Utilities Transformer Ground Connection

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Joseph P.

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I live in Long Island NY where the earth material is sand. My ground system with an was 215 ohms. I reduced it to 5.3 ohms by driving 70' of sectional ground rod. When I checked the utilities ground connection at the pole coming off of the transformer, it was 465 ohms. Does the utility have to follow the NEC code where you need under 25 ohms on the ground? I am having a stray voltage situation on the property near the pole and feel it is from their bad ground connection.
 
Joseph P. said:
I live in Long Island NY where the earth material is sand. My ground system with an was 215 ohms. I reduced it to 5.3 ohms by driving 70' of sectional ground rod. When I checked the utilities ground connection at the pole coming off of the transformer, it was 465 ohms. Does the utility have to follow the NEC code where you need under 25 ohms on the ground? I am having a stray voltage situation on the property near the pole and feel it is from their bad ground connection.
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A lot of free time on your hands I guess.

There really is no 25 ohm rule for either the NEC or the utility. You could have driven two 8' ground rods and been NEC compliant.

But let's look at this another direction, where is this stray voltage coming from, how are you measuring it, what problem is it causing and how will a better connection to dirt fix it?
 
If you have "stray voltage" at the pole, chances are the POCO has a bad connection on their MGN somewhere.

If you open your service disconnecting means and this problem is still present it is on the POCO equipment somewhere - call them and have them figure out where. If they are one of those POCO's that ignore you, threaten a lawsuit for safety concerns, it will at least get them to think a little harder about it.
 
Joseph P. said:
When I checked the utilities ground connection at the pole coming off of the transformer, it was 465 ohms.
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High, but not a deal-killer if there are other system grounds around. Might be a problem for an isolated tap.

Joseph P. said:
Does the utility have to follow the NEC code where you need under 25 ohms on the ground?
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No. And there is no 25 ohm requirement.

Joseph P. said:
I am having a stray voltage situation on the property near the pole and feel it is from their bad ground connection.
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A better ground could make it worse. Eliminate the possibility of it being your service them look further out. If you are friendly with the neighbors, see if opening their load removes the problem, otherwise get the POCO involved.

PS: Please describe the issue you have and the voltage levels.
 
The engineering manager for one of the larger utilities in our rural area had just finished a very thorough neutral /stray ground current investigation on their electrical distribution system.They concluded only 40 % of their neutral current was returning back to their substation on their overhead neutral wires--the rest of this neutral current was flowing back through their customer's grounding systems to the substation transformer.
 
ghostbuster said:
The engineering manager for one of the larger utilities in our rural area had just finished a very thorough neutral /stray ground current investigation on their electrical distribution system.They concluded only 40 % of their neutral current was returning back to their substation on their overhead neutral wires--the rest of this neutral current was flowing back through their customer's grounding systems to the substation transformer.
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Not too surprising when you consider there are millions of earth electrodes out on the system. If you only had one electrode at the source and one at the furthest point in the system, there would be very little current flow through the earth.
 
ghostbuster said:
The engineering manager for one of the larger utilities in our rural area had just finished a very thorough neutral /stray ground current investigation on their electrical distribution system.They concluded only 40 % of their neutral current was returning back to their substation on their overhead neutral wires--the rest of this neutral current was flowing back through their customer's grounding systems to the substation transformer.
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When looking at a multi-grounded system using the neutral for load current, a 50/50 or even a 60/40 split is not uncommon nor is it always considered an abnormal condition. Even a 70/30 split might be seen on extremes.

40% neutral current seems slightly high for an average but keep in mind that 50/50 could be considered normal. Load balancing and checking connections might be something the manager should spend some time on.
 
kwired said:
Not too surprising when you consider there are millions of earth electrodes out on the system. If you only had one electrode at the source and one at the furthest point in the system, there would be very little current flow through the earth.
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That and the fact water lines, gas pipes and TELCO lines are all parellel neutral paths with an impedance perhaps even lower than the total earth electrodes.
 
mivey said:
When looking at a multi-grounded system using the neutral for load current, a 50/50 or even a 60/40 split is not uncommon nor is it always considered an abnormal condition. Even a 70/30 split might be seen on extremes.

