Cascading sub panels


Old 06-01-06, 10:16 PM
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Cascading sub panels

I currently have a sub panel attched to my main panel with a 70 amp breaker and 3 conductor with ground 6 gauge wire. There is a a/c unit attched to the su panel with a 40 amp breaker. The a/c unit generally turns on in the late afternoon.

I would like to attched a sub panel to be located in a utility shed to the exsisting sub panel. From the new sub panel I need to attach a 240 volt electric instantaneous water heater. The install guide states the I need two double pole 32 amp breakers and run 8 ga 2 wire with ground to the heater. The length of the run is approx 100 feet from the existing sub panel to the newly planned sub panel.

If I want to locate the double pole breakers in the newly planned sub panel, what gauge wire to I need for the run and what size breaker.

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Old 06-02-06, 06:20 AM
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If at all possible, I recommend NOT feeding a sub panel from a sub panel. It would be better to feed the new sub panel from the main panel.

The answer to your question depends on what else you want to power in the shed. The requirement for two 240 volt breakers for one water heater does not sound correct.

What are ALL the loads you will have in the shed?
Old 06-02-06, 08:42 AM
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Actually, several models of electric demand water heaters are using multiple 240V circuits now. The device contains multiple heating elements that are turned on by a central control unit individually as demand increases. Each element or set of elements has it's own circuit. This makes it possible to run several smaller more easily managed cables to the unit instead of one honkin' hard to manipulate huge one.

Keeping in mind that this water heater is likely going to pull over 50 amps when it's running at full capacity, I'm not sure the sub can handle it at all. I hope this is a 200 amp service.

Doug M.
Old 06-02-06, 09:20 AM
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[QUOTE=racraft The requirement for two 240 volt breakers for one water heater does not sound correct.


It sounds like he has a tankless WH. This is a common requirement for that type of equipment.

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