service
- Thread starter jdr
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petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: service
(1)Specific Appliances or Loads. An outlet for a specific appliance or other load not covered in (2) through (11) shall be computed based on the ampere rating of the appliance or load served.
Based on this you have 375A, so would need a 200A 120/240 service.
Just MHO.
[ January 04, 2005, 11:58 AM: Message edited by: petersonra ]
220.3(B)
(1)Specific Appliances or Loads. An outlet for a specific appliance or other load not covered in (2) through (11) shall be computed based on the ampere rating of the appliance or load served.
Based on this you have 375A, so would need a 200A 120/240 service.
Just MHO.
[ January 04, 2005, 11:58 AM: Message edited by: petersonra ]
wirenut1980
Senior Member
- Location
- Plainfield, IN
Re: service
Bob, what demand factor are you using to get a 200 Amp service out of 375 Amp connected load? And is it in NEC?
Bob, what demand factor are you using to get a 200 Amp service out of 375 Amp connected load? And is it in NEC?
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: service
Its 200A on each hot leg, so the total available is 400A.Originally posted by wirenut1980:
Bob, what demand factor are you using to get a 200 Amp service out of 375 Amp connected load? And is it in NEC?
Re: service
jdr -
Where I live, engine heaters are a continous load. I would size the feeder (service?) at 188A X 1.25 = 234A. 250A panel.
As an aside, you can save your customer a little money on the power bills. Put in a timer, two thermostats, and a 250A contactor. First thermostat, set to 20F, energizes timer which pulls in contactor 1/2 hour on - 1/2 hour off. Second thermostat, set to 0F (zero deg F), locks contactor ON.
carl
jdr -
Where I live, engine heaters are a continous load. I would size the feeder (service?) at 188A X 1.25 = 234A. 250A panel.
As an aside, you can save your customer a little money on the power bills. Put in a timer, two thermostats, and a 250A contactor. First thermostat, set to 20F, energizes timer which pulls in contactor 1/2 hour on - 1/2 hour off. Second thermostat, set to 0F (zero deg F), locks contactor ON.
carl
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: service
You can?t add 200 amps plus 200 amps and get 400 amps. The math does not work that way, because the two ?200 amps? are not the same thing. You are adding apples to oranges. The difference between the two ?200 amps? is the phase angle.
But this type of problem should not be performed in terms of amps. You should always add loads in terms of power, and convert to amps at the end. In this case, you have 30 loads, each being 1500 watts. That gives you 45,000 watts total. Divide by 240 volts, and you get 187.5 amps. So that could go on a 200 amp panel. However, I do not know whether this type of heater would be running for more than 3 hours at a time. Coulter might be right about upsizing by 25%.
No, it?s 200 amps on each hot leg, so the total available is 200A.
You can?t add 200 amps plus 200 amps and get 400 amps. The math does not work that way, because the two ?200 amps? are not the same thing. You are adding apples to oranges. The difference between the two ?200 amps? is the phase angle.
But this type of problem should not be performed in terms of amps. You should always add loads in terms of power, and convert to amps at the end. In this case, you have 30 loads, each being 1500 watts. That gives you 45,000 watts total. Divide by 240 volts, and you get 187.5 amps. So that could go on a 200 amp panel. However, I do not know whether this type of heater would be running for more than 3 hours at a time. Coulter might be right about upsizing by 25%.
Re: service
bob -
If it were a 3phase panel, would you say there was 600A available?
I ask cause I work with an electrician that does something similar. For example, we were having trouble with a particular genset and he comes in and says, "There is a 1000A of load the generator." Now this freaks me out cause I know it's a 350kW and nameplate current is likely 526A or so.
So I question him a little, and he says, "Well it's 330A per phase, and that's about 1000A total."
We have a short discussion on this and he looks at me perplexed, and says, "So you want me to give the readings in a per phase number as opposed to adding them up.?"
"Yeah. (delivered with a straight face) That's what your ammeter reads. That's what the meter on the panel reads. It matches the units on the nameplate. And if you were sizing wire, that's the number you would use."
So where does this convention of adding up the phases to get the total load come from?
carl
bob -
If it were a 3phase panel, would you say there was 600A available?
I ask cause I work with an electrician that does something similar. For example, we were having trouble with a particular genset and he comes in and says, "There is a 1000A of load the generator." Now this freaks me out cause I know it's a 350kW and nameplate current is likely 526A or so.
So I question him a little, and he says, "Well it's 330A per phase, and that's about 1000A total."
We have a short discussion on this and he looks at me perplexed, and says, "So you want me to give the readings in a per phase number as opposed to adding them up.?"
"Yeah. (delivered with a straight face) That's what your ammeter reads. That's what the meter on the panel reads. It matches the units on the nameplate. And if you were sizing wire, that's the number you would use."
So where does this convention of adding up the phases to get the total load come from?
carl
Re: service
Just had a thought: You are likely industrial/commerical and may have 3phase available. Just so happens I put in a bunch of temp heater outlets lately.
With 3phase, 208V, load is 125A x 1.25 = 156A.
Now if your feed is 3ph, 480v, then put the xfmr at the outdoor panel, with a primary disconnect. assuming 45kVA, primary current is 54A X 1.25 = 68A. Contactor can be on the 480V side of the xfmr, which makes it a lot smaller.
carl
Just had a thought: You are likely industrial/commerical and may have 3phase available. Just so happens I put in a bunch of temp heater outlets lately.
With 3phase, 208V, load is 125A x 1.25 = 156A.
