I think that the NEC is missing the boat with it's FPN regarding voltage drop because it is a recommendation and it is not enforceable. To calculate voltage drop I use vd= 2xLxRxI/1000 I can not find anything in the NEC telling me what to use for I. Is it the size of the service 80% of the service or the calculated load of the dwelling ? Section 230.31 says service lateral conductors shall have sufficient ampacity to carry the current for the load calculated. So i guess it is the calculated load. But can the AHJ require a voltage drop calculation on a code recommendation ? I don't think so. I don't know why the NEC uses this FPN rather than carve it in stone.
voltage drop on service lateral
- Thread starter romeo
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physis
Senior Member
Re: voltage drop on service lateral
Usually you'd use the load caluculation from Article 220 as a place to start for a service.
I can only imagine what would happen if AHJ's where to get involved with voltage drop. I kind of think there should be some sturdier guidelines too, but I'm not sure that should be an NEC code.
Either way, it's up to you to determine what the load will be and size the conductors for an acceptable voltage drop.
The general rule of thumb I think is 2% Vd across the service conductors and feeders and 3% across the branch circuits, 5% total.
Just as a after thought, I think you would have problems with AHJ's becoming liable for bad engineering when they make a mistake on a service or feeder size requirement. I don't know, it's our job. I think at some point you have to allow the professionals to do what they do. Writing another code wont make voltage drop go away.
If we don't trust electricians to do the electrical I don't know why we should trust a building inspector.
Usually you'd use the load caluculation from Article 220 as a place to start for a service.
I can only imagine what would happen if AHJ's where to get involved with voltage drop. I kind of think there should be some sturdier guidelines too, but I'm not sure that should be an NEC code.
Either way, it's up to you to determine what the load will be and size the conductors for an acceptable voltage drop.
The general rule of thumb I think is 2% Vd across the service conductors and feeders and 3% across the branch circuits, 5% total.
Just as a after thought, I think you would have problems with AHJ's becoming liable for bad engineering when they make a mistake on a service or feeder size requirement. I don't know, it's our job. I think at some point you have to allow the professionals to do what they do. Writing another code wont make voltage drop go away.
If we don't trust electricians to do the electrical I don't know why we should trust a building inspector.
charlie
Senior Member
- Location
- Indianapolis
Re: voltage drop on service lateral
Some situations can have a large voltage drop and others can't handle much drop. The NEC makes a recommendation and it is up to the designer to make the call. You may be installing a lighting system that can stand 10% voltage drop or even more. Why should you be penalized by using larger conductors than are needed for the task?
The voltage drop formula you use is the one in the NFPA NEC Handbook and is the one I use also. It requires the use of Table 8 in Chapter 9 in the NEC instead of the exact value of K which kind of moves around. The nice thing about it is just replace the 2 with the square root of 3 and you are doing 3? calculations.
Some situations can have a large voltage drop and others can't handle much drop. The NEC makes a recommendation and it is up to the designer to make the call. You may be installing a lighting system that can stand 10% voltage drop or even more. Why should you be penalized by using larger conductors than are needed for the task?
The voltage drop formula you use is the one in the NFPA NEC Handbook and is the one I use also. It requires the use of Table 8 in Chapter 9 in the NEC instead of the exact value of K which kind of moves around. The nice thing about it is just replace the 2 with the square root of 3 and you are doing 3? calculations.
- Location
- Massachusetts
Re: voltage drop on service lateral
The NEC is a safety code.
Imagine a motor run severely under voltage, the motor overloads should open before damage to the motor happens.
Just following the minimum safety standards may not result in an efficient installation and the NEC recognizes that.
Wouldn't that be better left to the designer of the project?
You are free to provide as little voltage drop as you feel comfortable with.
The NEC is a safety code.
Running loads under voltage is not unsafe as long as the other parts of the code are followed.
Imagine a motor run severely under voltage, the motor overloads should open before damage to the motor happens.
Just following the minimum safety standards may not result in an efficient installation and the NEC recognizes that.
Finally the NEC is not a design specification.
Romeo can I ask why you think the NEC should put limits on voltage drop?
