# Help with subpanel sizing



## HandyHails (Feb 28, 2009)

A subpanel is going to be installed for a basement remodel.

Downstairs the subpanel will need to run an electric dryer, hot water heater, 20 or so recessed lights, and other miscellaneous outlets including GFI's at the bathroom sink for hair dryers and such.


My electrician was going over the game plan w/ me today. He is recommending a 75 amp breaker in the main leading to a 100 amp subpanel. 

I'm doing the math and I'm a little concerned. 

I figure the water heater and the dryer will actually pull like 20 amps each while they are running. The recessed lights w/ 60 watt bulbs should be about another 40 amps. Not to mention the TV, the mini fridge, wine cooler, hair dryer, vacuum cleaner etc, etc.

Now I realize that the chances of them running everything at once are slim at best, but in my mind the math just doesn't add up. 

Am I worrying over nothing?


----------



## Tinstaafl (Jan 6, 2008)

HandyHails said:


> Now I realize that the chances of them running everything at once are slim at best, but in my mind the math just doesn't add up.


The same could be said for the main load center in most homes. As a matter of practicality, you just don't try to allow for everything on the planet to be running at once.

If your electrician is bona fide, he ought to have experience with load calcs. You don't trust him?


----------



## TNTRenovate (Aug 19, 2010)

HandyHails said:


> A subpanel is going to be installed for a basement remodel.
> 
> Downstairs the subpanel will need to run an electric dryer, hot water heater, 20 or so recessed lights, and other miscellaneous outlets including GFI's at the bathroom sink for hair dryers and such.
> 
> ...


You also have to remember the sub panel is going to take up spots on the main. He should also be moving some stuff to the sub. But I really can't give much more than that. I am not a licensed sparky nor have I seen the setup.

With all that said, I did stay at a Holiday Inn Express a few years ago.


----------



## StreamlineGT (Jul 4, 2009)

80 cans seems a little excessive.


----------



## StreamlineGT (Jul 4, 2009)

Remember, you are dealing with different voltages. Yes the dryer and water heater will be in the 40-50amp range, but the remaining loads are 120v. You'll get another 50 amps of 120v loads on your 75 amp feeder. Oh, and 20 cans at 60watts is 10 amps, not 40.


----------



## rselectric1 (Sep 20, 2009)

HandyHails said:


> The recessed lights w/ 60 watt bulbs should be about another 40 amps.


It would take 80 cans lights running all at the same time to approach 40 amps.

Trust your sparky as long as he's qualified.


----------



## HandyHails (Feb 28, 2009)

Tinstaafl said:


> The same could be said for the main load center in most homes. As a matter of practicality, you just don't try to allow for everything on the planet to be running at once.
> 
> If your electrician is bona fide, he ought to have experience with load calcs. You don't trust him?


They've always done right by me before. I seem to over-analyze everything though. I didn't get into it with him at all though. I actually didn't give it any thought until I got home today. 



> 80 cans seems a little excessive


Doh!! I was thinking 2 amps each. I'm a dummy. Nevermind then. My electrician is a better electrician than me!!nline2long:


----------



## plummen (Jan 9, 2010)

StreamlineGT said:


> Remember, you are dealing with different voltages. Yes the dryer and water heater will be in the 40-50amp range, but the remaining loads are 120v. You'll get another 50 amps of 120v loads on your 75 amp feeder. Oh, and 20 cans at 60watts is 10 amps, not 40.


Figure the cans at max size bulb for fixture


----------



## mrmike (Dec 9, 2008)

StreamlineGT said:


> Remember, you are dealing with different voltages. Yes the dryer and water heater will be in the 40-50amp range, but the remaining loads are 120v. You'll get another 50 amps of 120v loads on your 75 amp feeder. Oh, and 20 cans at 60watts is 10 amps, not 40.


 Don't know what you are getting at here???? It is all load on that 75 amp breaker , That breaker is feeding both the 240 & 120v.

On the thread question I just don't why the electrician would opt for a 75 amp feeding that sub. Why wouldn't he go to a 100a feed & wire to make sure that load would be covered so as there wouldn't be trips on that 75?


----------



## Electricmanscot (Feb 6, 2005)

mrmike said:


> Don't know what you are getting at here???? It is all load on that 75 amp breaker , That breaker is feeding both the 240 & 120v.
> 
> On the thread question I just don't why the electrician would opt for a 75 amp feeding that sub. Why wouldn't he go to a 100a feed & wire to make sure that load would be covered so as there wouldn't be trips on that 75?


It won't trip. Not everything will be running at the same time. And even the stuff that is running won't be drawing constant full current at the same time. There are many many houses that only have 60 amp services.

I assume the electrician was hired for a reason. :whistling

BTW, I know why he went with a 75 amp breaker and it's actually a sign that this is a good electrician.


----------



## mrmike (Dec 9, 2008)

Electricmanscot said:


> It won't trip. Not everything will be running at the same time. And even the stuff that is running won't be drawing constant full current at the same time. There are many many houses that only have 60 amp services.
> 
> I assume the electrician was hired for a reason. :whistling
> 
> BTW, I know why he went with a 75 amp breaker and it's actually a sign that this is a good electrician.


 
???????????????????? You missed the point. Why would you supply that basement with so much in it, with just a 75 a when remodeling instead of a 100 ?????????????? What if they plug in an electric heater or a 15a vacuum with some of that stuff running???

We always Assume that all the appliances,etc will not be running at the same time, but at the same time, A good Electrician will factor in the capacity is there to handle it , and have room for expansion for anything else added in that Basement !!!!!! Your Reply Was ill directed......


----------



## woodchuck2 (Feb 27, 2008)

HandyHails said:


> Downstairs the subpanel will need to run an electric dryer, hot water heater, 20 or so recessed lights, and other miscellaneous outlets including GFI's at the bathroom sink for hair dryers and such.
> 
> I figure the water heater and the dryer will actually pull like 20 amps each while they are running. The recessed lights w/ 60 watt bulbs should be about another 40 amps. Not to mention the TV, the mini fridge, wine cooler, hair dryer, vacuum cleaner etc, etc.



I am thinking there will probably be a clothes washer too? So in reality while doing laundry the clothes washer, clothes dryer and hot water heater will be operating all at once as well as most of the lighting. We all know woman do not like to do laundry in the dark. I myself would install a 100 amp 20 slot panel on a 100 amp breaker. The OP probably could get away with a 75amp breaker but why take the chance of it operating close to or at peak operating amperage?


----------



## allenal (Feb 17, 2012)

*Stationary Engineer*

Hi, I'm allenal the new guy in the group, glad to be a new member. I'd like to share my experiences and ideas.


----------



## allenal (Feb 17, 2012)

* Amps calculation for the Sub-panel should be calculated base on the loads.
* Feeder conductor size (awg) should be calculated.
* Branch circuit conductor and overcurrent protection device must be sized no less than 125% of the total load.
Step 1: Determine the total load.
I=VA/E
I= 5,000 VA/240 V
I= 20.8A
Step 2: Conductor size at 125% for continues load
Conductor size=20.8A x 1.25
Conductor size=26.0A (round it up to 30A over current protection)
Conductor size=10 AWG at 75 Celsius
* What is the KW of the Dryer(name plate rating of the equipment)
* KW of the Water heater.
* Watts of the recessed and how many luminaries
* How many receptacles (base on the square footage of the basement)


----------



## allenal (Feb 17, 2012)

Running all appliances simultaneously is not a problem as long you have the right size of the conductor and the right amperage rating for the circuit breaker.So calculation is very important also, if they run with different amps it doesn't mean they have desame voltage


----------

