Tankless WH: when is subpanel required?

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Old 03-06-11, 06:37 PM
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Tankless WH: when is subpanel required?

My current subpanel for my tankless water heater is underrated for what I need.
The tankless WH is right next to the subpanel. It is about a 40 foot run from the main panel. 3 40amp circuits with #8 wire are required. I was considering installing another subpanel just for the water heater until I started doing calculations and pricing.

I'm finding out the wire and breakers required for a new subpanel (mostly the 1/0 wire and a 150 amp breaker plus 150 amp subpanel) would probably total in the $800 range.

Can I run the 3 required 40amp circuits directly from my main panel? I already have the breakers that would fit in my main panel. The wire cost will be a whole lot less.

Thanks

Dave
 
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Old 03-06-11, 06:50 PM
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Maybe you could do that, but it depends on how many amps your service is rated for, the existing load on that service panel and the manufacturer and catalog number of the service panel. If you have a typical 200 amp single phase loadcenter it is doubtful you could even get a 150 amp breaker to fit it. Typically, the bus stabs aren't rated for more than 125 amps on most loadcenters. You might be able to do it with a 125 amp subpanel depending on the service size and existing loads.
 
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Old 03-06-11, 06:57 PM
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Actually I did calculate using 125 amp instead. The 150 was including a lot of overhead, assuming continuous use.

I'm just wondering if I could go with 3 40amp double poles directly to the main box instead of running another subpanel.

Dave
 
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Old 03-06-11, 07:01 PM
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A run of 2/0-2/0-2/0-1/0 aluminum wire shouldn't cost that much paired up with a 200A QO or Homeline main breaker panel fed by a 150A breaker.
 
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Old 03-06-11, 07:04 PM
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Originally Posted by dsnowdy View Post
Actually I did calculate using 125 amp instead. The 150 was including a lot of overhead, assuming continuous use.

I'm just wondering if I could go with 3 40amp double poles directly to the main box instead of running another subpanel.
Sure, you could do that if you have 6 available spaces in at least a 200 amp service and adequate capacity in the main panel. Do you have any idea what loads you now have?
 
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Old 03-06-11, 07:06 PM
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Either way your existing service may not be large enough to provide enough power. Often times a separate service may be required just for the tankless.

Have you performed a demand load calculation?
 
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Old 03-06-11, 07:16 PM
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No. I still have to do a calculation on all the current loads. I'm off tomorrow so I'll probably finally do one.

I do have the tankless connected to the current ch subpanel and the feed to the subpanel blows the circuit when the ground water is really cold and I try to run the heater on high. I have the heater set very low and it is temporary!

The main panel is a 200amp, eaton/ch remodel, single phase.
 
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Old 03-06-11, 07:48 PM
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I do have the tankless connected to the current ch subpanel and the feed to the subpanel blows the circuit when the ground water is really cold and I try to run the heater on high. I have the heater set very low and it is temporary!
How many amps is the subfeed breaker that trips rated for? I am guessing it's probably 100 or less. If you have electric heat in the house you might save yourself some trouble and go ahead and plan on a larger service, probably 400 amp.
 
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Old 03-07-11, 06:33 AM
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Just in case...what brand of main panel do you have now?
 
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Old 03-07-11, 06:44 AM
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Originally Posted by JimElectric View Post
Just in case...what brand of main panel do you have now?
The main panel is an Eaton/Cutler-Hammer 200 amp panel.
 
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Old 03-07-11, 08:39 AM
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Which one? They make one that uses BR series plug in breakers(usually black) and one that uses the beige colored ones. See if you have a series on the cover and see if it uses either BR or BJ types. The BJ would be especially important.
 
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Old 03-07-11, 09:07 AM
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The reason I ask is that Cutler Hammer does have 2 pole 150 amp breakers for both series, so you COULD add a 2 pole 150 if needed, HOWEVER....they take up 4 spaces and, as advised by the others here, you would still have to have a load calulation done to be sure the 200 amp main is not overloaded. So you have still have to upgrade to 400 amps, if you have a lot of other usage. If not, then these panels had provisions for larger frames, such as the BJ2150 or CH2150. I might suggest that if you have to upgrade to 400 amps, Midwest makes a neat combination outdoor meter and disconnect package, that has two 200 amp mains and a 320amp residential meter socket. That way you could use your existing panel, add a new 200 amp panel near the tankless heater, and not have the clutter of a large junction box outside. Assuming it is approved by the local utility, model RS45508C.
 
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Old 03-07-11, 09:42 AM
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The 200 amp panel has the breakers from our previous panel, beige switches. This panel has 42 slots. We upgraded to this panel in 2006. Not sure of model... I guess I'd need to take the front panel to find it.

I did add up the loads with a worksheet, including almost anything that could be used.

