autecbernie
Member
If I'm running a 200 amp service a distance of 400', do I still consider the voltage drop based on 200 amps at a 3% voltage drop or a 5% voltage drop
voltage drop on services
- Thread starter autecbernie
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autecbernie
Member
Re: voltage drop on services
That's the way I look at it, I was thinking more in the way of calculating it at 100 amps
That's the way I look at it, I was thinking more in the way of calculating it at 100 amps
charlie
Senior Member
- Location
- Indianapolis
Re: voltage drop on services
Why don't you calculate the load in accordance with Article 220 and base your voltage drop calculations on something solid. Or just flip a coin and take your chances. Guessing is fine if it doesn't matter. If you are trying to do quality work, you can't guess.
Why don't you calculate the load in accordance with Article 220 and base your voltage drop calculations on something solid. Or just flip a coin and take your chances. Guessing is fine if it doesn't matter. If you are trying to do quality work, you can't guess.
physis
Senior Member
Re: voltage drop on services
I don't know if I would call 220 load calculations "solid".
To me, I would base my decision on a few different factors.
Is it a competetive bid?
Are you working under a general contractor who wants bottom line? (Lately I'm having trouble with one and wouldn't mind seeing him get stuck by his own bad decisions).
Is it something you just plain want done well?
If it were mine or something for a friend of mine I might add some additional quality that wouldn't necessarily be important to someone trying to keep cost down.
I don't know if I would call 220 load calculations "solid".
To me, I would base my decision on a few different factors.
Is it a competetive bid?
Are you working under a general contractor who wants bottom line? (Lately I'm having trouble with one and wouldn't mind seeing him get stuck by his own bad decisions).
Is it something you just plain want done well?
If it were mine or something for a friend of mine I might add some additional quality that wouldn't necessarily be important to someone trying to keep cost down.
charlie
Senior Member
- Location
- Indianapolis
Re: voltage drop on services
Sam, I understand all that but you have to have a starting point. The available choices should be based on something and you can't estimate your loads the same way I do.
Sam, I understand all that but you have to have a starting point. The available choices should be based on something and you can't estimate your loads the same way I do.
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
Re: voltage drop on services
Since we are talking about one of my favorite subjects, what is the opinion here of what an acceptable voltage drop is. I wire a lot of marinas and I'll have cable runs of 300, 400, .... 800' long. It is often feeding a power center that has two 50 amp 120/240 volt receptacles on it. Boats come in all flavors. Speaking with boat manufacturers, they tend to operate down to 200 volts. They load the boats differently. Some load all 50 amps, others only 30-40 amps.
The dock builder is always telling me that boats don't really use much power. I am always in a quandary about the best size wire to run. If you feed one power center with a 100 amp circuit (not increasing wire size) and only one boat is plugged in (50-amp receptacle) then you are fine. Add the 2nd boat, and you are fine if they do not draw 100% loads at the same time. You could always loop feed the power centers, but the costs goes up because the larger cable is more than twice the smaller, and the labor for the larger cable is a lot more than one of the smaller cables (plus other factors I won't get into here).
What I have been recommending as a minimum is to size the wire so at 100% load on the circuit, the voltage drop is not more than 10% with the power company maintaining 240 volts. The power company around here delivers about 246-252 during "normal" voltage, so we have a little fudge factor here. I then try to explain how voltage drop can be an issue, but that the demands of the boats (unknown at construction) will be the determining factor. Then I give a price to upgrade wiring (still can't usually get it to 3%) to help compensate for voltage drop.
Anyway, am I being practical, or am I doing my customer a disservice.
Since we are talking about one of my favorite subjects, what is the opinion here of what an acceptable voltage drop is. I wire a lot of marinas and I'll have cable runs of 300, 400, .... 800' long. It is often feeding a power center that has two 50 amp 120/240 volt receptacles on it. Boats come in all flavors. Speaking with boat manufacturers, they tend to operate down to 200 volts. They load the boats differently. Some load all 50 amps, others only 30-40 amps.
The dock builder is always telling me that boats don't really use much power. I am always in a quandary about the best size wire to run. If you feed one power center with a 100 amp circuit (not increasing wire size) and only one boat is plugged in (50-amp receptacle) then you are fine. Add the 2nd boat, and you are fine if they do not draw 100% loads at the same time. You could always loop feed the power centers, but the costs goes up because the larger cable is more than twice the smaller, and the labor for the larger cable is a lot more than one of the smaller cables (plus other factors I won't get into here).
What I have been recommending as a minimum is to size the wire so at 100% load on the circuit, the voltage drop is not more than 10% with the power company maintaining 240 volts. The power company around here delivers about 246-252 during "normal" voltage, so we have a little fudge factor here. I then try to explain how voltage drop can be an issue, but that the demands of the boats (unknown at construction) will be the determining factor. Then I give a price to upgrade wiring (still can't usually get it to 3%) to help compensate for voltage drop.
