Should I upgrade my breaker box from 100amps

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Small Cabin Forum / Cabin Construction / Should I upgrade my breaker box from 100amps


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Rifraf Member	# Posted: 31 Jan 2012 05:43pm - Edited by: Rifraf Reply Hi, I think I may have to upgrade my panel. I want to buy an electric tankless water heater that requires 2x40amp breakers , the heater is rated at 18kw, 75amps. My current panel is a 100amp panel (100 amp breaker is at the pole, will feed the panel) Now, im guessing I wont have to have the water heater settings cranked all the way up, but im not sure. I also have an ac with heat pump that can draw up to 15 amps while heating, a washer/dryer that pulls up to 30 amps, fridge about 3 amps, toaster over 12.5 amps, hot plate up to 12.5 amps, regular toaster, and microwave.. thats not counting the tv, playsation, lights, fan ect. I can do three things.. I can go ahead as planned and hope I dont have to use the heater on full to get hot water to the bathtub (18 ft away) , I can get a smaller 9kw version and hope its powerfull enough, or upgrade my panel to above 100 amps. Now what makes a panel that does not have a main breaker in it rated at a certain amperage ?? My main breaker for this panel will be at the pole, feeding directly into the panel leads, could it be the panel leads themselves can only handle 100amps before they get too hot ?? Suggestions welcome, Thanks!!!

Rob_O	# Posted: 31 Jan 2012 07:02pm Reply Quoting: Rifraf could it be the panel leads themselves can only handle 100amps before they get too hot ?? Yes, you need to have 200A service from the pole to the panel. All the wire, and the panels and disconnect must be rated for 200A

Bzzzzzt Member	# Posted: 31 Jan 2012 07:06pm Reply I concur with Rob_O

neb Member	# Posted: 31 Jan 2012 08:05pm Reply I agree with advise you have been given.

Rifraf Member	# Posted: 31 Jan 2012 09:02pm - Edited by: Rifraf Reply Thanks for the fast replies.. I was afraid you would say 200.. my service in total is 200 main breaker at the pole with 4 open spots below the pole meter, one breaker has to go to the well pump so I dont have 200 left. i just looked up my breaker box and its actually rated up to 125 amps, I called the rheem company and while they didnt have the data written the tech I spoke to said they usually pull 50 amps when set around 85%, and if you set them a little lower you can pull just 40amps.. you can get just as hot water but your flow rate would do down some to get it.. so if i can tune the unit to pull 40-50 amps and supplied the panel with a 125 amp breaker (Ive not run my wire from the pole so im not retrofitting new breaker on old cable) I wonder if that would do the trick. 125-50 still leaves me 75 amps for the other items. I guess its time to do some number crunching.. i may have to run the 125 amp breaker to the panel AND use the smaller heater. heres my current panel Panel info Thanks again!

neb Member	# Posted: 31 Jan 2012 09:47pm - Edited by: neb Reply That water heater you want to buy is a beast. I would really look at something smaller if it would work. The transformer that is required for just the water would have to be a 25 KVA transformer just to handle that one load. It is something that you may not be aware of but the Electric Company that supplies you with power may not even have the right size transformer to serve that water heater. A good sized home will only take a 15 KVA transformer to serve it. Once you have the water heater going and have other things on at the sametime you will have an issues if you don't upgrade ypur service to a 200 amp and like I said if the numbers you have given are correct you need to see what size transformer you have because it may be to small also. The Power Company built that service to size when it didn't have that load and now that you are adding more the transformer also maybe to small to handle it.

