400 amp service -- what is required?

[eepete]

Part of this is the inspectors tell you what you need, but it seemed close. This is an all electric house, let's look at the loads:

3 10KW resistive electric backup for heat pumps: 120 amps
1 five ton and 2 three ton heat pumps: 9KW, 37 amps
2 water heaters (2.5KW each): 20 amps
Cooktop: 20 amps
Dual oven and small oven: 27 amps
Central Vac: 4 amps
Septic Pump: 3 amps

So I'm at 231 amps and still have lights and small appliances left. Now I'll grant you that this would be the holiday throw-down of all time to have all these things going at once, but that's kinda what worst case engineering is all about. And when I build my outbuilding, there will be more power for that too.
Note also that taking two resistive-electric heat pump strips and placing them before the transfer switch makes this worst case load be about 151 amps. Then generator is 45KW --> 180 amps so I have 30 amps left for lights, TVs and computers. It all works out and none one has to think to live in the place- just the way I like it.

 

[MossRoad]

Part of this is the inspectors tell you what you need, but it seemed close. This is an all electric house, let's look at the loads:

3 10KW resistive electric backup for heat pumps: 120 amps
1 five ton and 2 three ton heat pumps: 9KW, 37 amps
2 water heaters (2.5KW each): 20 amps
Cooktop: 20 amps
Dual oven and small oven: 27 amps
Central Vac: 4 amps
Septic Pump: 3 amps

So I'm at 231 amps and still have lights and small appliances left. Now I'll grant you that this would be the holiday throw-down of all time to have all these things going at once, but that's kinda what worst case engineering is all about. And when I build my outbuilding, there will be more power for that too.
Note also that taking two resistive-electric heat pump strips and placing them before the transfer switch makes this worst case load be about 151 amps. Then generator is 45KW --> 180 amps so I have 30 amps left for lights, TVs and computers. It all works out and none one has to think to live in the place- just the way I like it.

Good grief you could fry some serious bacon with that load!

Thanks for the add-up of the loads. I had no idea.

 

[roamerr]

My 36 x 40 garage has a seperate 200 amp service. Now that is overkill but since it is 400 ft from the house I figured go ahead with 200 amp. I mainly needed 50 amp for an RV and then a little more for lights and a compressor. I do not weld but who knows -- I might wanna try it someday.

 

[roamerr]

eepete -- You just need to ad one those on demand electric hot water heaters. I heard 120 to 140 amps for those alone... not for me....

 

[eepete]

@roamerr: The geothermal heat pumps have the water heater feature on them. So we have two 80 gallon tanks. One for the master bedroom zone, one for the main house. We keep the main house at 110 degrees, the master at 120. For 5 months out of the year (heavy cooling cycles), the hot water is free (ok, it's really "pre-paid" with the electric bill). During the winter, the heat pumps can maintain the tanks but not increase the temperature. In the transitional seasons (like we're in now) is when the hot water heaters run the most. This also has an odd side effect of a fairly consistent electric bill.

You point is with merit, though. Who knows what might get added down the road (big air compressor, welding stuff, on demand hot water at some future shop).

@MossRoad: The average draw is less than 25 amps, but it is interesting the difference between average and worst case. I did fire everything up at once before move in and it was all happy. I love sleeping well at night. Off topic but the house also has fire sprinklers in it so it's a really deep sleep.

I've started a project today (just broke ground with my new box blade) that will tie into all this discussion. Should be in the project section in a bit.

 

[ultrarunner]

Part of this is the inspectors tell you what you need, but it seemed close. This is an all electric house, let's look at the loads:

3 10KW resistive electric backup for heat pumps: 120 amps
1 five ton and 2 three ton heat pumps: 9KW, 37 amps
2 water heaters (2.5KW each): 20 amps
Cooktop: 20 amps
Dual oven and small oven: 27 amps
Central Vac: 4 amps
Septic Pump: 3 amps

So I'm at 231 amps and still have lights and small appliances left. Now I'll grant you that this would be the holiday throw-down of all time to have all these things going at once, but that's kinda what worst case engineering is all about. And when I build my outbuilding, there will be more power for that too.
Note also that taking two resistive-electric heat pump strips and placing them before the transfer switch makes this worst case load be about 151 amps. Then generator is 45KW --> 180 amps so I have 30 amps left for lights, TVs and computers. It all works out and none one has to think to live in the place- just the way I like it.

Looks like you've done your homework... I have one place that is all electric... never worked on anything there. Next time I will have to look and see what my service is...

 

[roamerr]

eepete -- I like your details on the Geothermal. My parents built a new house 3 yrs ago and installed Geothermal. I never understood how the water heater worked until you described it. They are running $200 a month average for all electric 3000 sq ft home electric bill. Not too bad.

 

[eepete]

We're averaging $260 per month heating and cooling about 6000 sq. feet where about 1500 is effectively shut of via dampers (so that would be 4500 actively heated and cooled). The project I broke ground on today is a 7.7 KW solar array, the hope is to cut the average monthly bill to $100 to $120.

