My Demand Load Calculation

[Guido]

Can someone please review this to make sure I did it correctly?
Thanks.


Demand Load Calculation:

3600VA 1200ft2 X 3VA
3000 Small appliances (1500VA X 2)
1500 Laundry
8100VA Sub Total

3000VA
1785 ((8100-3000) X 0.35)

4785VA General Lighting Demand
2500 A/C (estimate based on 1.5 ton)
1250 Dishwasher
6000 Dryer (estimate)
11250 Range (estimate 7500 X 2 X .75 load)

25785VA Total Demand Load
107Amps (25785/240)

[Guido]

Personally I think this demand load stuff is mainly BS. If someone is trying to run a factory off their residential service then obviously there are problems, but to calculate VA based on square footage, etc. etc.? Gimme a break. I don't think it's very realistic.

Why do I think this?

My house has 100A service, with a panel of 16 breaker slots/row (32 breakers) AND a subpanel for the A/C and Dryer. A total of 36 breakers that are all being used.

My dad's house is 2.5X the square footage of mine and has exacltly the same electrical load as I do (except he has one electric range instead of two, but his A/C is double the size) on his 100A service.

According to my demand load calculations, my tiny house is already "overloaded" so his should be WAAAYYY overloaded. He has not had a single electrical problem is 20+ years. I think I can remember about 3 times a breaker tripped in all those years.

And the kicker? His panel has 2 rows of 12 breakers, for a total of 24, and he has NO subpanel. And he has a breaker dedicated to the alarm system (which I don't have). And he has one slot empty!

And here I am worrying that my 36 breaker setup is not enough. :rolleyes:

I wonder how many of these codes are really for our safety, and how many are constantly created and revised just to keep the code writers employed.

I'm racking my brain out trying to free up a 20A circuit to run to a shed - but after seeing my dad's panel I'm seriously thinking of freeing up some space in my panel by un-splitting my kitchen receptacles. My dad has a 850W microwave and a toaster oven on his counter (plus the occasional coffee maker, kettle, etc) and never blew a circuit. I figure if you're the type of person who operates 6 kitchen appliances at the same time, then you deserve to take a walk to the panel to reset the breaker.

Sorry for the rant. I'm a little frustrated wasting so much time trying to do it by code, only to realize that most of it isn't necessary. If it were, then the city should condemn 99% of the houses out there that do not meet today's code. why do they let people live in them?

Just because a brand new Mercedes is safer, that doesn't mean that last year's model will burn up and kill ya!

[Homer]

Personally I think this demand load stuff is mainly BS. If someone is trying to run a factory off their residential service then obviously there are problems, but to calculate VA based on square footage, etc. etc.? Gimme a break. I don't think it's very realistic...The demand load calculation is an attempt to determine an adequate service size. As you have seen, it is based on various assumptions of how people actually use electricity within their homes. Nobody behaves exactly the same. Some folks would never consider using a clothes dryer at the same time as a range and AC; others would.

According to my demand load calculations, my tiny house is already "overloaded" ...If you were to sell the home to more 'demanding' folks, it may very well be overloaded. A tripping main breaker would attest to it. Obviously you are not as demanding as the load calculation assumes.

Sorry for the rant. I'm a little frustrated wasting so much time trying to do it by code, only to realize that most of it isn't necessary. If it were, then the city should condemn 99% of the houses out there that do not meet today's code. why do they let people live in them?Much of the code relates directly to safety, and the rest relates indirectly to safety by ensuring an adequate arrangement of branch circuits. If you are continually tripping breakers or find the need to use extension cords, then you don't have a adequate setup, regardless if the wires are protected by properly sized breakers. If it's not adequate, then it may lead to unsafe conditions such as the use of extension cords under carpet and furniture.

Just because a brand new Mercedes is safer, that doesn't mean that last year's model will burn up and kill ya!If your home was wired to code at the time, there is no obligation to update it. Common sense should be used here. Just remember that a lot of thought and effort has gone into the evolution of electrical codes and a home wired 'by the book' now is much safer than one done 'by the book' in 1930.

Homer

[Guido]

The demand load calculation is an attempt to determine an adequate service size. As you have seen, it is based on various assumptions of how people actually use electricity within their homes. Nobody behaves exactly the same. Some folks would never consider using a clothes dryer at the same time as a range and AC; others would.
I believe that if my demand load calculation works out to 110A on a 100A panel, I don't think an inspector should force me to make changes, especially if I NEVER tripped a breaker. He should look into MY specific lifestyle, not assume I'm like the neighbor who runs his AC, Range and Dryer on extension cords all at the same time. Sure it's a good ball-park figure to get started, but not something that should be enforceable.
A house drawing 60A on a 200A panel can easily be much more dangerous than one drawing 150A on a 100A panel.

