DISTRIBUTION UTILITY AMPACITY REFERENCE FOR GROUNDED CONDUCTOR

[bobby ocampo]

You asked about service conductors. There is no OCPD to trip, they are unprotected conductors.

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.

 

[iwire]

This is the reason why it is important that the Grounded Service Conductor should have a standard to follow.

You should make one and force the world to follow it.

 

[mbrooke]

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.

Can you elaborate on this? Pardon me :dunce:

I cant think of any typical case where the utility neutral is so undersized that it will melt before the main OCPD opens. Unless you mean extreme length from POCO transformer to the service, and if that was the case, excessive neutral shift would be noticed first (assuming the general voltage drop did not hit you first).

In fact, its usually voltage drop concerns alone coupled with low Z POCO transformers that produces fault current most cases at least several times the main OCPD rating.

But, this is my 2 cents and could be wrong.

 

[mivey]

You should make one and force the world to follow it.

Only one? I see no reason to start simplifying things at this point.

 

[mbrooke]

You should make one and force the world to follow it.

There already is one...

 

[bobby ocampo]

Bobby O
Good to hear from you. Your trolls are always interesting. You always keep the subject sufficently nebulous, one can't always tell the context. For example, I can't tell if you are discussing residential of industrial - and yes it matters.

What is nebulous to you? Isn't it obvious that it is residential?

Starting from there, give some thought to the physics. The grounded service conductor resistance doesn't matter - high or low indifferent.

Why will it not matter? What type of meter is used for Single Phase Three Wire? If the neutral or the grounded service conductor used is of high resistance what could possibly happen on a single line to ground fault on the operation of the OCPD? Can you your physics on why there may be a possibility that the OCPD may not operate?

Your premisis is line to ground (earth) leakage after the meter is a problem (safety or money - can't tell) because the utility intentionally installs a higher than needed resistance service neutral. This is either cheating the customer, or unsafe because the leakage won't trip the unspecified OCP - I can't tell which concerns you.

Both concerns me. There is a probability that DU may cheat and at the same time it will be unsafe on a single line to ground fault in residential, single phase three wire. If you have read the original post, I am asking for the Code that DU is using for service conductors both for the ungrounded service conductor and the grounded service conductor.

Basic Physics:
The resisitance of a line to earth leakage connection will be much higher than any service neutral conductor. Other than gfci, the system is not designed to trip on earth leakage.

And you know this. You have a copy of IEEE green book. So, where are you going?

I want to know what Code is being used by the Distribution Utility to size up their Service Conductors.

Possibly:
The utility is undersizing neutrals in a effort to cheat the customer on metering?

So it seems that you understand. What do you think will be the meter reading if the neutral or the grounded service conductor is not undersized and what do you think will be the reading of the meter if the neutral is properly sized? What Code is the DU using?

The utility is, with forethought and malice, undersizing neutral conductors to prevent customer CBs from tripping on earth faults?

Either is pretty ludicrus. Because: Other than gfci, the system is not designed to trip on earth leakage.

Sorry to hit and run, but I got to get to work. Got a customer that wants to pay.


ice

Why do we have Authorities? Isn't it to make sure that all will be complying? Should Due Diligence be practiced?

 

[iwire]

Why do we have Authorities?

Why go on and on about this subject without any documentation at all that there is a problem?

 

[bobby ocampo]

Can you elaborate on this? Pardon me :dunce:

I cant think of any typical case where the utility neutral is so undersized that it will melt before the main OCPD opens. Unless you mean extreme length from POCO transformer to the service, and if that was the case, excessive neutral shift would be noticed first (assuming the general voltage drop did not hit you first).

In fact, its usually voltage drop concerns alone coupled with low Z POCO transformers that produces fault current most cases at least several times the main OCPD rating.

But, this is my 2 cents and could be wrong.

What is POCO?

Possiblity could be undersize or material of high resistance.

