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#49893 - 03/19/05 08:20 PM Service upgrade required?  
SteveFehr  Offline
Member
Joined: Mar 2005
Posts: 1,205
Chesapeake, VA
I'm trying to get a 2nd opinion...

I've got a 200A main panel now in a residence, with a 150A breaker. The addition will double the size of the house (1500 to 3000 sqft) and add a 2nd 3-ton heat-pump with emergency-heat backup, which alone sucks up the spare 50A on the panel. I can just *barely* justify the minimum service load calculations to fit on this 200A panel, but it's close- to the point where if I add the refrigerators into the calcuation on a dedicated circuit vice assuming them included in a 1500VA kitchen circuit, the calculations fail. Do you think we'll be OK with the 200A service, or is a call to VEPCO in order to get the service upgraded? I'd really rather avoid having to upgrade the existing main panel, but it seems to be quite a risk.


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#49894 - 03/19/05 09:10 PM Re: Service upgrade required?  
Active 1  Offline
Member
Joined: Feb 2003
Posts: 687
Grayslake IL, USA
We don't use heat in homes here so I have to ask. Does the heat pump draw 50a or is it just a 50a breaker? We can't check your math with out all the information. Myself I'm not the best person to ask on calc's. Depending on who you ask you can have a different interpitation of how to figure it.

I can say that 3000 sf does not seem out of line for a 200a service. For friges most new ones don't draw that much. A lot of home now have a few friges/freezers around the house. The other thing to figure is do you have enough circuit space or do you need a sub.

If it is close you may tell the HO that and let them make the call.

Tom


#49895 - 03/19/05 09:47 PM Re: Service upgrade required?  
SteveFehr  Offline
Member
Joined: Mar 2005
Posts: 1,205
Chesapeake, VA
The heater is an electric resistance emergency heater built into the air handler for when the temp drops below where the heat pump can operate efficiently. I'm sure it's not drawing exactly 60A 240, but finding out *anything* technical about heat pumps has been consistantly frustrating as their product information consists only of meaningless marketing gibberish, and SEER is about the only solid number you can get from them without being a HVAC professional. The air handler manual lists the blower as 15A 240, but I don't have any documentation on the resistance heater unit. Long story short, I'm conservatively estimating 14,400 VA for it.

Same goes for the electric range- I assumed the worst at 40A 240V, though I know that's going to be high as nobody will ever broil with all 4 burners on max. All-in-all, my numbers came to 409A for the house. Which I assume is slightly high because of my conservative estimates; but I doubt the heater is only drawing 25 or 40A, else it wouldn't be on a 60A breaker.

Actually, how long does a residential breaker typically run at overload- are there curves availible?

[This message has been edited by SteveFehr (edited 03-19-2005).]

[This message has been edited by SteveFehr (edited 03-19-2005).]

[This message has been edited by SteveFehr (edited 03-19-2005).]


#49896 - 03/19/05 09:56 PM Re: Service upgrade required?  
SteveFehr  Offline
Member
Joined: Mar 2005
Posts: 1,205
Chesapeake, VA
Calcs:
Quote
Code
For minimum service:	VA	A (120)
3VA/sqf (existing)	4500	38
3VA/sqf (addition)	6000	50
1500A App Ckts (exst)	1	13
1500A App Ckts (new)	2	25
Water Heater		4500W	32
Range			40A 240	80
Dryer			28A 240	56
Subtotal:		35217	293
First 10k:		10000	83
40% of rest:		10087	84
New Subtotal:		20087	167
Furnace		60A 240	120
Furnace		60A 240	120
[b]Total:		48887	407
per phase:		24443	204[/b]


Here's the panel loadouts:
Quote
Code
Old
150A Main Panel			
Dryer	30	A/C	30
Dryer	30	A/C	30
Bedroom	15	Bedroom	20
Bedroom	15	Fridge	20
Lights	15	Kitchen	20
Liv Rm	15	Kitchen	20
Bedroom	15	Washer	20
Furnace	60	Water	30
Furnace	60	Water	30
		Range	40
		Range	40
PH-A	260	PH-B	295

Reconfigured			
200A Main Panel			
Dryer	30	A/C	30
Dryer	30	A/C	30
Bedroom	15	Bedroom	20
Bedroom	15		
Lights	15		
Liv Rm	15	Library	20
Bedroom	15	Washer	20
Furnace	60	Water	30
Furnace	60	Water	30
Feeder	100	Range	40
Feeder	100	Range	40
PH-A	340	PH-B	375

New:			
125A			
Furnace	60	A/C	30
Furnace	60	A/C	30
Lights	15	Bedroom	20
Lights	15	Sewing	20
Lights	15	Kitchen	20
Bath	20	Kitchen	20
Doors	15	Fridge	20
Shed	20	Garage	20
Shed	20	Dining	20
Micwv	15	Living	20
		Outlets	20
PH-A	240	PH-B	255


[This message has been edited by SteveFehr (edited 03-19-2005).]