As for the geothermal hot water, think of it this way. The heat pump compresses the freon to produce about 140 degree freon. Before the main heat exchanger with the ground temperature water, there is a smaller heat exchange that is on a pump that circulates water to your hot water tank. The drain plug at the bottom of the hot water tank is removed and becomes the other connection to the tank (the 1st is the hot water outlet). Water is pumped and the temperature of the water coming back from the tank is monitored. When that hits 125 degrees, the pump shuts off for some amount of time. In this way, your hot water is free if there is sufficient cooling activity. The main heat exchanger is after this small one. It gets rid of the heat into the 60 to 65 degree ground. There is a closed loop system with water in it and the water lines are buried horizontally at 5 and 7 feet deep. So even when it's 95 degrees out the whole thing works like an air exchange heat pump on a 65 degree day. The temperature of the water leaving the exchange is only about 2-3 degrees warmer than what went in.

During the winter, you get 135 degree freon (the ground is a bit cooler since you've been sucking heat out of it). The same system is used, but the pump that pumps from that small heat exchanger for the hot water heater system runs at a much slower speed (it's a two speed pump). So some of the heat is available for the hot water heater. This is how it can maintain temperature, but cant really increase it a whole lot. This is done because you are trying to heat your house at the same time.

Since freon made heat is 3 times as efficient as resistive electric, even though you are taking some of your heat for the house it is still a win. Hope this addition "how it works" is of interest...

Pete

 

[theboman]

Part of this is the inspectors tell you what you need, but it seemed close. This is an all electric house, let's look at the loads:

3 10KW resistive electric backup for heat pumps: 120 amps
1 five ton and 2 three ton heat pumps: 9KW, 37 amps
2 water heaters (2.5KW each): 20 amps
Cooktop: 20 amps
Dual oven and small oven: 27 amps
Central Vac: 4 amps
Septic Pump: 3 amps

So I'm at 231 amps and still have lights and small appliances left. Now I'll grant you that this would be the holiday throw-down of all time to have all these things going at once, but that's kinda what worst case engineering is all about. And when I build my outbuilding, there will be more power for that too.
Note also that taking two resistive-electric heat pump strips and placing them before the transfer switch makes this worst case load be about 151 amps. Then generator is 45KW --> 180 amps so I have 30 amps left for lights, TVs and computers. It all works out and none one has to think to live in the place- just the way I like it.

You won't use electric heat backups and the heat pump at the same time..... More insulation and then more. MOVE if its that cold!

 

[roamerr]

I like your reply Pete. My parents were under the impression that the geothermal provided pretty much all of the hot water as long as it was running. I think their water heater tank is only 50 gallons. Their lines are 600 ft at about 5 to 7 feet also. I believe they were expecting a much lower bill than they have but they are still satisfied. I do like the geothermal system zoning and lack of noise.

I chose heat pumps for my new home mainly because I felt I could not justify the extra $15000 for the Geothermal. I assumed the Geothermal would use less amps at peak but I guess that is not correct...

 

[roamerr]

You won't use electric heat backups and the heat pump at the same time.....

Incorrect. When the heat pump defrosts the heat pump compressor runs (cools instead of heats) and the heatstrips come on. Boom -- Lots of electricity use for 2 to 5 minutes...

 

[ctgoldwing]

I have a 400A service in my house...Just a 400A meter on the outside wall feeding 2 200A 42 space panel's in the house. No disconnects between the meter base and the panel's-just the standard main breaker in the 200A panel's.

The main reason for the 400A service is breaker capacity because you run out of circuits quickly with all the dedicated circuits required today.
QUOTE]

I have a very similar setup. I wired my house myself and wanted the power company to run larger wire down the driveway (about 500 feet). They would only do it if I went with a 400 amp service. Sooo...

I hired an electrician to hang & wire the 400 amp disconnect box. Inside there are current transformers that he wired to the meter box on the outside of the house. From the disconnect I feed 3 200 amp boxes and 2 100 amp boxes. I didn't need anywhere near the 400 amp capacity but I did have a load of circuits.

 

[buckeyefarmer]

See NEC 220.82

100% of Heat pump compressor, 65% of supplemental backup heat. If compressor does not run when supplemental is used, you don't add both.

 

[eepete]

@thebowman: Depends. I have dipswitches on the unit that I can set which select if there is a 2-stage or 3 stage heat. 2 stage is the two speeds on the compressor. With 3 stage heat, you can set it up so that in addition to the heat pump compressor, the resistive electric strips run. The thermostats have to match (i.e. know or have their settings set for 3 stage heat). My main 5 ton unit uses restive electric for a quick warm up in the morning. My 3 ton for my work area does not since it has very few windows in it. If the power bill got to me, I could nuke the 3rd stage for the main unit and save about $20 per month during peak heating season. Typically, thermostats use 1, 2, and 3 degree difference between the call temperature (what you set it for) and the room temp to select how much heat to throw at the problem. Note also that when I have the dip switches in 2 stage mode, the system is smart enough to kick in the resistive electric if there is a compressor problem or a water temperature problem.

