Panel sizing for a single family home.

wrobotronic

Senior Member
Location
Colorado
My concern for doing the Calcs in the field is time. Shouldn't these be provided by the EC/ Homeowner during the plan review?
Also those conductors are #2 Al being used for the sub panels...
The EC has mentioned that they will be eliminating some circuits to make room for the new subs. And I'm very sorry for how that picture turned out...yikes it is plenty big!!! I think one panel is going to be plenty to be honest. I'm not sure why they want two subs when one will be enough for the scope...
Finally, being relatively new here I'm lost on some acronyms... what is a POCO? I assume it means power company.... thank you all as always for your help...

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iwire

Moderator
Staff member
Location
Massachusetts
POCO is power company.

Welcome to the forum.


Code wise you could put a 400 amp subpanel in every room all suppled by a 100 amp service if the load calculations support it. Not practical but compliant.
 
EZ Load Calculation for Residence, Michigander Technique.

1) Turn on everything in the house.

2) If 'everything' doesn't include 3 (ea) 1500 watt electric space heaters, bring them from home and plug them in and turn them on, too.

3) Take amp clamp to panel and measure the current on each leg of the feeder to the main or bus.

4) If home has air conditioning, make sure that is running during the test.

5) Make sure heat/furnace is running. If both heat and AC can't run at the same time, do two tests, one in each condition.

6) Keep taking current readings for several minutes while you walk around the house making sure everything is on and you are creating a worse case scenario.

7) Take the highest reading you get. That's pretty much your load.

I did the above at my dad's one year for sizing a generator. He had a good sized ranch home, like 70 feet by 30, full basement and attached garage.

The most I could get, even with AC running, was something like 47 amps on one side and 39 on the other.

I was surprised. I thought it would be higher. So I added 10 percent.

Far from perfect, but so are written load calcs. At least the Michigander is using an real world scenario in order to come up with a value.
 

iwire

Moderator
Staff member
Location
Massachusetts
He said "sizing for a generator"! An "over-estimate" would do good for him, IMO.
It's still not a compliant method and as far as over estimating I would prefer an accuate number that I can asign what I feel is the right amount of extra capacity.
 

topgone

Senior Member
It's still not a compliant method and as far as over estimating I would prefer an accuate number that I can asign what I feel is the right amount of extra capacity.
Well, we all have the exact figures at the back of our heads! My old mentor once taught me that: the extra capacity I specify in my designs should depend on how deep my client's pockets are. That is of course, based on the idea that we exist to make our customers satisfied.:D
 

iwire

Moderator
Staff member
Location
Massachusetts
Well, we all have the exact figures at the back of our heads! My old mentor once taught me that: the extra capacity I specify in my designs should depend on how deep my client's pockets are. That is of course, based on the idea that we exist to make our customers satisfied.:D
:D
 

kwired

Electron manager
Location
NE Nebraska
No it, doesn't but the UL standard for service equipment has been changed to require separation like shown in the picture. The change has been accepted by UL, but not sure when it takes effect for manufacturers.
I have only seen such a barrier in equipment that contains a meter socket. My guess on those is it is more of a POCO standard in most places then a listing issue to limit access to the unmetered conductors.

If it were a standard for all service equipment we should be seeing barriers for incoming lines on main breaker panels like they do in Canada.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
Is that the feeders wires coming in from poco on the right side?

Hope not, if so they should be on the left under the separation barrier to keep fused and unfused wiring separate.

I agree, I realize what Bob stated but I wonder if 110.3(B) comes into play here. I have never seen a power company wire exposed in a breaker area just the load side of the meter not the line.
 

iwire

Moderator
Staff member
Location
Massachusetts
I agree, I realize what Bob stated but I wonder if 110.3(B) comes into play here. I have never seen a power company wire exposed in a breaker area just the load side of the meter not the line.
Unfused service conductors enter electrical panels all the time, I really do not understand what you mean.

If you mean unmetered conductors that is less common but happens often in commercial switchgear with CT metering.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
Unfused service conductors enter electrical panels all the time, I really do not understand what you mean.