Wouldn't that be better left to the designer of the project?
Re: voltage drop on service lateral
Bob thank you for your reply. The truth is that I am a part time inspector in 2 small towns. Most of my inspections are residential new single family homes.
I find that new homes keep getting larger and the service trenches keep getting longer. I require a load calculation on any home over 2500 sq. ft. However I am seeing service laterals of 300 and 400 ft. and even 1 of 500 ft. and the contractor seems satisfied to increase the service conductors by 1 size and never do a voltage drop calculation and there is really nothing that I can do about it because of lack of support from the NEC. I worry that low voltage may become a problem in some of these homes some day.
You make a very good point 90.1 (c) NEC is not intended as a design or instruction manual. And I as the AHJ
I should not be trying to design an insallation. I am an inspector that realizes that I don't know it all just because I have the title and I am always ready to listen and learn.
I can't help but feel bad for the home owner who paid huge amounts of money for a home when I see a service panel loaded to the max some even with a couple of twin breakers in it and service conductors that may not be able to handle additioal loads. But i guess my job is to enforce the code as it is written and to keep my nose out of job design. That all of you for your remarks. Romeo Massachusetts
Bob thank you for your reply. The truth is that I am a part time inspector in 2 small towns. Most of my inspections are residential new single family homes.
I find that new homes keep getting larger and the service trenches keep getting longer. I require a load calculation on any home over 2500 sq. ft. However I am seeing service laterals of 300 and 400 ft. and even 1 of 500 ft. and the contractor seems satisfied to increase the service conductors by 1 size and never do a voltage drop calculation and there is really nothing that I can do about it because of lack of support from the NEC. I worry that low voltage may become a problem in some of these homes some day.
You make a very good point 90.1 (c) NEC is not intended as a design or instruction manual. And I as the AHJ
I should not be trying to design an insallation. I am an inspector that realizes that I don't know it all just because I have the title and I am always ready to listen and learn.
I can't help but feel bad for the home owner who paid huge amounts of money for a home when I see a service panel loaded to the max some even with a couple of twin breakers in it and service conductors that may not be able to handle additioal loads. But i guess my job is to enforce the code as it is written and to keep my nose out of job design. That all of you for your remarks. Romeo Massachusetts
charlie
Senior Member
- Location
- Indianapolis
Re: voltage drop on service lateral
Romeo, it seems strange to me the service lateral is not put in by the serving electric utility. We provide, install (actually, we pay a contractor to do the installation to our specifications), and maintain the service laterals to residences. Does the home owner actually own the service lateral or does the electric utility own the service lateral?
The reason I am asking that question is that we are responsible for the voltage drop to the meter location. I don't have a clue how it is done in Massachusetts but I expect it is the same as we do things.
Romeo, it seems strange to me the service lateral is not put in by the serving electric utility. We provide, install (actually, we pay a contractor to do the installation to our specifications), and maintain the service laterals to residences. Does the home owner actually own the service lateral or does the electric utility own the service lateral?
The reason I am asking that question is that we are responsible for the voltage drop to the meter location. I don't have a clue how it is done in Massachusetts but I expect it is the same as we do things.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Re: voltage drop on service lateral
Romeo, my best advice is to try and educate the EC's about the importance of it, and make it clear that you're speaking to them in a different role than your role as an AHJ.
It is difficult in your position as an inspector, because often the EC will percieve this as an attempt to enforce voltage drop, which we would fight tooth and nail.
The other side of the coin, is perhaps they have taken the connected load into perspective. I know that often in these houses, two or more 42 space panels are thrown at them when, if we actually knew the loads that were connected in these houses at rough-in, chances are they'd look a lot more like the code-minimum.
A 400-amp service is impressive, so people want to buy one. That doesn't mean they have more than 120 amps of connected load.
It's a crazy world we live in.
Romeo, my best advice is to try and educate the EC's about the importance of it, and make it clear that you're speaking to them in a different role than your role as an AHJ.
It is difficult in your position as an inspector, because often the EC will percieve this as an attempt to enforce voltage drop, which we would fight tooth and nail.
