Sub panel breaker box fed off main breaker box

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  #1  
Old 05-18-13, 12:39 PM
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Sub panel breaker box fed off main breaker box

The main breaker has 150 amp service (probably 100 amp service, just a 150 amp main breaker). There is a secondary breaker box in the garage. The main box has a 50 amp breaker to the garage box. The water heater breaker is 30 amp. I want to install a tankless heater. It requires a 60 amp. Can I replace the main box breaker (to the garage box) to a 60 amp AND the water heater breaker to a 60 amp?
 

Last edited by PJmax; 05-18-13 at 12:41 PM. Reason: corrected title
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Old 05-18-13, 12:41 PM
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Welcome to the forums.

I just edited your title to better represent your question.

You can only increase the breaker size to your sub panel if the wire is large enough to carry that load. It sounds like you'll need a larger cable run to the sub panel.

Can you see a size listed on the cable ? Like 6-2 w/gr or 6-3 w/gr
 
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Old 05-18-13, 01:50 PM
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I am not extremely electric savvy. Best I can tell, you are correct. The sub panel looks as though the previous owner (underground mine electrician) wired the sub panel himself. There are wires coming out everywhere. I am not opposed to replacing breakers or wiring, but this project may require a little more expertise, for safety and piece of mind. Thanks for the quick response and proper terminology. I will investigate further.

Thank You
 
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Old 05-18-13, 02:42 PM
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Assuming this is an attached garage best course of action may be to run NM-b from the main panel. If detached you will need to upgrade the wire or cable to the subpanel.

The main breaker has 150 amp service (probably 100 amp service, just a 150 amp main breaker).
Can you explain more fully. A 100 amp panel should not have a 150a breaker. A 100 amp service may not be able to power a instant water heater unless your major appliances are gas and heat gas or oil. Worse if it is truly a 100 amp panel with a 150 amp breaker there is a chance of damage to the panel or meter feed using a 60a IWH.
 
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