twin masts/one service

[apauling]

I have been having a non argument with a senior inspector over a install that I failed. a homeowner doing install wanted to have two seperate services, two adjacent service drops, meter mains next to each other. The next day he said that he went there and gave a list of corrections and the utility would connect both masts with one drop.

I see more than a few hazardous problems and said that it was not legal (99 nec, or cec). I can see legal with one set of risers, gutter, etc., but he said he had him correct the bonding and pg&e will connect it. I cannot see correct way to bond and ground this system ( one meter/main will feed granny on property, same address). One ground rod as well!!.

I won't sign for it.

Any commiseration welcome. Any thoughts as well.

any pg%e guys out there? will you connect it?

felling my sign on, paul

 

[cs409]

Re: twin masts/one service

so there are in all reality 2 separate services? each has its own mast/weather head, service wire, each has its own meter, and main panel? but i did read one ground rod!

 

[hurk27]

Re: twin masts/one service

Sounds like a dwelling split up to provide an apartment for granny. Would this be concidered a multi-family dwelling? If so then 230.40 Exception 4 does allow for this. But you are correct as far as the one service drop. Two risers is ok as this is still service entrance conductors. And only one grounding electrode system is needed as per 250.58 This is done for duplex's all the time and is not a violation. Now for the sticky part. The service disconects have to be grouped in one location, 230.71 because there most likely will not be a fire wall between the two dwellings. But as long as that is met then I cant see anything wrong with it.

 

[apauling]

Re: twin masts/one service

the problem I have with the two masts is that the two seperate risers are joined at the roof, descend to two seperate meter mains, are bonded by one ground rod. The panels are not metallically continuous. This is at the wall of a single family residence where one meter will serve the granny in back.

Since the neutral can only be bonded at one point in the service, where is it bonded for both panels?

How is the problem of parallel paths overcome for the two risers?

How is the second panel bonded and grounded as thereis no metallic connection between the twpaul

 

[hurk27]

Re: twin masts/one service

Since the neutral can only be bonded at one point in the service, where is it bonded for both panels?

Where does it say this in the NEC? Ahead of the service disconnect there is no requirement on how many times it can be bonded.

How is the problem of parallel paths overcome for the two risers?

You wont have a parallel path as the two services will not be joined at the load end.
Remember to have a parallel path it must be current carrying conductors, Not grounding conductors

How is the second panel bonded and grounded as theres no metallic connection between the twpaul

You run a GEC from each meter/main to the water pipe then to the ground rod or other electrode that might have been used. or run the GEC from one meter to the next then run to electrodes. Either way it's code compliant.

250.58 Common Grounding Electrode.
Where an ac system is connected to a grounding electrode in or at a building as specified in 250.24 and 250.32, the same electrode shall be used to ground conductor enclosures and equipment in or on that building. Where separate services supply a building and are required to be connected to a grounding electrode, the same grounding electrode shall be used. Two or more grounding electrodes that are effectively bonded together shall be considered as a single grounding electrode system in this sense.

 

[apauling]

Re: twin masts/one service

the neutrals are joined at both top of mast and at point where bonded to gec and are current carrying conductors. ergo parallel current carrying conductors.

AND since the neutral bond cannot occur in both panels and both panels are NOT connected, whatever the bondingfor the second meter/main path will be an irregular length parallel path for the neutral fron the other panel, a third neutral parallel path.

do not have books in front of me, but where the neutral is bonded at more than one point at a service do not apply here, and it is in the nec that the neutral/ground connection occurs at one point in that service. You are mistaken about the multiple points of bonding the neutral to the grounding system.

However the install is accomplished it violates some aspecdt of the rules for services.

For the install to be legal, single mast and metallically bonded panels, the point where the neutral and egc are joined would have to be in the gutter common to both, not in one panel.

the same electrode is used for bonding the metal enclosures, but you cn't run the same gec from the bonding point of one panel to bond the neutral of another.

no time to edit, later, paul, bye

 

[iwire]

Re: twin masts/one service

Paul I agree you will have some current flow on the electrode system.

That aside, code requires that both services be bonded and connected to a common grounding electrode system.

If you have the NEC handbook take a look at exhibit 250.26 and it shows exactly the situation you describe.

Also please take a look at Note 1 to Table 250.66

1. Where multiple sets of service-entrance conductors are used as permitted in 230.40, Exception No. 2, the equivalent size of the largest service-entrance conductor shall be determined by the largest sum of the areas of the corresponding conductors of each set.

