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3 phase electric


chicago
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Originally posted by chicago

I am inspecting a 150 year old farm house with what I"m told is 3 phase wiring.

Can anyone tell me anyhing to look for when doing this one, as it is not somthing I"m familiar with.

Links would help[:-dunce]

Fundamentally it is all the same as usual except there will be three hot lines coming in instead of the usual two that you would have with a single phase system. From the inspection end, unless you go well beyond normal scope of inspection there is no difference. Unless the new homeowner will be utilizing heavy machinery it won't make any difference to him & he can use it just like any other system. Personally I'm jealous, I would love to put the 3 phase motor back in my 100 year old 20 inch band saw...

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Thank you kyle. That gives me peace of mind.

Its only my second pro inspection and I have enough to worry about as it is.I suppose the main panel will have 3 rows instead of 2 as far as over current protection goes.Unless of coarse there is a second service entrance.

I"ll have my hands full just looking at my first stone foundation.

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Originally posted by chicago

Thank you kyle. That gives me peace of mind.

Its only my second pro inspection and I have enough to worry about as it is.I suppose the main panel will have 3 rows instead of 2 as far as over current protection goes.Unless of coarse there is a second service entrance.

I"ll have my hands full just looking at my first stone foundation.

The panel won't have three rows of breakers... There will be three lines feeding the hot bus and three legs for the hot bus instead of two. Still two rows of breakers, or even just one depending on the panel but every third breaker will be fed by the same leg (phase). Just like when you have a single phase with a double pole (220) circuit, one side of the breaker takes from leg one, the other side takes from leg two, if there was something running 3 phase power it would have a three pole breaker that takes power from each of the 3 sections of the hot bus.
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bobe,

When you are looking at 3-phase systems as a HI you are looking to ensure the proper bonding and grounding methods are taking place and in many older systems the understood concepts of proper bonding methods smply did not take place so keep those things in mind when viewing. Basically, since you are doing a visual inspection you are looking for the same typical issues in the panel enclosure as you would in a standard dwelling as the simple fact you have a 3 phase system does not negate the fact the other prinicples of safety and wiring should still apply.

If you find yourself STUCK questioning something feel free to give me a call......

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Bob,

Understand that the advice you are getting here is possibly helpful for your first 3-phase inspection, but there is a lot more to it.

Safety first! (Your experience indicates you already know that.) Then, as mentioned elsewhere, you MUST get Hansen's book. After that, I recommend Practical Electrical Wiring, 19th ed. by Richter and Hartwell - there is a smaller "Wiring Simplified," but I like to have more information.

I have a computer engineering BS from an electrical engineering department, but I'm an idiot with much of this ("electronic" is way different from "electrical"), but once I get through these materials, I'll be a much better inspector.

It's also fascinating to learn about Power factor, RMS, frequency differences between the phases, etc. (Ok, I think it's fascinating[:-paperba). Those things were covered in college but honestly, since it didn't apply to what I was doing with circuit boards, I let it go.

BTW, Paul... since you offered,

I haven't been able to get a good answer as to why this (picture) is ok. Facts: single drop to two meters, then SE to each panel. The left panel is for a downstairs apartment, right is for up.

Only the left panel has the big copper grounds. Sure the panels are bonded at the meters - and at the pole for that matter, but isn't it important to ask, "bonded by what?" There is a big difference between the neutral conductors and that big honkin' copper.

I'm sure it's ok, but I want to know why. Your help is much appreciated.

Originally posted by PAbernathy

bobe,

When you are looking at 3-phase systems as a HI you are looking to ensure the proper bonding and grounding methods are taking place and in many older systems the understood concepts of proper bonding methods smply did not take place so keep those things in mind when viewing. Basically, since you are doing a visual inspection you are looking for the same typical issues in the panel enclosure as you would in a standard dwelling as the simple fact you have a 3 phase system does not negate the fact the other prinicples of safety and wiring should still apply.

If you find yourself STUCK questioning something feel free to give me a call......

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Gary,

I do find some others issues in that panel if you do care to know what they are...but I will address your question.

1.) Basically the understanding of that " Big Honkin Copper" is the miscoception to its function if it is going to the GEC. The only real purpose in that connection is Lightning, High Voltage Surge and High Voltage Shunts for a lack of a better term and to aid in the POCO as well IF this is going to the GE.........it is very important to know that it plays no role in the fault or OCPD function of the system if again it is going to the GE.