[This message has been edited by SteveFehr (edited 03-19-2005).]

[This message has been edited by SteveFehr (edited 03-19-2005).]


#49897 - 03/19/05 10:41 PM Re: Service upgrade required?  
caselec  Offline
Member
Joined: Apr 2002
Posts: 558
San Jose, CA
Steve, what is the wattage of the emergency heat? As Tom stated you need to use the actual load not the circuit size. I also think the way you are doing the calcs is over inflating the numbers. Use volt-amps for all of you numbers then divide the final number by 240. Don’t forget to include the microwave, garbage disposal or dishwasher if they are going to be used. Provide some more information and we will help with the calcs.

Curt


Curt Swartz

#49898 - 03/19/05 10:44 PM Re: Service upgrade required?  
caselec  Offline
Member
Joined: Apr 2002
Posts: 558
San Jose, CA
I forgot to mention in my last post that 220.31 allows loads to an existing dwelling to be calculated using 100% for the first 8 KVA and 40% for the remainder.


Curt Swartz

#49899 - 03/19/05 10:55 PM Re: Service upgrade required?  
LK  Offline
Member
Joined: Jan 2003
Posts: 1,429
New Jersey
I also think, the way he is doing the calcs, is over inflating the numbers.


#49900 - 03/19/05 11:57 PM Re: Service upgrade required?  
SteveFehr  Offline
Member
Joined: Mar 2005
Posts: 1,205
Chesapeake, VA
Thanks everyone! I see I had a bunch of misleading values in there (like showing squarefeet in the VA column for the 3VA*sqft, etc.) which might have been confusing.

Unfortunately, I don't know the true watts of the emergency heat. The current is between 50-60, I can glean that much off the breaker panel, but I don't know what the existing heater is and was just going to provide for whatever the docs that come with the new heat pump call out. They're both 3-ton units heating the same sqft of finished space, so I assume they will be similar if not identical.

Likewise, I don't have hard numbers on the freestanding range, and (40A 240) UL listings don't help, so 20*240=probably overkill. Oddly enough, adding up all the heating elements on the range gives about 60A 240...

Quote
Code
Service Calcs:	VA:	
3VA/1500		4500	
3VA/2000		6000	
1500VA Ckts	4500	
Water Htr		5196	
Range		9600	
Dryer		6720	
Subtotal:		36516	
First 10k:		10000	
40% of rest:	10606	
New Subtotal:	20606	
Furnace 1		14400	
Furnace 2		14400	Amps:
Total:		49406	206
per phase:		24703	206


Swapping 10k for 8k gives exactly 200A load, coincidentally enough! Since the furnace and range were conservative estimates, that gives a *little* fudge room, but it's still awfully close.

As an aside, why would existing homes be allowed 8k vice 10k?

[This message has been edited by SteveFehr (edited 03-19-2005).]

[This message has been edited by SteveFehr (edited 03-19-2005).]


#49901 - 03/20/05 07:06 PM Re: Service upgrade required?  
Active 1  Offline
Member
Joined: Feb 2003
Posts: 687
Grayslake IL, USA
I have not seen a res. drier that draws 28 amps. Loads should not be more than 80% of the breaker. So a drier that has a 30a breaker should only draw 24a max continously.

You did not figure in for the water well pump or detached garage.

Tom


#49902 - 03/20/05 07:21 PM Re: Service upgrade required?  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Active 1

Quote
Loads should not be more than 80% of the breaker. So a drier that has a 30a breaker should only draw 24a max continously.


It is NEC and UL compliant to load a circuit 100% for non-continuous loads.

A dryer would be a non-continuous load as defined by the NEC. It does not operate for more than 3 hours at a time.


Bob Badger
Construction & Maintenance Electrician
Massachusetts

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