How to factor high-wattage appliances into load calcs & branch circuit design?

[Jon456]

I know from 220.14(I) that receptacle outlets are calculated at 180VA per each receptacle yoke. But what if you know that a particular appliance or piece of equipment that will be plugged in is a high-wattage device?

For example, let's say we have a kitchenette in an office building. There is a kitchen counter and we want multiple general use outlets available on that counter. But we know there will be a microwave placed somewhere on that counter, a coffee brewer, and an induction cooker. None of these appliances will be built in, so I don't see how they can have dedicated circuits (the appliances could be moved around in the future). But, for the sake of this example, let's say that each appliance draws 15A and is rated at 1,800W. Clearly, they can't all be on a single 20A circuit. Yet it's very likely that two or more devices could be in use at the same time.

1. How do we account for these anticipated loads in the load calcs if these are not on dedicated circuits?

2. How would you design the branch circuits serving this counter that allows flexibility in usage (the appliances listed above being moved around plus the addition of future loads, like a juicer or espresso machine) without the risk of a circuit being overloaded and having nuisance trips?

 

[PaulMmn]

I know from 220.14(I) that receptacle outlets are calculated at 180VA per each receptacle yoke. But what if you know that a particular appliance or piece of equipment that will be plugged in is a high-wattage device?

For example, let's say we have a kitchenette in an office building. There is a kitchen counter and we want multiple general use outlets available on that counter. ... None of these appliances will be built in, so I don't see how they can have dedicated circuits ...

2. How would you design the branch circuits serving this counter that allows flexibility in usage (the appliances listed above being moved around plus the addition of future loads, like a juicer or espresso machine) without the risk of a circuit being overloaded and having nuisance trips?

In our office's Microwave Row we have 4 'industrial' microwaves (suitable for use by amateurs), plugged into 3 20-amp duplex outlets. At lunch time, there's sometimes a wait for a free microwave. Around the holidays, the additional 2 outlets will often be occupied by crock pots or other 'heating' things for office parties.

Overbuild. I don't know if those 3 outlets are on individual circuits or not, but the 20 Amp outlets hints that they're planning on a heavy load.
What's wrong with individual circuits for each duplex outlet? Or a MWBC for each duplex?

As others have said, the code is a minimum, not an ideal!

 

[hbiss]

But what if you know that a particular appliance or piece of equipment that will be plugged in is a high-wattage device?

If you know that there will be several in use at the same time it would be prudent to provide enough circuits to supply them all, no? Isn't that why we provide at least two 20A SABC to kitchen countertops before we even know what will be there?

-Hal

 

[Jon456]

If you know that there will be several in use at the same time it would be prudent to provide enough circuits to supply them all, no? Isn't that why we provide at least two 20A SABC to kitchen countertops before we even know what will be there?

I suppose I shouldn't have written that we "know" these will be there. More like, we "anticipate" they will be there. This isn't exactly a real-world example; I'm trying to approach this problem to learn best practices.

You raised the valid point of (at least) two 20A SABC. But in the example I gave, two would be insufficient. Ok, so we make it three. Then what happens if someone adds a fourth high-wattage appliance in the future? Obviously, we can't design for every future possibility. So how do we strike the right balance?

And I still don't know how to account for any of this in the load calcs, since these (possible) appliances will pull far more than 180VA per yoke.

 

[PaulMmn]

The code for home kitchens says no more than 4' between outlets; most appliances nowadays only have a 2' cord.

Consider the length of the counter-- practically speaking, how many appliances will fit in that space? That's how many outlets you need!

If you wire each duplex as a separate MWBC (ie you've got 240/120 at each duplex outlet), that's more power than one of the 20Amp kitchen circuits can provide.

Don't forget-- you'll never outwit a creative user with a power strip!

 

[gar]

190620-1654 EDT

Jon456:

The NEC can't solve your problem.

Do analysis and discuss the problem with the customer.

I my kitchen I have 8 20 A circuits. Yet I have a problem. The one location where I now have both a microwave and a toaster oven I have one convenient 20 A circuit. How when I built the house would I have known that this location would have these two items rather than just a toaster? Run both and as expected the breaker will trip. So I just run one at a time.

Three of the circuits cover the refrig, disposal, and the dishwasher. Another 3 are countertop, and 2 are near the floor for vacuum use. Lights are totally separate.

Every room in my home has at least 2 separate 20 A circuits, and ceiling lights are separate from these. Two rooms may share the same breaker for ceiling lights. I have one shared 20 A circuit from the main panel that provides an outlet at each subpanel. Thus, power to a subpanel can be turned off and there is power close by.

Virtually none of you will use such a design. In 52 years I have never blown a main fuse, and never tripped the feed breaker to a subpanel. I constantly use some breakers as switches. These are all Sq-D QO. QOs used as switches are usually switched once per day.

.

 

[hbiss]

You raised the valid point of (at least) two 20A SABC. But in the example I gave, two would be insufficient. Ok, so we make it three. Then what happens if someone adds a fourth high-wattage appliance in the future? Obviously, we can't design for every future possibility. So how do we strike the right balance?

As far as I'm concerned EVERY receptacle in a kitchen should be on a dedicated circuit. I'm with gar.:thumbsup: You never can have enough!

-Hal

 

[kwired]

I know from 220.14(I) that receptacle outlets are calculated at 180VA per each receptacle yoke. But what if you know that a particular appliance or piece of equipment that will be plugged in is a high-wattage device?

For example, let's say we have a kitchenette in an office building. There is a kitchen counter and we want multiple general use outlets available on that counter. But we know there will be a microwave placed somewhere on that counter, a coffee brewer, and an induction cooker. None of these appliances will be built in, so I don't see how they can have dedicated circuits (the appliances could be moved around in the future). But, for the sake of this example, let's say that each appliance draws 15A and is rated at 1,800W. Clearly, they can't all be on a single 20A circuit. Yet it's very likely that two or more devices could be in use at the same time.

1. How do we account for these anticipated loads in the load calcs if these are not on dedicated circuits?

2. How would you design the branch circuits serving this counter that allows flexibility in usage (the appliances listed above being moved around plus the addition of future loads, like a juicer or espresso machine) without the risk of a circuit being overloaded and having nuisance trips?

For branch circuit considerations, you probably want minimal number of receptacles per circuit, especially in a non dwelling kitchen or even serving area where warming appliances are commonly used.

You have heavy loading on some of those branch circuits but the feeder or service loading may not be as high as you might imagine and that is why there is demand factors allowed for feeders and services but not for branch circuits.

 

[LarryFine]

Knowing expected loads supersedes receptacle-only calculations. One or two receptacles per circuit works.

 

[Little Bill]

The code for home kitchens says no more than 4' between outlets; most appliances nowadays only have a 2' cord.

Consider the length of the counter-- practically speaking, how many appliances will fit in that space? That's how many outlets you need!

If you wire each duplex as a separate MWBC (ie you've got 240/120 at each duplex outlet), that's more power than one of the 20Amp kitchen circuits can provide.

Don't forget-- you'll never outwit a creative user with a power strip!

The 4' rule allows for 2' cords. If you put a receptacle at a given location then measure 4' and install another one, then go half way (2') between the two, you will be within the reach of a 2' cord to either receptacle.

 

[romex jockey]

190620-1654 EDT

Jon456:

The NEC can't solve your problem.



.

No...but iirc, the CEC has.....:thumbsup:~RJ~