Adding an Electrical Subpanel

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  #1  
Old 02-04-08, 02:39 PM
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Adding an Electrical Subpanel

I want to add (3) 40 AMP 220 Double pole breakers to a Siemens 200 service panel for a tankless electical water heater. Counting the old water heater breaker there is only room for (2) breakers (4) slots the remaining are maxed out with tandem breakers. The Siemens box has no lugs at the bottom to tap off of. Can I add a subpanel and or can lugs be added to the Siemens box. The tankless heater is within site of the panel. Any thoughts?

Thanks

Bob H
 
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  #2  
Old 02-04-08, 03:02 PM
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Yes, you can add a subpanel off the main panel. This size of tankless heater requires a minimum 150A subpanel fed with #1/0 copper or #3/0 aluminum wire. Have you done a load calculation on the 200A service to see if there's enough capacity to handle the tankless heater? If you've already got a number of electrical appliances, you might need to heavy up to a 320A service to support the heater.
 
  #3  
Old 02-04-08, 03:28 PM
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Oh man .,,, anyway here it goes .,,,


Can you give me the Semens Breaker box #'s [ the model number ] the reason why i ask because it possible to do this route once i know what breaker box model number it possible to slap on a 125 amp breaker and run that to the subfeed box then hook up per instat waterheater instrusctions

BUT from my past experinice almost always have to hevey up to 400 amp load centre or use 2 X 200 amp load centre with class 320 metering socket and be forwarned it will make the light blink when the unit cycleing and if you do go ahead with it you have to give the POCO a head up with it sometime they will increase the transformer to feed your house [ most POCO only will size up if really need to. otherwise they will leave it alone depending on the area and type of disubation area and size of transformer in that area]

i have one comuster he did actally blew the POCO transformere [ the transformer just cant handle the load of instat waterheater.] that much power is have same punch as 3 full size range running full power

If you allready have 320 A service you will be fine with that but other than that size like a 200A service you may squeak by,

cost wise i dont know depending on the exsting setup now.

Merci, Marc
 
  #4  
Old 02-04-08, 04:40 PM
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Thanks for the responses. The Siemens catalog number is G204OMB1200 Series .B Enclosure type 1. The load calculation is right on the edge. I was hoping to avoid the upgrade if at all possible. Also how do I attach the #3 wire to the 200 amp service panel there are no lugs present?,

Thanks,

Bob H
 

Last edited by bhumes0912; 02-04-08 at 04:45 PM. Reason: Forgot to ask
  #5  
Old 02-04-08, 06:02 PM
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Having dealt with this recently - talk to your inspector and perhaps the POCO. If you're thinking otherwise, let me say that again - talk to your inspector (not trying to be a smart-a**, just giving you a heads up based on my experience). My inspector required me to go up and above what the manufacturer of the hot water heater recommended for the wire gauges. He didn't care what they said - he said you have to do your own calculations.

I like the idea of tankless hot water heaters, but MAN do they suck down the juice. Also not so good if you have/want recirculating hot water, but that's another story.
 
  #6  
Old 02-05-08, 10:00 AM
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Originally Posted by bhumes0912 View Post
Also how do I attach the #3 wire to the 200 amp service panel there are no lugs present?
It's not #3 aluminum -- it's #3/0 aluminum which is a much bigger conductor #3/0 = #000 (triple zero gauge). The breaker will have lugs large enough to hold the conductor, but you may need to buy a lug kit for the neutral conductor. It's also possible that you can save some money by not installing a neutral conductor at all.

But, before we proceed on this path... do you have ratings on the actual heater? Perhaps a link to a model number or install manual? I need to determine if the supply circuits are already sized for continuous loading or not. This will determine whether you need to install a 125A panel (40A + 40A + 40A) or a 150A panel ((40A + 40A + 40A) * 125%)
 
  #7  
Old 02-05-08, 11:34 AM
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Originally Posted by ibpooks View Post
But, before we proceed on this path... do you have ratings on the actual heater? Perhaps a link to a model number or install manual? I need to determine if the supply circuits are already sized for continuous loading or not. This will determine whether you need to install a 125A panel (40A + 40A + 40A) or a 150A panel ((40A + 40A + 40A) * 125%)
I would not think that an instant water heater is a continuous load based on the traditional definition. Is there a special requirement for these because of their unique operation?
 
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Old 02-05-08, 11:51 AM
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This goes back and forth. Some of the manufacturers claim it's not continuous, some do. Some inspectors require installation as a continuous load, others do not. The code does not specifically say one way or the other. I suspect that the poster a few lines above had a manufacturer that gave instructions for non-continuous install, but the inspector mandated continuous.

What I'm hoping is that the (3) 40A circuits spec'd by the manufacturer already include a 125% oversize factor so we don't have to worry about it in the subpanel design.
 
  #9  
Old 02-05-08, 01:59 PM
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Just wondering about the practicality of an electric tankless water heater. Sure, it may save a bit of energy through reduced standby losses; but when it runs, it sucks the juice.

It is very likely that hot water will be used during peak demand times for the utility, and when the unit is running, it will draw 4-5 times as much power as a tank heater.

