Service Calculation

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Sparky_1

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Hello,

I?m doing a service calculation for a modular home, it?s an all electric house,
with a 20 kw forced air furnace. I?m using the optional calculation 220.82.
Does the furnace fall under 220.82 C4 ( 65% of Nameplate Rating ) or do I use 220.82 C6 ( 100% of Nameplate Rating )?
The home owner wants to finish off and add a 2nd kitchen downstairs to this home, so I need to show service calculation that are under the 200 amp rated panel that is installed in this modular, if the furnace is rated at 100% it will be cutting it close.

Also, is there a code article that prevents me from using table 310.15 B6 for sizing the service entrance conductors, with the 20KW furnace load?

Thanks
 
You might be able to meet code reqiuirements with the 200 amp panel. But that's just a guess, that I wouldnt try to incourage somebody to use if they thought for any reason it wouldn't be sufficient. Just looking at your situation, I can't help but think that going to the next amperage panel might be the best plan.

How much money, between yourself and the property owner is going to be saved if you stay with the 200 Amp? ???
 
You need to use the 100% of the nameplate for the 20KW as well as 100% of the heat pump unless it is wired to not come on together.

In the case where the heat pump does not come on with the strips then you must use 100% of the heat pump plus 65% of the strips. You must use 100% if no heat pump is used.
 
Thanks Dennis,

Without knowing the actual nameplate rating for the two ranges, I used a 12 KW rating for each range. With the 20KW furnace at 100%, I have a calculated load of 196 Amps, is that to close for a 200 Amp
service? The owners are willing to eliminate the 2nd kitchen if we have to.


Sparky_1
 
Sparky_1 said:
Thanks Dennis,

Without knowing the actual nameplate rating for the two ranges, I used a 12 KW rating for each range. With the 20KW furnace at 100%, I have a calculated load of 196 Amps, is that to close for a 200 Amp
service? The owners are willing to eliminate the 2nd kitchen if we have to.


Sparky_1
Click to expand...

It is legal to install a 200 amp service up to 100% of the calculated load. Would I install a 200 in that situation- absolutely not- I would rather leave room for the extras that always seems to appear. Put in a 400 amp service -- they'll probably add a hot tub or pool later- who knows.
 
Sparky_1 said:
Thanks Dennis,

I have a calculated load of 196 Amps, is that to close for a 200 Amp



Sparky_1
Click to expand...

No.

But it seems like you don't actually know what the load is.

You can't find the current demands of the equipment?

Either way, I wouldn't install a new panel that's completely maxed out. It sounds to me like you're trying to satisfy a cheap scates need to get over on what it should actually cost. I've worked for many people like this, cheaping out is some form of conquest to them.


Sparky_1 said:
The owners are willing to eliminate the 2nd kitchen if we have to.
Click to expand...

All this over the size of a panel?
 
I agree with Dennis, legal to install a 200A, but a BAD practice. If the customer can afford to put in a SECOND kitchen, they can afford the larger service, the cost of the service is minimal compared to the cost of a kitchen.
Also, here in the southwest (think desert) we have a local code requiring a minimum of two spaces extra in the main panel and an extra 2400 va in the load calc to allow for the future addition of a pool.
 
I agree with you guys 100%, I fired off an email to them on my recommendation.

They are dealing with a bank that will only borrow them x amount of dollars for there project, due to the value of there acreage. A 400 amp service is not in the budget, I recommended that they reorder a propane or fuel oil furnace, so they could have there kitchenette

Physis, your right about the actual loads, I was informed two days ago
about the second kitchen & electric furnace, the owners are getting me
the namplates on the ranges, that is why I used the 12KW in the calculations.
 
Sparky_1 said:
Physis, your right about the actual loads
Click to expand...

I have no idea what the actual load is.

Sparky_1 said:
I was informed two days ago about the second kitchen & electric furnace, the owners are getting me the namplates on the ranges, that is why I used the 12KW in the calculations.
Click to expand...

If it were me the only way I would install a 200 amp panel for this application is if the HO was fully informed of what that all meant. And if having that information he or she still opted to use a 200 amp panel, then I would be very clear that it's stupid and I guess go ahead with the work.
 
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Dennis Alwon said:
You need to use the 100% of the nameplate for the 20KW as well as 100% of the heat pump unless it is wired to not come on together.

In the case where the heat pump does not come on with the strips then you must use 100% of the heat pump plus 65% of the strips. You must use 100% if no heat pump is used.
Click to expand...

I don't think you have this right per 220.82(C). If the heating is pure electric, you use either 65% (1 to 3 stages) or 40% (4 or more stages) of the nameplate. If it is a heat pump, and the HP and strips run at the same time (the most common setup), then it is 100% of the compressor + 65% of the heat strips. If they can't run together, then it is just 65% of the heat strips.

