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LynnX 01-09-2013 06:17 PM

Increase size of main breaker
Good Afternoon!
I am rehab'ing my California townhouse that was built about 33 years ago. It has a main disconnect panel outside rated 125A. A 70A two-pole main breaker is installed, and is connected to a 125A panel inside via #1 AWG AL feeders. All house circuits originate from this inside panel.
I loaded up one pole with about 94 Amp of load current (based on max. power specs for each appliance), including A/C condenser, space heater, washer, vaccuum, mixmaster, toaster oven, microwave, drill, blender and a dozen lights.
I expected the main 70A breaker to blow, but nothing happened. The breaker did not even get warm.
How long should it take for an overload (more than 10% of breaker rating) to trip a breaker?
Is it likely that I was using much less that the max. rated currrent on each appliance? Any suggestions for an AC clamp-type current meter?
I would like to replace the 70A breaker with a 100A breaker. I have worked with Aluminum wiring before and would use NOALOX.
Will #1 AWG AL support 100A entrance service? Section and Table 310.15(B)(6) in the 2010 Code appear to allow this.
The local poco said they would come out and unlock things so that I can pull the cover and perform this "repair".
Thanks for your comments and suggestions.

Jim Port 01-09-2013 06:50 PM

Breaker trip curves vary based on the amount of overload and the time taken to get to overload. A typical breaker will hold 125% for around 2 hours.

sgip2000 01-09-2013 07:07 PM

Is it a "Federal Pacific" panel?

Missouri Bound 01-09-2013 07:17 PM

#1 AL will support 110 amps in a service. I own an Amprobe clamp-on ammeter and it's just fine. If you are planning on doing a lot of work spend the money on a good meter. If it's just an occasional thing for you some are available for as little as $25. If it's service wires you intend to meter make sure the clamps are large enough to get you in the panel since you won't be pulling the wires out too easily in some installations.:yes:

LynnX 01-09-2013 08:11 PM


No, not Federal Pacific, but both panels are GTE Sylvania.

I will get to have a look inside the main panel tomorrow.

LynnX 01-09-2013 08:52 PM

I have been reading about problems with Federal Pacific and Zinsco/Sylvania equipment. I do not know if these apply to my panels.

I think I will pull all the breakers, inspect the points of contact, clean and NOALUX them. Or come up with a plan "B" if there has been overheating.

Connecticut Electric makes Zinsco-compatible breakers that are almost identical (physically) to GTE/Sylvania breakers. These are available at Home Depot and at Amazon. Is there a significant difference between "UL-approved" and "Conforms to UL Standard 489"?

rrolleston 01-10-2013 07:16 AM

If you are going to be doing a lot of DIY work in the future I would look at fluke meters they make a variety of nice meters.

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