 

[hurk27]

Re: twin masts/one service

Paul think of this:
Every house that is connected to the same transformer and uses a common water pipe that is electrically connected at each house for the grounding electrode will have a parallel path with the neutral. And this is code compliant. Yes in many types of installations you will have this type of parallel connection and it is allowed. The code is mute on this because it is unavoidable in some applications. Look at any duplex type building that has separate meter inclosure installed. they will have the same type of install and the same parallel path through the GEC this is very common. Now in some buildings you have a fire wall then each side would be treated as a separate structure. In this case many AHJ's will allow the service disconnects to be located in different locations and GE's to be kept separate, But that is a local call. I have seen town houses that are bought and sold as real property and services are located on each one as a separate structure. But there is a fire wall between them. in this case also the GE's are kept separated.

 

[david]

Re: twin masts/one service

__________________________________________________
The service disconnects have to be grouped in one location, 230.71 because there most likely will not be a fire wall between the two dwellings. But as long as that is met then I cant see anything wrong with it.
__________________________________________________

As far as the NEC is concerned I do not see a requirement for a firewall separation

 

[hurk27]

Re: twin masts/one service

The fire wall requirement is not in the NEC but I was told it is in another NFPA document or building code that gives the definition of a separate structure thus allowing individual services to be installed separated. as it treats each portion of the building as a separate building. Of course this will depend on weather or not your local or state code has adopted this.

If no fire wall then the disconects have to be grouped.

 

[apauling]

Re: twin masts/one service

still do not have books, but did peruse cec (calif) and picture ref to250.26 (this am) was not there. maybe 2002 ed. did see where min 1/0 was req where service cond in parallel in sep conduit (neutral).

I have never seen this install. I could understand if bonding was all seperate as panels themselves are not metallically continuous. The code does state that the ground rod connection shall be unspliced (i think that is the wording) and I cannot see the second panel being connected correctly to this ground rod path. it will always be down a looped/circular neutral path.

This is not the same electrically as a single riser feeding a gutter that feeds the panels, where the parallel path is extremely short and all the meter/mains are elelctrically continuous, and the circular path is within the enclosure.

Hurk: this is more like your neighbor getting his neutral from your panel and bonding it at his house as well.

I am willing to let it go as one of those local/area (inc BIG areas) accepted practice items, including the area that I now am in, but I can see one of these neutrals being a hazard for someone unaware that a grounding connection is carrying current.

thanks for the help

paul

eventually i will move my library and the rest of my home up here as well, (unless they fire me) and I can carry on a better conversation

 

[david]

Re: twin masts/one service

Not to press the point but, but if there is one service drop we are talking one service supplying a pair of service entrance conductors. 230.40 exception 1 says a single building with one or more one or more occupancy nothing about a separate building for each occupancy

 

[hurk27]

Re: twin masts/one service

David that is correct 230.40 ex.3 is only for a single building single owner (with or without a firewall). But when you have a firewall the two or more half's of the buildings can be treated as if they are totally separate buildings and this allows each one to have it's own service including service drop/laterals and meter. If you have ever worked in a city or town where buildings are connected together without separation you will see separate service drops to separate services. the same is true for any buildings that can be sold as a separate real property. Like a condo flat (duplex) or town houses. If this was not true then you will have electricians installing multi-gain meter packs on them and running the feeders across other owners properties even if they are ran under the slab it will still be on the other owners property. and if there is no built in utility easement in the deed's for the properties then this owner will have every right to cut and remove this feeder. say if he wanted to install a hot tub into his basement floor or even the slab floor on the first level and this feeder in in his way. This is why most local or states adopt this code to allow for each unit to be treated as a separate structure. How many strip malls have you seen with seperate services many I hope. So if there is a fire wall then it can get a seperate service. of course the POCO will be the finel say to this but as you can see in ones where they sell off each unit as a seperate unit I would hope it has a seperate service or a utility easement agreement.

 

[hurk27]

Re: twin masts/one service

Paul:

This is not the same electrically as a single riser feeding a gutter that feeds the panels, where the parallel path is extremely short and all the meter/mains are elelctrically continuous, and the circular path is within the enclosure.

No its not but the same parallel path is there. and the GEC that runs to the water pipe is not located in any cabnet is it?

Hurk: this is more like your neighbor getting his neutral from your panel and bonding it at his house as well.

If thats the way you understand it but power usage on the neutral does not make the meter spin it's what goes out the hots. otherwise many would have bigger utility bills than they should. And this is been done for a long time from one end of the U.S. to the other, Where ever there is a continous metal water pipe between the buildings.

Paul we must look at the wording of 250.58 and understand that the CMP's had to have known that this would create a parallel path with the neutral conductors. so I think that the intent of this instruction is to be followed. and if this is so then it would mean that this installation is code compliant.

I posted 250.58 above

[ July 16, 2004, 02:39 AM: Message edited by: hurk27 ]

 

[iwire]

Re: twin masts/one service

Paul check this out, this is the same set up.

