Wiring Tankless Hot Water Heater AE125

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  #1  
Old 04-17-06, 05:09 PM
pendoreilleskie
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Wiring Tankless Hot Water Heater AE125

So, I have the PowerStar AE125 (made by Bosch)

It requires 3 X double pole 40 A breakers ...

Can I use two runs of 8/3? My plan is to code one white from each and use them as a pair.

I will have an extra ground, should I leave it disconnected ... seems sloppy to leave it disconnected in the breaker box, but when I get to the wall unit ... should I crimp the two grounds together and run just one into the ground position?

Ideally I should have had a custom cable made, but the wires are already in place and with the cost of 8-3 I don't really care to waste it as both are 25-30 ft runs ... and in fact, the elec. guy pulled [email protected] 8-3, even though I gave him the schematics ... so I have already wasted one (the third pair) but will leave it in the wall cavity in case I need something down the road.
 
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  #2  
Old 04-17-06, 06:05 PM
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Originally Posted by pendoreilleskie
Can I use two runs of 8/3? My plan is to code one white from each and use them as a pair.
You may use one run of 8/4 and one of 8/2, or three runs of 8/2 or 8/3.

> I will have an extra ground
No, you won't.

> should I leave it disconnected?
Never.

> seems sloppy to leave it disconnected in the breaker box
And would violate Code.


> but when I get to the wall unit ...
> should I crimp the two grounds together and run just one into the ground position?
It appears that you need to pigtail all three to #6 to land on the grounding lug.
A single #8 is not adequate for the worst case scenario.


> Ideally I should have had a custom cable made,
Why not run conduit?

> the elec. guy pulled 3 of 8/3, even though I gave him the schematics
Then you are fine. Simply do not use the white wires.

> so I have already wasted one (the third pair)
Pair?

> but will leave it in the wall cavity in case I need something down the road.
You need it now.


> Electrical power is measured in watts.
Correct (the watt is one of many suitable units).

> In an electrical system power (P) is equal to the voltage (<s>V</s>) multiplied by the current/amps (I).
That is apparent power (P=I·E).
Fortunately, you don't have to pay for apparent power on a residential service. You have to pay only for true power (which is always less than or equal to E·I) multiplied by hours.
 

Last edited by bolide; 04-17-06 at 06:52 PM.
  #3  
Old 04-17-06, 06:51 PM
pendoreilleskie
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I cant understand why he pulled [email protected] instead of [email protected], the problem with using three 8-3's is having to deal with 12 wires going into the box instead of 9 with the 8-2 as he could have pulled. I don't have room in the water heater box for the extra wire.

So, the whites are wasted and I need to use the ground from each 8-3, and only use the red and black from each 8-3 (and ground)? [I'm guessing I can't use the whites from different sheathed cables to create a 240V circuit as it could create confusion down the road since they are not in the same sheath?]

So it is against code to use to use 2 runs of 8-3 for 3 240 volt circuits? [I can understand the reasoning ... I could go the conduit route as suggested if I wanted to waste a combined 75' of 8-3, which at this point I don't want to.

Why is is acceptable to leave the whites not connected, but the grounds must all be connected to the box and the unit? Do I just put a wire nut on the end of the whites in the box, or what is the proper way to handle them?

Originally Posted by bolide
You may use one run of 8/4 and one of 8/2, or three runs of 8/2 or 8/3.

> but when I get to the wall unit ...
> should I crimp the two grounds together and run just one into the ground position?
It appears that you need to pigtail all three to #6 to land on the grounding lug.
A single #8 is not adequate for the worst case scenario.
not sure I understand why a single #8 ground is inadequate, but pigtailing is fine if I need to. Slightly O.T. In 8-3 is the bare ground 8 guage, or less?
 

Last edited by pendoreilleskie; 04-17-06 at 08:22 PM.
  #4  
Old 04-17-06, 08:27 PM
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> I can't understand why he pulled [email protected] instead of [email protected]

Perhaps he didn't read carefully.
The same directions cover 120 and 240V appliances.


> the problem with using three 8/3' is having to deal with 12 wires in the box
> instead of 9 with the 8/2 as he should have pulled.
> I don't have room in the water heater box for the extra wire.
Unless there is a way to use a short nipple to an adjacent junction box, there is no easy solution.


> the whites are wasted
Correct.

> and I need to use the ground from each 8-3, and only use the red and black
> from each 8/3 (and ground)?
Correct.

> [I'm guessing I can't use the whites from different romex cables to create
> a 240V circuit as it could create confusion down the road since they are
> not in the same sheath?]

The main issue is that it creates EMF. Depending on how the cables are routed, it could create a lot of EMF.


> So it is against code to use to use 2 runs of 8/3 romex for 3 240V circuits?

Opinions vary. I think everyone agrees that it is always unnecessary and something to be avoided.


> Why is is acceptable to leave the whites not connected,
Because they are unused.

> but the grounds must all be connected to the box and the unit?

Because NEC requires that all circuits must be run with an EGC.
You have three raceways, therefore you need three EGCs.

They must all be connected at both ends.


> not sure I understand why a single #8 ground is inadequate,
NEC 250.122 requires a #6 EGC for 120A (though you could plead 250.122(C)).

> but pigtailing?
You can land one #6 on the heater terminal.
It won't take three #8. And one #8 is technically too small the way I see it.

If you connected only one, it still must be connected to the other two at the appliance end.

(Actually, the manufacturer should have provided three grounding lugs. But I suspect they thought you would use conduit.)


> In 8/3 romex is the bare ground 8 gauge, or less?
Sholud be #8. AfaIk, reduced EGCs are no longer manufactured.
 
