I have a client who wants to install a washer/dryer combination unit that only required 120v. The total load for the unit is 1200 watts. Not sure how well the dryer works on 120v. but I am told these are pretty common in small apartments where there is no space for conventional washer and dryers. My question is could the required laundry circuit function as the point of connection for this unit and the calculated load of 1500 watts be applied for sizing the panel and/or feeder. I originally used the dryer load calculation (since the unit functions as a dryer) of 5000 watts and argued that since it functioned as a dryer I would need to calculate based on Article 220.54, Electric Clothes Dryersthe nameplate or 5000 watts, whichever is greater.
Laundry branch circuit
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DrSparks
The Everlasting Know-it-all!
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- Madison, WI, USA
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The 5000 watt allowance is for doing load calculations not for determining the size of circuit you need for the dryer. I'm assuming you'll need a 20 amp dedicated circuit for the 120 volt dryer.
Sent from my A574BL using Tapatalk
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I would count this outlet as being the one required for the laundry, and assign a load of 1500 VA. Then I would add the 5000 VA for the dryer (for which you are not required to actually install a separate outlet) to the service load calculation. I would not include the 5000 VA to a calculation for the load of the panel or feeder that will serve the washer/dryer combination. But I think the service load needs to take it into account.
Thank you Charles for your reply. My condition is such that this is a 10 story apartment building. I have multiple feeders that rise up through the building, with each feeder serving stacked apartment panels. One feeder serves 10 apartments and each feeder is rated for 200 amps. There is a feeder tap at each panel rated for 100 amps terminating at a 100 amp main circuit breaker. Would you not apply the 5000 va dryer load to the main 200 amp feeder riser?
MyCleveland
Senior Member
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- Cleveland, Ohio
Please show the following calc data...
How you arrived at 100A for each TAP serving each apartment.
How you arrived at 200A for the rating of the RISER feeder size / OCP.
kwired
Electron manager
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- NE Nebraska
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I can easily see what he has is 100 amp rated supply to each apartment, actual load calculation isn't necessarily 100 amps though.
If you had a 200 amp 208 volt three phase feeder supplying 10 apts. that is about 7.2 kVA or 35 amps @ 208 single phase per apt. and reasonably possible, especially if gas is used for heating, cooking, water heating.
Coppersmith
Senior Member
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- Tampa, FL, USA
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- Electrical Contractor
:?:?:?
Each feeder is rated 200 amp and also is serving 10 apartments @ 100 amp each? Something is not adding up.
Also, how does one do a panel change/major repair without turning off power to 10 apartments? Is there a disco at each tap?
kwired
Electron manager
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- NE Nebraska
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- EC
Just because you run a 100 amp feeder to an apartment doesn't mean the load calculation for that apartment is 100 amps. Then add the 1.732 factor if it is a three phase feeder - it is equivalent to about a 300 amp 120/240 single phase feeder KVA capacity wise.
Coppersmith
Senior Member
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- Tampa, FL, USA
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MyCleveland
Senior Member
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- Cleveland, Ohio
The APT current is multiplied by 1.732 onto the RISER.
I have never seen a recent high rise apartment with GAS anything, related to the apartment.
The 35A number could be applicable, but that is why I asked to see the math.
Coppersmith
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- Tampa, FL, USA
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- Electrical Contractor
I agree with you. I recognised that each panel would get a very small share of the available power which is why I said it didn't add up. 35 amps is a far cry from 100 amps. I would expect a minimum of 60-70 amps available per apartment in these modern times with lots of electrical appliances. Regardless of gas appliances installed, there are a lot of countertop heating appliances. I personally have to stagger my usage of a coffee maker and an electric kettle each morning else I trip a 20 amp breaker.
kwired
Electron manager
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- NE Nebraska
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Which is why you need multiple branch circuits, but when you have several apartment units on same feeder you still get to apply demand factors, because the chances are not that great everyone is drawing their peak demand all at one time.
And remember my 35 amps was @ 208 volts, not 120 volts. Should be no problem running two hair dryers at the same time along with some other items.
Big difference in heat demand for same square footage as well for northern Minnesota Vs Tampa Bay:happyyes:
MyCleveland
Senior Member
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- Cleveland, Ohio
You have to meet the requirements of 220.84 to have access to Table 220.84.
kwired
Electron manager
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- NE Nebraska
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- EC
Aware of that and maybe should have said something more like "demand factors where applicable can apply to feeders and services, but never will apply to individual branch circuits."
The point I was trying to get across is you must have full capacity for the load at the branch circuit level, but with feeders (in any occupancy type) there is a chance you can lessen the load calculation with allowable demand factors.
So even though OP has 100 amp feeders to individual units, and maybe even with 50 or 60 amps load calculation for each unit, demand factors for 10 units plus the addition of third phase to that common feeder very well may make it possible for 10 apts to be on a 200 amp feeder.
MyCleveland
Senior Member
- Location
- Cleveland, Ohio
I would find it hard to believe you could get to 50-60 amps per apartment if you meet the requirements of 220.84.
Each unit equipped with electric cooking, and either electric heat or air conditioning loads.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Well if it has laundry in each apartments like OP's seems to have - those chances do go down even more.
Limited exterior walls, necessary heating or cooling load may not be as much as some think. but remember as I have been trying to point out, you don't get to take any demand factor on an appliance for the calculation of that one apartment, but you very well can take a demand factor for ten of the same appliances on a common feeder, which is why 100 x 10 doesn't equal 1000 here. Then to complicate it even more you likely have third phase in the common feeder but not in the feeder to each individual apartment.
Without real numbers of what is there I can't say for certain if OP's 200 amp feeder is enough, but it may be closer to enough then some may think.
You can still have 90 amps total load calculation for each apartment (18.72 kVA) but does not mean the load calculation for all ten is going to be 187.2 kVA, which would be about 520 if across three phases. Any significant demand factors plus just dropping to only 75 amps per apartment can get you close to 200 for a common feeder pretty easily before getting too deep into details.
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