To start this is a 70's fourplex w/detached garage. Garage has a sub panel with two 30 amp screw in fuses. Which are fed by a breaker 20 amp double pull sub panel in utility room. Have had no problems with it till recently. The garage breaker 20 amp double would trip. Checked the fuses in the garage are fine. Reset, fine for a few hours, and trip again. This went on for a few days, then the 100 amp breaker which feeds the 20 amp double pull would trip as well, shutting off hot water heater, outlets and lights in the common area. Thought there may be a short in garage panel so, disconnected contact bar, removing garage fro m equation. Reset the double pole breaker, and after about an hour the 100 amp breaker tripped. Have 120 through top and bottom of double, no burn marks wires are tight. Any Thoughts?

Pallidin,

I apologize for the advertisement you received. I will try to have that pulled from this thread.

I need to understand you configuration a little better, please.

1) Is the 100 Amp breaker the main breaker in your panelbox?
2) This double pole 20 amp breaker, is it being used to feed a multi wire branch circuit or is
It supplying the secondary panel board with 240 Volts as a feeder for the entire
Secondary panelboard.

This critical. If you are just trying to use a multi wire branch circuit and any one of the Neutral connection breaks, then you will be supplying 240 Volts across both parts of the multi wire branch circuit.. This can and will fry devices. Not only does the applied voltage double but so does the circuit's Amperage.

Also, normally, you use a dedicated 240 Volt 20 Amp circuit for the water heater. In code you can continue the circuit to other 240 volt devices unless themanufacturer's instruction call for a dedicated circuit.

What you cannot do is continue the circuit and start taking 20 amp 120 volt outlets for receptacles or devices.