Feeder Sizing

[MasterTheNEC]

Yes you are correct.:happysad: An electric water heater will heat ground water to 120? in less than an hour with the standard 4500 watt elements. But why are we on water heaters?

Not when the ground water coming in is 40 degrees. Based on one manufacturer's rate of rise to achieve 130 Degrees F (what mine is set on). If the water heater is depleted so that the total incoming water is around 40 degrees. The manufacturer of this specific water heater (4,500W) would be roughly 14 degrees per hour. Thus it could (in conceivable theory) take well more than 3 hours to achieve resumed storage temperature and thats not even counting if someone uses it while it is in recovery....But to your point...I have NO IDEA how we got on Water Heaters...:angel:

Below is a Rheem Rate of Rise Temperature chart that is handy, I guess it's handy...for something.:ashamed1:

http://www.rheem.com/docs/FetchDocument.aspx?ID=6e52d38f-9680-44dc-90af-dd6984c8a7d6

 

[kwired]

Not when the ground water coming in is 40 degrees. Based on one manufacturer's rate of rise to achieve 130 Degrees F (what mine is set on). If the water heater is depleted so that the total incoming water is around 40 degrees. The manufacturer of this specific water heater (4,500W) would be roughly 14 degrees per hour. Thus it could (in conceivable theory) take well more than 3 hours to achieve resumed storage temperature and thats not even counting if someone uses it while it is in recovery....But to your point...I have NO IDEA how we got on Water Heaters...:angel:



Below is a Rheem Rate of Rise Temperature chart that is handy, I guess it's handy...for something.:ashamed1:

http://www.rheem.com/docs/FetchDocument.aspx?ID=6e52d38f-9680-44dc-90af-dd6984c8a7d6

How many gallon tank? 4500 watt is 4500 watt no matter what size the tank is, so that part is consistent with quite a few models even with different volume of tank. Where are you located that has 40 deg water?

 

[tom baker]

The temp of water in the ground is the average mean air temp. Here our water is 55 deg F.
Northern Wisconsin may be 40 degrees http://www.epa.gov/athens/learn2model/part-two/onsite/ex/jne_henrys_map.html
At least we are not talking about hot water heaters.

 

[MasterTheNEC]

How many gallon tank? 4500 watt is 4500 watt no matter what size the tank is, so that part is consistent with quite a few models even with different volume of tank. Where are you located that has 40 deg water?

ummm...Alaska.. it's part of the US the last I checked...:roll:

Heck, even at 55 Degrees at 14 gallons an hour per the chart I linked to (Rheem) it would take over 4 hours to dead heat 55 degree water to 120 degree water in a single 4500 element water heater according to rheems documents. Just saying....it's possible.

 

[kwired]

ummm...Alaska.. it's part of the US the last I checked...:roll:

Heck, even at 55 Degrees at 14 gallons an hour per the chart I linked to (Rheem) it would take over 4 hours to dead heat 55 degree water to 120 degree water in a single 4500 element water heater according to rheems documents. Just saying....it's possible.

Well your displayed location said AR, I couldn't imagine they had that cold of water there unless something pretty rare is going on there.

You also said 14GPM, I was saying it would take just under 3 hours to heat 80 gallons 65 deg with no flow.

 

[GoldDigger]

I think he was just converting the listed steady flow recovery rate of 55 x 14 degree gallons per minute to the equivalent whole tank from cold recovery time.

 

[MasterTheNEC]

Well your displayed location said AR, I couldn't imagine they had that cold of water there unless something pretty rare is going on there.

You also said 14GPM, I was saying it would take just under 3 hours to heat 80 gallons 65 deg with no flow.

Hmmm...I don't see where I said GPM. It was GPH based on the Rheem chart. The chart said it would raise the temperature of the water at 4,500W at 16 GPH (Gallons per Hour of heating time based on the Rheem chart) which results in a need to raise 55 degree water to 130 degree water, results in over 4 hours if the total tank was depleted.

Just sayin...It's possible.

 

[kwired]

Hmmm...I don't see where I said GPM. It was GPH based on the Rheem chart. The chart said it would raise the temperature of the water at 4,500W at 16 GPH (Gallons per Hour of heating time based on the Rheem chart) which results in a need to raise 55 degree water to 130 degree water, results in over 4 hours if the total tank was depleted.

Just sayin...It's possible.

My bad, I meant to say GPH. What size of a tank?

I found my information at http://waterheatertimer.org/pdf/Water-heater-Formulas-and-terminology.pdf according to information there it takes 242 watt hours to raise 1 gallon of water 1 deg F. Take that times 80 gallons and times 75 degree rise and you should need 14,520 watt hours to fully raise an 80 gallon tank 75 degrees. Divide by 4500 watts and this leaves you needing 3.22 hours to heat that 80 gallon tank 75 degrees. Doesn't include heat loss from the tank but you would actually be gaining a little heat from the room until water reaches room temperature, and after exceeding room temp you then start to lose heat to the room - overall losses are likely fairly negligible for duration of initial tank heating.

