Wires in Weatherhead

Status
Not open for further replies.
S

Snipa

New member
Location
Nebraska
On a typical 120/240 service where the transformer pole has the meter and the service runs back up the conduit and overhead triplex to the customer. How many wires will
be in the conduit. Is 5 correct? Because you don't have to run the neutral from the bottom side of the meter back up the conduit. Just connect onto the neutral between the transformer lug and the weatherhead for your triplex?
thanks
 
That sounds right but there may be a power company rule on that. I don't believe the meter needs a load neutral.
 
Dennis Alwon said:
That sounds right but there may be a power company rule on that. I don't believe the meter needs a load neutral.
Click to expand...
I don't think it needs a line neutral either... but it does need to be grounded... and the neutral is the grounding conductor on the line side of the service disconnecting means.
 
Smart $ said:
I don't think it needs a line neutral either... but it does need to be grounded... and the neutral is the grounding conductor on the line side of the service disconnecting means.
Click to expand...


I believe some meters have a fifth jaw for the neutral. Not sure why it is needed.
 
I have never heard of Service line and customer Load side in the conduit. Even if it is just going to a weather head.
 
Dennis Alwon said:
I believe some meters have a fifth jaw for the neutral. Not sure why it is needed.
Click to expand...
Most places I have seen the fifth is where you have 120/208 single phase three wire instead of 120/240 single phase three wire. I am guessing the phase angle maybe has something to do with it,though I don't really know exactly how the meters work.

If the two ungrounded are 180 degrees from one another one can simply use a single core with the line conductors entering opposite sides and the current measurement effect is additive - it is actually metering based on 120 volts but has twice the current when there is 240 volt loads, any remaining unbalanced 120 volt current only passes through the CT one time in one direction instead of two times in opposite directions.

Take a 208/120 system and try to put it through same meter and you possibly have some error because the voltages are not 180 degrees apart.

I'm guessing three phase meters often have a 7th jaw for similar reasons.
 
Sierrasparky said:
I have never heard of Service line and customer Load side in the conduit. Even if it is just going to a weather head.
Click to expand...
And you probably never will. POCO's always want a permanent barrier between pre- and post-meter conductors (other than in a sealed meter can or CT cabinet).
 
Smart $ said:
And you probably never will. POCO's always want a permanent barrier between pre- and post-meter conductors (other than in a sealed meter can or CT cabinet).
Click to expand...
All our POCO guidebooks state something like " no metered and unmetered conductors in the same conduit, trough or raceway".
 
Most of the time when I see that kind of install it is on POCO side of service point, and therefore NEC doesn't apply to it.

If NEC does apply however I would think the grounded conductor would only need be sized per Table 250.66.

Also keep in mind that if you have two ungrounded conductors in and two back out in the raceway - that is four current carrying conductors in the raceway and an ampacity adjustment also applies to those conductors. It would only be 80% and likely still can use same size conductor as you otherwise would unless ambient temperature adjustment also applies.
 
Dennis Alwon said:
I believe some meters have a fifth jaw for the neutral. Not sure why it is needed.
Click to expand...
With single phase three wire 120/240 you theoretically need five jaws to get 100% accuracy: two currents for a total of four jaws plus two voltages which you get from two of the four plus the neutral on the fifth jaw.
But as long as you can assume that the voltages on the two legs are equal, even after accounting for voltage drop.
If you draw from only one side of the 120/240 and the voltage drops to 115 you will be paying for current times 117.5 instead of current times 115.
Since the couple of percent maximum error is always in favor of POCO they don't mind. :)

If the service is two out of three phase, the line to neutral voltage is not half of the line to line and the phase is even more of a problem, so the fifth jaw is mandatory.


Sent from my XT1585 using Tapatalk
 
Last edited:
GoldDigger said:
With single phase three wire 120/240 you theoretically need five jaws to get 100% accuracy: two currents for a total of four jaws plus two voltages which you get from two of the four plus the neutral on the fifth jaw.
But as long as you can assume that the voltages on the two legs are equal, even after accounting for voltage drop.
If you draw from only one side of the 120/240 and the voltage drops to 115 you will be paying for current times 117.5 instead of current times 115.
Since the couple of percent maximum error is always in favor of POCO they don't mind. :)


Sent from my XT1585 using Tapatalk
Click to expand...
Now change the supply to 208/120 three wire, how much does that complicate measurement with the 120 degree phase angle involved?
 
kwired said:
Now change the supply to 208/120 three wire, how much does that complicate measurement with the 120 degree phase angle involved?
Click to expand...
See edit to original post.
Among other things 10A line to line is not the same power consumed as two 10A line to neutral loads.

Sent from my XT1585 using Tapatalk
 
Last edited:
Yup....fifth jaw is for a 120/208 single phase neutral (Form 12S). Called a network meter. Fifth jaw can be at either the 6:00 position of the 9:00 position. Each voltage element is 120V and is calibrated for the 120 deg phase angle. Current is line in to line out on each phase, as it is with the 120/240 meters (Form 2S). Also correct that a single phase 120/240 does not use a neutral because the voltages line to neutral are assumed to be balanced. I don't really think that power companies did that to cheat anybody out of a few bucks. Those meter standards were established decades ago when metering was still in it's infancy, network services were rare and the cost of each additional component was high. Now, with solid state meters, the cost to use neutral would be negligible, but forcing people to add a fifth jaw or replace the meter panel altogether would not be popular. POCO's have a bad enough rep with the new smart meters. Just try explaining the need for a modified meter base.
 
Snipa said:
On a typical 120/240 service where the transformer pole has the meter and the service runs back up the conduit and overhead triplex to the customer. How many wires will
be in the conduit. Is 5 correct? Because you don't have to run the neutral from the bottom side of the meter back up the conduit. Just connect onto the neutral between the transformer lug and the weatherhead for your triplex?
thanks
Click to expand...

I would think that by having only the two line conductors in the meter conduit you could get some inductive issues if the line to neutral load was imbalanced. Same reason that on three phase parallel runs, we have to run all three phases in the same conduit if it's metallic. Of course, that's if you separate metered and unmetered conductors, which, as stated, is a requirement of most POCO's.
 
meternerd said:
I would think that by having only the two line conductors in the meter conduit you could get some inductive issues if the line to neutral load was imbalanced. Same reason that on three phase parallel runs, we have to run all three phases in the same conduit if it's metallic. Of course, that's if you separate metered and unmetered conductors, which, as stated, is a requirement of most POCO's.
Click to expand...
No, because if you have 10 amps on line 1 you have 10 amps in the opposite direction in the raceway on load 1 conductor, same with the L2 conductors.
 
kwired said:
No, because if you have 10 amps on line 1 you have 10 amps in the opposite direction in the raceway on load 1 conductor, same with the L2 conductors.
Click to expand...

True...but I mentioned that I wondered about induction IF the line and load conductors were in separate conduits due to POCO rules that do not allow line (unmetered) and load (metered) conductors to be be the same raceway or sealed compartment. I know that's not what the OP asked, but that was my question. No disagreement that few, if any POCO's allow metered and unmetered conductors to share any compartments/raceways except in the meter socket or CT enclosure itself, so the OP question is kind of a "non-question".
 
Status
Not open for further replies.
Top