Not including electrical service upgrades, it will cost more than another tank heater.
 
  #10  
Old 02-06-08, 07:53 AM
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The tanklees unit is a Bosch Power Star AE 125 rated at (3) times 40 Amps. The unit has (3) elements rated at 40 amps each. Depending on the voltage and the inlet water temperature, the elements will be activated to provide an ajustable outlet teperature up to 135 degrees. The manual and spec sheets did not specify continuos or intermittant. The unit is within sight of the breaker panel, so it can be wired direct. The specify #8 wire for each connection.
 
  #11  
Old 02-06-08, 08:17 AM
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Be sure to do a demand load calculation and then follow it. Otherwise you may have trouble with the home inspector when it comes time to sell your house, and be faced with two expensive options: remove the tankless and replace it with a standard tank, or upgrade the service. The electrical costs are often the dominant factor in tankless installations.
 
  #12  
Old 02-06-08, 08:36 AM
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The manufacturer website listed the rating as 26,850W @ 240V on (3) 40A circuits. This works out to 112A which means that the manufacturer does not include a 125% oversize for continuous load. It would be a good idea to get a ruling from your inspector as to whether you need to design for continuous.

For non-continuous, install a 125A subpanel fed from a 125A breaker in the main panel with #1 copper hots and #6 copper ground. (for aluminum wire use #2/0 hots and #4 ground)

For continuous, install a 150A subpanel fed from a 150A breaker in the main panel with #1/0 copper and #6 copper ground. (aluminum: #3/0 with #4 ground)

In either case, you'll want to run from the subpanel with three 40A circuits using #8 copper.
 
  #13  
Old 02-06-08, 10:07 AM
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Are the 125 AMP or 150 double pole breakers sized to fit in the branch circuit (double pole) of the Siemens breaker box?
 

Last edited by bhumes0912; 02-06-08 at 10:58 AM.
  #14  
Old 02-06-08, 11:57 AM
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The 125A breaker is Siemens part no Q2125 and will fit in 2 slots of the panel just like any other 240V breaker.

The 150A breaker is part no Q2150 and takes up 4 slots.
 
  #15  
Old 02-06-08, 12:10 PM
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let you know the Q2125 breaker is two pole and it will take two space which it is not much a issuse putting in the breaker box at all but other hand the Q2150 and larger one will take 4 space and this is kinda tricky [ i rather mount them on the lower part of panel box ] due the termation connections there and you may have some issues running large cable like 3/0 al or 1/0 copper into the fitting.

I just read the model number of your breaker box it state 2040 verison so you can add tadeam breakers in there to open up the room there.

but if you going to add the tadeam breaker just watchout if you see red wire it can be either 240 volt circuit or MWBC if it is MWBC this will get tricky you have to land it right other wise you will overload the netural wire on that affected circuit pretty easy.

The 125 amp breaker i am not sure if they will have this in the big box store but i know for sure the 150 amp verison it more like electrical supply centre item or can specal order from big box store [ i rather go thru the electrical supply they useally stock this big breaker anyway.]

As far once you get the manufacter info for termating it.

most tankless water heater [ the whole house ] have multi stage operation so expect some flickering light when the unit cycle in 2 or 3 stage depend on water flow.

Merci, Marc
 
  #16  
Old 02-06-08, 12:12 PM
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Thanks for all the responses. I think I have it and will advise of the outcome.


Thanks,
Bob H
 
  #17  
Old 02-06-08, 02:40 PM
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As an afterthought, do the the feeds need to be enclosed in conduit? Either from the main to the sub panel or the sub panel to the water heater?
 
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Old 02-07-08, 10:31 AM
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If you want to use individual conductors (THHN wire), it must be in conduit the entire run. If you use a service cable like type SER for the subpanel or NM-B for the heater circuits, conduit is not required unless the cable is in a location where it could be damaged. Up in the basement ceiling is considered protected from damage. The advantage to using individual conductors in conduit in this case from the heater to the subpanel is that all three circuits can share one ground wire saving on some copper. If you choose to use cables instead, it is typical to run a few feet of conduit up from the heater to the ceiling to protect the cables vertically down the wall. What are the distances between main, sub and heater?
 
  #19  
Old 02-07-08, 08:49 PM
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About 9 feet from the main to the subpanel and about 2 feet to the heater. The subpanel is mounted adjacent to the heater on 3/4 inch plywood lagged into the basement poured concrete wall. Most of the run from main to the subpanel is in the ceiling. I used #1 copper cable from the main to the subpanel with a # 6 copper ground cable. The three leads from the subpanel to the heater are 8/2 with ground.

THANKS,

Bob H
 
  #20  
Old 02-09-08, 11:45 AM
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Adding a subpanel for a tankless water heater.

To All that Cared.

The whole house tankless electrical water heater went in like a charm. It is way more an electrical effort than plumbing. I ran the electric heat pump and 2 showers at the same time without a wink or blink. It does take more time for hot water to appear but once there, never-ending. I am struck by how light and small the Bosch unit is. The next test is consumption! Thanks for everybody's help. It looks and works great.

Thanks Again!
Bob H
 
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