  #5  
Old 04-17-06, 08:53 PM
pendoreilleskie
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man, you are awesome!!!!!! Thanks, I would not have thought about the EMF issue ... if I cannot get 12 in the water heater box then I will just scrap it and use conduit from the box to the unit and use #6 conductors and #6 ground ... even if it fits I like the idea of conduit with that much amperage involved ... there are different types of #6 right? (as far as the type of sheathing) Would I want THHN #6, and a solid #6?

The cost of potentially scrapping the #8 is irritaing, but with no sheetrock up I like the idea of doing it the best way.
 
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Old 04-17-06, 09:11 PM
pendoreilleskie
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if I used 6 THHN @ #6 conductors and a #6 ground and nonmetalic tubing then I need to use a minimum of 1 1/4" tubing ... and looking at page 109 of my "Ugly's Electrical Ref"" book (2005) I see your concern for the #8 as a ground ... thanks for the NEC reference.
 
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Old 04-17-06, 09:14 PM
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> if I cannot get 12 in the water heater box then I will just scrap it and use conduit
> from the box to the unit
The unit is built to accept 1" or 1.25" conduit (I can't tell for sure what they mean by 1.25" hole).
So you could use a short 1" diameter nipple (perhaps bush the hole to 1") to a big junction box right underneath.
Then you send only the 7 wires that you need through the nipple.


> and use #6 conductors and #6 ground ... even if it fits
> I like the idea of conduit
I'm surprised the electrician didn't recommend this.

> there are different types of #6 right?
> (as far as the type of sheathing)
You mean insulation. (Sheathing is the jacket covering some cables.)

> Would I want THHN #6, and a solid #6?
THHN, yes. I would not use solid unless the run is straight (even at that, stranded is better). For #6 THHN, I carry only stranded anyway.
For the ground you could use green stranded THHN or maybe bare solid. I carry both. Are you using metal of plastic conduit?
You can use 1" EMT or 1.25" RNC (sch40 PVC).
 
  #8  
Old 04-17-06, 09:24 PM
pendoreilleskie
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man, you are full of good ideas

the solid #6 was just in reference to the ground ... so it is acceptable to just pull a green #6 (stranded) THHN insulated as the ground, stranded would be a lot easier to pull thru the conduit. I have supplies for the Schedule 40.

I get what you are saying about the use of a junction box beneath, but would I need to leave the junction box exposed (faceplate) ... I mean I cant just cover it up in the wall cavity, right?

Thanks for the correction on the sheathing/insulation.s
 
  #9  
Old 04-17-06, 09:34 PM
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> ... nonmetalic tubing then I need to use a minimum of 1 1/4"
Correct. The unit should accept this. If not, reduce right at the box, perhaps with a condulet.


> I see your concern for the #8 as a ground
Yeah, depending on how you view it, #8 might be a tad small.

Technically, #8 EGC (#10 EGC if you use #8 ungrounded conductors) is large enough for the conduit. But the appliance probably ought to have a #6 either way just to be on the safe side. Though perhaps it is engineered such that three line to ground faults can't happen affecting just a single leg.
 
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Old 04-17-06, 09:39 PM
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> it is acceptable to just pull a green #6 (stranded) THHN insulated as the ground?

Yes.

> stranded would be a lot easier to pull thru the conduit.

If it is just one solid, that's not bad. But if you have three or four bends, any solid makes you work harder.


> I get what you are saying about the use of a junction box beneath,
> but would I need to leave the junction box exposed (faceplate)
> ... I mean I can't just cover it up in the wall cavity, right?

It may not be concealed. The same applies to a condulet if you use conduit.
 
  #11  
Old 04-18-06, 08:59 PM
pendoreilleskie
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okay, so I went up to the cabin today to see about using the existing wiring, and to measure in case I need new #6 ... question about "pigtailing" the #8's and running the #6 into the lug on the water heater ... can I use a ground bar kit (4 space ground bus bar) to join up the three #8's from the box with the #6 that is running to the lug on the unit?
 
  #12  
Old 04-18-06, 09:29 PM
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> can I use a ground bar kit (4 space ground bus bar) to join up the
> three #8's from the box with the #6 that is running to the lug on the unit?

I cannot think of anything reversible that would work better.


Where are you joining the wires? Inside the heater's box?

I would prefer that you drill and tap a hole to mount the bus bar to the box. If you use a separate junction box, I would insist on it.
 
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Old 04-18-06, 09:54 PM
pendoreilleskie
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Its going in a 2X6" wall, so there is enough depth to brace behind the box and then drill thru and mount the ground bar kit inside the heater box ... or I could skip the bracing and just use a bolt and nut from behind

Would you use a screw into wood behind the box or bolt/nut?

Originally Posted by bolide
Where are you joining the wires? Inside the heater's box?

I would prefer that you drill and tap a hole to mount the bus bar to the box. If you use a separate junction box, I would insist on it.
 
  #14  
Old 10-02-09, 07:10 AM
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i am just reading along this post-it appears this started in 2006.-so they might not be watching the replys.
but on a 240v,you have 2 120v wires-red & black.
& a ground
(i am by no means an electrician! just a diy guy)
 
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Old 10-02-09, 07:20 AM
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Originally Posted by newtofta View Post
i
but on a 240v,you have 2 120v wires-red & black.
& a ground
(i am by no means an electrician! just a diy guy)
No you do not.
You have 240 v, A modern power distribution system in the US uses a step down transformer with a center tap that is grounded. The leads off the secondary are 240v. That is what is used for 240v in the hone. You can get half of the available voltage, 120v, by connecting to the grounded center tap (AKA neutral.).
 
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