40% neutral current seems slightly high for an average but keep in mind that 50/50 could be considered normal. Load balancing and checking connections might be something the manager should spend some time on.
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What is the rule behind sizing the MGN noodle? Half the lines around here has a thinner neutral than the phases. I assume this has engineering thought behind it?
 
mbrooke said:
What is the rule behind sizing the MGN noodle? Half the lines around here has a thinner neutral than the phases. I assume this has engineering thought behind it?
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The engineering thought is that the neutral carries only imbalance current among the phases.

mobile
 
GoldDigger said:
The engineering thought is that the neutral carries only imbalance current among the phases.

mobile
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I can understand that, but I've seen it carried out on single phase latterals. Maybe its just that the hot conductor is jacketed, but I swear Ive seen a few of those in the wild.
 
mbrooke said:
I can understand that, but I've seen it carried out on single phase latterals. Maybe its just that the hot conductor is jacketed, but I swear Ive seen a few of those in the wild.
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There is still single phase extensions here and there on the system, but overall they try to achieve as much balance as possible on the main line.
 
mbrooke said:
I can understand that, but I've seen it carried out on single phase latterals. Maybe its just that the hot conductor is jacketed, but I swear Ive seen a few of those in the wild.
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No worries, half the unbalanced neutral current gets back to the source through dirt.
 
iwire said:
No worries, half the unbalanced neutral current gets back to the source through dirt.
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Unless you have electrodes with resistance like OP mentioned on the single phase extension off the main line, then you get a voltage to ground on everything connected to it (including the customer secondary neutral) if the MGN has a high resistance point somewhere.
 
kwired said:
Unless you have electrodes with resistance like OP mentioned on the single phase extension off the main line, then you get a voltage to ground on everything connected to it (including the customer secondary neutral) if the MGN has a high resistance point somewhere.
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:slaphead:

It was a joke. :roll:
 
The neutral/ground is usually carried out on single phase laterals. For a 120\240 split phase transformer on a wye system the service ground is required. The center tap of the trans, the case , and your neutral from your service drop are all tied to the service ground. On a 2 bushing transformer one bushing is connected to phase, the other to the service ground. Typically high resistance at one pole rod, won't cause trouble since it will just bleed down on the next one. Normally when we run the service neutral we use the same wire as the primaries, jacketed.

Now for a twist, on an ungrounded delta system there is no service ground. So when we set a single phase service, we use a double bushing trans and run 2 phases out to the dead end. The case of the trans, the center tap and the neutral from your drop gets tied to the pole and we set a rod at that pole and another rod 1 pole away and string a ground between them.

It is not uncommon to see high resistance on a good amount of rods on a system. And often times you will see voltage on the service ground; it's normally not a problem or hazardous unless they become ungrounded.



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mbrooke said:
What is the rule behind sizing the MGN noodle? Half the lines around here has a thinner neutral than the phases. I assume this has engineering thought behind it?
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The Earth may normally carry more than half the single-phase load so for single-phase circuits you could use 1/2 the conductivity of the phase conductor with some caveats. Caution must be used on heavily loaded taps since the division is not immediate and the neutral at the end carries most of the current and very little is in the Earth.

For two-phase circuits, you need at least 70% conductivity.

For balanced three-phase circuits you could use 20% conductivity but single-phasing conditions dictate using at least 50% conductivity.

20% in any case is considered the minimum.

Other factors:

Future phase conductor upgrades may need a bigger neutral. Sag characteristics (unequal sag/creep, conductor and ground clearance, long spans might need taller poles, etc.) and spacing. Minimum conductor strength for loading and reliability. Use of primary neutral for secondary currents. Fault clearing times are longer with smaller neutrals. Harmonic loading. Minimum sizing for fault withstand.
 
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