I will try to keep this basic.........the function of the grounded conductor is to create the return path for the electrons to low and is a low impedance path as such...the earth is not....while it could flow on it during a parallel environment it is not a good conductor and plays no role in protecting the inside components or personal safety...just needed to get that out of the way. However the "Grounded" conductor itself plays a very important role in allowing the OCPD to function properly.

(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.

Now....Section 230.40 ex. 2 is what firstly would permit this installation.

Now personally I look at this picture and ( not knowing where exactly the stranded copper conductors on the left are going ) feel it should have a bond between each panel OTHER than using the "Grounded" connection at the meter enclosure....but over the years that section of the NEC has been so screwed up it is not until 2008 that it is being revamped....

The NEC says that all enclosures likely to carry fault current path should be tied together so the debate is...are they tied together via the "Grounded" conductor at the meter enclosure on this type of setup....probably are and many will argue that they are......personally I like to see a bonding jumper between these enclosures as they may be separate in function they share a common service and a common fault current path back to the source.

Man....this is hard to explain in type....this is why I said....anyone feel free to call me 540-607-0116 if better explanations are needed....I get calls from all over the country daily.

So the arguement is......is it ok to run the GEC to the Meter or only the (1) service panel in question here....based on current language it does not disallow it. However the other issues come into play here is are the water piping systems different...are they separated....and if so is that piping system for the panel on the RIGHT tied properly back to it's own panel.....

very hard to tell with these pictures and I hope this has not been confusing...please by all means call me if it is because I am typing it between many phone calls.

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Thank you for the posts.

I have been away from my laptop due due Valentines day obligations.

Paul I received an E-mail from my local chicago

N>A>C>H>I chapter regarding your upcoming NCE event on March 3.Not sure if I can make it,but I will look for future chances to attend one of your events.

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Thanks Chicago.....yeah gotta watch out for that spam...:)

I also wanted to explain why I like to see a bond between these enclosures.....

1.) if the "Grounded" conductor comes loose within the enclosure the bonding path to the second panel becomes a pathway for the fault current and still allow the operation of the OCPD.....

In the image posted alot depends on the design of the system when it comes to bonding it...as if each level is separated by lets say metal piping and a non-metalic jumper gets between these systems...then you would need it's own individual bond back to it's own enclosure.....many variables in this setup and we need to know all the factors involved.

Lastly I think the 2008 NEC will clear this up alot but many people also believe that in the setup you have shown it would require a seperate GE from the second enclosure to the GEC as well....but it is looked at in many ways but factually they are tied together at the meter enclosure...so they are technically tied together conductivly at that point.

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Paul,

One went to a rod, the other to the plumbing. The plumbing system for the duplex is combined - but that gives me something else to think about in the future.

Your explanation is clear. I was told that things would be different in a heavy lightning area, but not why it is ok otherwise. Now, it makes perfect sense.

I can't believe you have time to answer calls. I won't be bothering you, but your helpful attitude is greatly appreciated.

Originally posted by PAbernathy

I would be very interested in knowing where those " Big Honkin Conductors" go to within the system itself so we can look at it furthur.

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Yes, that's what I inferred from your previous explanation. The fact that you have now posted thrice for this shows that you care about the 'student.' Again, MUCH appreciated.

Originally posted by PAbernathy

Thanks Chicago.....yeah gotta watch out for that spam...:)

I also wanted to explain why I like to see a bond between these enclosures.....

1.) if the "Grounded" conductor comes loose within the enclosure the bonding path to the second panel becomes a pathway for the fault current and still allow the operation of the OCPD.....

In the image posted alot depends on the design of the system when it comes to bonding it...as if each level is separated by lets say metal piping and a non-metalic jumper gets between these systems...then you would need it's own individual bond back to it's own enclosure.....many variables in this setup and we need to know all the factors involved.

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(2) Buildings of Multiple Occupancy In buildings of multiple occupancy where the

metal water piping system(s) installed in or attached to a building or structure for the

individual occupancies is metallically isolated from all other occupancies by use of

nonmetallic water piping, the metal water piping system(s) for each occupancy shall be

permitted to be bonded to the equipment grounding terminal of the panelboard or

switchboard enclosure (other than service equipment) supplying that occupancy. The

bonding jumper shall be sized in accordance with Table 250.122.