If you mean unmetered conductors that is less common but happens often in commercial switchgear with CT metering.
I understand it is compliant but if the equipment is listed for the service conductors to be in the designated space then you have a violation. I have not seen unmetered conductors in a panel but I trust it happens.
 

iwire

Moderator
Staff member
Location
Massachusetts
I understand it is compliant but if the equipment is listed for the service conductors to be in the designated space then you have a violation.
I agree that it could be a listing violation but really don't know as I have never worked on a panel like that.

It would be interesting to see if the listing requires the use of that gutter or if it is simply an option to use it if the power company requires separation.

For instance I can get wireway that has places for power companies to place seals on them.

Does the listing require seals to be used?
 

kwired

Electron manager
Location
NE Nebraska
If you happen to top feed that equipment I don't see why you couldn't remove the line barrier and gain some extra wiring space for the loadcenter area. All of the ones I have installed have provisions for bolt on hubs in the top wall, and many even have a hub with a chase through the meter section to the load side compartment which is on the right side for any load side wiring you may want to run out the top of the cabinet.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
I have only seen such a barrier in equipment that contains a meter socket. My guess on those is it is more of a POCO standard in most places then a listing issue to limit access to the unmetered conductors.

If it were a standard for all service equipment we should be seeing barriers for incoming lines on main breaker panels like they do in Canada.
It is a very recent change in the UL standard to require that for equipment sold in the US. I am not sure of its effective date for the manufacturers to comply. I think it may only require a barrier for the service conductor terminations and not the conductors themselves.
 

junkhound

Senior Member
Location
Renton, WA
re: 'turn everything on and measure current" -- and previous comment: That is not an NEC compliant method and will likely result in an over estimate.

Boy oh boy, if I tried that at my house I'd trip the 200 A breaker.

Range (2), 5T heat pump, oven (3), elec dryers (2), elec WH, 4 different welders in outbuildings and garage, 2HP water pump, 5 HP milling machine, 2 HP lathe, 3 1 HP drill presses, 3 4 HP table saws, 10 HP pressure washer. I'd have to ;hire some folks form out in front of the big box to run everything, but it would add up to:

30+30+24+30+30+30+24+24+24+50+50+50+50+20+24+13+10+10+10 +20+20+20+48 > 500 A, sure to trip. But never has.

I'd love to dexterous enough to be able to operate 2 different welders or table saws at the same time though!
 

kwired

Electron manager
Location
NE Nebraska
re: 'turn everything on and measure current" -- and previous comment: That is not an NEC compliant method and will likely result in an over estimate.

Boy oh boy, if I tried that at my house I'd trip the 200 A breaker.

Range (2), 5T heat pump, oven (3), elec dryers (2), elec WH, 4 different welders in outbuildings and garage, 2HP water pump, 5 HP milling machine, 2 HP lathe, 3 1 HP drill presses, 3 4 HP table saws, 10 HP pressure washer. I'd have to ;hire some folks form out in front of the big box to run everything, but it would add up to:

30+30+24+30+30+30+24+24+24+50+50+50+50+20+24+13+10+10+10 +20+20+20+48 > 500 A, sure to trip. But never has.

I'd love to dexterous enough to be able to operate 2 different welders or table saws at the same time though!
The reality is you wouldn't run all those at same time. Even if you did some of them will cycle at least part of the load as needed to maintain operating temperature like the range, oven, electric dryer, so they don't consistently draw full capacity. The motor operated items, only draw the load that is put on them and not necessarily full load all the time. Some by nature do cycle on/off as needed like the water pump the heat pump or an air compressor, and possibly at varying load levels. Welders - chances are you don't have any with very high of a duty cycle, and even then you probably do not weld at maximum output setting often if ever.
 

peter d

Senior Member
Location
New England
It is a very recent change in the UL standard to require that for equipment sold in the US. I am not sure of its effective date for the manufacturers to comply. I think it may only require a barrier for the service conductor terminations and not the conductors themselves.
That's definitely a step in the right direction.
 
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