If you were to sell the home to more 'demanding' folks, it may very well be overloaded. A tripping main breaker would attest to it. Obviously you are not as demanding as the load calculation assumes.
Before buying my house I noticed the 3 kitchen counter-top receptacles were wired to ONE 15A circuit. I asked the owner and he said do not operate more than one appliance - if necessary use the 120V range outlet for another appliance. Is this to code? Nope. Did it work for them? I guess. Did I care? No, because I didn't have to buy that house. I upgraded to 3 split-receptacle circuits out of pure convenience (not having to reset the breaker), not because of code or safety. It's probably been like that for 20 years and all of a sudden it's unsafe? If the house was wired to 1901 code, I'd be ****ed. This is where a good home inspection comes into play.

It's like changing the brake shoes on your 1953 Chevy and the code says you must upgrade to ABS disc brakes because they're safer, for you and the next owner. The next owner should get MINIMUM what the original owner received when buying new. Anything upgraded should be considered a bonus.


If your home was wired to code at the time, there is no obligation to update it. Common sense should be used here. Just remember that a lot of thought and effort has gone into the evolution of electrical codes and a home wired 'by the book' now is much safer than one done 'by the book' in 1930.

I just think when renovating you should be allowed to follow a code no older than the age of the house. If you can't buy K&T wiring or asbestos insulation, then you're FORCED to upgrade, otherwise it's up to the owner. And if someone buys a 75 year old house, they should be well aware that it quite possibly contains 75 year old technology. They should expect the house to meet the standards of when it was built - even if it was renovated.

I agree that a lot of thought and effort has gone into the codes, but how many of them are practical? Why don't they make it mandatory to install a grounding rod for each receptacle or quadruple-insulate anything you plug in? (I hope they're not reading this, haha) It's safer than current standards, but is it practical?

Progress is good, and we need it, but we shouldn't be forced to upgrade our wiring, breaker, switch, etc, just because we want to change the color of our 70 year old receptacle to match the decor.

I once read the specs on a new phone that said it includes "lightning strike" technology that helps prevent electrocution in a lightning storm. At first I laughed, then I wondered how long will it be before this technology becomes code and we're required to upgrade every time we buy a new phone?

If you're still reading this Homer, remember that it isn't directed to you (although I did use your quotes in my reply). It's just a general rant that makes me laugh (cry?) every time I learn something new about residential wiring.
On the surface it makes sense: safety, safety, safety. But when you question certain things in detail, not even the experts understand the reasoning. Something fishy is going on :rolleyes:

[Mr Fixit eh]

To reply to the OP, the demand load calculation under CEC is different from the NEC, so the calculation by the OP is different from that required by the CEC.

Briefly, the "basic load" is 5000 watts for the first 968 square foot of floor space (not including basement), then 1000W for the 2nd 968sq.ft (or portion thereof), then 1000W for the next 968sq.ft or portion... You need to account for basement floor space by considering 75% of the actual footprint of the basement.

"Basic load" includes all lights and 15A receptacles, gas furnace, gas water heater, and any appliance that draws less than 1,500 W (12.5A@120V).

Add to this "basic load" 6,000W for any range up to 12KW, plus 25% of the dryer's nameplate rating, plus A/C at 100% of it's rating (electric heat at 100%, if that draw is larger).

Take the total and divide by 240volts and this is your demand load.

Given your example:

5,000w 1st 968 sq.ft
1,000w 2nd 968 sq or portion (202 sq.ft)
6,000w range
1,500w dryer
2,500w A/C (check the nameplate)

For a total of 5,200W /240 = 66.66 A So you'd have plenty of room in your 100A service per CEC.

If you have a basement, you may be within the allowed 6,000W for up to 1936 sq.ft. Eg. if you have a 600 sq.ft. basement, then you have to consider 0.75 x 600 = 450 sq.ft plus the 1,200 sq. ft. main floors is still less than the 1,936 allowed. If you have a basement that is 1,200 sq. ft, then you'd have to consider 0.75 x 1,200 = 900 plus your 1,200 already, so you'd have to add another 1,000W to your demand load calculation.

If you have electric hot water than you have to add this to the calculation, and since I don't have electric hot water, I forget the formula. I can get it if you need it.

[Guido]

Excellent help!
My basement is the same size as my main floor (it's a bungalow), so even at 75% I'll have to add the 1KW as you stated.

There is another range in the basement - so another 6KW?

I have gas hot water and gas heat.

I'll check my A/C and dryer nameplate tonight.