Rob_O	# Posted: 31 Jan 2012 11:03pm Reply Quoting: neb The Power Company built that service to size when it didn't have that load and now that you are adding more the transformer also maybe to small to handle it. The only good advice I ever got from a utility employee was "build it as big as you will ever need". He was trying to get me set up with a 50 KVA transformer but I think the line will only handle a 37.5, there's already 4 transformers on the line and I'm all the way at the end Quoting: Rifraf I called the rheem company and while they didnt have the data written the tech I spoke to said they usually pull 50 amps when set around 85%, and if you set them a little lower you can pull just 40amps.. you can get just as hot water but your flow rate would do down some to get it.. Depending on the groundwater temp, you might not get enough flow from your water heater for a good shower. It takes 120 amps for a 60 degree temp rise at around 2.5 GPM on the Bosch units I'm familiar with. Find the temp rise @ flow charts for your particular unit and you can "guesstimate" from there how much flow you will get, if that number is real close to the minimum flow required to keep the unit running you may have problems.

neb Member	# Posted: 31 Jan 2012 11:26pm Reply Quoting: Rob_O The only good advice I ever got from a utility employee was "build it as big as you will ever need". He was trying to get me set up with a 50 KVA transformer but I think the line will only handle a 37.5, there's already 4 transformers on the line and I'm all the way at the end Rob_O it doesn't matter how many tubs are on the primary line what makes the differance if the tub is sized right at the service. That primary line can have many transformers on it. The big picture is that the sub is balanced and consists of all circuits that come from that sub.

MtnDon Member	# Posted: 31 Jan 2012 11:37pm Reply Any reason you selected an electric heater over propane? Be careful with matching the well water temp rise and needed flow as was mentioned. Also how hard is the water? Does the manufacturer place any hardness limits that affect warranty. Our deep well water at the house was marginal a few years back and as more and more water is drawn by more wells it is getting worse.

Rifraf Member	# Posted: 1 Feb 2012 12:04am Reply MtnDon, Ive not dug the well, the best I can do is ask the neighbors what the water quality is like, I have two that are within half a mile or less. I do not know of hardness limits, ive viewed the spec sheets on the heater and not seen any data on that. I dont have any solid reason for electric over propane except that gas prices of all kinds seem to be escalating in price increases much more than electric.. and the ease of having one utility bill from one company I guess. Neb, Well the power company used a standard 200amp service install because when they put the transformer and meter on the pole all I had was a gravel pit, no building and they didnt ask me any questions about what was going up.. I dont know without calling them what size transformer it is, but it looks like its the size of a 5 gallon bucket. I can try the 9kw heater that takes one 40 amp breaker the reviews for it are not promising. ROB_O, i have access to the flow rate temp rise stuff for the rheem units, my ground water is about 55 degrees im told, so 35 degree rise would be fine for any use i could think of unless I want to burn myself. I dont use hot water for clothes washing at all. Home depot has a pretty good return policy so I dont have alot to loose if I want to try the 9kw 40amp unit first I guess... ive been reviewing lots of electric units and ive not seen any aside from commercial units that pull 120 amps. Thanks again for all the replies , ive got alot to check on now.

Rifraf Member	# Posted: 1 Feb 2012 11:42am - Edited by: Rifraf Reply ok, well you were right neb The electric company confirmed I have a 10kva transformer, but they will upgrade me to a 25kva so I can have more options available.. I do think after talking to them I may check on some alternatives before buying the electric one, and if I do it will probably be the 9kw version not the 18kw Does anyone know of any propane or natural gas units that can be connected to small refillable tanks instead of the larger yard mounted tanks ? Thanks again

wakeslayer Member	# Posted: 1 Feb 2012 01:55pm Reply I had our propane fueled Takagi TK-Jr being fed by a small 12v pump, from a 150 gallon tank. it worked fine. Shower pressure was as strong as any at home.

MtnDon Member	# Posted: 1 Feb 2012 03:15pm Reply Quoting: Rifraf Does anyone know of any propane or natural gas units that can be connected to small refillable tanks instead of the larger yard mounted tanks ? What works and what won't depends on a number of variables. One main one being how many BTU's per hour input the heater requires. Then the distance from the heater to the tank and the size of the pipe from one to the other. Then the temperature of the tank (air temperature where it sits) is also a big factor as is the size of the cylinder. Small cylinders (20#) can not supply the required volume for some heaters on even a warm day. When the temperature drops things worsen quickly.

