Voltage drop distance for service

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Tjh4405

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Farmington NM
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Master Electrician
If there is overhead lines at my property line but the transformer is a few hundred feet away… Does my distance for my voltage drop calculation begin at the transformer or at the tap point?
 
Tjh4405 said:
If there is overhead lines at my property line but the transformer is a few hundred feet away… Does my distance for my voltage drop calculation begin at the transformer or at the tap point?
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The service point.
 
Tjh4405 said:
I just read it in NEC definitions. Makes sense now and thank you for pointing me to the answer and making me find it.
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No problem. The utility is responsible for delivering the electrical service within a specified range at the service point. Anything beyond this is no longer within the control of the utility, so it becomes the premises owners responsibility. Your calculations and installation begin there.
 
Lets just say the POCO conductors will still have voltage drop across them dependent on what the load is. If your extension from their conductors is significantly long you can compensate some by increasing your conductor size, but there is still a fixed resistance in their conductors. Also if transformer happens to be marginally sized - you get some significant drop just across the source, before even factoring in conductors.
 
kwired said:
Lets just say the POCO conductors will still have voltage drop across them dependent on what the load is. If your extension from their conductors is significantly long you can compensate some by increasing your conductor size, but there is still a fixed resistance in their conductors. Also if transformer happens to be marginally sized - you get some significant drop just across the source, before even factoring in conductors.
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This isn’t a problem if you base your calculations on the lowest possible voltage the utility is allowed to give you.
 
Xptpcrewx said:
This isn’t a problem if you base your calculations on the lowest possible voltage the utility is allowed to give you.
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It is not utility's problem. If you have equipment that don't like the voltage it is seeing you still have a problem.
 
kwired said:
It is not utility's problem. If you have equipment that don't like the voltage it is seeing you still have a problem.
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Staying within 5% of the lowest utility voltage will most likely not cause a problem.
 
electrofelon said:
I don't think it is unreasonable to account for utility conductors such a service drops when evaluating voltage drop, particularly when you're dealing with PV systems.
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It’s already accounted for in the minimum utility voltage. Considering this in your calculations will result in accounting for it twice.


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Kwired is trying to tell us, the desire of POCO is not DEFACTO installation.

When 120A amp tankless water heater's are wired to existing 100 amp services, the utility's #6 aluminum triplex becomes the fuse.

When linemen complain they wern't called to upgrade the line, they are replacing the fast acting #6 triplex fuse, with time-delay #4.

Yes, NEC Table 310.60(C)(68) says its good for 100 amps, and voltage drop for a typical 60ft #4 aluminum triplex on that 120Amps tankless is only 3.25%, but that Temp Rise is ~102°C, in contact with residential breakers listed for 40°C max ambient, and Romex rated at 60°C max.
 
VD shouldn’t be that big of a deal anyway with current standards.

nominal is 120, utility is +-5%. So we are 114V-126V
Utilization is -13+6, so it’s 104.4 to 127.2.
If your motor nameplate is 115, the NEMA is +-10%.
thats 103V-126.5.

most utilities like to stay about 124 at the demarcation point if possible, if for no other reason than to increase revenue.
 
ramsy said:
Kwired is trying to tell us, the desire of POCO is not DEFACTO installation.

When 120A amp tankless water heater's are wired to existing 100 amp services, the utility's #6 aluminum triplex becomes the fuse.

When linemen complain they wern't called to upgrade the line, they are replacing the fast acting #6 triplex fuse, with time-delay #4.

Yes, NEC Table 310.60(C)(68) says its good for 100 amps, and voltage drop for a typical 60ft #4 aluminum triplex on that 120Amps tankless is only 3.25%, but that Temp Rise is ~102°C, in contact with residential breakers listed for 40°C max ambient, and Romex rated at 60°C max.
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If they are taking out #6 and putting #4 after the electrician is changing the service to 200 amps, they need a new engineering group.
#6 tpx or dpx is for area lighting with our group.
#2 tpx is minimum overhead wire
 
ramsy said:
When 120A amp tankless water heater's are wired to existing 100 amp services, the utility's #6 aluminum triplex becomes the fuse.

When linemen complain they wern't called to upgrade the line, they are replacing the fast acting #6 triplex fuse, with time-delay #4.

Yes, NEC Table 310.60(C)(68) says its good for 100 amps, and voltage drop for a typical 60ft #4 aluminum triplex on that 120Amps tankless is only 3.25%, but that Temp Rise is ~102°C, in contact with residential breakers listed for 40°C max ambient, and Romex rated at 60°C max.
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Seriously this has nothing to do with voltage drop or the OP…
 
The higher the voltage drop, the longer it takes to clear ground faults. Always something to consider.

Although I know you can’t control what the POCO installs.

Whats some typical max footages that POCO will run there secondary transformer conductors to a service? I’ve seen upwards of over head drops probably close to 200’.
 
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Xptpcrewx said:
It’s already accounted for in the minimum utility voltage. Considering this in your calculations will result in accounting for it twice.


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I get what you are saying, and agree from a theoretical standpoint. I don't know exactly what the OP is trying to do but, I would say in practice the answer depends on what exactly you are trying to do. We all know VD is not a code requirement 99.9% of the time, so there aren't really any hard-and-fast rules, one can do whatever they want or their judgment tells them. The choice of current a person uses in the calculations is usually a WAG anyway (I use 65 amps for most dwelling services). Most of the time VD is an art rather than a science, balancing cost, likelihood and frequency of a given voltage deviation, and power quality.

If you are dealing with something like a definite fixed load or a PV system, then yeah it's a science, and the science will tell you you're going to want to take into account that long utility service drop to keep your inverters from shutting down. Us PV people run into it all the time.
 
electrofelon said:
I get what you are saying, and agree from a theoretical standpoint. I don't know exactly what the OP is trying to do but, I would say in practice the answer depends on what exactly you are trying to do. We all know VD is not a code requirement 99.9% of the time, so there aren't really any hard-and-fast rules, one can do whatever they want or their judgment tells them. The choice of current a person uses in the calculations is usually a WAG anyway (I use 65 amps for most dwelling services). Most of the time VD is an art rather than a science, balancing cost, likelihood and frequency of a given voltage deviation, and power quality.

If you are dealing with something like a definite fixed load or a PV system, then yeah it's a science, and the science will tell you you're going to want to take into account that long utility service drop to keep your inverters from shutting down. Us PV people run into it all the time.
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I don’t think what I’m suggesting here is anything theoretical. If the objective is to balance cost and ignore infrequent excursions, then you would want to know where those excursions are and the minimum size conductor you could get away with.

It sounds like the main difference between our methods is you use the nominal voltage and “some” impedance before the service point; whereas I like to use the minimum allowable service voltage and not have to worry about any impedance before the service point. If I have historical/empirical data, I use actual conditions, but most of the time there is no guarantee what those will be so it’s safe to assume the minimum allowable service voltage (given that you have no control of it).

From my perspective this is not an art. Art is largely subjective. I am merely attempting to compare approaches - which is something objective and can be quantified. If you’re interested, let’s discuss the pros and cons of each approach.

As far as voltage drop not being a code requirement… maybe not explicitly; however, if the equipment has a nameplate that could implicitly trigger a 110.3(B) requirement.
 
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