Is it me, the meter, or the load?!

[wanderer]

I have been tasked to take voltage/amperage/wattage readings of various light fixtures on a lighting upgrade job. I was told to use the company's AEMC 8220 power quality meter with an MN-193 clamp. The meter and clamp were NIST certified within the last 6 months. I've checked multiple fluorescent and LED fixtures with it since the certification and everything seemed fine. I've used this meter before and it works well.

A couple of days ago, I was trying to get readings on 400w pulse start metal halide fixtures and nothing seemed to make sense. The wattage is was getting was around 300-340 watts input. I tried again today (after some advice from AEMC tech support) and ended up getting a reading of 1.6 amps and about 163 watts at 120 volts. To try to convince myself that something was wrong with the meter, I used a Fluke i400 plugged into a 3000 FC meter and pulled out my old Amprobe amp clamp and both showed 1.6 amps! I've double checked the settings on the clamp and meter and they seem to be correct.

I've verified that the lamp is a 400 watt pulse start and the ballast is a 400 watt ballast. Each reading was taken after the light was on for at least 15 minutes to warm up the lamp. Since we are removing the lights, I've been able to test several fixtures and get results well short of the roughly 460 watts we would expect to see.

I'm sure I'm missing something obvious, but I can't figure it out. The meter seems to work fine for fluorescent and LED loads, but seems to be grossly wrong on this metal halide. Either that or I've found a 400 watt rated fixture that only consumes 160 watts.

Thanks in advance for any input!

 

[Another C10]

seems to be grossly wrong on this metal halide. Either that or I've found a 400 watt rated fixture that only consumes 160 watts.

The fixture may be capable of providing for a 400 watt power consumption but maybe they used a smaller wattage lamp which would consume less wattage accordingly, maybe the voltage is higher at that specific time of the day or that phase of the circuit. Troubleshooting can be quite a challenge.

 

[hillbilly1]

Seems like they are able to retrofit with a 320 watt lamp, but that still wouldn’t get the amps down that low.

 

[hillbilly1]

I would think that meter would do true power, not apparent power, after re-reading it, I see you verified the lamp as a 400. Maybe do a foot candle check and see if it is close to spec. I wouldn’t know what a manufacture would gain by incorrectly stating the wattage.

 

[texie]

I'm not an HID lighting expert but is it possible that as MH lamps age they consume less wattage?

 

[ptonsparky]

Are you using the 120v tap? I just had to ask. I don’t know how they would react with 120 to the 208 or whatever. Guessing the magic smoke would come out.

 

[Hv&Lv]

Just how old are these lamps?
could be your meter is right If they are very old.

 

[wanderer]

Thanks for all of the replies. The lamps are in fact Venture MP 400W/C/V/UVS/PS/737 and the ballasts are Advance autotransformer 71A6092. The lamps have probably been replaced as they failed (as opposed to group relamping). I've tested the newest looking lamps. The fixtures themselves don't look too bad. I'd guess maybe 10 years old tops. All of the ballasts and capacitors I've looked at appear to be original.

Since a couple of people have asked about aging lamps, I had always figured that the wattage of a HID lamp stayed more or less the same as they age, but the lumens depreciate. Am I mistaken in this?

I also wondered if the fixture was tapped wrong, so I double checked that the ballast is connected at 120 volts.

The meter does do true power, I am probably getting some terminology wrong. Sorry, I don't usually have to analyze these readings this deeply.

 

[Hv&Lv]

Thanks for all of the replies. The lamps are in fact Venture MP 400W/C/V/UVS/PS/737 and the ballasts are Advance autotransformer 71A6092. The lamps have probably been replaced as they failed (as opposed to group relamping). I've tested the newest looking lamps. The fixtures themselves don't look too bad. I'd guess maybe 10 years old tops. All of the ballasts and capacitors I've looked at appear to be original.

Since a couple of people have asked about aging lamps, I had always figured that the wattage of a HID lamp stayed more or less the same as they age, but the lumens depreciate. Am I mistaken in this?

I also wondered if the fixture was tapped wrong, so I double checked that the ballast is connected at 120 volts.

The meter does do true power, I am probably getting some terminology wrong. Sorry, I don't usually have to analyze these readings this deeply.

Input wattage depreciates as they age also.

 

[hillbilly1]

As

Input wattage depreciates as they age also.

As does light output, FC readings would probably verify that.

 

[wanderer]

Input wattage depreciates as they age also.

As

As does light output, FC readings would probably verify that.

Ok, that's good to know. The meter is working fine, the fixture is fine, and I've learned something. The footcandles in the area were pretty low (about 10-14), but I don't have access to what they would have been when the lamps were new. I might try to get my hands on a new 400w pulse start lamp as an experiment.

Thanks to everyone who replied, everyone on this forum and Mr. Holt! I've been coming here for years to learn and it has been a huge resource.