| My community has low voltage (12 volt) lighting that illuminates our entrance signs. It’s 4 – 20 watt halogen bulbs connected to a 300w transformer. There’s a problem that has made them go dim. The setup is relatively simple; a transformer and two pairs of lights wired in parrallel. |
Since the installed system uses four 12 volt bulbs that are 20 watts each, I duplicated that setup on a test board. With all four bulbs installed and connected to the transformer, all bulbs light at full brightness when I test at my house. BUT, when I return to the scene of the crime where the transformer is normally plugged in, they glow dimly. In the breaker panel at the problematic location, with no load, I measure 248 volts across the two hot legs and 124 volts from each hot leg to neutral. So far, so good, right? When I add the load, the leg the load is on drops to 63 volts and the other leg goes to 185 volts. If I move the circuit to the other leg, that leg goes to 63v and the opposite leg goes to 185v. In other words the voltage drop follows the load and the opposite leg increases to 185v. I didn’t find any loose connections, but tightenend everything anyway. All of these measurements were made in the breaker panel on both the bus and leads that come in to the main breaker. I didn’t get into the meter. Any thoughts?
Replies
Quickstep,
The transformer has a 120V primary and a 24V secondary? You are plugging in into a 120 volt supply both at your house and at the entrance sign?
Rich
120V primary and 12V secondary. And yes, I am plugging in to 120v at both places.
PS, I should have mentioned, - this did work properly when first installed a few years ago.
QS,
I have run across several faulty breakers over the years at my business. They exhibit similar symptoms. Read proper voltage until you put a load on them, then they drop :(Bill Koustenis
Advanced Automotive Machine
Waldorf Md
I tried two different breakers with the same results.
sounds like a bad nuetral/ground for the centertap on the utility companys transforner
Like boahet said, somewhere upstream of where you're measuring the neutral has come loose. When that happens, you aren't going to have 120V across each leg. Rather, the voltage will divide itself according to the impedance of each the loads of each leg.
Are there any other loads connected to the utility transformer? Everything downstream of the problem will have the same issue. Might be yours, might be the utility's problem. Good luck!
You might wanna post this over at Breaktime, but the universal response in cases like yours seems to be "bad neutral connection." I wouldn't doubt that therein lies the problem.
Mike Hennessy
Pittsburgh, PA
Mike, I'll send this to you even it is old hat. Most assuredly, this is a bad neutral connection. To tell if the problem is yours or the providers, put your meter on the terminals or wires right where it comes into your entry panel. If you find uneven voltages there, it the providers problem. When you call them and tell them of the different voltages, they should be there within minutes. From the time you report the problem until they appear on the job, any damages, injuries etc. is their responsibility. I had this problem with a house where there was a wide discrepancy of voltages. When I mentioned the problem I got this ho hum attitude until I mentioned the exact voltage differences. She stopped me in the sentence and said she would send someone right out.
Thanks to the help from you folks, my problem is now fixed. The guy from the power company was pretty impressed with my troubleshooting and the fact that I had isolated the problem for him. Little did he know I have a bevy of experts behind me! He also indicated that they take bad neutrals pretty seriously and the problem was corrected the next day. Thanks for all the great advice!
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