would do that apart from empty argument?

A professional who follows the rules.

 

[Haji]

By the labeling. The ballast and lamp both have labels and must match

Matching must be checked with the listing of the ballast and lamp: For a ballast of given wattage, one or two sizes of lamps may be used. For example, for 40W, 4' fluorescent tube light magnetic ballast, 40 W or 36 W 4' fluorescent tube light may be used.

 

[kwired]

Matching must be checked with the listing of the ballast and lamp: For a ballast of given wattage, one or two sizes of lamps may be used. For example, for 40W, 4' fluorescent tube light magnetic ballast, 40 W or 36 W 4' fluorescent tube light may be used.

Linear fluorescent ballasts are often designed to drive multiple lamp types, HID ballasts are typically only designed to drive one lamp type. Some will drive same/similar wattage mercury vapor and metal halide lamps but other then that they all are specific to just one lamp.

 

[iwire]

Matching must be checked with the listing of the ballast and lamp: For a ballast of given wattage, one or two sizes of lamps may be used. For example, for 40W, 4' fluorescent tube light magnetic ballast, 40 W or 36 W 4' fluorescent tube light may be used.

You are absoulutly correct and I agree with this 100%.

That ballast will list both (and more) allowable lamp types.

But ...

We are talking about a 250 watt HPS ballast and that 250 HPS watt ballast will not list a 400 watt HPS lamp as acceptable.

Personally I look for the ANSI code on the ballast and order a lamp with the same ANSI code.

The ANSI code for 250 watt HPS ballast is S50

The ANSI code for a 400 watt HPS lamp is S51

The codes do not a match and should not be used together.

http://www.kolmart.com/HID-ANSI-Code-Guide_b_3.html

 

[Haji]

Linear fluorescent ballasts are often designed to drive multiple lamp types, HID ballasts are typically only designed to drive one lamp type.

What may be the reason.........

 

[kwired]

What may be the reason.........

I honestly don't know. From experiences I will say that older magnetic ballasts were a little more specific to a limited number of lamp types then newer electronic ballasts seem to be, so I will guess the electronic ballasts are in a sense able to sense the needs of the lamp and deliver what is needed. Many electronic ballasts even work on multiple input voltages - without the user having to configure them for the input voltage. A magnetic ballast is designed for a farily specific input voltage range, but may be changeable by manually re-configuring input taps.

I'm sure there is probably electronic ballasts for HID lamps but the magnetic ballasts still dominate the HID's in use from what I can tell. Those electronic ballasts that are out there may possibly work on more then one lamp type whether automatically or manually configured to match the lamp - I haven't a clue.

With the rapidly changing LED world - I don't know that anyone is focusing much on improving HID's either. HID days are not over yet, but I think it is coming.

 

[GoldDigger]

It is common for electronic ballasts for fluorescent tubes to accommodate different numbers, but they have separate wires for each lamp.
It is less common for the ballast to accommodate different lsmp types. Except ones with compatible electrical characteristics, such as 40W and 36W economy tubes of the same length.