I want to install a tankless water heater.

Currently there is a broken electric tank heater with a 10/2+grnd wire. It seems the white and black are going to the 120v rails (heater at 240v) and there is no neutral. I'm not even sure if that's OK for the heater and I know the colors are wrong. Doesn't seem as though the heater needs a neutral anyway.

The electric tankless calls for 240v, 88amps max draw and the installation instructions say 2 separate 50amp breakers. It suggests using 2 8guage cables. But although I know 8guage can carry 50amps and much more in air, code says I can only use it with 40 amps. So would it be OK to use the mfg recommended 8/3, or should I use 6/3? Going up and down the walls, it will be between 35-50ft run per cable.

Also I have 200amp main. Is that enough? The total amperage of all the breakers can be higher than 200 since it's not all used at once, correct?
Now there's:
On Left:
60A dipole for the AC
15A lights
20A all 3 bathroom lights+fans
15A pantry outlet
20A bed 3 / living room, (half) bath 1 sockets
20A bed 1&2 / bath 1&2
Blank
On Right:
30A dipole old hot water
20A washer/dryer (gas)
20A kitchen/dining sockets
20A stove(gas)/disposal/fridge
20A dishwasher /closet socket
30A unknown? (asked in separate question)
30A unknown? (left off)


And there is only 1 blank, so if I remove the current 30A dipole,
There still isn't room for 2 50 dipoles, unless I also remove the two
Unknowns. Is there a way to consolidate some of the sockets?


Thanks,
Adam


EDIT: my place is about 1100sqft, 2 story, 3bed 2bath upstairs and 1/2 bath kitchen livingroom downstairs

Last Insta Heat I installed close to that, I ran a Pair of #4's from main panel protected by a 100 Amp Breaker, then to the InstaHeat Disconnect- 2 50 Amp 2 pole Breakers.
Wonder If someone added 2 Jumpers to work off Double Pole Breaker, instead of 2 Double Pole Breakers?

I just went out and looked at the breaker right after the meter.
There are two large breakers that each 100A and the handle is connected.
Does that mean I only have 100amp service?

[EDIT]:
Or is it 2 100A in parallel giving me 200A?

I flipped the main off and opened the breaker box. The main is distant so the box was 100% dead as I checked with a multimeter.

The cable going into the box is pretty thick. It looked like it was Al not Cu. I'm not sure what gauge it was. I'm not sure how to calculate
Equivalent gauge when each wire in the cable is made of a number of smaller wires.
I measured the individual wires with a caliper and they were about 2.5mm. There were 7 of them.

So what gauge is 7 10gauge wires equivalent to? Will that handle 200amps?

Thanks,
Adam

Sounds like only #2 wire and a 100 amp service. To use the water heater ,the service will need to be increased.

Pictures will help.

I wonder how many people installed one of these water heaters on a service that is too small.

Hmm, I just calculated the cross sectional area of a 10ga. Multiplied by 7 and found 7 10ga. Would have about the same cross sectional area as a 2ga.
But cables in parallel add up amperage so why wouldn't it just be, since 10ga. Is good for 30amps, 30*7 = 210amps ?
Also, due to the skin effect, wouldn't 7 10ga bundled wires carry more than a single 2ga anyway?

Oh yeah, the panel has 4 wires coming in from the main. A black one for the left rail, a black one w/red strip for the right rail, a white one goes to the white bar on the bottom, and the other goes to the ground. Since the 2ga can handle 100amps, wouldn't 2 of them handle 200amps?

I can take some pics of it tomorrow.

Here are the pics:



http://phazei.8m.com/ext/electric/104_0064.jpg

http://phazei.8m.com/ext/electric/104_0065.jpg

http://phazei.8m.com/ext/electric/104_0069.jpg

http://phazei.8m.com/ext/electric/104_0074.jpg

http://phazei.8m.com/ext/electric/104_0079.jpg

http://phazei.8m.com/ext/electric/104_0080.jpg

And the rest:

http://phazei.8m.com/ext/electric/104_0081.jpg

http://phazei.8m.com/ext/electric/104_0082.jpg

http://phazei.8m.com/ext/electric/104_0083.jpg

I notice the Paint on inside of Electrical Box, Not Protected When painting During Construction, Most very likely Buss where Breakers Plug on to have paint and if not cleaned. It will cause burning of buss and overheating. Likely scraped clean with breakers.
If confident with electric and your house, I would Remove Power and clean Buss.
Has Nothing to do with your question, I just saw the Paint.
Do Not Power Up with Neutral Disconnected as Damage to Electrical Devices/Bulbs/Appliances will MOST likely occur.

Help?

Is 200AMP service 100AMPs per phase with 2 phases?

You have 100 amp service, which is 100 amps at 240 volts (uses both service legs together) or 200 amps at 120 volts (uses each service leg separately). It's still a single phase service--the two service legs are in phase with each other, but have opposite directions (so one is positive when the other is negative).

Since your tankless heater pulls 88 amps at 240 volts, you would only have 12 amps remaining to power all your other household things. No using hot water while the A/C is on for sure, and you'd probably have problems with much smaller loads. You'd constantly be tripping the main breaker.

You'll need 200 amp service to run an electric tankless heater. Upgrading to 200 amp service involves replacing your breaker panel, the cables bringing service into your house, and most likely your electric meter. My understanding is that a service upgrade can easily run $2500.

If I were you, I'd either stick with a tank water heater or go with a gas tankless. May run into the same issue with your gas lines not being sized for a tankless heater's demands as well.

I believe the above poster meant the 2 Hot legs are Single Phase. However they are 180
Degrees out of phase of each other?