Anyway, am I being practical, or am I doing my customer a disservice.
resistance
Senior Member
- Location
- WA
Re: voltage drop on services
I would say: To get 50 amps on a 240v circuit, with only a 3% VD, you may need 3/0 copper (or 250 MCM) to maintain the the load one way.
Not in stone, so wait for others. Just throughing this out there. Once I get home I will be better able to calculate my thought. Sitting here waiting on my wife at my mother-in-laws. (Bored)
Wait for others!
I would say: To get 50 amps on a 240v circuit, with only a 3% VD, you may need 3/0 copper (or 250 MCM) to maintain the the load one way.
Not in stone, so wait for others. Just throughing this out there. Once I get home I will be better able to calculate my thought. Sitting here waiting on my wife at my mother-in-laws. (Bored)
Wait for others!
charlie
Senior Member
- Location
- Indianapolis
Re: voltage drop on services
a 200 ampere service is usually an increment and not the result of actual calculations. If the calculated load is 110 amperes, a lot of people will just install a 200 ampere service to allow for future growth. Also, what size service would you set if your calculated load were 155 amperes?
a 200 ampere service is usually an increment and not the result of actual calculations. If the calculated load is 110 amperes, a lot of people will just install a 200 ampere service to allow for future growth. Also, what size service would you set if your calculated load were 155 amperes?
wirenut1980
Senior Member
- Location
- Plainfield, IN
Re: voltage drop on services
Just my opinion, but I disagree with this line of thinking somewhat. True, the panel is sized for future load growth, but the service conductors or feeders are not sized for future load growth. So it's like you're halfway there, I guess. But I guess most of the time upgrading components for future load growth is not required so its kind of a bonus for the customer. Ok I'm done being snipity.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: voltage drop on services
Please note that this deviates from the original question. I?ll give my opinion on this one, but let us keep the issues separate, or else open a new thread to address the second issue.
NEC Article 555 (2002 version) gives us demand factors to apply to marina loads. I think the process is straight-forward, though perhaps a bit tricky to see at first look.
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I don?t agree with this recommended design approach.
Please note that this deviates from the original question. I?ll give my opinion on this one, but let us keep the issues separate, or else open a new thread to address the second issue.
NEC Article 555 (2002 version) gives us demand factors to apply to marina loads. I think the process is straight-forward, though perhaps a bit tricky to see at first look.
</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">The load for every boat slip must be counted as if the boat will draw all of the current for which the largest available receptacle is rated. If you have both a 30 amp 125 volt receptacle and a 50 amp 250 volt receptacle, you count it as 12,000 VA (i.e., 50 amps times rated source voltage of 240 volts).</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">Any branch circuit that feeds one or more slips is sized per the total VA of all the slips times the demand factor of Table 555.12 for that many slips. Call this the ?calculated branch circuit load.?</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">Any feeder that powers a number of such branch circuits is sized per the total VA of all the slips (i.e., add up the load on all the branch circuits, without using their individual demand factors) times the demand factor of Table 555.12 for the total number of slips supplied by that feeder. Call this the ?calculated feeder load.?</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">The service to the marina is sized by adding all the load from all the slips, then multiplying by the demand factor that applies to the total number of slips. Call this the ?calculated service load.?</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">When all this is done, you check the voltage drop along all conductors. The current you use for this voltage drop calculation is the current that corresponds to the ?calculated load? (branch circuit, feeder, or service), as described above.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">Size the conductors to keep voltage drop below 3 % along feeders and 5% along feeder and branch circuit conductors.</font>
james wuebker
Senior Member
- Location
- Iowa
Re: voltage drop on services
Charie wrote
quote:
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a 200 ampere service is usually an increment and not the result of actual calculations. If the calculated load is 110 amperes, a lot of people will just install a 200 ampere service to allow for future growth. Also, what size service would you set if your calculated load were 155 amperes?
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I agree with Wirenut 1980. If i'm going to put a 200 amp service in then the wire size should be good for 200 amps for the furture. Now if the load is only figured at 110 amps then just install the 150 amp panel.
Bye now,
Jim
Charie wrote
quote:
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a 200 ampere service is usually an increment and not the result of actual calculations. If the calculated load is 110 amperes, a lot of people will just install a 200 ampere service to allow for future growth. Also, what size service would you set if your calculated load were 155 amperes?
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I agree with Wirenut 1980. If i'm going to put a 200 amp service in then the wire size should be good for 200 amps for the furture. Now if the load is only figured at 110 amps then just install the 150 amp panel.
Bye now,
Jim
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: voltage drop on services
So would I. But do keep in mind that that is a design choice, not a code requirement.
james wuebker
Senior Member
- Location
- Iowa
Re: voltage drop on services
Charie, You are correct on that.
Jim
Charie, You are correct on that.
Jim
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