@roamer: The geothermal units uses about the same amount of power. For a given tonage, the compressors are the same. The water pumps that move the water in the ground loop about trade with the fan in the outside unit on a traditional heat pump. The savings are shorter run times of the unit when compared to an outside unit. Put another way, an air exchange heat pump in the San Francisco bay unit would fare about the same as a geothermal. A geothermal in New England would woop an air exchange. Most geothermal systems also have 2 speed compressors in them. I think the systems are overpriced due to low volume, and so the two speed compressor is an attempt to justify that. Biggest win of two speed compressor is when your cooling. At low speed you use less power but run longer which means you can take more water out of the air (lower humidity).
Another way to say this: I can get 98 degree air out of a register when it's 10 degrees out. That doesn't happen with an air exchange system.

Pete

 

[buckeyefarmer]

I have a 400A service in my house...Just a 400A meter on the outside wall feeding 2 200A 42 space panel's in the house. No disconnects between the meter base and the panel's-just the standard main breaker in the 200A panel's.

The main reason for the 400A service is breaker capacity because you run out of circuits quickly with all the dedicated circuits required today.

I can get pictures if you need them...

Kennyd, you on BGE or Allegheny? I know what you mean about running out of breaker space.

I had a neighbor put in two 200A panels once. Don't remember if it was a 320A or 400A meter base, but he ran from the meter base straight to each 200A panel. The utility did not replace the feed from the transformer to the meter base.

 

[kennyd]

Kennyd, you on BGE or Allegheny? I know what you mean about running out of breaker space.

I had a neighbor put in two 200A panels once. Don't remember if it was a 320A or 400A meter base, but he ran from the meter base straight to each 200A panel. The utility did not replace the feed from the transformer to the meter base.

BGE. I built my house so the feed was sized correctly from the beginning. I have a lot of 240v circuits wired so panel space get taking quickly.

Some 240v circuits include:
Table Saw
Cyclone dust collector
Mill
Lathe
Welder
Garage Heater
Heat pump x2
Attic Air Handler
Well Pump
Air Compressor
1 BaseBoard Heater
100A Feed to Subpanel in OutBuilding

Some Dedicated 120v circuits include:
Drill Press
Water Heater
Basement Freezer
Stove/Range
Refrigerator
Entertainment Center
Sewage Ejector Pump
Attic lights
Attic Outlet
Garbage Disposal


So, add it all up and that's why the 2 200A 42 space panels!

 

[turbo36]

Back in 1994 I bought a cottage that had 100 amp service with something like a 24 circuit panel. I immediately had the panel upgraded to a 200 amp 42 space panel. Shortly thereafter I built a 40 by 60 outbuilding about 375' from the main house. In the barn I installed a 100 amp 42 space panel that was fed by a 100 amp breaker in the new house panel.

I called the power company to up-size the pole transformer and service entrance wire to 200 amp and was told they would not do it until my actual use exceeded 100 amps. If it was a new service they would size it to the main panel breaker size but in the case of a remodel they go by historical use. I saw the potential for problems with voltage drop if I had "everything running" at the same time and challenged this decision. The response from field service rep was "when the transformer starts smoking give us a call"!
What is interesting about this is that the electric company sizes your service based on "typical load" and not connected load. However, when I built my new hose 4 years ago I found out the gas company sizes the meter to "connected device potential". I have 2 gas fire places, 2 overhead heaters in the garages, big gas water heater, professional gas cook top, gas furnace, 2 gas grills and a back up generator. I was told I had to go to a commercial meter and regulator!!!!

 

[MossRoad]

We're averaging $260 per month heating and cooling about 6000 sq. feet

Well, that explains it.... our house is 1350.

$260 for that size home sounds very reasonable. We run around $100 electric in summer due to air conditioning, pool pump and chlorine generator. In winter it drops to around 40-50 for lights and small fans to circulate wood burner heat. I should average it out over the year to see what I get for a per month average. We backup heat, cook and make hot water with gas.

 

[ctgoldwing]

The geothermal units uses about the same amount of power[/COLOR]. For a given tonage, the compressors are the same. The water pumps that move the water in the ground loop about trade with the fan in the outside unit on a traditional heat pump. The savings are shorter run times of the unit when compared to an outside unit.
Pete

OK, I admit it, I'm no expert BUT. . .

Given that we are comparing a geothermal heat pump & conventional air to air heat pump of the same size:

The units for a given load in the house will run the same amount of time. How could they not? The only thing that might affect run time would be if they were variable speed or multispeed compressors but lets assume we are comparing the same (geothermal & conventional) of whatever you want. ie If we are talking about 30,000 btu units and the house load at a given time is 30,000 btu/hour each unit will have to run continuously to keep up with the load. The savings comes from the much higher efficiency of the geothermal - it can provide this amount of heat while consuming much less electricity than the conventional unit. Its as simple as that.

 

[roamerr]

The units for a given load in the house will run the same amount of time. How could they not?

As I understand it no. If the temp outside is 60F then yes since ground temp is about the same. At colder temps like 32F the geothermal is using 60F water whereas the air heat pump is pulling 32F air. The geothermal will run much less for the same heat output.