Now if your feed is 3ph, 480v, then put the xfmr at the outdoor panel, with a primary disconnect. assuming 45kVA, primary current is 54A X 1.25 = 68A. Contactor can be on the 480V side of the xfmr, which makes it a lot smaller.
carl
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: service
My point was you need 375 amps @ 120V.
You have 200A available on each hot leg for a total of 400A of 120V.
I think truck heaters have internal thermostats so this would not be a continuous load.
My point was you need 375 amps @ 120V.
You have 200A available on each hot leg for a total of 400A of 120V.
I think truck heaters have internal thermostats so this would not be a continuous load.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: service
There would be 600A of 120V available, and thats whats needed.
lady sparks lover
Senior Member
Re: service
I'm going to throw in my 2 cents!
[ January 04, 2005, 05:01 PM: Message edited by: lady sparks lover ]
I'm going to throw in my 2 cents!
[ January 04, 2005, 05:01 PM: Message edited by: lady sparks lover ]
jimwalker
Senior Member
- Location
- TAMPA FLORIDA
Re: service
Lady , how do you get 600 amps at 120 ? 1500 divided by 120 =12.5 x 30=375 amps x125% =468.75 amps and i find it hard to believe this is continues load.If 120 /240 is available i agree on a 200 amp service.
Lady , how do you get 600 amps at 120 ? 1500 divided by 120 =12.5 x 30=375 amps x125% =468.75 amps and i find it hard to believe this is continues load.If 120 /240 is available i agree on a 200 amp service.
jimwalker
Senior Member
- Location
- TAMPA FLORIDA
Re: service
The bill would be like $4 an hour or $100 a day
The bill would be like $4 an hour or $100 a day
Re: service
Uhh Jim -
You live in Florida - of course you don't believe it's a continous load.
Last week it was -38F here, for a couple of days. This is called normal. Truck and car heaters are definitely a continuous load.
As for the dollars, "Welcome to the Great North".
carl
Uhh Jim -
You live in Florida - of course you don't believe it's a continous load.
Last week it was -38F here, for a couple of days. This is called normal. Truck and car heaters are definitely a continuous load.
As for the dollars, "Welcome to the Great North".
carl
jimwalker
Senior Member
- Location
- TAMPA FLORIDA
Re: service
-38
[ January 04, 2005, 06:52 PM: Message edited by: jimwalker ]
-38
[ January 04, 2005, 06:52 PM: Message edited by: jimwalker ]
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: service
Here is how the math works (single phase example):
</font>
I tried once to discourage this manner of describing current flow. I would like to try to discourage it again. For the single phase example, 200 plus 200 equals 200; it does not equal 400. For the three-phase example, 330 plus 330 plus 330 equals 330; it does not equal 1000. As Dave Barry was wont to say, ?I swear that I am not making this up.?
Here is how the math works (single phase example):
</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">Put 200 amps of 120 volt load on the left-hand (even-numbered) breakers of a 120/240V panel.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">Put 200 more amps of 120 volt load on the right-hand (odd-numbered) breakers of the same 120/240V panel.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">The left-hand side has 200 amps times 120 volts, or 24,000 watts of load. Please note that load is power, it is not current.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">The right-hand side also has 200 amps times 120 volts, or 24,000 watts of load.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">The total load is 24,000 watts plus 24,000 watts, or 48,000 watts.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">The total current associated with this total load is 48,000 watts divided by 240 volts, or 200 amps.</font>
jimwalker
Senior Member
- Location
- TAMPA FLORIDA
Re: service
Charlie ,now you have me confused.We agree that on a 120/240 single phase 200 amp service we have 48,000 watts available.We also seem to agree that that 48,000 is from 2 sides supplying 24,000 each at 120 volts.Why is it wrong to look at this as 400 amps at 120 volts ? If i had 10 20 amp breakers all on even numbers do we agree that i can add them to get 200 amps ? Then why not do the same on the odd number breakers and then say i have 400 amps at 120 volts available
by the way the breakers on left are odd
[ January 04, 2005, 09:08 PM: Message edited by: jimwalker ]
Charlie ,now you have me confused.We agree that on a 120/240 single phase 200 amp service we have 48,000 watts available.We also seem to agree that that 48,000 is from 2 sides supplying 24,000 each at 120 volts.Why is it wrong to look at this as 400 amps at 120 volts ? If i had 10 20 amp breakers all on even numbers do we agree that i can add them to get 200 amps ? Then why not do the same on the odd number breakers and then say i have 400 amps at 120 volts available
by the way the breakers on left are odd
[ January 04, 2005, 09:08 PM: Message edited by: jimwalker ]
jimwalker
Senior Member
- Location
- TAMPA FLORIDA
Re: service
Do i not really have 2 200 amp 120 volt breakers with a tie bar ?
Do i not really have 2 200 amp 120 volt breakers with a tie bar ?
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: service
Because the nominal voltage is 120/240, not 120.
Sounds good, but I'm bluffing.
Because the nominal voltage is 120/240, not 120.
Sounds good, but I'm bluffing.
-38
[ January 04, 2005, 09:14 PM: Message edited by: georgestolz ]
jimwalker
Senior Member
- Location
- TAMPA FLORIDA
Re: service
George move to FL ,but get ready to take some really low pay.I will think about you wed while i wipe swet from my face right now i have sunburned face
George move to FL ,but get ready to take some really low pay.I will think about you wed while i wipe swet from my face
right now i have sunburned face- Status