The other side of the coin, is perhaps they have taken the connected load into perspective. I know that often in these houses, two or more 42 space panels are thrown at them when, if we actually knew the loads that were connected in these houses at rough-in, chances are they'd look a lot more like the code-minimum.
A 400-amp service is impressive, so people want to buy one. That doesn't mean they have more than 120 amps of connected load.
It's a crazy world we live in.
Re: voltage drop on service lateral
Charlie
The utility company provides secondary power to the last pole on the proprerty.The home owner owns the service lateral from the conduit going up the pole to the meter socket. It is installed by the electrical contractor.
Thanks again Romeo
P.S. the bonding of the metal conduit going up the pole is another issue. I say it must be bonded to the service neutral but some electricians seem to think a ground rod will do the job. The conduit in the trench is PVC. That is a question for another day.
Charlie
The utility company provides secondary power to the last pole on the proprerty.The home owner owns the service lateral from the conduit going up the pole to the meter socket. It is installed by the electrical contractor.
Thanks again Romeo
P.S. the bonding of the metal conduit going up the pole is another issue. I say it must be bonded to the service neutral but some electricians seem to think a ground rod will do the job. The conduit in the trench is PVC. That is a question for another day.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Re: voltage drop on service lateral
</font>
Around here, we have umpteen different POCO's to deal with. Generally, they supply the lateral, with a few exceptions:
</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">Longmont, CO: Longmont L&P CO. The EC installs the lateral from the street, and after the EC's warranty lapses in a year, the L. L&P Co annexes the conductors, and assume ownership. In this way, they don't have the initial cost of conductors for houses.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">Outlying areas: REA. Generally, overhead primary lines to a transformer on a pole. A disconnect is placed at the pole at the road and the feeder run underground. Sometimes the meter is hundreds of feet from the house, so while it's not technically a "service lateral", the same conditions apply.
As far as replacing existing service drops, I have only been involved on two occasions that I can recall, and both times we supplied and installed the triplex.</font> - <font size="2" face="Verdana, Helvetica, sans-serif">City of Loveland: For residential customers, the lateral is provided.
For greater than duplexes, the lateral is provided by the EC, and I'd imagine the POCO will assume responsibility for them after a time.</font>
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Re: voltage drop on service lateral
How will that fault current open an OCPD if it's not bonded in some fashion to the neutral? A ground rod is not good enough! 250.92(B).
How about today?
How will that fault current open an OCPD if it's not bonded in some fashion to the neutral? A ground rod is not good enough! 250.92(B).
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- Semi-retired engineer
Re: voltage drop on service lateral
One of the things with VD is that the calculations done often end up with a load much higher than is actually seen most of the time.
This results in larger conductors than are actually needed for the real loads being seen.
If you have a 200A service, but only actually use 50A of it, regardless of the load calculation, does upsizing the conductors make any sense?
To my way of thinking, if a service is installed and you actually use most of it, it is really too small to begin with.
[ May 22, 2005, 12:41 PM: Message edited by: petersonra ]
One of the things with VD is that the calculations done often end up with a load much higher than is actually seen most of the time.
This results in larger conductors than are actually needed for the real loads being seen.
If you have a 200A service, but only actually use 50A of it, regardless of the load calculation, does upsizing the conductors make any sense?
To my way of thinking, if a service is installed and you actually use most of it, it is really too small to begin with.
[ May 22, 2005, 12:41 PM: Message edited by: petersonra ]
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- Semi-retired engineer
Re: voltage drop on service lateral
Isn't this part of the utility's scope? If so, how would the local inspector even have a say in what they do? It would seem to be under the NESC rather than the NEC.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Re: voltage drop on service lateral
Whether the POCO or the EC installs it, services are well within the scope of the NEC. The inspector would be well within his rights to fail an unbonded service drop.
Regardless, I'd imagine the NESC won't allow the earth to serve in the place of a bonding conductor...!
Whether the POCO or the EC installs it, services are well within the scope of the NEC. The inspector would be well within his rights to fail an unbonded service drop.
Regardless, I'd imagine the NESC won't allow the earth to serve in the place of a bonding conductor...!
