dual fed not?

[tesi1]

recently I just purchased (2)- tru-tankless vero water heaters for my new home, model # br36, kw rating 36 at 240 volt, the spec book shows using (2)- 80 amp circuits for each. upon receiving the units we noticed the (2)- 80 amp circuits were to be connected onto a single double barrel lug at the terminal strip, this concerns me due to if only one breaker is off in the panelboard the second breaker would be backfeeding the first and may create a unknown safety situation. these units were listed by intertek & etl.
would this installation be allowed under 2011 nec or would it be a code violation. it really seem to be un under 1/0 parallel circuit.:happysad:

 

[GoldDigger]

It is not parallel hot wires, since they have different sources. It does, however, look like two breakers in parallel feeding one circuit, which is not allowed with very limited exceptions. I do not think that any of them apply to this situation.
It seems both a technical violation, and a safety hazard as you notice.
Looking specifically at the neutral wire, I do think that they could be considered parallel as long as they originate in the same panel.
If the two breakers were in different panels it would be a very severe safety issue as it could end up backfeeding an entire panel.

How did that unit pass UL? Changes since approved?

 

[JFletcher]

HD supply mentions this:

Model requires 150-amp dedicated

can you post a pic of the terminals on the heater or what the specs read? I was under the impression that these large, on-demand heaters had multiple independent strips when over 80A.

eta: tho there is typically no polarity with 240V, if you wire one double-lug terminal with one wire from A leg and the other from B, you're going to have a nice mess on your hands. At best, two tripped breakers, at worst, you've created a bolted fault that could destroy the terminals.

seta: sure there is only one terminal strip?

teta (third edited to add): you have 2 of these? at 150A a piece? at your house... what sized electric service? Even with ng everything else, wouldn't this exceed what a 320/400A service can provide?

 

[JFletcher]

It is not parallel hot wires, since they have different sources. It does, however, look like two breakers in parallel feeding one circuit, which is not allowed with very limited exceptions. I do not think that any of them apply to this situation.
It seems both a technical violation, and a safety hazard as you notice.
Looking specifically at the neutral wire, I do think that they could be considered parallel as long as they originate in the same panel.
If the two breakers were in different panels it would be a very severe safety issue as it could end up backfeeding an entire panel.

How did that unit pass UL? Changes since approved?

here we go:


https://www.lowes.com/pd/Square-D-Homeline-150-Amp-2-Pole-Double-Pole-Circuit-Breaker/3467881

no backfeeding issue. didnt know they came that large. still have to make sure you dont cross legs at the heater tho. guessing one would pull 4 #4 THHN for CCC and a #6 ground or use a metal raceway, tho it still seems IS paralleled to me if they land on a common terminal per leg in the eqpt. Two #4s (or 3s or 2s) cannot supply 150A.

 

[GoldDigger]

here we go:


https://www.lowes.com/pd/Square-D-Homeline-150-Amp-2-Pole-Double-Pole-Circuit-Breaker/3467881

no backfeeding issue. didnt know they came that large. still have to make sure you dont cross legs at the heater tho. guessing one would pull 4 #4 THHN for CCC and a #6 ground or use a metal raceway, tho it still seems paralleled to me if they land on a common terminal per leg in the eqpt.

The device you cited is really just a single two pole breaker despite its construction from four units. I has been tested and designated by the manufacturer as a single unit breaker (one of the exceptions that I mentioned.)
Notice that it only has two terminals, probably not rated for two wires each.
And even if that were the case you would still be paralleling wires below the NEC allowed length for paralleling.

BTW, at a minimum in the OP's case I would insist on handle ties!
Possibly the heater design was for such a single unit breaker and rather than get it the original installer just put two individual two pole breakers into the panel.

 

[JFletcher]

The device you cited is really just a single two pole breaker despite its construction from four units. I has been tested and designated by the manufacturer as a single unit breaker (one of the exceptions that I mentioned.)
Notice that it only has two terminals, probably not rated for two wires each.
And even if that were the case you would still be paralleling wires below the NEC allowed length for paralleling.

BTW, at a minimum in the OP's case I would insist on handle ties!
Possibly the heater design was for such a single unit breaker and rather than get it the original installer just put two individual two pole breakers into the panel.

I did not notice that. So for a 150A (36kw@240V) load it needs 1/0 copper (or 3/0 AL) from it. No parallel wire, no backfeed issue. I'm going to assume the heaters can have that double lug removed and can accept 1/0? Begs the question why the double lug in the first place tho, save for installer decision. I didn't get the impression the heaters were already installed.

eta: if they are truly made from the factory that way (double lug), the setup as described would absolutely backfeed another panel if the 2 2p 80A breakers came from different panels. I can only guess that the instructions preclude that install thus creating a 110.3(B) violation if done so (probably say "copper wire only" too). Dont see any other way w/o two+ elements to do it legally with more than 1 breaker and 1 set of wires.