Electrical Wiring in the Home/balancing 240V panel


I want to replace my old hot water tank with a tankless electric.
The existing breaker is 220V 20A  
   The manufacturer (Stiebel Eltra 20) says 2 separate 50A breakers and two runs of #8 wire. This makes no sense to me, there is a potential of 2 50A breakers on the same phase.
  why not a double 50A 220V breaker cabled in with 8-3? Or am I missing something?

Hi Jim,

These units require a lot of power to keep hot water flowing instantaneously.

Here is a quote from their installation manual:  

"TEMPRA 15, 20 or 24 B/Plus: These units require two independent circuits. Use two supply cables protected by two separate double pole breakers (see 2 )."

You need two 50 amp double pole breakers, which means double the wiring.

I suggest checking with local codes to make sure the #8 is sufficient for a 50 amp breaker. Usually it requires #6.

The two double poles will help balance out the load.

Your adding 80 amps to your panel so make sure it is large enough to handle the new load.

Hope that helps.
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Electrical Wiring in the Home

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Greg Hughes


Troubleshooting electrical including appliances and HVAC.


34 years of experience.

Both college and tech schools in this field.

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