Sub Panel

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jetlag

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Eatonton, Georgia
I am considering installing a 100 amp sub panel instead of making home runs on some circuits . Do you derate the sub panel demand the same way you would a main panel . I am trying to decide how many of these items I can install in the sub panel , range, 10 kw air handler, 2.5 ton heat pump, whirlpool bath with heater, 1 - 20 amp and 1- 15 amp general lighting. I usually never load a sup panel to capacity so wasnt sure about the demand calculations.
 
jetlag said:
Since we are nit picking. . .
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A ?nit? is the larvae or egg of a parasitic insect. If you don?t pick them, then the adult insects will come back to annoy you. ;)
jetlag said:
. . . one does derate a panel for ambient temperatures.
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I don?t think a panel rated for 225 amps will have to be derated to 200 amps (or to some other value), if you put it in a high temperature environment. So I will have to ask for a code reference. :confused:
jetlag said:
I meant to say figure the demand for subpanel.
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You can apply demand factors to the loads, if they meet the rules in 220. You don?t apply a demand factor to the panel as a whole, or to the entire set of loads on a panel. So here again, without trying to be a pain in the neck, I will say that I do not understand the question. 408.30 says that a panel?s rating must be at least as high as the calculated load. It does not matter if this is a sub panel or a main panel.

 
charlie b said:
A ?nit? is the larvae or egg of a parasitic insect. If you don?t pick them, then the adult insects will come back to annoy you. ;)
I don?t think a panel rated for 225 amps will have to be derated to 200 amps (or to some other value), if you put it in a high temperature environment. So I will have to ask for a code reference. :confused:
You can apply demand factors to the loads, if they meet the rules in 220. You don?t apply a demand factor to the panel as a whole, or to the entire set of loads on a panel. So here again, without trying to be a pain in the neck, I will say that I do not understand the question. 408.30 says that a panel?s rating must be at least as high as the calculated load. It does not matter if this is a sub panel or a main panel.

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No one else has a problem understanding the question , I dont understand your answer so we are even :roll:
 
jetlag said:
I am considering installing a 100 amp sub panel instead of making home runs on some circuits . Do you derate the sub panel demand the same way you would a main panel . I am trying to decide how many of these items I can install in the sub panel , range, 10 kw air handler, 2.5 ton heat pump, whirlpool bath with heater, 1 - 20 amp and 1- 15 amp general lighting. I usually never load a sup panel to capacity so wasnt sure about the demand calculations.
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You only need to count the larger of the AC. The heat pump stops if the 10 kw heat strip kicks in. Heat pumps dont work at 32 degrees so they have backup of 10 KW. Most likely a 100 amp sub will handle load and maybe even a bit less. Keep in mind the 10 KW is a heat load at 125 %
 
jetlag said:
Well sometimes it causes use to think harder and it is fun when we can prove them wrong , but also fun if we learn something :grin:
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What you asked was a valid question. We could have closed this thread after post #2.
 
infinity said:
What you asked was a valid question. We could have closed this thread after post #2.
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I was happy after post #2 , it was dead on , i guess it was a weird way to look at it but in my mind I was thinking about derate the load to a lower amount for the demand , I guess the word derate left me open to get corrected :grin:
 
Jim W in Tampa said:
We have almost never ended any that fast. Bet we can run this up to 100
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It will go 100 plus if someone jumps on the comment about derate the panel for ambient temp . This is the same panel I started the thread about " sub panel in unfinished attic ". What i could gather from the replies the panel cant go there because of the heat unless insulated from the unfinished attic. I have another place for the panel now in the air handler closet . I had to make the closet larger for the clearance
 
Thanks Jim

Thanks Jim

Jim W in Tampa said:
You only need to count the larger of the AC. The heat pump stops if the 10 kw heat strip kicks in. Heat pumps dont work at 32 degrees so they have backup of 10 KW. Most likely a 100 amp sub will handle load and maybe even a bit less. Keep in mind the 10 KW is a heat load at 125 %
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I couldnt remember that the the heat pump stops when the strips kick in . I will look at that again in the examples
 
Jim W in Tampa said:
You only need to count the larger of the AC. The heat pump stops if the 10 kw heat strip kicks in. Heat pumps dont work at 32 degrees so they have backup of 10 KW. Most likely a 100 amp sub will handle load and maybe even a bit less. Keep in mind the 10 KW is a heat load at 125 %
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You must not get very good heat pumps down south. Around here I have HVAC contractors installing an outdoor lockout thermostat (more recently the indoor thermostat is capable of connecting to an outdoor probe and you can program the lockout temperature) and setting the lockout temperature at 20 degrees and some a little lower yet. There is still heat in the air at low temperatures but it is harder to collect enough to keep up with demand. It is all about where they feel the system no longer runs more economically than the back up heat source. The back up heat source is not always electric. But when it is electric, 10Kw is a small unit. Most are 15 or 20 Kw and occasionally there are 25Kw units.
 
Jim W in Tampa said:
You only need to count the larger of the AC. The heat pump stops if the 10 kw heat strip kicks in. Heat pumps dont work at 32 degrees so they have backup of 10 KW. Most likely a 100 amp sub will handle load and maybe even a bit less. Keep in mind the 10 KW is a heat load at 125 %
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jetlag said:
I couldnt remember that the the heat pump stops when the strips kick in . I will look at that again in the examples
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Mgraw said:
I didn't know that. So even in 2nd stage mode the heat pump kicks out? (I know the answer to this question)
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You need to check the system you are dealing with. Particularly the thermostat, that is what controls the compressor and aux heat. Some turn off compressor if aux heat is on, some do not. Some electronic thermostats can be programmed to do it either way. Many of them will run simultaneously during defrost cycle, but it will be for a short duration, and the compressor load is usually well below its full load rating when it is cold outside
 
kwired said:
You need to check the system you are dealing with. Particularly the thermostat, that is what controls the compressor and aux heat. Some turn off compressor if aux heat is on, some do not. Some electronic thermostats can be programmed to do it either way. Many of them will run simultaneously during defrost cycle, but it will be for a short duration, and the compressor load is usually well below its full load rating when it is cold outside
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Example d2c in the back of the nec handbook says you dont have to add the heat pump if it doesnt come on at same time as heat strips. I think the low temp cut off for the heat pump is not the only thing. If you move the T stat up a few degrees past the room temp, only the heat pump comes on, but if you move it on up to far , The aux heat light will come on with the hear pump. When the room gets close to the t stat setting , the strips drop out and let the pump finish . At least all the systems I know work this way , so the strips and pump do run together if the room temp gets to far below the t stat setting , at least for short periods. Only the heat pump runs in a normal cycle if you dont move the t stat to far.
 
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