 

[MasterTheNEC]

My bad, I meant to say GPH. What size of a tank?

I found my information at http://waterheatertimer.org/pdf/Water-heater-Formulas-and-terminology.pdf according to information there it takes 242 watt hours to raise 1 gallon of water 1 deg F. Take that times 80 gallons and times 75 degree rise and you should need 14,520 watt hours to fully raise an 80 gallon tank 75 degrees. Divide by 4500 watts and this leaves you needing 3.22 hours to heat that 80 gallon tank 75 degrees. Doesn't include heat loss from the tank but you would actually be gaining a little heat from the room until water reaches room temperature, and after exceeding room temp you then start to lose heat to the room - overall losses are likely fairly negligible for duration of initial tank heating.

Oh lets say 80 gallon that was 100% depleted due to a 16 year old son who does not care about other people in the house needing to take a shower...oh wait...TMI...sorry.

 

[MasterTheNEC]

FYI..man we just totally HIJACKED the original thread....sorry MODS...My Bad !:thumbsdown:

 

[Dennis Alwon]

FYI..man we just totally HIJACKED the original thread....sorry MODS...My Bad !:thumbsdown:

I am sorry also--LOL -- see below


From personal experience I have seen tanks heat up faster than what you stated. Around here I tell people one hour and that is about all it takes. Also it is rare that the entire tank would be filled cold except when the tank is installed.

 

[kwired]

I am sorry also--LOL -- see below


From personal experience I have seen tanks heat up faster than what you stated. Around here I tell people one hour and that is about all it takes. Also it is rare that the entire tank would be filled cold except when the tank is installed.

Ban me while you are at it

One hour usually is long enough to have a fair quantity of heated water available, how much depends on what the incoming water temp was. After one hour the tank may not have reached set point and switched the heating elements off, but there is heated water available.

You probably do not have 40 degF incoming water in your region which would result in nearly most extreme temp rise needed scenario. Municipal water vs. domestic well does make some difference - most of the time. Domestic well water is more directly from the cool source, where municipal water has typically had some time in storage tank or in the lines and has gained some heat before it enters a user's premises.

 

[MasterTheNEC]

I am sorry also--LOL -- see below


From personal experience I have seen tanks heat up faster than what you stated. Around here I tell people one hour and that is about all it takes. Also it is rare that the entire tank would be filled cold except when the tank is installed.

Oh dear...I knew it was just a matter of time:angel:

 

[m sleem]

I am sorry also--LOL -- see below


From personal experience I have seen tanks heat up faster than what you stated. Around here I tell people one hour and that is about all it takes. Also it is rare that the entire tank would be filled cold except when the tank is installed.

So that means 422.13 is just an exception from the definition of continuous load for sizing the branch circuit but still non continuous load for feeder sizing.

 

[kwired]

So that means 422.13 is just an exception from the definition of continuous load for sizing the branch circuit but still non continuous load for feeder sizing.

I think it makes it clear it is to be considered continuous load for branch circuit calculations, but it could still be either continuous or non continuous for feeder and service calculations.

 

[cppoly]

Just a thought, if the code considers AC units & electric heaters continuous loads for branch circuits, wouldn?t the same be true for feeders considering the only thing that is changing is the conductor location of the circuit. The equipment itself would still be a continuous load right? Yes, thanks for hijacking the thread too?

 

[kwired]

Just a thought, if the code considers AC units & electric heaters continuous loads for branch circuits, wouldn?t the same be true for feeders considering the only thing that is changing is the conductor location of the circuit. The equipment itself would still be a continuous load right? Yes, thanks for hijacking the thread too?

I think NEC wants you to treat those (and a few other specific items) as continuous load for branch circuit calculations whether they can/will run for three hours or not. For feeder/service calculations you should still consider them continuous if they will run for three hours or more at a time. JMO.

 

[ActionDave]

Just a thought, if the code considers AC units & electric heaters continuous loads for branch circuits, wouldn?t the same be true for feeders considering the only thing that is changing is the conductor location of the circuit. The equipment itself would still be a continuous load right? Yes, thanks for hijacking the thread too?

My opinion would be no. You only need to include 100% of those loads for service and feeders.

 

[kwired]

215.2(A)(1)(a):"Where a feeder supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum feeder conductor size shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load."

Continuous load is still to be considered for feeder calculations, but you need to determine what is continuous load primarily based on whether it runs for three hours or more. For some of the items in question here you must treat them as continuous for branch circuit calculations even if they will not run for three hours, only because NEC has a section somewhere requiring you treat that item as a continuous load for branch circuit calculations.