It could be possible in other circumstances to have to use 100% of the compressor value instead of the heat strips, if the heat strips were small and the heap pump was large. But you're not going to find a residential heat pump compressor that draws more amps than 65% of 20 KW.

The tougher question for me is what is the nameplate amps of the compressor -- the MCA or RLA number on the nameplate?
 
$200.00 is gonna blow this deal? Hmm.

What bank are these people using?

We both know, at least I do, that this is a cheap guy project. I can't even say that I hope I'm wrong, cause I'm not.
 
physis said:
$200.00 is gonna blow this deal? Hmm.

What bank are these people using?

We both know, at least I do, that this is a cheap guy project. I can't even say that I hope I'm wrong, cause I'm not.
Click to expand...

It would cost more than $200 more if I did it. Closer to $400 but still minimal.
 
220.82 How about some more opinions on this question, 20KW electric furnace, no heat pump, 100% of furnace nameplate or 65% of furnace nameplate for the service calculation?
Dennis Alwon said:
You need to use the 100% of the nameplate for the 20KW as well as 100% of the heat pump unless it is wired to not come on together.

In the case where the heat pump does not come on with the strips then you must use 100% of the heat pump plus 65% of the strips. You must use 100% if no heat pump is used.
Click to expand...

suemarkp said:
I don't think you have this right per 220.82(C). If the heating is pure electric, you use either 65% (1 to 3 stages) or 40% (4 or more stages) of the nameplate. If it is a heat pump, and the HP and strips run at the same time (the most common setup), then it is 100% of the compressor + 65% of the heat strips. If they can't run together, then it is just 65% of the heat strips.

It could be possible in other circumstances to have to use 100% of the compressor value instead of the heat strips, if the heat strips were small and the heap pump was large. But you're not going to find a residential heat pump compressor that draws more amps than 65% of 20 KW.

The tougher question for me is what is the nameplate amps of the compressor -- the MCA or RLA number on the nameplate?
Click to expand...
 
Sparky_1 said:
220.82 How about some more opinions on this question, 20KW electric furnace, no heat pump, 100% of furnace nameplate or 65% of furnace nameplate for the service calculation?
Click to expand...

I tend to agree with Mark but I cannot explain 220.82(C)(3). It appears to say what I said but... I have been wrong. Obviously the heat strips would always draw more current than the heat pump so logic would say 100% of heat strips-- it is just not what I am reading.
 
Part of this depends on which code book you're reading. In the 2005, heat pump strip heat was 100%. In 2008, it is 65%, which is better because it really is no different than any other electric furnace and 65% was always used for those.

Read the 2008 for 22.8.2(C)(3) words, and I've broken it up a bit:

100 percent of the nameplate rating(s) of the heat pump compressor

and 65 percent of the supplemental electric heating for central electric space heating systems.

If the heat pump compressor is prevented from operating at the same time as the supplementary heat, it does not need to be added to the supplementary heat for the total central space heating load. (This last section won't apply in most cases. If it does, you get to toss out the heat pump compressor amp value for this section).

Now what do you use for the heat strip nameplate -- its MCA value or its FLA value? 20KW is large enough that this becomes significant to a load calculation.
 
Sparky_1 said:
220.82 How about some more opinions on this question, 20KW electric furnace, no heat pump, 100% of furnace nameplate or 65% of furnace nameplate for the service calculation?
Click to expand...

Now that you've clarified this isn't a heat pump, that may simplify it.

220.82(C)
(4) 65 percent of the nameplate rating(s) of electric space heating if less than four separately controlled units.
(5) 40 percent of the nameplate rating(s) of electric space heating if four or more separately controlled units.

You need to know how many heat stages it has, but most central electric heaters would be 2 or 3 stages. Therefore, subsection (4) applies.
 
suemarkp said:
Now that you've clarified this isn't a heat pump, that may simplify it.

220.82(C)
(4) 65 percent of the nameplate rating(s) of electric space heating if less than four separately controlled units.
(5) 40 percent of the nameplate rating(s) of electric space heating if four or more separately controlled units.

You need to know how many heat stages it has, but most central electric heaters would be 2 or 3 stages. Therefore, subsection (4) applies.
Click to expand...

I disagree. The stages of the unit are different than four separately controlled units. I believe 220.82(C)(4) is really dealing with separate systems as in baseboard heaters. It is not talking about central electric heat.
 
So what section of 220.82(C) would you apply to a central electric furnace? The only other choice that makes sense is (3) which is the heat pump section we've been discussing. That also applies a 65% factor.
 
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