Which wiring method is best for tankless water heater??

[rt66electric]

Which method would you select ?? and why??

Dwelling has 200 amp SquareD homeline panel with open slots.
Heater has (3) 240v 40amp elements (50amp max breaker)
Water hear closet is 40 ft away.

Method A
...... IN the main panel install (3) 50 amp breakers and run (3) 8/2 romex to individual 60amp pull-out disconnects.........then to the unit.

Method B
... Install 125 breaker in main panel to 1/0-1/0-2 Al SE cable to a 125 amp Main-lug subpanel located In the heater closet, then, use (3) 50 amp 2-pole breakers , then(6) #8 to feed the unit

Thank you for your input

Dennis

 

[JFletcher]

This has come up before. Unless the elements are all completely electrically separated inside the heater, you could potentially backfeed your panel bus. If this happened out of phase, you'd have a 240V short circuit.

What model and kw is the heater? There is no need to calculate then as continuous loads as they are not; a 125A breaker would be fine.

Eta: 3 runs of #8 or #6 from either panel to the heater is a no-go unless everything is completely separate; you would have those wires in parallel carrying a 120A load

second eta: I looked at an Ecosmart 27kw unit, and it does use 3 40A breakers with #8 wire for a 112.5A load. If you've got the space in your main panel for that, I'd be more inclined to pull 3 runs of 8/2 NM than to add a subpanel. Then again, wiring up 3 discos and their cost may make them vs a subpanel a wash.

 

[jumper]

A sub panel would need 4 wire SER cable.

 

[LarryFine]

Method A
...... IN the main panel install (3) 50 amp breakers and run (3) 8/2 romex to individual 60amp pull-out disconnects.........then to the unit.

Method B
... Install 125 breaker in main panel to 1/0-1/0-2 Al SE cable to a 125 amp Main-lug subpanel located In the heater closet, then, use (3) 50 amp 2-pole breakers , then(6) #8 to feed the unit.

Generalizing, Method B.

 

[LarryFine]

This has come up before. Unless the elements are all completely electrically separated inside the heater, you could potentially backfeed your panel bus. If this happened out of phase, you'd have a 240V short circuit.

Not an issue.

Then again, wiring up 3 discos and their cost may make them vs a subpanel a wash.

No, because the sub-panel would (hopefully) be located within sight of the water heater.

 

[LarryFine]

A sub panel would need 4 wire SER cable.

Not if there are no line-to-neutral loads on that panel.

 

[JFletcher]

Not an issue.



No, because the sub-panel would (hopefully) be located within sight of the water heater.

For #1, ok, tho I could have sworn I've seen some tankless water heaters that require one 100+A breaker and one feed.


for the 2nd point, you would have to have 3 discos or a subpanel next to the heater if it's not in sight of the main panel.

 

[Coppersmith]

Assuming the heater is located within sight of the panel or subpanel would the breakers require a lockout device?

 

[LarryFine]

for the 2nd point, you would have to have 3 discos or a subpanel next to the heater if it's not in sight of the main panel.

Which, to me, is one of the main reasons to use the sub-panel in the first place.

 

[LarryFine]

Assuming the heater is located within sight of the panel or subpanel would the breakers require a lockout device?

Negatory, within 25 feet.

 

[Coppersmith]

I've gotten several calls from people in condos with 100/125 amp panels (and no way to upgrade) to install those. They seem confused and sad when I tell them I can't add a 120 amp load to their panel.

 

[jumper]

Negatory, within 25 feet.

50’

In Sight From (Within Sight From, Within Sight).
Where this Code specifies that one equipment shall be “in sight from,” “within sight from,” or “within sight of,” and so forth, another equipment, the specified equipment is to be vis- ible and not more than 15 m (50 ft) distant from the other.

 

[LarryFine]

I've gotten several calls from people in condos with 100/125 amp panels (and no way to upgrade) to install those. They seem confused and sad when I tell them I can't add a 120 amp load to their panel.

I've often had to tell that to customers with 200a services.

50’

That's what I meant. :ashamed1:

 

[jumper]

That's what I meant. :ashamed1:

Easy to transpose. HVAC convenience receptacle and some tranny secondary tap conductors are 25 feet.

Note: new receptacle required for non resi electrical services, within 50’. 210.64

 

[rt66electric]

Diso's or panel would be located in heater closet.

Diso's or panel would be located in heater closet.

Diso's or panel would be located in heater closet.

THe 3 runs OF #8 would be cheeper than a sub panel.

Labor would be about the same either way.

I see the logic of a 4wire feed... next guy would want to add a 120v recept.

One of my concerns is that... I have seen alot of 125amp breakers melt-down.. but seldom see 50amp breakers have issues.

 

[jumper]

My comment about a 4 wire SER had nothing to do with any forethought concerning a future 120V receptacle.

I simply was not paying attention.

I see sub panel and immediately say 4 wire, but as noted above by Larry, not required if all 240V loads.

 

[JFletcher]

Diso's or panel would be located in heater closet.

THe 3 runs OF #8 would be cheeper than a sub panel.

Labor would be about the same either way.

I see the logic of a 4wire feed... next guy would want to add a 120v recept.

One of my concerns is that... I have seen alot of 125amp breakers melt-down.. but seldom see 50amp breakers have issues.

Perhaps its due to 3 50A breaker taking up 6 spaces in the panel vs 2 on the 125A - on a water heater pulling 120A, there's a third the surface/bus area with a 125A breaker vs 3 40s or 50s.

 

[LarryFine]

Actually, when I first read the OP, I thought of saying "Method 3: upgrade service and add panel near water heater."

 

[Little Bill]

]For #1, ok, tho I could have sworn I've seen some tankless water heaters that require one 100+A breaker and one feed. [/B]


for the 2nd point, you would have to have 3 discos or a subpanel next to the heater if it's not in sight of the main panel.

Don't have my book handy but you can't have heater loads above 60A. They have to be divided.
This is from memory so the 60 may be wrong but do know you have to split up heavy heater loads.

 

[kwired]

Don't have my book handy but you can't have heater loads above 60A. They have to be divided.
This is from memory so the 60 may be wrong but do know you have to split up heavy heater loads.

I know there is wording like you mentioned, mostly applies to electric space heating from recollection. Might still be some instances where it doesn't apply.

Sometimes you run into a unit with a large supply circuit but still gets subdivided within appliance to circuits of 60 amps or less.