Electrical Questions? Ask an Electrician Online.
A Master Electrician here to help. I am a double qualified; USA & UK electrician. Please give me a moment to formulate a reply.
Your first step is to contact your local Utility company and tell them you have a partial power outage
From what you describe the fault is on their end. Even if it is not they will not charge for checking it out
Wouldn't that cause the problem to other sub panels and the main panel as well?
Also you say power drops to zero amps. Do you mean zero volts?
Absolutely it would yes, but if the sub-panels are fed through the main panel as they should be then if they are OK then the main panel should be too
No, I mean Amps. Their is no load
The main panel is OK
This occurs on one of three subpanels
You need to use a 2 lead voltmeter and check for incoming volts across each leg at neutral (120 volts) and across both legs (240 volts) on main panel and subpanesl
I must have misread.
OK so it is not a utility problem
The electrican did that but, when the system was working properly. He did it at each breaker as well
still do those voltage checks
It needs to be done at the main lugs of the sub panels and the main panel breakers feeding them when the fault is there
What will that determine
The dryer bringing the one leg back on identifies this as a lost leg
That you have lost a leg and the location where it is lost
I know we are losing a leg
Do you know where?
If not follow my procedure
All I know is that I lose an entire leg of alternating breakers on the one subpanel
OK so do you weant to follow my advice?
All I know is that when I put a tester on it, the leg was drawing a 6A load and then it drops to 0A. Then I turn the dryer on and it jumps up to 26A. Then when I turn the dryer off, it returns to 6A ( or whatever it was based on what was on at the time).
You need to identify if the fault is at the sub panel, at the main panel or in the wiring between them
I am ready to try anything
NOT AMPS We need volts. Please re-read all I have written
When the system is working propery, both legs are drawing 120V. The electrician checked it accross both legs and siad it was fine as well (240V I assume)
OK good luck I am opting out. I cannot help if you do not listen.
To start with forget about the amps, we are looking for a loss of voltage.
The problem will be with either the breaker feeding the sub-panel or the connection at the sub-panel.
What I want you to do is to turn on every appliance that is powered off of the sub-panel and let me know if the power starts to drop.
I'll wait here.
You would use a volt meter.
I am asking to to put a load on the circuit so we can find the location of the problem.
Let it run for a little bit. What this is doing is heating up the bad connection. Once it is heated up, the connection will start causing the problem you described.
Check the voltage from hot to neutral, do this for both hot lines and tell me the voltage.
Are you checking the voltage at the main panel or the sub-panel?
Yes, make sure the scale is set to 240v if it is a multi meter. Becareful you don't get shocked.
I see that the breaker for this panel is 50A.
What appliances are being fed from the sub-panel?
Well I can tell you it is probably the 50A breaker that has gone bad.. That is way too much load for that size breaker.
How big is the main panel in your home?
How far is the sub-panel from the main panel?
If all of the connections look good, and there are no splices in the cable and this problem only happens in the sub-panel.
I would say it's a bad breaker or the connection where the breaker connects to the panel bussing.
Let me know if you need more help.
Correction on the dryer breaker size. It is a 30A breaker. It is a quadplex breaker and the inner 50A section is for the double oven. The outter 30A is for the dryer. Sorry about the confusion. I am going to check on splices in the main feeder to the subpanel tomorrow
I had another person mention a bad neutral to me at work the other day. We tightened all the neutral connections at the subpanel but, I haven't checked the neutral connection for the subpanel feeder at the main panel. I will do that today.
You confused though me when you said that "The oven is probably on another sub panel and that's why it doesn't affect the power". The oven is definitely not on another sub panel. In fact, it is off the same quadplex breaker that the dryer is served from. If turning the oven on doesn't restore power to the affected outlets the same way that the dryer does, does that rule out the neutral as being the problem? It seems that if the impacted circuits would pass the bad neutral thru the dryer element, it would do the same thing thru the oven.
Unfortunately (or fortunately), I haven't dropped power in the past 24 hours so, I cannot check the voltage across the impacted leg during an outtage.
If you were dropping the neutral, none of the 110v loads in the panel would work and most likely any 110v electronic loads would have burnt up due to the imbalance.
More data. Just lost power a few moments ago. Entering the subpanel,I get 120V on one leg. I only get 6V on the other leg. Then went to the main panel and checked the conducter coming out of the breaker that feeds the subpanel. I got 121.5V on both legs. I am guessing that this implies that there must be a splice between the connection to the breaker in the main panel and the connection to the lugs in the subpanel that is causing the problem but, who knows.....
Up into the very skinny attic space to see what I can find.
I also noticed that the conducters were aluminum instead of copper.
I would also check the terminations in both panels very carefully.
I have come across a few cases where I could read voltage on the wires and the lugs but not have it on the buss bar.
Regardless of where it is I would think you will see some sort of an indication of heating. This can be a discoloration or an actual sign of melting.
Please keep me informed of what you find and if you need help fixing it.
I have an electrician that specializes in service related issues from a larger electrical firm that I work with regularly coming by tomorrow AM. I am going to give him all the correspondence that was conveyed in this forum and see if it helps him determine the problem. I am tempted to just replace the 125A feeders from the main to the subpanel along with the subpanel breaker located in the main panel and move on.....I am hoping he can find the root cause but, I doubt we will lose power while he is here and I fear that wil make it hard for him to zero in on th issue. Hope still prevails though.
FYI, I plan on accepting each of the opinions listed on this forum that the electrician feels helped him diagnose the problem. Unfortunately, I still think electricity is magic and can't determine what the proper fix is from the recomendation listed. Thank all of you for your help though and I will post the findings later tomorrow. - Scott
Sounds good Scott.
I'm anxious to know the final out come, so please keep me posted.