Objectionable current

[gar]

090805-2029 EST

erickench:

This is in response to your post #18.

I do not know what a lightning arrestor is. Ideally it would be something that would prevent lightning currents from entering a building.

I think some of the goals would be:

Low pass filters on all wiring into or other conductors into a building.

No supplemental paths to earth within a building.

Low pass filters imply shunt capacitance from all conductors into the building.

An incoming water pipe is already in contact with the soil. Connecting it to the ground electrode system outside of the building would be desirable.

All connections to and including the ground electrodes should be wide thin sheets of copper to provide low inductance and RF resistance.

On conductors at the entry point to the building should be shunt transient voltage limiters including gas discharge, and semiconductor transient limiting devices.

From some old references on my web site;
http://www.harvardrepeater.org/news/lightning.html
grounding paths
http://www.electrical-contractor.net/ESF/Lightning_News/Standard_780_Removal.htm

.

 

[erickench]

I thought a lightning or surge arrestor would contain dielectric material that would block current until the voltage reaches a high enough level that would cause the current to break through.

 

[iwire]

How is this meter enclosure bonded to the neutral? It should'nt be.

It has to be bonded to the neutral, there is no EGC on that side of the service disconnect.

250.142(A) and (B) is worth a look along with 250.92(B)(1).

 

[infinity]

How is this meter enclosure bonded to the neutral? It should'nt be. I don't even think the grounding electrode should be connected to the meter enclosure.

Yes, it needs to be. If the wiring method were PVC or SE cable the metal meter enclosure would be isolated from all of the service bonding. The only way to keep the metal meter enclosure from potentially becoming energized is to bond it the neutral.

 

[don_resqcapt19]

How is this meter enclosure bonded to the neutral? It should'nt be. I don't even think the grounding electrode should be connected to the meter enclosure.

The code permits the grounded conductor to be used for all bonding that is required on the supply side of the service disconnect. The GEC is permitted to be connected at any point from the service disconnect to the service point. For residential services in this area the Utility requires that the GEC from the ground rod be connected in the meter.

 

[don_resqcapt19]

I believe that communications cable shield is just there to guard against electromagnetic interference. ...

While that may be the purpose, the actual installation results in a parallel path for the neutral conductor current. I watched the cable ground connection start the exterior siding of a house on fire after a storm had broken the service grounded conductor, but not the two hot conductors.

 

[erickench]

If the neutral were bonded to the meter enclosure then any fault inside that enclosure would bypass the OCPD inside the disconnect because it is downstream. The path of least resistance would be directly back to the utility. I don't think the circuit breaker would trip.

 

[erickench]

It has to be bonded to the neutral, there is no EGC on that side of the service disconnect.

250.142(A) and (B) is worth a look along with 250.92(B)(1).

Bob, the word 'require' is not used for the above NEC sections. However, the NEC does not seem to limit the number of main bonding jumpers to one. The connecting metal conduit provides a path for the current to flow from meter enclosure to the service disconnect enclosure containing the main bonding jumper. One main bonding jumper in the disconnect is enough.

 

[iwire]

Bob, the word 'require' is not used for the above NEC sections. However, the NEC does not seem to limit the number of main bonding jumpers to one. The connecting metal conduit provides a path for the current to flow from meter enclosure to the service disconnect enclosure containing the main bonding jumper. One main bonding jumper in the disconnect is enough.

Eric it is REQUIRED to bond the meter enclosure to the neutral.
If you did not bond the neutral to the meter enclosure there would be nothing preventing that enclosure from becoming energized.

Furthermore all meter sockets and CT cabinets used in this area have the neutral lugs firmly bonded to the enclosure and there is no way to 'un-bond it'.

 

[hurk27]

If the neutral were bonded to the meter enclosure then any fault inside that enclosure would bypass the OCPD inside the disconnect because it is downstream.

Any fault ahead of the service OCPD's will not trip the OCPD's and yes it will flow back to the transformer hence why we are required to not go very far inside a building with service entrance conductors, They are not protected!

The path of least resistance would be directly back to the utility. I don't think the circuit breaker would trip.

Current takes all paths back to source, and no it won't trip the service OCPD's

All the meters used here, all have the neutral bar bolted right to the can.
I would expected a statement like that from a 2nd week apprentice, not for someone who holds an EE degree:-?