The INTENT is this...

Section 250.104(A)(2) recognizes that the increased use of nonmetallic water piping

mains can result in the interior metal piping system of a multiple-occupancy building

to be isolated from ground and from the other occupancies. Therefore, the water pipe is

permitted to be bonded to the panelboard or switchboard that serves only that particular

occupancy. The bonding jumper, in this case, is permitted to be sized according to

Table 250.122, based on the size of the main overcurrent device supplying the

occupancy.

So in your case it is a common water piping system and could go back to the common GEC that is running to the first panel enclosure. But it is important for those out there who run into a system where the piping is seperate that this must be taken info considering in the information I posted above.

Gary if you or anyone ever is in the middle of an inspection and has a question please call......I carry my phone with me everywhere when doing seminars or in the ditch....Sometimes I have a hard time typing what I am trying to convey and it works much better if someone is really questioning something they can always give me a call....

However again I would like to see a bond between those panels to create a loop for fauly current in case one becomes disconnected but what are the odds...;)

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Understood. I'll add you to my cell.

Originally posted by PAbernathy

(2) Buildings of Multiple Occupancy In buildings of multiple occupancy where the

metal water piping system(s) installed in or attached to a building or structure for the

individual occupancies is metallically isolated from all other occupancies by use of

nonmetallic water piping, the metal water piping system(s) for each occupancy shall be

permitted to be bonded to the equipment grounding terminal of the panelboard or

switchboard enclosure (other than service equipment) supplying that occupancy. The

bonding jumper shall be sized in accordance with Table 250.122.

The INTENT is this...

Section 250.104(A)(2) recognizes that the increased use of nonmetallic water piping

mains can result in the interior metal piping system of a multiple-occupancy building

to be isolated from ground and from the other occupancies. Therefore, the water pipe is

permitted to be bonded to the panelboard or switchboard that serves only that particular

occupancy. The bonding jumper, in this case, is permitted to be sized according to

Table 250.122, based on the size of the main overcurrent device supplying the

occupancy.

So in your case it is a common water piping system and could go back to the common GEC that is running to the first panel enclosure. But it is important for those out there who run into a system where the piping is seperate that this must be taken info considering in the information I posted above.

Gary if you or anyone ever is in the middle of an inspection and has a question please call......I carry my phone with me everywhere when doing seminars or in the ditch....Sometimes I have a hard time typing what I am trying to convey and it works much better if someone is really questioning something they can always give me a call....

However again I would like to see a bond between those panels to create a loop for fauly current in case one becomes disconnected but what are the odds...;)

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Felt I should explain HOW it would be done IF I was the electrical contractor doing it...

1.) The panels are being Back-fed so they need to have a support designed to hold in the breaker but then again I would not have done a back fed here.

I would have ran a single common GEC to the Ground Rod(s) and ran it to the FIRST enclosure....then I would have run a TAP out of the second enclosure and connected it to the GEC going into the first enclosure.....but thats me...:)

Thats what is so messed up about this section of the NEC...and the 2008 NEC clears it up ALOT.....

Basically most people will simply run to the first enclosure OCPD since they are technically on the same single service ( ignore the fact it has (2) meters...because of the location ) and then simply bonded from one enclosure to the other...but they better make sure the bonding jumper is sized right......thats where they mess up.

Since the ability to TAP is explained in the NEC as optional no one really can STICK their finger on the exact intent as in the end it is all considered connected at the meter enclosure in this installation......however I happen to think a bond connection between enclosures is needed......and from what I can gather is not in place.

Now...since we are only talking a Ground Rod in your images...a # 6 CU is all that would be needed to the Rods....so technically if you wanted to do the tap method...simple bring the # 6 CU into the first panel and then run a # 6 CU from the second panel out and SPLIT BOLT it to the GEC going into the first panel....the one going into the FIRST panel needs to be continuous ( with exceptions ) but the tap to it from the second one does not need to be continuous to the rod...that is why the split bolt is allowed....

Now the bond to the water pipe is done here technically since it is all the same service and they share the water piping system...anything other would create a parallel path and is not really needed...so that is fine to the first panel...remember electrons are trying to get to the source...and in this case...the source is shared...so it's all good....:)

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