Just took a state test in oregon

Status
Not open for further replies.
M

morg123452000

Member
Location
maine usa
My questions are on figuring dwelling units..on a three phase feed..why do we only figure the cooking equipment on a three phase system with single phase equipment and not dryers that are 220 volt or electric heat that is also 220 volt...my other question is...what fixed appliances are calculated with those besides dishwasher garbage disposel and water hearter (which are always figered) the test had a oven vent fans wasn't sure if I should include that which I did and it put me over 3 appliances...which makes a difference. ..please help ..Jeff
 
Welcome to the forum... :thumbsup:

We also figure electric clothes dryers similar to how we figure cooking equipment, but with a much smaller table [220.54].

Electric heat is required to be calculated at 100% assuming it is a noncoincident load with a greater cooling load [220.51, 200.60].

I agree an oven vent hood (aka range hood) is a fixed-in-place appliance. Electric heating and cooling units are also appliances which may be fixed in place [422.11].
 
Cloths dryer

Cloths dryer

Yes I know about demands for dryers...my question has to do with three phase feed..and the calculations that done with 3 phase..take the highest amount between two phases times 2...then demand chart for that amount then devising by 2 and mutiplying by 3..that caculation...
 
morg123452000 said:
Yes I know about demands for dryers...my question has to do with three phase feed..and the calculations that done with 3 phase..take the highest amount between two phases times 2...then demand chart for that amount then devising by 2 and mutiplying by 3..that caculation...
Click to expand...
See below...
220.54 Electric Clothes Dryers — Dwelling Unit(s). The
load for household electric clothes dryers in a dwelling
unit(s) shall be either 5000 watts (volt-amperes) or the
nameplate rating, whichever is larger, for each dryer
served. The use of the demand factors in Table 220.54 shall
be permitted. Where two or more single-phase dryers are
supplied by a 3-phase, 4-wire feeder or service, the total
load shall be calculated on the basis of twice the maximum
number connected between any two phases. Kilovolt-amperes
(kVA) shall be considered equivalent to kilowatts
(kW) for loads calculated in this section.

...

220.55 Electric Cooking Appliances in Dwelling Units
and Household Cooking Appliances Used in Instructional
Programs. The load for household electric ranges,
wall-mounted ovens, counter-mounted cooking units, and
other household cooking appliances individually rated in
excess of 13⁄4 kW shall be permitted to be calculated in
accordance with Table 220.55. Kilovolt-amperes (kVA)
shall be considered equivalent to kilowatts (kW) for loads
calculated under this section.
Where two or more single-phase ranges are supplied by
a 3-phase, 4-wire feeder or service, the total load shall be
calculated on the basis of twice the maximum number connected
between any two phases.
Click to expand...
 
morg123452000 said:
So what is I want to calculate just one unit from the multi....it was on the test
Click to expand...
You'd typically be running 120/208V 1Ø 3W to a single unit, so the 3Ø calc would not apply.

If you did run 208/120V 3Ø 4W to a dwelling unit, you'd calculate it the same as a multi-unit feeder.
 
The reason I'm asking is... on my test they asked me to calculate one unit...if I'm reading the code right it's says _two or more_ for the dryer and the stove...just your opinion on how to answer this question bud...by the way thanks for all your help...Jeff
 
morg123452000 said:
The reason I'm asking is... on my test they asked me to calculate one unit...if I'm reading the code right it's says _two or more_ for the dryer and the stove...just your opinion on how to answer this question bud...by the way thanks for all your help...Jeff
Click to expand...
So there's your answer, or the path to your answer. You'd have to assume one unit only has one dryer and one range. IMO a test should not ask you to assume facts not stated to deduce the answer.
 