 

[bobby ocampo]

I do not see where the NEC has anything to do with the size of the conductor the utility chooses to use. :huh:

To whom will the DU be responsible? Who regulates the DU? What Code will DU comply on the size of their service conductor? Are they self regulating?

 

[bobby ocampo]

My Original Post

What ampacity table are Distribution Utility using in sizing the grounded service conductor?

Is there a code other than the NEC that DU is using for the ampacity of their service conductors?

 

[mbrooke]

What is POCO?

Possiblity could be undersize or material of high resistance.

Power company.

But, what do you mean by OCPD not tripping? Can you give me a scenario?

Not discouraging, just want to a typical scenario that might cause the problem described.

 

[kwired]

My Original Post

What ampacity table are Distribution Utility using in sizing the grounded service conductor?

Is there a code other than the NEC that DU is using for the ampacity of their service conductors?

Someone already mentioned they are either using the NESC or their own engineers are coming up with calculations that they deem acceptable. Most likely stick with NESC to help reduce potential liabilities since it is a recognized standard. Engineers own calculations would need more justification should something unusual come up.

 

[bobby ocampo]

Someone already mentioned they are either using the NESC or their own engineers are coming up with calculations that they deem acceptable. Most likely stick with NESC to help reduce potential liabilities since it is a recognized standard. Engineers own calculations would need more justification should something unusual come up.

Please post what part of NESC.

 

[bobby ocampo]

Power company.

But, what do you mean by OCPD not tripping? Can you give me a scenario?

Not discouraging, just want to a typical scenario that might cause the problem described.

Imagine using a high resistance material for the neutral conductor. If the Grounded service conductor or the neutral conductor is of high resistance or not a good conductor. The return path will be of high resistance and OCPD may not trip or will not trip.

 

[mbrooke]

View attachment 13960

Imagine using a high resistance material for the neutral conductor. If the Grounded service conductor or the neutral conductor is of high resistance or not a good conductor. The return path will be of high resistance and OCPD may not trip or will not trip.

II could be wrong, but I would imagine other problems coming with that like neutral shift under normal operating conditions.

 

[user 100]

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.

I believe you are seriously overthinking this and creating a problem where one doesn't normally exist. How often does a poco screw up and run a poorly alloyed/undersized neutral to an average residence in this day and age? Seems to me that utilities have this down pat- no epidemic of fires, or even warm service neutrals because of bad specs on part of poco engineers, so why the need for increased oversight?

If it isn't broken......

 

[GoldDigger]

If it isn't broken......

.....claim you fixed it!
:angel:

 

[kwired]

Please post what part of NESC.

I have no idea as I don't use that publication, but most POCO's do use it to some extent.

View attachment 13960

Imagine using a high resistance material for the neutral conductor. If the Grounded service conductor or the neutral conductor is of high resistance or not a good conductor. The return path will be of high resistance and OCPD may not trip or will not trip.

Imagine the main terminal to the center tap of the transformer developing a high resistance for whatever reason, or any other connection along the path. It happens, and you get similar or even worse results.

Unless they use some cheap alloy from some no name producer - they still have fairly low resistance with almost any metal alloy - terminations will be the part that needs the most attention for potential failure. On top of that the neutral is only carrying the imbalance of the other conductors and unless there is a situation where you have full capacity on only half the winding the neutral current will likely be pretty low to begin with.

There is a possibility of undersized neutral conductor - but usually is only a problem with excessively long runs. Ungrounded conductor size often can be an isssue as well on such long runs. Otherwise you are trying to make a problem where none normally exists for most average service drop lengths.

 

[mivey]

Imagine using a high resistance material for the neutral conductor. If the Grounded service conductor or the neutral conductor is of high resistance or not a good conductor. The return path will be of high resistance and OCPD may not trip or will not trip.

Well now that is quite a stretch. Do you have a specific example of that you have actually seen?

 

[kwired]

Well now that is quite a stretch. Do you have a specific example of that you have actually seen?

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.