Rob_O	# Posted: 1 Feb 2012 07:48pm Reply Quoting: neb Rob_O it doesn't matter how many tubs are on the primary line what makes the differance if the tub is sized right at the service. That primary line can have many transformers on it. By my calculations, that line can support well in excess of 500KW (probably double that). I have no idea why they were making such a big deal about it, maybe it's their way of appearing intelligent to the "uneducated masses"

Rifraf Member	# Posted: 1 Apr 2012 05:19pm - Edited by: Rifraf Reply Hey guys, sorry to dig up an old topic but i did decide to go with the 9kw electric on demand rheem heater. The power company already upgraded my transformer based on my new electric needs so I should be good there.. now im trying to figure out what service wire to run from a 125amp breaker at the pole to my 125amp box in the cabin. From what I can tell it would be #2 copper, but im going to bury this so is there a all in one cable I can buy somewhere that has the ground ,and all in the main insulator. Someone told me to get this and that sizes for ground and different for the hot which made it seem confusing. I was really hoping for an all in one purchase. My other worry is that the 125-130amp rated wire wont fit into the GE breaker hole . Any recommendations ?? Oh, not sure it would make a difference in the suggestions but its a 60 foot run from A to B. Thanks

neb Member	# Posted: 1 Apr 2012 06:30pm - Edited by: neb Reply Rifraf If you are running the wire from the breaker under your meter I would check on code to make sure you don't have to run quad. Quad is 4 wires bundled (twisted) togather. The 4 wire there will be 2 hot one ground and a neutral. Why I say that is the service starts at the meter and in the area I live you need 4 wires running from breaker by the meter to your breaker in the cabin. Now the PC only has to supply 3 wires from transformer to the meter. I also would use 1/0 AL wire instead of copper. It will be cheaper and has more amp caring capacity but very close to copper. I do believe 1/0 is good for up to 225 amps. You need to check before you go buy wire to make sure you don't need quad (4 wire) instead of just 3 wire (2 hot and a ground). As far as the distants you will be just fine. The voltage drop in 60 feet doesn't amount to nothing. Where you can get in trouble with running to far is that some use to small of service wire. I like to always go bigger on wire so that problem does't happen.

Rifraf Member	# Posted: 1 Apr 2012 07:23pm - Edited by: Rifraf Reply neb, thanks for the reply. i dont have any codes where I am. I just want to do it properly. Will #1 aluminum fit into a standard 125amp GE breaker though ? I was considering copper because you can get thinner cable for the same amperage right ? Neb, I wouldnt mind running quad anyway .. there are 4 spots to run from so naturally that seems the way to go. Two from the breaker then neutral and ground bars in the pole meter box, as well as two mains /ground & neutral in my breaker box I didnt look when I was in it last, but im guessing the neutral and ground in the poles meter box are both running to the same grounding rod ? So would I need the same guage for ground as I do the hots ? If it all comes in one bundle , I guess thats that. However if I have to buy each one separately would grounding and hots all need to be #1 AL and/or #2 copper?

neb Member	# Posted: 1 Apr 2012 07:40pm Reply Rifraf If you got the right box 1/0 Al would fit in that size of box. I wish I could tell you for sure but the only way is to try a small piece of it and see if it fits. It depends on the box but you can get the right connection to land the size of wire. Remember it isn't #1 AL it is 1/0 AL that I was talking about. #1 Al is not a common wire size in my area. If there is no code I would go just with the TPLX (3 wire) 2 hot and a ground. And yes the ground and nuetral are all bussed togather on the system. In the box that you have like I said you can change the connections so 1/0 will work and you can check on that. Good luck I hope I helped and not messed you up.