Now here's the kicker... how does all this change if the basement is a rental apartment (with shared laundry)?

[Mr Fixit eh]

Your Knights will likely give you instructions. You'd likely have to treat the basement rental unit as 100% floor space, and the range would be another 6KW. I don't have my book in front of me, but something is nagging me that rental units require a separate service to meet code.

My calculation has an obvious error. The total wattage is 16,000W, not 5,200, but the result (66.6 A) is still correct.

With what you've described, I calculate 95.8

Upgrading your kitchen outlets was for convenience and didn't add any new load on your service. Adding circuit (s) to a shed does introduce new load that wasn't there before.

I'm thinking you will need to upgrade your electrical service if you want to run even one 15A circuit to your shed. Ouch.

I feel your pain. Truly this sucks, but the codes are for our protection. In addition, the upgraded service will give you all the ability to upgrade to a full-blown shop, and add that hot tub to soothe your achin' bones at the end of all this :cool:

The only other option would be to proceed with the installation without a permit. There are lots of threads on that topic, but in this case I think if your wiring caused a fire you could be held liable--especially because you knew better.

[Guido]

If I remember correctly previously a apartment required a sub-panel that contained all of the apartment's circuits, and nothing more. This is not required anymore. You can have everything in one panel if it fits, or have a sub-panel and mix and match the circuits between the two (they don't have to be separated apartment/rest of house).
If the service is overloaded you need to either upgrade the main service, or add another service (then you're forced to have the apartment fed off it's own panel). That's how I remember reading it.


Adding circuit (s) to a shed does introduce new load that wasn't there before.
...
I feel your pain. Truly this sucks, but the codes are for our protection.

See this is where I disagree (with the code, not you).
Adding circuits to my shed doesn't introduce a new load, because I currently work out of my shed. The only difference is now I run a 25' extension cord from my house, across my lawn. Is this safer than having proper, permanent wiring?
That's why I think the Demand Load Calculation should be regarded as a starting point, or suggestion, not something that's enforceable.
I personally will use the same power tools, and perform the same work whether there are 400 receptacles attached to my house, or 40.

[Mr Fixit eh]

You're right. Here is a link to the Electrical Safety Authority (Ontario) http://www.frontlines247.com/frontlines247Info/EU_S1c.asp?FaqID=61

I see your point about the new circuit carrying no new loads. I guess from the authorities' perspective, for a new owner moving into your house, it is alot easier to overload the existing service with the new circuit. The "funny" thing is that if this new shop circuit was in your basement, it would already be covered by the "basic load" part of the demand load calculation.

Are you planning to have your work inspected? If yes, you could probably get an opinion from the inspector. Once you have paid for a permit, you can phone and ask questions. If no, you can go to www.esasafe.com Click on "FAQ", "Ask a Question." A code expert will reply to your email within a couple of days.

[Guido]

Your first link doesn't work for me, but your second one can be useful sometime. I'll keep it handy.

Just curious but what if I were to wire the shed, but NOT run a permanent feeder to the house and instead use an extension cord to plug it in the GFCI outlet on my house? I know this is mikey mouse and I wouldn't do this, I'm just wondering if theoretically I can be a way to eliminate the shed from the demand load calculation. It's not permanently wired so you wouldn't have to include it right? Or not?

[Mr Fixit eh]

I actually did that a number of years ago. I built a little 8'x5' play house for my little girls. I wired up a light and a receptacle. The feed was an extension cord to an exterior GFCI receptacle at the house (20 feet away). I only supplied power when they were using it. They thought it was pretty cool at the time.

Now is that sort of set up code compliant? I suspect not, but I'm not sure.

The biggest problem would be the loading of the circuit you plug the extension cord into. If there are already loads on the circuit at the house, you could get overloaded quickly and "pop" goes the breakie.

[Mr Fixit eh]

I actually did that a number of years ago. I built a little 8'x5' play house for my little girls. I wired up a light and a receptacle. The feed was an extension cord to an exterior GFCI receptacle at the house (20 feet away). I only supplied power when they were using it. They thought it was pretty cool at the time.

Now is that sort of set up code compliant? I suspect not, but I'm not sure. I certainly wouldn't encourage it for your set up.

The biggest problem would be the loading of the circuit you plug the extension cord into. If there are already loads on the circuit at the house, you could get overloaded quickly and "pop" goes the breakie.

[Guido]

I wouldn't do this myself, I was just wondering if it would help in the demand load calculations and look better on paper.

Both of my outdoor receptacles are on dedicated, separate circuits. I plan on putting them both on the same 15A breaker and replacing the other 15A breaker with a 20A and run that new circuit to the shed.