 

[erickench]

Bob, I'm using the NYC Electrical Code which is based on the 2005 NEC and I have the "Analysis of Changes NEC-2008" book. The word "permitted" is used but I don't see the word "required". These words have two different meanings. Unless there is something in the 2008 NEC that the 'Analysis' book is not showing.

 

[infinity]

Bob, I'm using the NYC Electrical Code which is based on the 2005 NEC and I have the "Analysis of Changes NEC-2008" book. The word "permitted" is used but I don't see the word "required". These words have two different meanings. Unless there is something in the 2008 NEC that the 'Analysis' book is not showing.

Which code section are you quoting?

 

[iwire]

Bob, I'm using the NYC Electrical Code which is based on the 2005 NEC and I have the "Analysis of Changes NEC-2008" book. The word "permitted" is used but I don't see the word "required". These words have two different meanings. Unless there is something in the 2008 NEC that the 'Analysis' book is not showing.

Yes , permitted and required have different meanings, thanks.

But interestingly different code sections also have different requirements.

So how about you explain the proper way to connect the meter enclosure to the electrical system to ensure that the enclosure can not become energized?

If it seems I am getting cranky it is because I am. This is basic first year stuff and you seem to be making firm statements about a subject you have no first hand knowledge of. :roll:

 

[erickench]

250.142(A) and (B) is worth a look along with 250.92(B)(1).

I'm looking at the sections that you quoted Bob. The only way to guard against a fault occuring in the meter enclosure is to connect it downstream from the disconnect but maintain the main bonding jumper in the disconnect enclosure. This way the circuit breaker would be able to sense the fault.

 

[don_resqcapt19]

250.142(A) and (B) is worth a look along with 250.92(B)(1).

I'm looking at the sections that you quoted Bob. The only way to guard against a fault occuring in the meter enclosure is to connect it downstream from the disconnect but maintain the main bonding jumper in the disconnect enclosure. This way the circuit breaker would be able to sense the fault.

I'm sorry but there is no way that the current from a ground fault on the line side of the service OCPD will pass though that OCPD no matter how you try to move the bonding around.

 

[hurk27]

I wondering if it is common in Brooklyn to have a meter disconnect ahead of the meter, and maybe this is the confusion, he has?

erickench, this is not how service are done in most parts of the country, if the above is true, we rarely have a disconnect with OCPD's ahead of the meter, and even the primary fuses at the transformer are not sized to open in a secondary fault, so many time the SEC's are the fuse, and are require to just burn free.

This is the reason of the two codes (230.6 and 230.70(A)(1)

hope this helps with the confusion.

 

[erickench]

I just looked into the 'Analysis' book. A new change in the 2008 NEC was made to section 230.82(3). Meter disconnect switches are required to have the capability of interrupting the load. This would protect against an fault occurring in the meter enclosure. There must be an OCPD on the line side of the meter in order to solve this problem. Maybe the city of New York will adopt this change. It's not that I'm confused about what the NEC says and how it's done throughout the country. All I'm saying is this what you have to do in order to deal with this. Now as for the weatherhead and the connecting conduit, I guess they would have to be nonmetallic. Nonmetallic weatherheads anyone?

 

[iwire]

I just looked into the 'Analysis' book. A new change in the 2008 NEC was made to section 230.82(3). Meter disconnect switches are required to have the capability of interrupting the load.

There is no overcurrent protection in a meter disconnect switch.

 

[erickench]

Well then interrupting capacity must mean a plain old short circuit and not overload. The new change say's the meter disconnect must be capable of interrupting the load served. Excuse me Don, you're right. NEC 250.24(B) say's that the main bonding jumper must be inside the service disconnect which is on the load side of the meter.

 

[Pierre C Belarge]

If it seems I am getting cranky it is because I am. This is basic first year stuff and you seem to be making firm statements about a subject you have no first hand knowledge of. :roll:

I don't think this statement helps the thread or the Erik. If you are unhappy with the way this thread is going, stop posting. If you want to help, help.


Erik, I think you have a misunderstanding of the theory behind this topic.

Draw an illustration, draw it linearly. The POCO transformer to the left. The service drop and weatherhead next, followed by the meterpan and last followed by the panel.

Whenever there is a fault condition, the fault current will flow in the direction of the POCO transformer, not away from the transformer. If the fault condition is on the supply side of the service overcurrent device, the current will flow towards the POCO transformer, and the service overcurrent device will never see the event.
That is the reason we use the grounded conductor bonded to the enclosure on the supply side of the service overcurrent/disconnecting means.