Rifraf Member	# Posted: 1 Apr 2012 08:05pm Reply I just found this on CR, wouldnt three runs of this at my required length do the trick ? if i can get the guy to sell me just the length i need that is. http://kansascity.craigslist.org/mat/2932235859.html

neb Member	# Posted: 1 Apr 2012 08:18pm Reply Yes that would work just fine. It is actually 30 thousands smaller in diameter then 1/0 AL wire. Just make sure this is wire that you can bury in the ground and not inside wire. I can't remember the name for outside direct burial wire. You maybe able to ask that question. If it is inside wire then you will need underground wire. It being small wire size that will help if you have an issue with landing that size of wire. You will plenty of amp capacity with that copper wire. Good luck but do some checking.

MtnDon Member	# Posted: 1 Apr 2012 08:25pm Reply As long as that is THHN/THWN it could be used in conduit. Mosdt THHN is also THWN but that W is important as it signifies water resistance. Conduit is considered to be a wet place. THHN/THWN is not UV resistant so it can not be used where it is exposed. That has to be stamped/imprinted on the wire itself; just don't believe the seller. There may be no code enforcement officer but make sure the power company okays it.

Rifraf Member	# Posted: 1 Apr 2012 08:47pm Reply Thank you

Rob_O	# Posted: 1 Apr 2012 09:30pm Reply Quoting: Rifraf From what I can tell it would be #2 copper, but im going to bury this so is there a all in one cable I can buy somewhere that has the ground ,and all in the main insulator. Underground service entrance cable is what you are looking for.

Rifraf Member	# Posted: 1 Apr 2012 09:40pm - Edited by: Rifraf Reply am i reading that right ? $13.23 per ft Rob_o thank you very much for the information. I dont doubt that it would work but in that price I cant afford to buy it like that. The guy with the copper 1/0 wire will sell me 200ft (more than i need ) for 250.00 USD, then I can buy some non metalic conduit but ill have to wait and see the copper wire to know what diameter of conduit i need. Shouldnt run me more than 50.00 - 100.00 for the conduit i should think. 350.0 max investment in the wiring. I can handle that or a little less

Rob_O	# Posted: 1 Apr 2012 09:55pm Reply Quoting: Rifraf am i reading that right ? $13.23 per ft Rob_o thank you very much for the information. I dont doubt that it would work but in that price I cant afford to buy it like that. I don't remember what it cost me last time I bought a length, but it was not $13 per foot. More like 3 or 4 bucks a foot, check your local home store

Rifraf Member	# Posted: 2 Apr 2012 04:12pm Reply I was curios about the THHN vs THWN wiring. when i go to see this copper wire if it doesnt have the W imprinted on the insulation then its not water resistant? One person asked me that if I am placing the wire in water tight conduit anyway, why worry about that. I didnt have an answer but was curious if you can fill me in on that. I havent seen the wire yet so this may be a moot point, but it will be sad to turn it down if its not absolutely required, im getting such a good price on it after all.

MtnDon Member	# Posted: 2 Apr 2012 07:03pm - Edited by: MtnDon Reply That's right, without the wire showing THWN or THHN/THWN it can not be used in underground conduit. Even if you swear the conduit is perfectly glued at all joints. According to the NEC (National Electric Code) underground conduit is considered a wet location. Any conduit in a wet location is considered wet for that matter. Outside running up or along a wall it is considered wet. Outside it rains; conduit is therefore wet if outside. This is an example of the markings....

Rifraf Member	# Posted: 2 Apr 2012 10:11pm - Edited by: Rifraf Reply whew, he's bringing it by tomorrow. I asked him to check for the label on the insulation very excited to hear it does read THWN. Ill be saving about 300 - 400 bucks on this Thanks

Bzzzzzt Member	# Posted: 4 Apr 2012 08:15pm Reply Just FYI: Most manufacturers here in the US make all their wire as THHN/THWN as a standard. I think it is also classified as MTW and a couple others.