Re: voltage drop on service lateral
Please allow me to clarify something. When I inspect an underground service with a mteal conduit going up the pole the conduit gets bonded to the neutral or the service is not connected.One method of doing this is to use a bonding bushing tie a ground wire to it ( 250.66 ) and leave a coil of wire so the utility can tie it to the transformer neutral.
Romeo
Please allow me to clarify something. When I inspect an underground service with a mteal conduit going up the pole the conduit gets bonded to the neutral or the service is not connected.One method of doing this is to use a bonding bushing tie a ground wire to it ( 250.66 ) and leave a coil of wire so the utility can tie it to the transformer neutral.
Romeo
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Re: voltage drop on service lateral
Good to hear, Romeo!
Good to hear, Romeo!
charlie
Senior Member
- Location
- Indianapolis
Re: voltage drop on service lateral
Petersonra, the rules for service drops and service laterals are in the NEC for customer owned drops and laterals.
George, you are absolutely right.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: voltage drop on service lateral
I have a great respect for an inspector who don't try to inforce more than the codes allow. Keep up the good work.
I know you job isn't to educate electricians, but one that thinks the Earth can ever take the place of a solid conductor for return current, needs to understand that a ground rod @ 25 ohms can only fault 4.8 amps of current @ 120 volts. using a ground rod in this manner is getting people killed on light pole's all over the country! Mabe a little word of wisdom will get them to think other wise.
I have a great respect for an inspector who don't try to inforce more than the codes allow. Keep up the good work.
physis
Senior Member
Re: voltage drop on service lateral
You seem like a pretty reasonable guy Romeo. After reading this thread I think I would have the same concerns. If you are seeing a lot actaully undersized service runs maybe you should see about having an ordinance written. I really wouldn't feel to good about a building where I found 105 volts on the service.
You seem like a pretty reasonable guy Romeo. After reading this thread I think I would have the same concerns. If you are seeing a lot actaully undersized service runs maybe you should see about having an ordinance written. I really wouldn't feel to good about a building where I found 105 volts on the service.
Re: voltage drop on service lateral
My rule of thumb is that you need about 200 amps of service capacity for a service panel that is 200 to 220 feet from the supply transformer in order to start a 3 ton single phase air conditioner without dimming the lights.
What that means is that for a 500 foot long service lateral you need 500 amp or 600 amp wiring for the air conditioner to start without noticeably dimming the lights.
However, for a large enough house, why not install heat pumps with fossil fuel backup heat during utility peak periods and power them from 277Y480 volts 3-phase? By putting the heat pumps on their own service lateral, transformer, and meter the voltage drop problem is a lof easier. Actually, this is an old fashioned solution that dates back to the days of design A motors although some energy saving design B motors suck a lot of current when starting as well.
I have installed York's relay box for a heat pump and a natural gas furnace that uses an outdoor thermostat to switch from heat pump to gas when the weather is too cold. The outdoor thermostat needs a form C contact. I suspect that this will be popular as the price of natural gas goes up. Here is Cleveland most of the winter is mild enough for a heat pump that uses the natural gas on the few days that it is beastly cold.
My rule of thumb is that you need about 200 amps of service capacity for a service panel that is 200 to 220 feet from the supply transformer in order to start a 3 ton single phase air conditioner without dimming the lights.
What that means is that for a 500 foot long service lateral you need 500 amp or 600 amp wiring for the air conditioner to start without noticeably dimming the lights.
However, for a large enough house, why not install heat pumps with fossil fuel backup heat during utility peak periods and power them from 277Y480 volts 3-phase? By putting the heat pumps on their own service lateral, transformer, and meter the voltage drop problem is a lof easier. Actually, this is an old fashioned solution that dates back to the days of design A motors although some energy saving design B motors suck a lot of current when starting as well.
I have installed York's relay box for a heat pump and a natural gas furnace that uses an outdoor thermostat to switch from heat pump to gas when the weather is too cold. The outdoor thermostat needs a form C contact. I suspect that this will be popular as the price of natural gas goes up. Here is Cleveland most of the winter is mild enough for a heat pump that uses the natural gas on the few days that it is beastly cold.
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