Thread: disconnect for tankless electric water heater?

I'm roughing in for an 80 amp tankless electric water heater that will go under a bathroom sink. The manuf calls for 2 40Amp circuits with 8 gauge wire. Am I required to have an electric disconnect for it?

If so, would it have to be a small metal box with 2 40amp breaker switches? From there the wire would go directly into the water heater, just like a hot tub. Or is there an easier way?

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Originally Posted by corky kay

I'm roughing in for an 80 amp tankless electric water heater that will go under a bathroom sink. The manuf calls for 2 40Amp circuits with 8 gauge wire. Am I required to have an electric disconnect for it?

If so, would it have to be a small metal box with 2 40amp breaker switches? From there the wire would go directly into the water heater, just like a hot tub. Or is there an easier way?

Yes a disconnect is needed if it is not within site of the breaker box. The easiest way I could think of is to use two A/C disconnect boxes, one for each circuit.

Originally Posted by corky kay

I'm roughing in for an 80 amp tankless electric water heater that will go under a bathroom sink. The manuf calls for 2 40Amp circuits with 8 gauge wire. Am I required to have an electric disconnect for it?

If so, would it have to be a small metal box with 2 40amp breaker switches? From there the wire would go directly into the water heater, just like a hot tub. Or is there an easier way?

Originally Posted by Jim Luttrall

Yes a disconnect is needed if it is not within site of the breaker box. The easiest way I could think of is to use two A/C disconnect boxes, one for each circuit.

Yes you will need secondary disconnects even if the panel is within sight if you do not have a main disconnect (i.e. split bus).

Most tankless of such a size (two 40 amp feeds) that I am familiar with would require two circuits each protected by a minimum 50 amp breaker at the panel, some further require secondary protection at the disconnect some incorporate it. Double check your description, specifications and manufacturer installation instructions. Consult an electrician and your local building department for requirements in your area.

CK, U can use a lockout at the point where the circuit originates (breakers in the panel) as an alternative. Most breaker manufacturers have pad-lockable clips that install on the breaker itself, under the panelboard cover.
The only exception would be a local code requirement requiring a disconnect at the unit itself.
Bob Smit, County Electrical Inspector

The closer to the point of use the better ... under the bathroom sink is pretty darn close....

I also concur with Bob.. and breaker lockouts for double pole breakers are a simple installation. Just be sure they will work for your make of breaker .. some do some don't.

You can if you want have remote disconnects, that's up to you. I'm sure there are those who do not like the breaker itself as the disconnect.The disconnect is meant for routine maintenance or repair to the heater.

The other option is a panel close by the heater with two double 40's installed in it and this panel is fed from a double pole 90 or 100 amp breaker in the service equipment panel.. Basically install a panel specifically for this heater. Probably doesn't work for you but still an option.

There used to be a manufacturer (no longer in business) that included a panel with breakers just for this type installation

Thanks guys.

Here's one other option - how about an outlet, one for each 40 amp circuit? That is considered a disconnect, right?

Corky

Originally Posted by corky kay

Thanks guys.

Here's one other option - how about an outlet, one for each 40 amp circuit? That is considered a disconnect, right?

Corky

The WH would need to be listed for use with a cord.

There has been some problems with tankless water heaters being installed on Progress Energy distribution systems. Rather than trying to explain it here is a link to the information. It may or may not apply to your installation. If you have a heat pump with electric aux heat the likelihood goes up that it may be an issue.

Tankless Water Heaters - Progress Energy

Originally Posted by corky kay

I'm roughing in for an 80 amp tankless electric water heater that will go under a bathroom sink. The manuf calls for 2 40Amp circuits with 8 gauge wire.

The answer to for the disconnect question has been given, as well as an option for it, however, ...

You stated it was an 80 amp tankless electric, and that the manufacturer calls for 2 40 amp circuits - is that 2 40 amp 240 volt circuits (80 amps)? Or is it 1 40 amp 240 volt circuit (40 amps)?

I've not seen one yet but have heard of those things on 2 40 amp 240 volt circuits, seems like someone posted the installation instructions here for one a few months ago.

Jerry


It's 80 amps or two 40 amp 240 volt circuits. A 120 amp one is wired like this in most cases

Originally Posted by Roger Frazee

It's 80 amps or two 40 amp 240 volt circuits. A 120 amp one is wired like this in most cases

That is what I thought, but was verifying it based on the wording used in the original post.

Which brings up the point that the disconnect would need to be capable of turning off all power to the appliance, which would get back to your other post of having a double pole breaker, say an 80 amp breaker, supply a feeder rated for 80 amps, to a panel which then had the two double pole 40 amp breakers in it. The two double pole 40 amp breakers would provide the overcurrent protection, the double pole 80 amp would provide the disconnect needed.

You can run 2- 240 volt, 40 ampere circuits and set 2, 240 volt disconnects also, as long as they are grouped together.

Originally Posted by ken horak

You can run 2- 240 volt, 40 ampere circuits and set 2, 240 volt disconnects also, as long as they are grouped together.

And tied together and trip together. Guess you might be able to do that with a quad breaker and tie the handles together ... if they made a tie for that?

Originally Posted by Jerry Peck

And tied together and trip together. Guess you might be able to do that with a quad breaker and tie the handles together ... if they made a tie for that?

No not needed, Nice try

The equipment is calling for 2 - 240 volt circuits.
Water heaters either a storage tank type or tankless, fall under the code section 422 ( appliances).
422.30 tells us that when an appliance is supplied by more then one source the disconnecting shall be grouped and identified.

2 - 240 volt circuits are 2 sources of power for said appliance.

Side note - you can special order a 4 pole fusible disconnect. I have used them in the past on elevators with battery back up instead of an onsite generator.

Originally Posted by ken horak

No not needed, Nice try

It was a better try than you think ...

The equipment is calling for 2 - 240 volt circuits.
Water heaters either a storage tank type or tankless, fall under the code section 422 ( appliances).
422.30 tells us that when an appliance is supplied by more then one source the disconnecting shall be grouped and identified.

And that is supplied by ONE SOURCE ... not more than one CIRCUIT, but more than one SOURCE.

(underlining and bold are mine)
- 422.30 General.
- - A means shall be provided to disconnect each appliance from all ungrounded conductors in accordance with the following sections of Part III. If an appliance is supplied by more than one source, the disconnecting means shall be grouped and identified.

Here is an example of "more than one source""
- source a) utility power
- source b) back-up generator power

Side note - you can special order a 4 pole fusible disconnect.

If you install any of those two-CIRCUIT tankless water heaters you would need to order more of those 4 pole disconnects.

I have used them in the past on elevators with battery back up instead of an onsite generator.

Now you are back to using "source" correctly.

More than one source IS NOT more than one circuit.