Without the new water heater, it's 98 amps.
With the new water heater, it's 189 amps.

Dave

Originally Posted by JimElectric View Post
The reason I ask is that Cutler Hammer does have 2 pole 150 amp breakers for both series, so you COULD add a 2 pole 150 if needed, HOWEVER....they take up 4 spaces and, as advised by the others here, you would still have to have a load calulation done to be sure the 200 amp main is not overloaded. So you have still have to upgrade to 400 amps, if you have a lot of other usage. If not, then these panels had provisions for larger frames, such as the BJ2150 or CH2150. I might suggest that if you have to upgrade to 400 amps, Midwest makes a neat combination outdoor meter and disconnect package, that has two 200 amp mains and a 320amp residential meter socket. That way you could use your existing panel, add a new 200 amp panel near the tankless heater, and not have the clutter of a large junction box outside. Assuming it is approved by the local utility, model RS45508C.
 
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Old 03-07-11, 09:52 AM
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At 189 that is too much for the 200 amp main to handle.
 
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Old 03-07-11, 10:06 AM
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I can see that more service is required. Then I would be able to add almost anything in the garage area near where the heater is. Luckily the Bosch heater I have is designed to also run on 2 out of the 3 circuits with diminished performance for now.

What does that sort of upgrade of service usually require?
I understand the outside panel must change and I could keep the current 200 amp panel and add service to a 2nd 200 amp panel.

Would the feed to the original panel remain the same?

Much thanks.

Dave
 
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Old 03-07-11, 10:18 AM
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It will vary somewhat from place to place, and you will need to contact your utilty for sure for guidelines. Here our customers normally get a larger mast, say 3" and then utilize a large outdoor splice box and sometimes a 400 amp switch. We have sold several of the Midwest units I spoke of as they make a cleaner job of it but they may or may not be approved by your utility(all untilities have an "approved list" for equipment, can't be sure about yours. You should be able to keep your existing wiring but that is no guarantee. I am sure the other folks on here can guide you better on this than me. My knowledge is more product than code. But I am sure you will need a utility engineer out there to advise what they want to see.
 
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Old 03-07-11, 12:00 PM
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First question is are you city or rural. Rural it might be the electric company doesn't have the excess capacity and isn't willing to upgrade just for you. If city and they have to change out the transformer perhaps some lines they may want to charge you for that. Could be thousands, just a guess so as Jim suggested first is a talk with your electric company.

I would go for replacing single lug meter socket with a 400a double lug meter socket. You could the just connect the existing panel with out touching the existing wiring and attach a new panel for the WH to the second set of lugs on the new meter socket. Of course the AHJs have final approval. Add another $2000 or more for this up grade.

Bottom line you may never recover what it costs to install this new IWH. Why not use a conventional water heater in conjunction with your current water heater. The IWH would supply water to the CWH. The conventional water heater would act as a holding tank and to provide a bit more heat. You could use a by pass valve so the CWH is bypassed in the summer when the instant water heater is adequate. You could also have the CWH first so the IWH receives slightly warmed water in the winter.
 
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Old 03-07-11, 01:03 PM
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Originally Posted by dsnowdy View Post
What does that sort of upgrade of service usually require?
It's a major job, pretty much an overhaul of the entire service all the way back to the pole and sometimes even the power company transformer.

Would the feed to the original panel remain the same?
No, it would need to be upgraded to a four-wire feeder, separate ground and neutral, and reconfigure the grounding electrode conductors that currently go to the 200A main panel to go to the new outdoor main panel.

A retrofit 320/400A service is typically many thousands of dollars by the time you get through with the electrician, power company and inspection and permits.

You would almost certainly be better off in the long run either continuing to use this heater in the restricted power mode and getting by with that, or reducing electrical consumption on other items to be able to use the instant heater within the bounds of the 200A service.

If however you have other major electrical plans (standby generator install, metal shop, spa, etc) then planning for all of that in addition to the IWH would make sense to bite the bullet and have the 320/400 installed and get it done all at once.
 
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Old 03-07-11, 07:13 PM
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I'm just outside of the incorporated area of a town of about 30,000.

The area I live in is about 40 miles outside of New Orleans and was hit harder than New Orleans in hurricane Katrina. Most of the city was flooded. Transformers are on the ground and lines are buried. Not sure how much got replaced and modernized in the cleanup.
I have a call in to an engineer at the local poco. I'm going to find out regardless of what I end up doing. Of course I'm expecting the worst. Cost will prohibit these changes. What I've heard here and elsewhere, it'd be cheaper to replace the heater.

The water heater actually works really well on 2 out of 3 circuits.

I may run the circuits to the main panel after all so I don't overload the old subpanel (1980-ish with a few tandems in it), and continue to use only 2 out of the 3 circuits and clean up the old subpanel.

Thanks

Dave
 
 

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