Then there's the 208 heat or a/c...I quess that should be figured on the 3 phase calculations as well..I quess I should take John Powels course like everyone elese does..I really want this license
 
Then there's the 208 heat or a/c...I quess that should be figured on the 3 phase calculations as well..I quess I should take John Powels course like everyone elese does..I really want this license
 
Hello jumper thanks for replying...I don't have a copy..because it's on the test I just took..but it's semi burned into my brain..here's from memery....480/208..three phase feed to a 10 unit multi unit figured standard method. .stove...dryer...electric heat was larger...all the other stuff I figured as normal you know sq ' footage x 3 two kitchen circuits all that stuff..I didn't figure the stoves dryers or heat for three phase I probely should have but wasnt sure what they wanted...I failed so I assume I should have..any more specifics let me know...Thanks again Jeff
 
morg123452000 said:
Hello jumper thanks for replying...I don't have a copy..because it's on the test I just took..but it's semi burned into my brain..here's from memery....480/208..three phase feed to a 10 unit multi unit figured standard method. .stove...dryer...electric heat was larger...all the other stuff I figured as normal you know sq ' footage x 3 two kitchen circuits all that stuff..I didn't figure the stoves dryers or heat for three phase I probely should have but wasnt sure what they wanted...I failed so I assume I should have..any more specifics let me know...Thanks again Jeff
Click to expand...
There is the problem, we don't know what was specifically worded, only what you think you recall.

If you missed a seemingly small but important detail - I doubt you will pass it on to us just from memory.
 
morg123452000 said:
My question is basicly is do I calculate the dryers just like the stoves on the three phase feed
Click to expand...

Pretty much so, there are slight differences in the method for ranges vs dryers but they are mostly similar.

220.54 Electric Clothes Dryers — Dwelling Unit(s).
The load for household electric clothes dryers in a dwelling unit(s) shall be either 5000 watts (volt-amperes) or the nameplate rating, whichever is larger, for each dryer served. The use of the demand factors in Table 220.54 shall be permitted. Where two or more single-phase dryers are supplied by a 3-phase, 4-wire feeder or service, the total load shall be calculated on the basis of twice the maximum number connected between any two phases. Kilovolt-amperes (kVA) shall be considered equivalent to kilowatts (kW) for loads calculated in this section.
Click to expand...
If the nameplate is unknown you use 5000 watts.

If you have only three dryers and are balanced across all three phases you only have one unit connected between any two phases, but you must double that figure, so you have a net of 10,000 VA before applying demand factors even though there is actually three 5000 VA dryers. Sort of don't seem right but that is how I read the requirement. But with only three there is no reduction for demand factor either.
 
kwired said:
...
If you have only three dryers and are balanced across all three phases you only have one unit connected between any two phases, but you must double that figure, so you have a net of 10,000 VA before applying demand factors even though there is actually three 5000 VA dryers. Sort of don't seem right but that is how I read the requirement. But with only three there is no reduction for demand factor either.
Click to expand...
That's because the calculation is not finished.

  1. Determine maximum number connected between any two phases (aka lines or legs)
  2. Multiply load in kVA by 2.
  3. Determine demand load per Table 220.54.
  4. Divide the above result by 2 and multiply by 3 to determine overall demand load.
Note you get the same result with two or three dryers and a maximum of one connected between any two legs.
 
Smart $ said:
That's because the calculation is not finished.

  1. Determine maximum number connected between any two phases (aka lines or legs)
  2. Multiply load in kVA by 2.
  3. Determine demand load per Table 220.54.
  4. Divide the above result by 2 and multiply by 3 to determine overall demand load.
Note you get the same result with two or three dryers and a maximum of one connected between any two legs.
Click to expand...
I think we both did the same thing just in a little different way.

What doesn't seem quite right is that two or three dryers (balanced across the phases) comes out to 10 kVA. But then if you consider the dryer is likely rated 5000 to 5500 watts at 240 volts, and you put it on a 208 volt system it will probably only operate at 3750 to 4100, though you are using 5000 in your calculation. Plus the fact you need more then 4 before a demand factor less then 100% applies.

I really have little concern that you would be short on supply capacity with that calculation method.
 
Status
Not open for further replies.
Top