It also shows that you are allowed to use taps to the grounding electrode conductor.

No time to give code references now but GEC taps are common.

 

[apauling]

Re: twin masts/one service

iwre, where did the picture come from?

I do not have the 99 in front of me but how do you deal with 250.28, an unspliced main bonding jumper brought to each disconnect?

in this case also the service drop wires are 100 amp residential, no largerthan #2, and 250.24 (i think) says that where conductors are in parallel and in seperate conduits (the neutral here is in parallel), the neutral shall be no smaller than #1/0.

I respect your experience and I know regional differences exist, but this is for new construction, where it would have been easy to put the m/m on the second house, the second unit is remote with a sub panel. i believe even that the inspector is going to let them get away with no real disconnect at the seperate building (residence)(more than six seperate brekers with no main disc)

i'm not going to lose sleep over it, but in this case i can find no reason to void the provisions of the code, (250.28 and 250.24), merely for the convenience of the primary homeowner. If he wanted control over the second unit, he could have put in a disconnect at his house, without the seperate service.

thanks again for the help,

paul

 

[roger]

Re: twin masts/one service

Paul,

I do not have the 99 in front of me but how do you deal with 250.28, an unspliced main bonding jumper brought to each disconnect?

the bonding jumpers are unspliced in the drawing. The only splices shown are on the GEC.

in this case also the service drop wires are 100 amp residential, no largerthan #2, and 250.24 (i think) says that where conductors are in parallel and in seperate conduits (the neutral here is in parallel), the neutral shall be no smaller than #1/0.

These conductors are not parallel, they are going to seperate meters, in order to be parallel they would have to terminate on common connections points.

If there were two drops from a common pole monted transformer it would be the same scenario, the only difference being, the conductors would come together at the pole.

Roger

[ July 17, 2004, 02:39 PM: Message edited by: roger ]

 

[apauling]

Re: twin masts/one service

roger, since i have the 2002 in front of me, i must say that i stand corrected as far as main bonding jumper and as far as parallel conductors. The phrase "phase" conductors was dropped from my brain when i read that along time ago. I also was suffering some misunderstanding about main bomding jumper, as my memory racked that one up as the gec.

sorry for the argument. it does help to have one's books on hand to keep mouth in check.

paul

 

[hornetd]

Re: twin masts/one service

Originally posted by iwire:
Paul check this out, this is the same set up.

It also shows that you are allowed to use taps to the grounding electrode conductor.

No time to give code references now but GEC taps are common.

If that illustration is copied from the handbook can someone give me some coaching on how to do it. I have an electronic handbook and I would love to know how to copy out the illustrations so I could use them in corespondance and proposals.
--
Tom H

 

[iwire]

Re: twin masts/one service

Hi Paul thanks for the kind words, and you know I would avoid parallel paths if I could and remain code compliant, in this case it can not be avoided.

First 250.58 requires all services to a building to be bonded together

250.58 Common Grounding Electrode.
Where an ac system is connected to a grounding electrode in or at a building as specified in 250.24 and 250.32, the same electrode shall be used to ground conductor enclosures and equipment in or on that building. Where separate services supply a building and are required to be connected to a grounding electrode, the same grounding electrode shall be used.
Two or more grounding electrodes that are effectively bonded together shall be considered as a single grounding electrode system in this sense.

And 250.28 Requires grounded systems to be bonded at the service disconnect.

250.28 Main Bonding Jumper.
For a grounded system, an unspliced main bonding jumper shall be used to connect the equipment grounding conductor(s) and the service-disconnect enclosure to the grounded conductor of the system within the enclosure for each service disconnect.

If you had 5 services in one structure you would have to bond each one and tie them together to the same grounding electrode system.

If for some reason we only bonded one of the services a ground fault on the other services would have to use the grounding electrode system as the fault path back to the 'one bond' and finally to the power source.

250.64(C) Is the section that requires only the GEC to be "continuous length without a splice or joint, unless spliced only by irreversible compression-type connectors"

But one more section down, 250.64(D) allows us to connect taps to the GEC when we have more than one service or service enclosure.

250.64(D) Grounding Electrode Conductor Taps. Where a service consists of more than a single enclosure as permitted in 230.40, Exception No. 2, it shall be permitted to connect taps to the grounding electrode conductor. Each such tap conductor shall extend to the inside of each such enclosure. The grounding electrode conductor shall be sized in accordance with 250.66, but the tap conductors shall be permitted to be sized in accordance with the grounding electrode conductors specified in 250.66 for the largest conductor serving the respective enclosures. The tap conductors shall be connected to the grounding electrode conductor in such a manner that the grounding electrode conductor remains without a splice.

[ July 18, 2004, 08:00 AM: Message edited by: iwire ]