Subpanel Load Help

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Old 03-14-18, 05:55 PM
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Subpanel Load Help

Hi!

My house is a circa '26 Bungalow and my gas lines need to be replaced. The only gas I'm using in my garage apartment is for a water heater which I want to switch to a electric tank less so I don't have to run gas lines all the way out to the garage.

I've got a garage sub panel that has been wired to my main house panel via a two pole 100 amp breaker. The sub panel, pictured here, was wired by a licensed electrician and was setup to accommodate the wiring of my wife's electric kiln which you can see is on the two 50 amp pole breaker on the right. The panel has a number of breakers not in use. The only ones in use are:
Left: 20 amp, 15 amp, and 20 amp
Right: 20 amp, 20 amp, 20 amp, 2x50 amp ( kiln ), 2x20 amp window ac unit.

The main tank less unit I'm looking at requires a 2x40 amp breaker with a max draw of 75amp.

Considering I never plan on using the tank less and the kiln at the same time would this be acceptable? If not what would be the max breaker/ amp draw I could use?

Thanks for your help!
 
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Old 03-14-18, 05:59 PM
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Welcome to the forums.

The main tank less unit I'm looking at requires a 2x40 amp breaker with a max draw of 75amp.
If the water heater has a 75A requirement... you would need a 2P80A breaker.
 
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Old 03-14-18, 06:07 PM
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I'm just going by their spec sheet. So their information is incorrect?
 
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Old 03-14-18, 06:18 PM
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This is their wiring schematic.
 
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Old 03-14-18, 07:37 PM
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Ok.... so you need two) 2P40A breakers. That is four breaker spaces.

That load will be pushing that panel to the limit. Normally a load of that size is connected to a 150A or larger panel. If you keep the other circuits use light you may squeeze by but if the A/C is running.... it will be close.


Just as an aside.... you have several problems in that panel. There should be a connector at the bottom where the main wires enter the panel. I see 4 wires were run to the panel which is required for a subpanel but the neutral and grounds are combined which defeats the whole purpose of running 4 wires. The white connection on the right bar is neutral. It is carried over to the left side. That green wire should be on it's own ground bar bolted directly to the panel. All the bare grounds should be on that ground block. The bond strap with the green screw should not be in use.
 
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Old 03-14-18, 07:49 PM
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You also have Square D breakers in a non Square D panel that should not be used there.

I hope the feed is in conduit and not just conductors entering the panel.
 
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Old 03-19-18, 10:13 AM
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Thanks for your help. Due to the load demands I decided to just switch out my gas hot water to a regular electric one. Comparing the amp draws of about 72amps to 18amps kinda made the decision for me.

With regards to the panel issues, yes the main wiring is in a conduit that comes up just behind the panel. I will switch out the SqD breaker for a 20 amp Siemens This panel was the one originally on the house and was reused for the garage service upgrade. After reading your comments I noticed a bar at the bottom that connects the common bus on the right to the ground buss on the left. So I should disconnect that large jumper bar and put all the commons on the right and grounds on the ground buss on the left? Does changing this depend on how its wired at the main panel?

Thanks
 
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Old 03-19-18, 11:51 AM
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Due to the load demands I decided to just switch out my gas hot water to a regular electric one. Comparing the amp draws of about 72amps to 18amps kinda made the decision for me.
For what it's worth, the on-demand water heaters aren't necessarily a good investment. They are more expensive, and though they may save money, many people run into the same issue you are where their electrical system (or gas piping) needs to be upgraded to support it. They also seem to have more repair issues - though I'm not certain of the statistics on that.

So I don't think it's a bad change!

You'll set up a standard water heater circuit - 30A double pole breaker and 10/2 (with ground) wire.
 
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Old 03-20-18, 06:59 PM
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You also have Square D breakers in a non Square D panel that should not be used there.

I also see a GE 2 pole and a Challenger 1 pole breaker. I don't believe either of them should be in a Siemens panel either.
 
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Old 03-20-18, 07:13 PM
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I recommend adding two ground bars, one to each side, and moving all the grounds to them. Leave both of the existing bars in the panel as neutral bars.

Considering I never plan on using the tank less and the kiln at the same time would this be acceptable?
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I don't see how this is possible since kilns will run for many hours at a time and it is common to need hot water many times a day.

I would agree that installing a larger tank water heater is the better option. You may have an off peak program in your area. Also check out the poly Marathon water heaters.
 
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Old 03-20-18, 10:24 PM
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Given gas WH may cost one third less to heat water as electric in some parts of the country have you considered moving the WH to the house? Of course it depends on gas$ vs electric$ in your area. It would also mean quicker hot water at the tap.
 

Last edited by Tolyn Ironhand; 03-21-18 at 07:42 PM. Reason: typo
 

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