60 amp Attic sub-panel question

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  #1  
Old 02-15-06, 12:05 PM
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Question 60 amp Attic sub-panel question

Greetings to all,
I recently had a 60 amp sub-panel run up to my attic to accomodate a Central a/c air handler and an upcoming bathroom and attic renovation, I would like to install a "point of use" water heater for the bath (any recommendations as to brand would be appreciated) and I have noticed that they require anywhere from 30-50 amp double pole breakers, so my question is what is the maximum double pole breaker that can safely be installed in this sub-panel ????and will this limit the capacity for this sub-panel???Where as I also plan to run circuits for a whirlpool tub, computer, and other electronics for use in the finished attic. The box itself is a Murray load center with 20 spaces, the feed to the box from the 60 amp double pole breaker main panel is #6/2.

Thanks for your comments, Triple B
 
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Old 02-15-06, 01:40 PM
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Originally Posted by tripleb923
I recently had a 60 amp sub-panel run up to my attic
I have no idea why anyone would install a mere 60A general purpose subpanel. It should have been 100A. Add a second subpanel.
Make it 100A this time so you don't run short so soon.
 
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Old 02-15-06, 02:21 PM
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Originally Posted by tripleb923
so my question is what is the maximum double pole breaker that can safely be installed in this sub-panel
The label on the inside cover of the panel will specify this. It's usually phrased like "maximum amps per stab". You will probably be fine with up to a 60A breaker no problem.

Originally Posted by tripleb923
the feed to the box from the 60 amp double pole breaker main panel is #6/2.
Did you mean #6/3? If it is actually fed with 6/2, then you cannot run any 120V loads like standard receptacles or lighting from this panel.
 
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Old 02-15-06, 02:24 PM
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Hello, it sounds like you have a least a 100 amp rated sub-panel (20 spaces) and you are powering it from a 60 amp double pole in the main panel. This is going to probably limit your options somewhat, since you are not powering it at its rated amperage. You mention that you have a #6/2 cable feeding the box. It should be four wire copper 6-3-Grd cable (H-H-N-Grd). Neutral and equipment ground (egc) must be seperated at the sub-panel. It's really not a matter of how big of a breaker you can install in the sub panel as how much demand that sub-panel is going to have and does the 60 amp breaker that feeds it need to be upsized.
The sub-panel demand is limited by the breaker that feeds it (60 amps) and the branch circuits in the sub are limited by the breakers that protect them. In turn your main panel (service rated panel) has to have enough "reserve" to supply the demand of the sub-panel.
So you need to take a look at present and future equipment and general purpose items that you are going to power from this sub panel. You can do a demand load calculation on both panels and determine the necessary requirements.
Without having to run new cable though...your demand needs to be less than 60 amps for the sub. With the 60 amp in place if you use a 50 amp point of use heater then that doesnt leave much else that can be operated at the same time ... 10 amps or so. If you increase the amperage of the breaker feeding the sub then you may have to change out the cable.**

** You might be able to go to 70 amps with the same cable you have. It will have to be something other than NM-B type though and you will have to verify temperature ratings of the terminations at both panels.

So you really need to decide what you are going to need for your point of use heater and its electrical requirements. Whirlpool requirements would be great to have also.

Now if your heater is just for the bathroom sink you can probably get by with the lower amperages. But if your wanting to have a tankless type heater that will heat the water for the whirlpool then this becomes a little bit bigger problem and more than likely will require the 50 amp model. I'm not to sure you will be happy with that either unless there are models that have better hot water supply to demand ratios than I have been around. The ones I have some familiarization dont do a very good job when a lot of hot water demand is needed.

Having breifly touched on some of the things you need to consider can you tell us what your utility service to the house is.... 100, 150, 200 amp?

Looks like my reply is somewhat redundant with the others ...
 
  #5  
Old 02-15-06, 08:29 PM
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Thanks Guys,

My main service panel is 200 amps and the cable going to the sub-panel #6/3copper romex (H+H+N+Grnd) , my sub panel is rated for 125 amps....So should I run a larger size cable???what would you suggest?? the main loads will be the a/c handler on a 15amp dble pole breaker>>the whirlpool tub (I think thats a 30 amp dble pole breaker)>>> the point of use tankless heater(I saw one with a 40 amp dbl pole )>>>> then a 20 amp single pole for computer,>>>>15 amp for lights etc in the attic and bathroom (separate of course)>>>>>and another 20 amp for the t.v./stereo in he finished attic.

Thanks for the input......Triple b
 
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Old 02-15-06, 09:29 PM
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What I'm suggesting is that you keep the 60A and that you pull a new 100A for your a/c, twh, and whirlpool. Use the 60A for the other circuits.
I think this will work out well for you since the extra feeder means that the brownout for the lights, electronics, and computers won't be aggravated by sharing the same feeder with the other loads.

It has been debated elsewhere whether a twh is a continuous load (on the argument that someone could leave the hot water run all day). You are safest if you calculate it as continuous; but I think it is normally intermittent.
 
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Old 02-16-06, 01:48 AM
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The 200 amp service is great and in most homes provides for adequate additions like yours.
You could probably spend hours debating the options and designs for what you are wanting to do.
First it is important that you know if you have enough extra spaces in your main panel to install two double pole breakers to feed two subs as bolide suggests. I do see an appeal to get the computers off the panel with the motor loads and the tankless heater. IMO you would consider this as an improved design not necessarily a needed one.

If you would opt for this two subs design I think I would just install a new 100amp rated cable to the existing 125 amp sub and mount a 60 amp panel next to it and use the existing 6/3 cable and 60 amp breaker for it. Most 60 amp subs will provide 2 one inch spaces from which you can run four 120 volt circuits using tandem breakers or 1/2 " breakers.

It seems to me from what you have mentioned for your needs the real key here is how big is that point of use heater going to be. If it needs to be 50 amps then I'm not seeing a way to avoid a running a higher amperage supply to the existing sub-panel.

Most whirlpools are one or two 20 amp gfci protected circuits, it depends on how many power cords are supplied as part of the unit.

Bathroom receptacles must have a 20 amp circuit by code and gfci protected. If you only supply that one bathroom's receptacles with a 20 amp circuit you are allowed to also supply the lights from the same circuit. However, nothing else can be on that bathroom circuit.

There are other options .... IMO we really need to know what your heater requirements will be and verify the whirlpool and the a/c air handler amperages in order to avoid speculation.

Lesson learned here is before you install a sub-panel be sure of its future requirements and supply it as needed or just supply it at its rated amperage.
 
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