Measure voltage from the top/incoming of each breaker to the bus below it. IF the breaker is good the voltage will be zero, if bad it will be something other than zero. forget about the water heater or anything else. If you have 240 to the main breaker and anything other than 240 AFTER it, the problem is in the breaker or its connections. You are making your problem WAY too difficult. All you have to do is make FOUR measurements and you will know where the problem is. Feed to feed, bus to bus, feed to bus1 and feed to bus2.
Last edited by hj; 02-18-2012 at 04:55 PM.
Licensed residential and commercial plumber
I'm not sure if this house was ever getting more than ~200V combined.
Look at it this way...the CB are just smart disconnect switches. A switch connects the input to the output. There should be effectively a direct short between the input and the output. If you were to measure with your meter on one end of the bus bar to the other end of the same bus bar, with the meter you likely have, you'd measure zero volts, since the bus bar is acting like a short connecting the two ends. A CB is similar. So, if you measure from the inlet to the outlet across the CB, it should read zero volts since the switch inside should be closed (or shorting the inlet to the outlet). If you measure some voltage, that means that the switch isn't working properly and is acting like a load - dropping some voltage inbetween.
It can get a little messy depending on the load, if any, and sometimes you need a load to get an accurate reading.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013
Is is a Federal Pacific panel?
ok I think I see...but I'm pretty sure the two suspect breakers are working ok since I tried those circuits on other breakers with the same result...albeit I did do a lot of different measurements putting the panel back together and may have got confused over what I was doing. I'll measure that way and see though.
Apparently the panel is made by Zinsco...the breakers look like this:
The Zinsco panels are well known to have problems with degradation of the buss and the breaker to buss connections.
If it were my panel, I would have the meter pulled and remove all the breakers including the main to inspect for any sign of corrosion or arcing at the buss to breaker contact points.
Many electricians recommend replacing these panels due to their reputation alone.
A good case made for better metals on the bars and the use of anti-oxidants. I had nearly the same problem, had to change the hot main, [bolted in, so not a fun bit of work] didnt want to go thru the hassle with the smart meter pull. One leg of the main gave partial readings relative to the meter bars.