DISTRIBUTION UTILITY AMPACITY REFERENCE FOR GROUNDED CONDUCTOR

[mbrooke]

I've seen it, not as extreme on any POCO service conductors that I can recall, but in particular on a poorly selected/designed feeder on a golf course to a remote maintenance shop. Probably about a 1900 foot run of 2 AWG (been a while but close to that size anyway) aluminum set of conductors feeding the shop. They complained the place had voltage issues for years - but it wasn't just voltage drop you get on simple two wire circuit, but because of the voltage drop on the neutral it would give classic signs of open neutral with dimming of lights on one line and brightening of lights on the other line.

I could see a breaker in that case taking its time to clear a fault, but the neutral shift and voltage drop gave it away.

 

[iwire]

I've seen it, not as extreme on any POCO service conductors that I can recall, but in particular on a poorly selected/designed feeder on a golf course to a remote maintenance shop.

So the answer to mivey's question was no. He was talking specifically about power company wiring like the OP was talking about.

We all know a circuit can be poorly designed, the question is if the utilities are doing that poor of a job. I don't believe they are.

 

[kwired]

So the answer to mivey's question was no. He was talking specifically about power company wiring like the OP was talking about.

We all know a circuit can be poorly designed, the question is if the utilities are doing that poor of a job. I don't believe they are.

Wouldn't say they never have poor designs, but have never run into them having a 1900 foot run on a 120/240 service either. Have had them move transformers/add additional transformers closer to customer premises a few times because an air conditioner or air compressor starting up was causing too much voltage drop. But those were maybe only reducing overhead secondary from 300 to 100 feet or something like that.

 

[jaggedben]

I understand that they are unprotected conductors. However if the GROUNDED SERVICE CONDUCTOR will be of high resistance, The OCPD in the Service Equipment may not trip or operate. This is the reason why it is important that the Grounded Service Conductor should have a standard to follow.

The utility has an obligation to maintain the voltage at the service within a proscribed window. (e.g. within +10% or -12% of nominal). The windows are proscribed by federal and/or state regulations. If your service or any of your customer's services are not being maintained at that voltage and the utility is not responsive you can complain to your local and/or state Public Utilities Commission, typically. You could probably sue them if you have the time and money.

If utilities went around seriously under sizing neutral conductors everywhere, this would lead to voltage drop on all the services and undermine their ability to meet the obligations described above. The voltage drop would also lower power draw according to Ohm's law, thus reducing meter consumption readings and losing the utility money. So those are the checks on them undersizing neutrals. Utilities don't want to be responding to complaints. Sending out a crew to respond to a complaint costs as much to a utility as the savings on a couple hundred feet of wire sized one size smaller, especially when those wires are intended to last decades. If undersizing ever actually caused damage, much bigger losses accrue to the utility. So utilities have that financial interest to ensure that their service conductors are adequate for service and safety.

As long as the utility neutrals are sized to avoid voltage drops that jeopardize their service obligations, then there really is no danger of OCPDs not tripping due to service conductor neutral sizing. Certainly not on the load side of the service OCPD.

 

[mivey]

So the answer to mivey's question was no. He was talking specifically about power company wiring like the OP was talking about.

We all know a circuit can be poorly designed, the question is if the utilities are doing that poor of a job. I don't believe they are.

That is what I meant. We don't use:

...a high resistance material for the neutral conductor...or not a good conductor

 

[mivey]

The utility has an obligation to maintain the voltage at the service within a proscribed window. (e.g. within +10% or -12% of nominal). The windows are proscribed by federal and/or state regulations. If your service or any of your customer's services are not being maintained at that voltage and the utility is not responsive you can complain to your local and/or state Public Utilities Commission, typically. You could probably sue them if you have the time and money.

If utilities went around seriously under sizing neutral conductors everywhere, this would lead to voltage drop on all the services and undermine their ability to meet the obligations described above. The voltage drop would also lower power draw according to Ohm's law, thus reducing meter consumption readings and losing the utility money. So those are the checks on them undersizing neutrals. Utilities don't want to be responding to complaints. Sending out a crew to respond to a complaint costs as much to a utility as the savings on a couple hundred feet of wire sized one size smaller, especially when those wires are intended to last decades. If undersizing ever actually caused damage, much bigger losses accrue to the utility. So utilities have that financial interest to ensure that their service conductors are adequate for service and safety.

As long as the utility neutrals are sized to avoid voltage drops that jeopardize their service obligations, then there really is no danger of OCPDs not tripping due to service conductor neutral sizing. Certainly not on the load side of the service OCPD.

Yes. Also, seriously undersized neutrals would add significantly to system losses which is something else the POCO tries to minimize.

 

[kwired]

Yes. Also, seriously undersized neutrals would add significantly to system losses which is something else the POCO tries to minimize.

When I run into seriously undersized conductors by POCO it is usually the length of run that is causing the most trouble. They can get away with smaller conductors then we can from the ampacity perspective, but voltage drop doesn't care who is designing or enforcing any rules and only cares about the resistance of the conductor.

Often times when I have seen those situations there is a service drop that currently has more load on it then when it was initially installed as well. I usually can get POCO to make changes in that situation.

 

[mbrooke]

When I run into seriously undersized conductors by POCO it is usually the length of run that is causing the most trouble. They can get away with smaller conductors then we can from the ampacity perspective, but voltage drop doesn't care who is designing or enforcing any rules and only cares about the resistance of the conductor.

Often times when I have seen those situations there is a service drop that currently has more load on it then when it was initially installed as well. I usually can get POCO to make changes in that situation.

Its possible to reverse engineer something like this. If you know the voltage drop for a given load you can roughly calculate the impedance of the conductors and in turn what the short circuit currents might be.

In fact, when UL was researching arc faults, they also did a study where they found the lowest possible anticipated short circuit current for a dwelling service was 500amps. In most cases it is much higher.

 

[mivey]

Often times when I have seen those situations there is a service drop that currently has more load on it then when it was initially installed as well. I usually can get POCO to make changes in that situation.

I would say that most POCO folks want things to work right but not all POCO staff know what they are talking about as there tends to be some wierd ideas about how stuff operates at times. Urban legends so to speak.

Communication and finding the right person to talk with can be a problem at some POCOs so kudos to you for being able to cut to the chase. It is not always as simple as it should be.